Healthy Societies built from Healthy Ecosystems: How Australia and Aotearoa New Zealand are Working at the Intersection of Human Health and Ecological Restoration for a Healthier World

Adam Cross (Curtin University), Kiri Wallace (University of Waikato), and James Aronson (Missouri Botanical Garden) discuss the newly formed Four Islands EcoHealth Network, a regional coalition allied with the global action initiative EcoHealth Network, which aims to increase the amount and effectiveness of ecological restoration throughout the world. The new papers they discuss are published in the journals EcoHealth and Restoration Ecology.

We live in an age of environmental challenges and crises that require societies to sit up and pay more attention to how they function. From heatwaves and water shortages to megafires and sudden floods (sometimes one after the other), new virulent viruses and infectious diseases, salinization where it doesn’t ‘belong’, plastic pollution in our oceans (where it really doesn’t belong), climate change and compromised food and job security for hundreds of millions of people, the combined impact of these challenges on human life are significant, to say the least.

While low-intensity seasonal or episodic fires are a natural part of the ecology in many regions of Australia such as the Kimberley (top left, photo A. Cross), intense, aseasonal or too-frequent fires can be devastating to ecosystems such as kwongan heathland (top right, photo A. Keesing) or seasonal peat wetlands (bottom; photo D. Edmonds).

The ecological and economic impacts of the environmental disaster known as climate change have resulted in thousands of jurisdictions in dozens of countries declaring a climate emergency, including many in Australia and Aotearoa New Zealand. Both countries are predicted to experience a hotter, drier climate in the coming years, a trend already showing itself through ominous impacts on forests and other ecosystems on land and at sea, including the oceans on Australia’s eastern coasts, where coral reefs and kelp forests are showing clear early signs of collapse. In both Australia and New Zealand, aseasonal or large-scale fires appear to be pushing some endangered species towards extinction and vital habitats and ecosystems to the brink. During the Australian summer of 2019-2020, unusually intense wildfires burnt an estimated 18.6 million hectares (46 million acres) across Australia and left ecosystems and communities reeling: the fires killed 34 and destroyed approximately 3,000 homes, and are estimated to have killed over a billion native animals.

Australia’s exceptional biodiversity includes many unique species, such as the Thorny Devil (Moloch horridus; Left), Emu (Dromaius novaehollandiae, Center), and Echidna (Tachyglossus aculeatus; Right). All photos Sophie Cross.

These fires and their aftermath have created a flashpoint where conflicting responses to climate change and its effects are emerging in sharp relief. Strong social divisions have long existed over expanding gas, oil, and coal mining projects in mainland Australia and Tasmania, all of which of course contribute massively to anthropogenic climate change. Debate and conflict over logging in the remaining natural forests has also intensified. The degradation of ecosystems can also cause significant public health impacts. Studies have linked high rates of depression and even suicides in farming communities to the stresses of drought and fire. The fragmentation and clearing of forests for timber and unsustainable agricultural practices has isolated and displaced Indigenous Peoples and communities, leading to conflict, loss of cultural identity, and damage to livelihoods, and has contributed to a rise in zoonotic (animal-transmitted) diseases such as the catastrophic and ongoing effects of Covid-19. Smoke from the recent Australian bushfires reduced air quality to dangerous levels in cities around Australia, potentially killing 12-times more people than the flames did, and the smoke plume travelled over 11,000 km across the Pacific Ocean to South America.

Time for Deep Change

In support of the upcoming UN Decade on Ecosystem Restoration (to run from 2021–2030, concurrently with a Decade on Ocean Science for Sustainable Development), two recent articles by Breed et al. and Aronson et al. bring new weight to the argument that ecological restoration is one of the most promising strategies we have to stop and reverse our current trajectory of environmental chaos. Indeed, Breed and colleagues suggest that the human health benefits of undertaking and engaging in ecological restoration might be so significant that restoration could be considered an economically and politically effective large-scale public health intervention. These benefits might be at the scale of the individual, resulting from direct participation in restoration activities (e.g., the act of working together on restoring an area can reduce anxiety and depression-related diseases). Or, they might be at the population and community levels, resulting from the indirect outcomes of ecological restoration (e.g., restored ecosystems and reintegrated landscapes provide cleaner water, and more health-promoting microbiomes, reducing a number of disease risks).

Restoration projects, such as the Arbor Day planting events of People, Cities & Nature, at Waiwhakareke Natural Heritage Park in Hamilton, New Zealand, can bring community together and may have significant public health benefits for participants. All photos C. Kirby.

Breed and colleagues proposed five key strategies to help us better understand the potential of ecological restoration as a public health initiative:

  1. Collaborations and conversations. Promoting greater collaboration among scientists of various disciplines, health professionals, restoration practitioners, and policymakers to better understand the links between ecological restoration and human health and wellbeing (including jobs and livelihoods).  
  2. Education and learning. Restorationists need to learn about human health, and health professionals must in turn learn about the real potential of ecological restoration as a public health intervention.
  3. Defining the causal links. Research is needed to determine the causal links between ecosystem restoration and health outcomes, to provide the empirical evidence required to understand and advise communities and decision makers.
  4. Monitoring restoration and health outcomes. We need better and standardized methodologies for the effective, cost-efficient monitoring and evaluation of the public health benefits from ecosystem restoration.
  5. Community ownership and stewardship. A global movement toward a restorative culture needs community involvement and engagement, and embracing of the importance of traditional ecological knowledge.

Putting these strategies into action at a scale required to meet the aspirations of the coming UN Decade means we must collaborate across continents and disciplines to identify and build links between ecological restoration and human health.

One such initiative is the Ecohealth Network (EHN), established in 2017 to bring together pioneering sites, hubs, and regional networks to work cohesively towards rapidly increasing the amount and effectiveness of ecological restoration throughout the world, and to accelerate understanding and awareness of its feasibility and benefits, especially for public health.

The first EHN regional network emerged from a workshop held in February 2020. The group calls itself the Four Islands EcoHealth Network, in reference to North Island and South Island, the two largest islands of Aotearoa New Zealand, plus Tasmania, and mainland Australia. It aims to explore how different sites and hubs with various climatic and cultural contexts can come together to share insights and pursue research into the physiological, psychological, and societal health benefits of ecological restoration. It also aims to advance the ecological and microbiological knowledge needed to achieve effective, durable restoration. The aspirations, aims and issues to be considered by the group were laid out in the Hobart Declaration, a charter document stemming from the workshop. Keith Bradby, the founder and CEO of Gondwana Link, agreed to be the first coordinator of the regional network.

The Four Islands EcoHealth Network also embodies a shared desire to foster support for long-overdue efforts in both countries that work in close collaboration with Indigenous Peoples and local communities to make radical changes in cultural, educational, and land care practices. A recent popular science article by Dr. Kiri Joy Wallace highlighted the significance of these aspirations to the public health sector, native ecosystems, and people of Aotearoa New Zealand. There are also many Australian contexts bringing insight and direction to the initiative. For example, Gondwana Link is working to restore ecological resilience to thousands of hectares of marginal farmland following long colonial histories of Neo-European style agricultural use and severe salinization in southwestern Australia; Gondwana Link is exemplary in its huge regional scope and sustained work for greater interaction and cooperation not only with local conservation groups, but also with Noongar and Ngadju Traditional Owners. This effort, based on a vision shared by all members of the EHN, is part of the essential process of “decolonizing” both conservation and ecological restoration.

Other members of the Four Islands EcoHealth Network tackle the restoration and assisted recovery of wilderness areas in north-eastern Tasmania following industrial tree cropping with Monterrey pine (Pinus radiata), undertaken with great success by the North East Bioregional Network; vast regional, multi-state initiatives such as the Great Eastern Ranges work to conserve and reconnect habitat at large scales; and science-led and community-focussed programs such as the UN-endorsed Healthy Urban Microbiome Initiative, which explores the human health benefits of biodiverse green space in urban areas via the microbiome and smaller local studies examining the mental health benefits of urban schoolchildren participating in restorative activities.

