By Eva Colberg, postdoctoral fellow at Cornell University. Nearly all of Mauritius’s contemporary conservation plights are rooted in or exacerbated by the effects of invasive, non-native species. To see what restoration can do for the island’s few remaining forests, Dr. Eva Colberg joined members of the Tropical Island Biodiversity, Ecology & Conservation research group to visit (and weed) one of the island’s forest restoration sites.
Red stems of strawberry guava (Psidium cattleyanum) form a wall dense enough to prevent walking through most of Mauritius’s remaining forests. Beyond impeding movement, the thick guava understory also reduces overstory tree fitness and disrupts native forest growth and succession. Originally from South America, strawberry guava is a classic case of a non-native, invasive species outcompeting and reducing habitat quality outside its native range (and islands are particularly vulnerable to invasion).
The ongoing onslaught of invasion means there’s no time to waste for restoration ecologists like F.B. Vincent Florens, Associate Professor at the University of Mauritius. “We have so many rare species on the brink of extinction [over 80% of the island’s endemic flowering plants are threatened], and have to work at the same time and learn as we go.” His life experience and ecological studies point to invasive species management as the island’s best hope for restoration and conservation, which he likens to healthcare. “First you save the person from dying and then you can treat the other issues.”
Despite decades’ worth of evidence pointing to the efficacy of invasive plant removal in Mauritius, it still isn’t widely implemented. Less than 5% of the island’s few remaining forests have been weeded of invasive plants, and even the best-protected forests are already dominated by invasive undergrowth. Frustratingly, some of the resources that could be used for invasive removal have instead hindered restoration via removal of native pioneer and nurse tree species. “We can do a lot of science, can come up with a lot of facts, but how do we get people to do what they don’t want to do?” Indeed, it’s far easier to uproot a small plant than to change someone’s mind, and Prof. Florens has an entire country to convince that saving their native forests is not only possible, but worth the effort.
Leighton Reid describes new research linking slow forest recovery to the ancient and protracted isolation that has made Madagascar a hotspot of global endemism – plus an example of working with local farmers to overcome these challenges and restore native rain forest.
Madagascar is a special place with a special history. Separated by ocean from Africa and India for the last 88 million years, this isolated tropical island has fostered the evolution of plants and animals found nowhere else on Earth. Lemurs, couas, and the plant family Sarcolaenaceae are all examples of organisms that evolved only in Madagascar. Collectively, such endemic species make up more than 80% of all plants and animals there.
Madagascar also has special problems. Almost half of the island’s forest has been cleared for agriculture since 1953, and remaining forests are at imminent risk. One recent study projected that if deforestation rates do not diminish soon, 93% of eastern Malagasy rain forest could be gone by 2070.
The combination of a large proportion of endemic species and a high degree of habitat loss makes Madagascar a biodiversity hotspot. Some people call Madagascar one of the hottest hotspots because its endemism and habitat loss are so extreme.
This week, a new study led by UC Berkeley PhD student Kat Culbertson identified another special problem in Madagascar: following disturbance, Malagasy forests recovery very slowly. Compared to other tropical forests around the world, Malagasy rain forests recover only about a quarter (26%) as much biomass in their first 20 years of recovery. Dry forests in Madagascar also recover more slowly, recovering just 35% as much biomass as American tropical dry forests over the same time period.
Why do Malagasy forests recover more slowly than forests in other regions? The answer may be related to Madagascar’s unusual evolutionary history. Culbertson and her co-authors developed four hypotheses and reviewed an array of scientific literature to evaluate support for each one.
Four ways that Madagascar’s unique history could lead to slow forest recovery
1. Native Malagasy forests lack resilience to shifting nutrient and fire regimes from current farming practices.Many rural people across Madagascar practice tavy, a farming method that involves clearing forest, burning it, and then growing rice – a staple crop. After one or a few years of growing rice, the land is allowed to recuperate for several years before it is cultivated again. In other tropical forest locations, such as southern Mexico where humans have farmed for thousands of years, similar practices can coexist with native forests, but Malagasy forests seem to have little resilience to tavy, as least at the intensity with which it is practiced today. For example, in eastern Madagascar, a 3-5 year tavy cycle can cause a native forest to transition to permanent herbaceous vegetation in just 20-40 years. The soil nutrient stocks in that fallow field may be as little as 1-6.5% of soil nutrients stocks in intact forest.
2. Madagascar is an island, and islands tend to have more problems with invasive species. Goats in the Galapagos, brown tree snakes in Guam, acacia in Hawaii, and rats everywhere – these are just some of the ways that island ecosystems have been overwhelmed and transformed by invasive species. Madagascar is no exception. Rain forest regeneration at Ranomafana is stalled by invasive guava, eucalyptus, and rose apple, while dry forest regeneration at Berenty is inhibited by a vine – Cissus quadrangularis. People in Madagascar have many more anecdotes about problems with invasive species like silver oak and Melaleuca quiquenervia, although the extent and impact of these invaders on forest recovery have not yet been studied.
3. Old, weathered soils have favored the evolution of slow-growing native plants. Madagascar is not only an island, it is a very old island, and as such its soils have been weathered and depleted of important nutrients like phosphorus. It’s hard to separate the effect of inherently low nutrient availability due to being an old island from the effect of human-induced nutrient scarcity through tavy, but one comparison of phosphorus content in rice stalks showed that phosphorus content was 10× lower in Madagascar compared to the rest of sub-Saharan Africa. If native trees have evolved to grow more slowly in Madagascar because of low nutrient availability, then on average exotic tree species should grow faster than native Malagasy ones in the same gardens. This has been shown in a few cases, but a more compelling analysis would need more species.
4. Finally, Malagasy forests have dysfunctional seed dispersal. One way in which Madagascar is different from other tropical areas is that by and large its trees have evolved to have their fruits dispersed by lemurs. Unfortunately, many of the lemurs that could disperse Malagasy tree fruits are either extinct or endangered – in many cases due to a combination of hunting and habitat loss. Moreover, the lemurs that remain are reluctant to venture outside of forest fragments (perhaps with good reason) and so they are unable to disperse seeds to regenerating farmlands that most need them.
In essence, the ancient and protracted isolation that has made Madagascar so unique has also made it uniquely vulnerable to contemporary changes like deforestation, fire, and agriculture. The result is an unfortunate combination: Madagascar not only has some of the highest deforestation rates, it is also one of the places least ecologically equipped to rebound from those disturbances.
The way forward – working with local people
Despite these challenges, Madagascar has committed to restoring four million hectares of lost habitat by 2030, an area nearly 7% the total national territory. This is a tall order in a country where technical difficulties are high and financial resources are often low, but it can be done, and the way forward, undoubtedly, is to work with local people.
One group that exemplifies bottom-up restoration is GreenAgain, a non-profit restoring native rain forest and supporting rural livelihoods in eastern Madagascar. GreenAgain is led and staffed by farmer-practitioners whose neighbors, family, and friends contract with GreenAgain to design, plant, and monitor diverse native forests on their lands. Last year, GreenAgain staff planted 20,000 trees across central eastern Madagascar, each one carried by hand, on foot, from one of eight regional tree nurseries. The rural farmers at GreenAgain collect rigorous data on tree survival and growth and collaborate with scientists to analyze and share the results of their tree planting experiments.
For example, one of the earliest experiments at GreenAgain was an assay of tree planting strategies intended to improve native tree seedling survival during plantings that occur in the dry season. Trees planted during the dry season typically have