These experiences in the Four Islands context, and the insights and expertise of its founding members, are helping to anchor and inform efforts by the wider EcoHealth Network to link similarly ambitious initiatives in other regions and build a broad global network stretching across the globe.

Restoration can and must underpin every aspect of human society, as our health and welfare, and those of future generations, are dependent on the ecosystems of which we are part. If we are to achieve the aspirations of the coming UN Decade on Ecosystem Restoration, we need to work towards a culture of healing and renewal to replace the damaging models of colonialism, systemic injustice, unrestrained resource extraction, and ecological destruction. The accelerating climate catastrophe and the Covid-19 pandemic have profoundly impacted people’s lives in every nation, increasing awareness about the direct link between human health and the environment. We need to ensure this catalyzes a shift to a restorative culture globally, toward what we can only hope will one day be a world of truly united nations.

To learn more about the Ecohealth Network or the work of the members of the Four Islands Ecohealth Network, visit our website or read our recent papers in EcoHealth and Restoration Ecology.

Do we really need to plant a trillion trees? Tree islands are an ecologically and economically sound strategy to facilitate tropical forest recovery

Karen Holl (UC Santa Cruz) and Leighton Reid (Virginia Tech) describe lessons learned from a 15-year study of tropical forest restoration in southern Costa Rica. Their new paper is published in the Journal of Applied Ecology.

It seems that everybody from business people to politicians to even Youtubers is proposing that we should plant millions, billions, or even trillions of trees. They cite a host of reasons, such as storing carbon, conserving biodiversity, and providing income. These efforts should be done carefully and with a long-term commitment to ensure that the trees survive and to prevent unintended negative consequences, such as destroying native grasslands, reducing water supply in arid areas, or diverting attention from efforts to reduce greenhouse gas emissions.

Another important question is whether we really need to plant that many trees to restore forest. In a new paper in the Journal of Applied Ecology, we summarize some the lessons we have learned about a different approach.

Volunteer plants tree seedlings in one of our plantations in southern Costa Rica. Photo: Karen Holl

Over 15 years ago, we set up an experiment in southern Costa Rica to test whether planting small patches or “islands” of trees could speed up forest recovery for a lower cost than typical tree plantations. The idea is to plant small groups of trees that attract birds and bats, which disperse most tropical forest tree seeds. The tree canopy also shades out light-demanding grasses that can outcompete tree seedlings. As a result, over time these tree islands spread as they grow and facilitate the establishment of a lot more trees.

Compared to tree plantations, the tree island approach has two major benefits. First, it better simulates the patchiness of natural forest recovery. Second, it costs much less than planting rows and rows of trees.

Trade-offs in forest restoration strategies. Planting fewer trees leaves more to chance and can require more time, but tree plantations are more expensive and leave a bigger ecological footprint. Our study tests an intermediate option, and after 15 years it appears to provide a good balance. Figure modified from Corbin & Holl (2012).

In our experiment, we planted tree islands that covered about 20% of a 50 × 50 m plot of former cattle pasture. We compared that to plots where no trees were planted (natural recovery) and to the more intensive and more typical restoration strategy of planting trees in rows throughout the plot (plantation). We repeated this set-up at 15 sites in 2004-2006.

Over the past 15 years, we have monitored the recovery of vegetation, litterfall, nutrient cycling, epiphytes, birds, bats, arthropods, and more. Our data reveal a few key lessons about how to restore tropical forests more ecologically and economically.

First, our data show that planting tree islands is as effective as bigger tree plantations, despite cutting costs by around two-thirds. Compared to plantations, tree islands have similar recovery of nutrient cycling, tree seedling recruitment, and visitation by fruit-eating animals. Both tree islands and plantations speed up tropical forest recovery compared to letting the forest recover on its own. After 15 years, cover of trees and shrubs in the island planting plots has increased from 20% to over 90%.

Artist's depiction of three tropical forest restoration treatments: natural regeneration, tree islands, and plantation.
Drawing of our three treatments showing a few trees establishing in the natural regeneration plots, the tree island merging canopies merging in the island plots, and the rows of trees in the plantation. Artist: Michelle Pastor.

Second, we have found that larger tree islands are more effective than smaller islands in enhancing the establishment of fauna and flora, as larger tree islands attract more birds and shade out competitive grasses.

Third, while tree islands cost less than plantations, some landowners won’t use the tree island approach because the land looks “messier” than orderly tree plantations. Some people prefer to plant lots of trees that are valuable for timber or fruit, rather than having the diverse suite of species that are typical of a tropical forest. So, the tree island planting strategy will be more suitable in cases where the goal is to restore forest.

Natural recruitment of trees seedling in the understory of a canopy of planted trees.

Our results and those of others show that the tree island planting approach holds promise as a cost-effective forest restoration strategy in cases where there are seed sources nearby to colonize and animals to disperse them, and where the spread of tree islands is not likely to be slowed by fire or invasive species. But we need more long-term studies to judge whether tree islands will be effective in other tropical forest ecosystems and to test other questions, like how the particular tree species used affect forest recovery, or what is the best distance to leave between tree islands.

More broadly, our study shows that tropical forests can recover some species quickly but it will take many decades, or longer, for forests to fully recover. So, preserving existing rain forests is critical to conserve biodiversity and the services that intact forests provide to people.

Yes, carefully-planned tree planting can help accelerate tropical forest recovery. But, in many cases we don’t need to plant trees everywhere. Rather we should use restoration strategies that encourage trees to plant themselves.

To learn more about our research, read our new article in the Journal of Applied Ecology, visit our websites (Holl Lab, Reid Lab), or watch a 7-min. video below.

Karen Holl describes the tree planting restoration approach and our long-term experiment in southern Costa Rica.
Los investigadores principales describen el método de applied nucleation y nuestro experimento a largo plazo en el sur de Costa Rica.

A ten-year woodland restoration trajectory

Leighton Reid describes a long-term ecological research project at Shaw Nature Reserve (Franklin County, Missouri, USA). To learn more, read the new research paper (email the author for a pdf copy – jlreid@vt.edu) or tune in for a webinar from the Natural Areas Association on April 21 (register here).

In 2000, the Dana Brown Woods were dark and dense. Brown oak leaves and juniper needles covered the sparsely vegetated ground, and invasive honeysuckle was creeping in around the edges. Biologically, the woodland was getting dormant.

In contrast, the woods today are lit by sunlight everywhere except the lowest-lying streambanks, and the ground is hardly visible beneath a green layer of diverse, ground-level foliage. These changes were most likely caused by two actions: burning the woods, and cutting out invasive trees and shrubs.

Many practitioners have seen woodlands recover to some extent when they are burned, but few have documented the recovery as thoroughly and over so long a period of time as Nels Holmberg and James Trager.

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Nels Holmberg (left) discussing the finer points of Rubus identification with Quinn Long in the Dana Brown Woods.

Nels is an ecologist and sheep farmer in Washington, Missouri. He has inventoried the plants at several state parks and natural areas. In 2000, Nels teamed up with Shaw Nature Reserve’s resident natural historian, James Trager, and together they designed a study to describe how ecological restoration was changing the woodland flora at the reserve. They picked the Dana Brown Woods as their study area.

In a nutshell, Nels and James chose 30 random points on a map. They divided the points evenly across three ecological communities. They placed 10 points in mesic woodlands – the gently sloping parts of the property where white oak and shagbark hickory were most prevalent. Ten points were in areas dominated by eastern red cedar – mostly thin-soiled ridgetops that faced the south, and ten points were in forest – the lower, thicker-soiled toe slopes where northern red oak and Shumard oak were dominant in the canopy with paw paws and spicebush down below.

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Three ecological communities in the Dana Brown Woods: (A) red cedar dominated areas which, after removing red cedar, looked more like dolomite glades in some parts; (B) mesic woodlands with lots of oak and hickory in the canopy; and (C) forest – which had a much darker understory.

At each point, Nels hammered in a t-post, then walked 50 m in the steepest direction and hammered in another t-post. This was his transect. Every year for more than a decade (2000-2012), Nels walked the transects and recorded every stem of every species that was inside of 10 0.5-m2 study plots. Actually, he did this twice per year – once in the spring to capture the ephemeral plants, and once in early summer. Over the course of the study he spent more than 200 days in the field.

Canopy Cover

Dana Brown Woods before (left) and after (right) red cedar removal, with Nels’s 30 transects. The horizontal axis of the image is about 0.9 km. Imagery is from Google Earth.

During this time the stewards at Shaw Nature Reserve were busy restoring the woods. From 2001-2012, they burned the woods five times. This amounted to about one fire every three years. In 2005-2006, they brought in a logging crew to remove all of the eastern red cedars.

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James Trager lights a fire in a woodland at Shaw Nature Reserve.

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One of several thousand red cedar stumps from trees that were harvested from the Dana Brown Woods in 2005-2006.

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One of Nels’s sampling quadrats in the Dana Brown Woods. Photo: Nels Holmberg.

I met Nels and James in 2014. I had just joined Missouri Botanical Garden’s Center for Conservation and Sustainable Development as a postdoc, and I was looking for a local research project. I heard that Nels Holmberg had a giant dataset about woodland restoration, so I called him and asked if I could look at it. Nels said “Sure!”. I imagined he would send me an Excel file. Instead he brought in a giant cardboard box full of yellow legal pads where he had recorded his data.

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One of hundreds of datasheets where Nels recorded his detailed observations.

It took a long time to digitize all of the data. There were more than 50,000 data points. But once we had it all together, this is what we learned:

After eleven years of restoration, the number of native plant species in Dana Brown Woods increased by 35%, from 155 species in 2001 to 210 species in 2012. This increase was linear. That is, the number of native species was still increasing at the end of the study. If we repeated the study today, we expect the number of native species would be even greater than in 2012.

The number of native species increased at different speeds and to different degrees in different ecological communities. In the lower and wetter forest areas, the numbers didn’t really shift very much. They jumped around but not in one direction. In the woodland areas, the number of native species increased by about 23% in the first three years and then leveled out. But in the higher and drier areas where red cedars had been dominant, the number of plants increased linearly by 36%.

Native Species Richness

Changes in the number of native plant species recorded over time in the Dana Brown Woods. On the left are overall changes for the whole management unit. On the right are changes for different ecological communities within the management unit. The management interventions are shown in gray.

The plant species that benefited from the restoration were mostly forbs and grasses. A couple of the biggest “winners” were black snakeroot (Sanicula odorata) and nodding fescue (Festuca subverticillata). There were also some “losers”: Virginia creeper (Parthenocissus quenquefolia) and spring beauty (Claytonia virginica) both declined over time. Relatively few of the species that became more common were “conservative” – i.e., dependent on intact habitat. Mostly they were more widespread and tolerant species.

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Co-author Olivia Hajek demonstrates a hog peanut (Amphicarpaea bracteata) – a good representative of the type of species that benefited most from the restoration. Hog peanut is an herbaceous legume that is common in many woodlands, including disturbed ones.

Our study did not include a control treatment, but counterfactuals exist at Shaw Nature Reserve (although they are becoming fewer and fewer with the excellent stewardship of Mike Saxton and many others). There are still thick patches of eastern red cedar covering remnant glades on parts of the property. Woodlands that have not been regularly burned are now filled with bush honeysuckle (Lonicera maackii), wintercreeper (Euonymus fortunei), and other invaders. And low-lying forest that has not been restored is very dark with fire-intolerant sugar maple (Acer saccharum) casting much of the shade. If we had included a control treatment in our experiment, these are probably the trends we would have found – definitely not a spontaneous resurgence of diverse native plants.

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Fragrant sumac (Rhus aromatica) was present at the outset of restoration and remained relatively stable.

Why does this work matter? The biggest value of this study is that it shows a relatively long-term restoration trajectory, and it does so in fine botanical detail. Many managers and scientists already have data to show that fire and tree thinning increase woodland plant diversity. This study adds another dimension. It shows how quickly plant diversity recovered. It also shows how the speed and shape of the recovery varied across the landscape. We hope that other scientists and practitioners will compare the recovery trajectories in the Dana Brown Woods to their own natural areas. To facilitate that, we have made all of the underlying data freely available online.

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Buffalo clover (Trifolium reflexum) is a conservative species that is present in Dana Brown Woods but was not detected in any of the survey plots.

One of the next steps for this research is to figure out how and when to re-introduce some more conservative plants. Although the Dana Brown Woods became much more diverse as it was being restored, most of the plants were early successional or generalist species. We found very few habitat specialists that cannot tolerate disturbance, which suggested to us that some of these species may have been lost from the site at some time in the past. To learn how conservative plants might be re-introduced, we have started a new experiment testing the effects of soil microbes, competition, and time since the start of restoration on the success of introduced seedlings from seven conservative plant species. In the next year or two, we hope to have new information and recommendations for restorationists looking to add more specialized biodiversity to their woodlands.

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Freemont’s leather flower (Clematis fremontii) is a restricted species occurring on dolomite glades in southeastern Missouri. Although it is present at Shaw Nature Reserve less than one kilometer from Dana Brown Woods, it has not colonized the restored glade habitats there. This photo is from Valley View Glade near Hillsboro, Missouri.

To learn more about this research, you can read the original research paper in Natural Areas Journal. Email me for a pdf copy (jlreid@vt.edu). You can also tune in on April 21 for a webinar on this work. Register here.

New book: Primer of Ecological Restoration

Karen Holl is a professor in the Environmental Studies Department at the University of California Santa Cruz. She describes her new book, which provides an introduction to the field of ecological restoration. Primer of Ecological Restoration is available from Island Press (Use promo code PRIMER to get 20% off).

My husband teases me that it took me over 25 years to write my new book, Primer of Ecological Restoration. Indeed, I was working on a restoration ecology textbook the summer of 1994 when we met. But I decided that writing a textbook during my post-doc wasn’t a smart career move if I wanted to succeed in becoming a tenured professor. So, I put the book project on hold. I periodically revisited the idea over the next two decades as I developed my research programs on restoring tropical forests in Latin America and grasslands and riparian forests in California; taught a yearly undergraduate restoration ecology course; and collaborated with many restoration practitioners. A few years ago, when Island Press asked me if I would write a succinct, “primer” for the field of ecological restoration, I decided the time was finally right. So, my husband is correct that I have been working on this book in some form or another for many years, and I am thrilled that it is finally available from Island Press and most major book sellers.

Book Cover

Primer of Ecological Restoration (March 2020) introduces restoration in short chapters written to be read by students, land managers, and anyone interested in the topic.

The science and practice of ecological restoration have grown exponentially over the past few decades, as we aim to compensate for the negative impacts humans have had on the ecosystems that we and millions of other species depend on. With the growth of ecological restoration has come a plethora of resources: thousands of articles in the peer-reviewed and management literature, countless websites describing individual projects, and many books focused on restoring specific ecosystems.

My goal with this book is to provide a broad but succinct introduction and guide to the rapidly growing field of ecological restoration for a few audiences.

  1. I and a few other instructors, including blog editor Leighton Reid, are already using my book as an introductory text for undergraduate courses in Ecological Restoration and Restoration Ecology. Instructors can complement the book with in depth readings on specific topics and case studies tailored to the focus of the course.
  2. My primer could be used as one of a few texts in courses on Conservation Biology and Resource Management where ecological restoration is not the only topic covered.
  3. I hope this book will be of interest to natural resource managers and others who want a short introduction to ecological restoration.

To that end, I have aimed to keep jargon to a minimum and define terms in both the text and the glossary.

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Approaches to increasing habitat connectivity through restoration. From Primer of Ecological Restoration. Credit: Alicia Calle.

Restoring ecosystems requires an interdisciplinary background. It is essential to understand the ecology and natural history of the ecosystem being restored and know appropriate restoration methods. But, as any practitioner knows, successful projects require familiarity with many other topics, including managing stakeholder involvement and public outreach; experience with planning, goal setting, and monitoring; and knowledge of relevant laws, permitting processes, and funding sources. My book could not possibly discuss all these topics in detail while achieving the goal of brevity, so I provide an overview of key points and illustrate them with brief examples. I co-wrote several online case studies that provide detailed information and integrate various themes illustrated by the project.

The saying that “a picture is worth a thousand words” couldn’t be truer for ecological restoration. There is no substitute for seeing before and after photos of projects and visiting restoration sites in person. Nonetheless, I used selected diagrams and tables in the book and incorporated color photos in the online case studies, to make the book cheaper and more accessible to a broad audience. The book website has links to many restoration project websites, photos, and videos available on the internet, which I will continue to update over time to reflect new approaches in this rapidly changing field.

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Key habitat features in a restored meandering river. From Primer of Ecological Restoration. Credit: Michelle Pastor.

This book is not intended as a thorough guide of how to restore specific ecosystem types, so readers are likely to want more in depth resources on specific topics. To this end, I have provided short reading lists at the end of each chapter. On the website, I provide questions for reflection and discussion that ask readers to apply the ideas presented in the book to a restoration project of their choice. The website also has examples of restoration project design plans that restoration practitioners have kindly shared, and I welcome suggestions from readers for additional resources to include.

I hope you find the book interesting and stimulating, and look forward to your feedback. You can review a detailed table of contents here. Finally, a quick tip that you can get a 20% discount on the book if you purchase the book at the Island Press website and use the promo code PRIMER.

 

Global pledges to restore forests face challenges, and need increased support

Matthew Fagan is an assistant professor in Geography and Environmental Systems at University of Maryland Baltimore County. Here he describes the challenges confronting countries as they attempt large-scale forest restoration, and why many countries will need help to fulfill their goals. For more information, read his new, open-access paper in Conservation Letters.

Degraded and deforested landscapes are widespread, and tropical forests are being lost at a rate of 15.8 million hectares a year. But there is good news—temperate forest area is increasing, and more and more countries are voluntarily pledging to restore vast tracts of degraded land. Restoring forests benefits biodiversity and society, and can combat global warming as well, as growing trees lock away carbon dioxide.

International interest in restoring trees to landscapes emerged out of policy discussions last decade, and resulted in the 2011 Bonn Challenge and the creation of voluntary national restoration targets by many countries. The Bonn Challenge seeks to bring 150 million hectares into restoration by 2020, and 350 million hectarees by 2030 (that’s roughly 700 million American football fields, 350 million rugby fields, 500 million FIFA football fields, or an area a bit larger than India).

Current Bonn Challenge pledges total some 172 million hectares. That’s a massive international commitment, and when you add in internal commitments by countries, the potential restoration area swells to 318 million hectares.

All that area voluntarily committed to restoration got my co-authors and I excited, but also skeptical—were countries really going to follow through on their commitments?

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A rain forest blow-down in northeastern Costa Rica, with a storm-downed tree cut to clear a path. Silviculture restoration promotes the recovery of disturbed forests like this one. Photo credit: Matthew Fagan.

To try to answer that question at this early stage, myself, Leighton Reid (Virginia Tech), Maggie Holland (UMBC), Justin Drew (UMBC), and Rakan Zahawi (University of Hawaiʻi at Mānoa) asked three related questions in a recent paper in Conservation Letters.

  1. Is the amount of land a country pledged to restore related to their past record of restoring forested landscapes and implementing sustainable development?
  2. For the small group of countries that have publicly reported their progress on commitments, is the amount of restoration they completed predictable by their development level or other risk factors, like deforestation?
  3. Which countries will likely face the greatest challenges to meet their commitments and maintain restored land into the future?

We then set to gathering published information on country commitments and progress, and recent national rates of forest loss, agricultural expansion, and forest recovery.

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Recent natural regeneration in northeastern Costa Rica of varying ages. Photo credit: Matthew Fagan.

All of these programs seek to reforest landscapes in ways that benefit both nature and people, including options like natural regeneration (letting natural forests recover and expand), silviculture (interventions to restore standing forests, like preventing forest fires and promoting recovery from selective logging), tree plantations (often tree monocultures to produce timber and pulp on degraded lands), and agroforestry (planting trees on and around farmland to shade crops or protect streams and fields). These options are not all equal in their benefits for biodiversity, carbon, and society, but a diverse menu of options allows countries to consider committing to at least some form of restoration over large areas.

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A tree plantation in northeastern Costa Rica funded by the national payments for environmental services program. It is a monoculture of a single native species, Vochysia guatemalensis, grown for timber. Photo credit: Matthew Fagan.

In a nutshell, what we found was both discouraging and encouraging.

First, after adjusting for the size of a country and how much restoration they had done previously, we found that less-developed countries committed more land for restoration. This might be for positive reasons; for example, they may be taking proactive action against the greater risk they face from climate change. Or it might be because they underestimated how challenging it would be to achieve a large pledge.

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Silvopastoral restoration, a type of agroforestry, in northeastern Costa Rica. The understory is a cattle pasture, while the overstory is plantation of a native tree species, Dipteryx panamensis. Photo credit: Matthew Fagan.

Second, for twelve early-reporting countries, restoration progress was predictable based on a risk index. Countries with higher risk (risk factors included deforestation rates and progress on sustainable development goals, among others) had less restoration progress.

Third, countries made massive individual commitments that will be hard to achieve without wholesale transformation of their food systems. One third of countries committed >10% of their land area (with a maximum of 81%, in Rwanda). A quarter either committed more area than they had in agriculture, or committed more area than they had in forest. And one quarter of countries had more forest loss and agricultural conversion in 2000–2015 than their restoration commitment for 2015–2030.

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Coffee plantation under tree cover, a type of agroforestry, in central Costa Rica. The understory is a monoculture of coffee shrubs, while the overstory is scattered planted trees. The partial cover helps the shade-loving coffee plants stay healthy, but many coffee farmers are moving away from this traditional farming approach. Photo credit: Matthew Fagan.

As noted in our paper, “If voluntary commitments like the Bonn Challenge fail to precipitate meaningful restoration across large areas, the UN’s vision of a sustainable future will become less attainable.” But what this study found is not countries that have failed on their restoration pledges. We are still in the first days of the UN Decade of Ecosystem Restoration. What we have identified is countries that will need help to restore their lands.

We believe it is time for the international community to step up and aid all countries in achieving their restoration goals. To quote Thoreau, “If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them.”

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A regrowing forest in central Costa Rica, showing the promise of restoration. Photo credit: Matthew Fagan.

A foray in the Mojave Desert

Thibaud Aronson describes the botany, ecology, and degradation of southern California’s unique desert woodlands.

There are four deserts in North America – the Great Basin, Chihuahuan, Sonoran, and the Mojave. Both the Great Basin and the Chihuahuan deserts can have bitterly cold winters, and as a result their vegetation is quite stunted compared to the other two, with precious few trees. A few years ago, my father and I spent a fair amount of time in the Sonoran desert, both in Arizona and in Baja California, documenting its remarkable trees.

To fill an important gap in our survey of desert trees of the world, I recently visited the Mojave desert, home to one of the most iconic desert trees on the continent. Indeed, just about every time one mentions desert trees, at least in the US, the most common response is: “Oh, like Joshua trees?” Like Joshua trees, indeed.

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The iconic Joshua tree (Yucca brevifolia) in the national park that bears its name in southern California’s Mojave desert.

As is typical in California, very different landscapes succeed each other in a relatively small area. So, over a week and surprisingly small distances, I traveled the region to get a sense of its rich tapestry of habitats  (see my itinerary).

Heading east from LAX Airport, I drove up a winding road into the San Gabriel Mountains. By the time I reached 2000 meters (6500 feet), I was completely surrounded by tall, dense forests comprising six or seven intermingled conifer species, and a number of ski resorts, deserted in the summer season. At my campsite that night, the temperature dropped to just a hair above freezing, quite a contrast from the stifling August heat I’d experienced that very morning!

The next day, I followed the spine of the mountains through the San Gabriels and on to the San Bernardinos. Driving along the glittering blue waters of Big Bear Lake, I went past “Starvation Flats Road”, a warning of what lay ahead. And indeed, I soon reached the eastern slopes, which gave me a striking view of the Mojave desert below – stark yellow plains that disappeared in the haze. Making my way down, the conifers began to thin out, and soon the first Joshua trees began to appear, some of them nearly as tall as the oaks they grew with.

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On the eastern foothills of the San Bernardino mountains, Joshua trees grow together with Valley oaks (Quercus lobata) and California Black oaks (Q. kelloggii).

Turning back to look at where I had come from, I could see Old Greyback, the tallest summit in southern California. Then I headed southeast, hugging the base of the mountains, to the famous town of Palm Springs. Originally the town was named for the freshwater springs that flow down from the mountains and the California Palms (Washingtonia filifera) that grow along the canyons. Today the palms line every street in town, towering above the low buildings.

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The skinny, carefully trimmed palms that define the look of Palm Springs are in fact unnatural, as wild fan palms develop thick skirts from their dead leaves that can extend almost all the way down to the ground. See below.

The landscape to the east of town is desolate, highlighting how precious and unusual the springs are. Creosote shrubs, their leaves a characteristic greyish yellowish, grow on the dusty flats as the incessant wind spins the thousands of turbines of the San Gorgonio Pass wind farm (the third largest in the state). Suddenly, a green ribbon appeared in the distance, and as I got closer, it resolved itself into a copse of large cottonwood trees, towering over an incredibly thick mesquite thicket. This is Big Morongo Canyon, the largest freshwater spring in the region.

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The thick canopy of cottonwoods (Populus fremontii) at Big Morongo canyon.

As soon as I stepped under the trees, it was clear that I had entered an oasis of life: orioles, goldfinches and hummingbirds flitted in the undergrowth, while jays pestered a great horned owl that they had found perched in a cottonwood. Cottontail rabbits hopped on the path ahead of me, and a coachwhip (Masticophis flagellum) rattled its tail at me, this tiny, harmless snake attempting (as many other local snakes do) to look like a rattlesnake to scare off potential predators.

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A female Anna’s hummingbird (Calypte anna) and some bees drinking at Big Morongo.

Before it got too hot, I continued on my way farther east, until I reached Yucca Valley, and from there Joshua Tree National Park. It is a surreal experience, as they appear almost out of nowhere, the phantasmagorical silhouettes of these giant tree Yuccas stretching to the horizon, the unique bluish grey tinge of their leaves giving a peculiar appearance to the air itself. It is a landscape quite unlike any I had ever seen. Though it is hard to understand how the first pilgrims decided that one of these trees was the prophet Joshua, pointing them in the direction of the promised land, as each tree seems to point a different way!

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Right on the edge of the national park, a Greater Roadrunner (Geococcyx californianus) looks for its next prey perched in a Joshua Tree.

While the northern parts of the Mojave are low-lying, making up the famously inhospitable Death Valley, Joshua Tree National Park sits at the southern edge of the desert, on a plateau about 1200 meters (4000 ft) above sea level. The cooler temperatures at that altitude are what allow the Yuccas to thrive, in truly remarkable numbers.

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A typical scene from the northern section of the park. I couldn’t find any data on this, but there must be tens, if not hundreds of thousands of Joshua Trees in the park.

While Joshua trees are the most distinctive – and seemingly the hardiest, growing even in the most exposed flats – they are not the only trees of the park. Many sandy desert washes cross the plateau, and along each of them grow various dicot trees. Most noticeable among these is Chilopsis linearis, in the Bignonia family. In the vernacular, it is known as ‘Desert willow’ because of its unusually long, narrow leaves and the fact that it grows in riparian habitats. Another tree found in the Mojave is the Papilionoid legume Psorothamnus spinosus, known as ‘Smoke tree’, as its pale grey leaves look like a cloudy puff of ashes, brightened in  summer when the trees are covered with gorgeous indigo-tinted, pea-like, flowers.

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Smoke trees in the aptly-named Smoke Tree Wash, inside the Joshua Tree National Park.

Finally, there are two species of the legume tree Palo Verde (Parkinsonia), one of which I found providing shelter for a desert bighorn one evening near my campsite.

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A young desert bighorn sheep (Ovis canadensis nelsoni). Bighorn populations have recovered quite well in recent decades, though they are still facing various threats in the California deserts. There are fewer than 300 found in Joshua Tree National Park (ca. 800,000 acres, or 3,200 km² in size).

Furthermore, the park is known for its elaborate formations of basaltic rock, which add to the surreal beauty of the landscape, and attract rock-climbers from all over the world. These rock piles, with the shelter and extra moisture that they provide, also allow oaks, pinyon pines, and junipers (all trees that typically grow on the higher mountain slopes) to survive down on the plateau as well.

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At Hidden Valley, in the central section of the park, large pinyon pines (Pinus monophylla) grow among the basalt rock piles.

There are also several fan palm oases in the park, from Fortynine Palms, standing on its own amid the bare rocky slopes, reminding me of the mountains of northern Oman, to the glorious Cottonwood Springs, where massive cottonwoods barely top over the enormous palm trees, who formed a dense cluster sheltering a family of barn owls.

The saddest fan palm oasis is undoubtedly Mara, also known as Twentynine Palms. It is said that the Serrano Indians who used to live in the area planted one palm tree for each son that was born to the tribe after they first settled there. Last year, a criminal fire swept through the area, killing several of the palm trees. Some blackened trunks still stand, while several others had to be completely cut down. All in all, it is a sadly apt metaphor for what has befallen these first nations of indigenous people who called the area home for centuries prior to the arrival of Europeans.

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Compare the glorious Cottonwood spring, protected as it is in a remote part of the national park, with the sad oasis of Mara, still showing the scars from last year’s fire that was set by an arsonist.

From there, I drove south through the park, and the landscape began to change markedly, as this is the where the Mojave gives way to the Sonoran desert. It got warmer and drier as the elevation decreased. The Joshua trees disappeared, replaced by ocotillos and in some areas, fields of teddybear cholla cacti (Cylindropuntia bigelovii). Passing through spectacular layers of exposed rock, I reached the Bajada, a grassy savanna with large ironwood trees (Olneya tesota, also a tree legume) a scene more akin to an African savanna than the landscapes I had left behind that same morning! This was quite striking as we had found ironwood trees to be much scarcer in Baja California!

From there, it was only a short way to the final stop on my trip: the Salton Sea. Lying about 70 meters below sea level, this is actually a depression, which was periodically filled by exceptional flooding on the Colorado River. The last time this happened was in 1905. Since it has no outlet, the lake progressively becomes more saline and eventually evaporates, until the Colorado floods its banks and fills it again.

Furthermore, because of repeated Colorado River floods, the surrounding soils are very fertile, despite the extremely dry climate. As a result, in the early 20th century, at the height of the hubris that characterized the development of the American Southwest, massive irrigation projects were put in place in the Coachella and Imperial valleys, at the northern and southern ends of the Salton Sea, respectively. The latter – formerly called Valley of Death, was rebranded as Imperial Valley – in a remarkable feat of marketing well described by Fred Pierce in When the Rivers Run Dry (2006). Today, the landscape as seen from the sky is surreal: the deep blue waters contrasting with the yellow of the surrounding desert, while the valleys at both ends are an incongruous green. The perfectly rectangular fields stretch all the way to the Mexican border, for a combined irrigated area equal to nearly three times that of the Salton Sea itself! These fields produce a large portion of the state’s lettuce, broccoli, carrots, and especially alfalfa, to feed California’s behemoth dairy industry. The sight of the hundreds of sprinklers going full tilt in the midday heat, to water alfalfa that could be grown in the East for a fraction of the cost, was rather off-putting, to say the least. (For a comprehensive and depressing history of water usage in the American West, read Cadillac Desert (1986), by Mark Reisner).

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Irrigated vineyards in the southern end of the Coachella Valley. Note the extremely arid ranges in the distance, which stretch between Joshua Tree National Park and the Salton Sea.

As is by now well known, the Colorado has been well and truly “tamed”, its once wild run dammed in fifteen places, and every ounce of its water used to irrigate the thirsty cities and fields of the West, so that hardly a drop reaches its once mighty delta. In other words, the Salton Sea may soon be gone for good. And what else can we look forward to?

In a nutshell, the whole area is a mess. For a century, agricultural runoff has ended up in the Salton Sea itself and now, as the Sea is shrinking, more and more of its bed is being exposed and sediments heavily contaminated with salt and pesticides are being picked up by the winds. This is a massive public health issue. Not to mention the ecological disaster as the waters become too saline to support the fish that dwell in it, depriving the millions of birds that pass through the area of some of the only food available on that portion of the migration flyway. Furthermore, the well-publicized water shortages and catastrophic wildfires of California get worse with every passing year.

Obviously, agriculture in southern California will continue, but in what fashion? According to the California Department of Agriculture, more than half of the irrigated cropland in the state is badly affected by salinization. Surely this should be a wake-up call to explore alternative futures. For one thing, as Richard Felger, doyen of US-based Sonoran desert botanists and explorers, puts it, we need to learn to “Fit the crop to the land, not the land to the crop.”

Even though desert organisms are tremendously well-adapted to the harsh conditions they face on a daily basis, even they can only take so much. According to a recent study, rising temperatures are rapidly making the national park unsuitable for Joshua Trees themselves. In the best-case scenario, major efforts to reduce greenhouse gas emissions could save around 20% of suitable habitat for Joshua trees within the park after the year 2070. In the worst case, with no reduction in carbon emissions, 50 years from now,  the Joshua Tree National park will retain a mere 0.02 percent of its Joshua tree habitat.

The first white explorers who saw the Western deserts of North America thought them so hostile that they could never support settlement, disregarding the Native Americans and the wealth of fauna and flora who had long been living in the desert, in a very delicate balance. But in the frenzy of the twentieth century, through truly prodigious amounts of effort, descendants of the European colonists radically reshaped these landscapes to suit their needs with very little understanding of the long-term consequences of their actions. The entire enterprise is clearly and dangerously unsustainable, as water reserves that accumulated over hundreds of thousands of years were drained in just a few decades.

We often hear about the fight against desertification, which is conflated with some sort of fight against advancing deserts. But it is important to remember that deserts, while harsh, can still be beautiful and full of vibrant and unique life. Joshua Tree National Park, the Mojave National Preserve, and a few other protected areas give us a glimpse into what once was. But they are mere handkerchiefs. If the region is to have a chance at a sustainable future, we need new paradigms, new laws based on a much better understanding of how life can balance itself in arid lands. Based on that understanding, it is imperative that we move away from the pattern of careless exploitation and transformation, stretching farther and farther away from what these deserts once were. Instead, it is past time to commit to ecological restoration and allied activities for the Mojave and indeed all degraded and mis-used deserts and semi-deserts, especially as climate chaos unfolds.

Hard times for hemiepiphytes: Aroids have trouble making a comeback in second-growth forests

Estefania Fernandez Barrancos is a PhD student and Christensen Fellow at the University of Missouri St. Louis, where she is affiliated with the Harris World Ecology Center and the Center for Conservation and Sustainable Development at the Missouri Botanical Gardens. Estefania has previously written about how to restore bromeliad populations. Here she describes a recent study asking how well hemiepiphytic aroids recover in secondary forests in Panama.

Most people know aroids as the familiar swiss cheese plants found growing in hotels and shopping malls. But few people realize that the aroid family (Araceae) is the fifth most diverse plant family on Earth. These plants provide essential food and refuge for birds, bats, insects, and primates in tropical forests throughout the world.

Like many other plants, aroid populations are dropping because the rainforests where they live are being converted into farms. My new research shows that aroids are also slow to recolonize new forests that become available.

City Aroid Country Aroid

City aroid (left, Monstera deliciosa in a building), country aroid (right, Monstera sp. in a Colombian forest). Photo sources: Left Maja Dumat CCBY 2.0; Right – Thomas Croat via Tropicos.

Before I describe that research though, here is some botanical jargon for the uninitiated. Epiphytes (a.k.a. air plants) are plants that grow on other plants (but not as parasites). Hemiepiphytes are plants that grow on other plants but only for part of their lives. Many aroids are hemiepiphtyes because they start life in the soil of the forest understory and grow until they find a tree. Then they climb up the tree and live above the ground, but they always keep a connection to solid earth.

To study their recovery, I surveyed hemiepiphytic aroids in native tree plantations (9-years old), natural secondary forests (8-14-years old), and mature forests (>100-years old) near the Panama Canal. These forests are part of Agua Salud – a tropical forest restoration experiment led by the Smithsonian Tropical Research Institute. In the dense forest, I found aroids by looking for their stems coming down from the trees, then I followed the stem with binoculars until I found their leaves, which helped me identify the species. In all, I surveyed 1479 trees this way.

Estefania surveying mature forest tree Panama

Estefania Fernandez (below) and field assistant Carlos Diaz (above) look for aroids in a mature forest tree in Panama.

I found out that there were virtually no aroids in secondary forests or plantations. I recorded more than 2000 aroids from at least ten species growing on trees in mature forest, but in secondary forests and plantations I found less than 1% as many aroids and only three species.

Why do aroids have recovery troubles?

One reason for the lack of aroids could be that seeds from adult aroids in mature forests can’t reach the new forests. This seems unlikely because all of the secondary forests and plantations in my study were close to mature forests full of aroids, less than one kilometer away. Also, birds that are present in secondary forests are known to eat aroid fruits and disperse their seeds.

Another reason could be that the young forest canopy is too open for aroid seeds to germinate and grow. Unlike most plants, some aroids start out life growing away from light and towards darkness. (This has another great word: skototropism). It seems counterintuitive since most plants need light. But it is actually a good strategy. By growing away from light, aroid seedlings are more likely to run into a tree, which they need to climb up into the canopy and get to the light that they need to photosynthesize. So it is possible that there is too much light in the young forests and it keeps the aroid seedlings from finding a host tree.

Whether dispersal or establishment limits aroids in secondary forests, it is likely that more time will help. As forests become older and darker and birds bring in more seeds, aroid populations should eventually begin to recover. My research suggests that there is a considerable lag time required for aroids to recolonize disturbed habitats such as secondary forests and plantations.

More importantly, my study highlights how important it is to hold onto old forests. Forest restoration is a poor substitute for mature forest conservation. To the extent that we can prevent older forests from being cut down, it will help preserve many species of aroids as well as other plant and animal species that are threatened by habitat loss.

Aroid being pollinated by scarab beetles at Barro Colorado Island, Panama. Source: www.aroid.org.

You can read more about Estefania’s research in her new open-access paper in Tropical Conservation Science, or on other posts from Natural History of Ecological Restoration (here and here).

Cove forests on the southern Cumberland Plateau are losing trees

Rich, cove forests are losing tree species faster than sandy, upland forest, according to long-term research in Sewanee, Tennessee led by Jon Evans (University of the South), Callie Oldfield (University of Georgia), and Leighton Reid (Virginia Tech).

The southern Cumberland Plateau in Sewanee, Tennessee is a ribbon of stacked limestone and sandstone rising above the valley by some 275 m, about four-fifths the height of the Eiffel Tower. From above, the plateau’s forests stand out dark green against the surrounding farmlands and give the impression of a large, homogeneous block of habitat.

The reality is somewhat different. The forests of the southern Cumberland Plateau are botanically distinct, and they are changing differentially over time.

Dick Cove Map

The southern Cumberland Plateau near the borders of Tennessee, Alabama, and Georgia. Imagery © Google Earth 2019.

The plateau’s sandstone cap is dry and craggy. Blueberries thrive in acidic soil under a canopy of oaks and hickories. Where the soil is especially shallow, the forest opens up onto exposed outcrops with fence lizards and prickly pear cacti. Just a stone’s throw away, the cove forests are a world apart. Wet and calcareous, the plateau’s deep, dark coves are famous for limestone caves and ephemeral wildflowers. Even though they are close neighbors, the two dominant forest communities of this region share less than 25% of their plant species.

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Upland forest on the top of the Cumberland Plateau, underlain by the sandstone. Photo by Jon Evans.

As part of a long-term forest change study, in 2014 we surveyed tree communities in upland and cove forests that had been previously surveyed in 1995 and 2005. Our results, published in the Natural Areas Journal, showed that upland forests maintained the same suite of tree species in roughly the same numbers, but cove forests became considerably less diverse. For example, we detected nine fewer tree species in the plots in 2014 compared to 1995. Understory trees were hardest hit – less than 1/3 of the species that were present in 1995 were still represented in the understory in 2014.

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Cove forest in Thumping Dick Hollow, underlain by limestone. Photo by Jon Evans.

Being neighbors, upland and cove forests have been subjected to similar disturbances over the past few decades. For example, both forests have comparable exposure to wind storms, pathogens, and herbivores – particularly deer. White-tailed deer have become overpopulated due to the loss of their natural predators, and few tree seedlings escape their browsing. We have seen PVC plot markers chewed to the ground by ravenous deer. Our observations suggest that cove forest tree species are less resistant to these disturbances than their upland counterparts.

We speculate that some trees on the sandy uplands might be pre-adapted to the new deer browsing regime. Several upland tree species are clonal. For example, sassafras, sourwood, and chestnut oak trees can share resources with smaller seedlings that sprout from their bases or roots. The parental subsidy might help these species maintain their populations in the droughty, acidic upland soils of the Cumberland Plateau. It could also help seedlings keep growing after they have been munched by a deer.

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Sassafras (Sassafras albidum) is a clonal tree species common in upland forests on the Cumberland Plateau. Photo by Callie Oldfield.

Clonal species are less common in the cove forest. There the dominant trees like sugar maple and tulip poplar typically reproduce via seeds. Paw paw is one of the few clonal species that grows in the cove forest, and it is also one of the few species that increased in abundance there from 1995-2014.

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Leighton Reid (left) and Callie Oldfield (right) survey tree communities on the southern Cumberland Plateau in 2005 and 2014, respectively. Photos by Jon Evans.

The southern Cumberland Plateau is regarded by some conservation groups as a resilient southeastern landscape, and indeed its variable topography and large extents of natural habitat may help many species resist or respond to new environmental challenges. However, our research highlights that the two dominant tree communities of the southern Cumberland Plateau respond to disturbances differently and may have a limited capacity to buffer one another from ongoing change.

 

For more information, see our new paper in Natural Areas Journal. To request a pdf, email jon.evans@sewanee.edu.

Desert Trees of the World – A new database for ecological restoration

For the past five years, James and Thibaud Aronson have been traveling to the driest parts of the world to collect data about the distribution, ecology, uses by humans, and up-to-date systematic botany of  the soul-satisfying and mind-boggling trees that grow in Earth’s beleaguered, beloved, and mega-diverse drylands. Here they describe the content and purpose of their new Tropicos database. This work builds on more 3 decades of collaboration between James and Edouard Le Floc’h, who is also a co-author of the database and a book-in-progress on desert trees and their role in ecological restoration and allied activities.

Desert Trees of the World represents a multi-purpose, participatory database in which we have gathered a vast array of information about dryland trees, where and how they live, the communities they are part of, the many ways in which they are used by people, and some elements about their successful cultivation.

Our database brings together the most up-to-date botanical, biogeographical, ecological, and ethnobotanical information on 1576 species of trees from the arid and semi-arid regions of five continents and many islands. And because it is hosted on Tropicos, the Missouri Botanical Garden’s vast botanical database, a user can seamlessly access any supplementary information that may be available for a given species thanks to research carried out in other MoBot projects. Further, maps of collection sites, as well as full nomenclatural, bibliographic, and voucher specimen data accumulated digitally at MBG these past 30 years are available.

The data base is intended for students of natural history, practitioners, policy-makers, and scientists working in ecological and biocultural restoration, conservation, and sustainable and restorative environmental management.

Trees in the desert?

Most people think that deserts are – by definition – devoid of trees. Not true! Indeed, some of the strangest, oldest, and most remarkable tree species on the planet are found in drylands, a term often used to refer to deserts and semi-deserts, also known as arid and semi-arid lands.

For our purposes, drylands are all the lands of the globe that receive less than 400 mm (ca. 16 inches) of rain in an average year. In total, this concerns over 42% of all lands on Earth, so listing all the tree species that occur in them was no small task! But, we were drawing on decades of travel, research and residence in quite a spectrum of the world’s deserts and semi-deserts. We also pored over specimens housed in three dozen major herbaria, and read thousands of technical scientific articles and floras in several languages. And, as this is the 21st century, we used information already online in another Tropicos project, the Catalogue of the Flora of Madagascar as well as many other online sources.

Saguaro and boojum

A cardón (Pachycereus pringlei) and a boojum (Fouquieria columnaris) in the Central Desert of Baja California, Mexico. In the harsh conditions of deserts, evolution has favored some of the strangest-looking trees on the planet.

Boswellia Oman

In southern Oman, we explored the remote Wadi Aful, where wild frankincense trees (Boswellia sacra) grow between sheer rock walls.

Astrotricha hamptonii

The irontree (Astrotricha hamptonii) is not among the most impressive-looking desert trees in our database. And yet, because it only grows on ironstone formations, clever prospectors used its distribution to discover some of the largest iron ore deposits in Western Australia.

Since there had been no previous attempts at documenting the trees of all the deserts in the world, we weren’t sure how many species we would end up with. And the end result was truly remarkable: a sum of 1576 species of trees native to deserts around the world, occurring in  422 genera and 100 families of flowering plants. Of course, new tree species are still occasionally being discovered, mainly coming out of Namibia, Somalia, and southern Arabia, but we are confident that we have captured the great majority of all extant dryland trees in this database.

jordan woods

Then again, some desert trees are not so unfamiliar to visitors from Europe or North America, such as these junipers (Juniperus phoenicea) and oaks (Quercus calliprinos), growing in the central mountains of Jordan.

What does a desert tree look like?

If asked about what a desert tree looks like, you might think of spiny or resinous, sticky trees. And you would be right. Fabaceae, the legume family, make up just over a quarter (403) of all species, and of those, 217 are Acacia sensu lato. The next ‘big’ family is the Myrtaceae (the Eucalyptus family), with 133 species, all but one found in Australia, the exception, Myrcianthes ferreyrae, being restricted to the fog oases of Peru’s hyper-arid coast. And in third place are the Burseraceae, with 111 species. This is the family of myrrh and frankincense, two desert trees whose importance for humans dates back millennia, tied as they are to the great cultures of the Old World. For reference, people’s most common images of desert trees are palms (think – oasis) and tree cacti. But there are only 28 desert palm species, and 49 tree cactus species.

We also have some remarkable oddities, such as one arborescent member of the cucumber family (Dendrosicyos socotrana), and several rose relatives (Polylepis spp.) that grow above 4000 meters in the most parched areas of the Andean cordillera!

Where do desert trees grow?

Interestingly, the different desert areas of the world are not equal in terms of their contributions to our database (see the table below, the full version of which is posted on the homepage for our database).

Region Number of Species Endemic species* Number of Genera Number of Families
Australia 389 373 62 34
Madagascar 355 311 160 55
North America 272 222 126 55
Northeast Africa 233 80 87 42
West Asia 224 86 97 46

*Endemic to the country or region indicated.

Five regions alone account for two thirds of all the species in our database, with the deserts of Australia and Madagascar being almost preposterously rich in tree species. But of course the area of arid Australia is vastly greater than that of Madagascar, so that in fact the numbers of families, genera and species in the latter country are really the most impressive of all.

 

baobabs Mada - pete

Highly degraded spiny thicket vegetation at the edge of the Ranobe PK32 Protected Area near the town of Ifaty, in western Madagascar, with few trees other than the emergent baobabs, Adansonia rubrostipa (Malvaceae) remaining. Young plants of the spiny tree, Didierea madagascariensis (Didiereaceae) developing in the bare sandy soil around the baobab in the foreground. 11 September 2006. © Peter Phillipson, Missouri Botanical Garden. http://www.tropicos.org/Image/100624586.

spiny thicket - pete

Secondary growth spiny thicket near the Ranobe PK32 Protected Area north of Toliara, in Madagascar, with occasional individuals of the locally endemic spiny tree Pachypodium mikea (Apocynaceae) – center image, but dominated by mature Didierea madagascariensis (Didiereaceae). 03 December 2018. © Peter Phillipson, Missouri Botanical Garden.

A zoom on the astonishing dryland tree species richness and diversity of Madagascar can already be found in an article we published last year, covering the remarkable assemblages of 355 tree species found in the driest part of Madagascar, of which no less than 311 are endemic to the country. This is all the more remarkable considering that they are all crowded into a narrow coastal strip in the Southwest, which is a mere 14,480 square kilometers (5591 square miles), or the same size as Connecticut.

For us, a key feature when discussing desert trees is the fact that even in the harsh areas where they found, trees can grow densely enough to form true woodlands, sometimes even with dense canopies, which has enormous importance for desert ecosystems and people. In previous blog posts we have reported on striking examples – in northeastern Jordan, and coastal Peru, among others, where evidence of former woodlands provide rays of hope and guidance for people attempting ecological restoration in desert lands.

Back in 2013, James and Edouard published a first book in French (Les Arbres des Déserts: Enjeux et Promesses) profiling desert trees and developing the subject of desert woodlands. We now have a more comprehensive book in preparation, called Desert Canopies: Reimagining our Drylands. Three chapters on animal-tree relations, and photos and drawings by Thibaud will help make this of interest for a wider audience, not just specialists. We also develop the theme of ecological restoration and provide profiles and virtual field trips from many restoration programs in drylands around the world.

 Where can one see living Desert Canopies today?

Unfortunately, most drylands are found in poverty-stricken regions of developing countries, where trees are an extremely valuable resource. In recent decades, desert canopies have been hammered by rising populations of people and livestock. As a result, today these canopies are so degraded and fragmented that it’s hard to imagine what they once looked like. Western Australia is one of the few places where reasonably intact desert woodlands still cover large areas.

Great western woodlands

A typical landscape of the Great Western Woodlands, in the semi-arid southwest of Australia (mean annual rainfall 250 – 400 mm), with gimlet eucalypts (E. salubris) growing over a beautiful understory of blue bush daisy (Cratystylis conocephala).

In our last blogpost, we reported on some notable trees, tree canopies, and indigenous peoples of the Guajira peninsula in northern Colombia.

macuira stream

From looking at the tree cover, it is hard to believe that this area of Colombia is technically a desert!

wayuu family

Young Wayuu and their donkeys, standing in the shade of a tree, on their family farm in the Serranía de Macuira, a mountain oasis in the middle of the Colombian desert. The Guajira, as the region is called, is a microcosm of the problems and drivers of arid lands everywhere, as well as a good example of the diversity and life and beauty that can be found in deserts.

Other striking tree canopies can still be found in diverse places today, including some of the driest places on Earth.

Prosopis cineraria

The Rub al Khali, the famous Empty Quarter of Arabia. Even there, trees can thrive amid the sand dunes (in this case, the venerable khejri, Prosopis cineraria), that we were lucky enough to observe in northern Oman.

Prosopis pallida Peru

On the arid coast of northern Peru, Prosopis pallida and other trees can grow in the ever-so-slightly richer soils at the bottom of gullies amid the plains.

As noted earlier, drylands make up more than two-fifths of all lands on Earth, at present. Furthermore, despite their harsh conditions, drylands are presently home to well over 2 billion people, and indeed many of these are among the poorest and most vulnerable populations on Earth. The United Nations, and many other organizations are working hard on the problems of drylands and their peoples, but it is very much an uphill battle… As we passed Earth Overshoot Day on July 29th this year– the earliest date ever – it is timely to stress once again that the restoration and rehabilitation of degraded ecosystems will be key if we are to hope for a sustainable future. Restoration is undeniably harder in arid lands than in many other places, but that only means that it is more necessary. We are happy to relate that the Society for Ecological Restoration’s scientific journal, Restoration Ecology, is launching a new initiative devoted to dissemination of scientific advances on ecological restoration and rehabilitation in arid lands. Our database is offered in that spirit.

isla guadalupe

The small, arid Isla Guadalupe, off the coast of northwestern Mexico, is home to several endemic tree species, which were almost extirpated by introduced goats. But now that the goats have been removed from the island, the trees are making a comeback. Pictured here is the endemic cypress Cupressus guadalupensis, and some of the people who’ve made this recovery possible.

A large number of the trees included – 932 out of 1576 to be exact – are endemic to a single country – and most are in urgent need of committed conservation, restoration, and better management. We hope that our database can act as a reminder of the wealth of life forms that can thrive in arid lands, and an exhortation to not give up on their desert homes, scarred and battered as they may be, but rather to try and help them flourish once again.

Things are not always better on the sunny side!

Chris Birkinshaw is an assistant curator in the Missouri Botanical Garden’s Madagascar Program, based in Antananarivo. He describes his observations on forest succession at Ankafobe, a site in the central highlands.

Anyone flying over Madagascar’s highly dissected central highlands will be struck at first by the vast grasslands that dominate this landscape.  But, those looking more carefully will also detect pockets of forest within the rich network of valleys.  These forests have a distinct fauna and flora but, perhaps because of their small size, they have attracted little interest from conservationists.  Consequently, in the last few decades, the majority have been degraded or entirely destroyed as their trees were cut for timber or charcoal and the relicts burnt by wild fires that rage over this landscape in the dry season.

The Ankafobe Forest, located some 135 km NW of Antananarivo, is currently being designated as new protected area by Missouri Botanical Garden’s Madagascar Research and Conservation Program.  It is one of the larger remaining areas of highland forest but, here too, the forest has been impacted by exploitation for timber and charcoal and burning by wild fires.

Efforts are underway to restore this forest to its former extent in the recent past.  This is no easy task because away from the current forest edge tree seedlings are subjected to harsh conditions: soils impoverished and compacted by annual burning, grasses that compete greedily for water and nutrients, an extended 7-month long dry season, and exposure to hot sunshine and strong desiccating winds.  Even when firebreaks are used to prevent wildfires from penetrating the grassland surrounding the forest, few tree seedlings naturally colonize outside of nurturing limits to the forest.

Few but not none.  A closer inspection of the landscape reveals some woody plants in the grassland on the less sunny south-facing slopes surrounding the forest (south is less sunny because Madagascar is in the southern hemisphere). Perhaps then the forest could be helped to expand by planting young trees preferentially on these slopes?

Ankafobe Forest South-facing on left.JPG

Vegetation is lusher on south-facing slopes (left) compared to north-facing slopes (right) at Ankafobe, a proposed conservation area in highland Madagascar.

To test this idea in 2017 we planted 25 nine-month old seedlings of each of four native tree species in grassland 20 m from the forest edge on both a south-facing slope and a north-facing slope.  The species were selected for this test are native to the Ankafobe Forest and were available at the local tree nursery when the experiment was installed.  After 12 months the survival and growth of these young plants were measured.

All four species survived well on the south-facing slope but only one species, Nuxia capitata, had good survival on the north-facing slope.  Mortality of Uapaca densifolia was total on the north-facing slopes.  Growth was sluggish on both the south-facing and north-facing slopes with the exception of Nuxia capitata on the south-facing slope that had a mean 12-month growth exceeding 20 cm.  These results suggest that south-facing slopes may provide the best results, at least at Ankafobe, for forest restoration endeavors.

South- facing North-facing
Species % Survival Average growth (cm) % Survival Average growth (cm)
Eugenia pluricymosa 72% 4.1 8% 3.0
Baronia taratana 88% 9.1 28% 12.4
Nuxia capitata 96% 21.5 100% 8.7
Uapaca densifolia 72% 10.5 0%

Aspect – the direction that a slope faces – makes a big difference for vegetation in the temperate zone, especially in dry places. But it is not often considered in tropical ecology. Directly or indirectly, the difference in sun exposure between the slopes at Ankafobe can make the difference between life and death for young trees growing in this hostile, water-stressed environment.

To read more blog posts about the restoration efforts at Ankafobe, please click here. You may also read a 2019 open access paper about seedling trials at this site here.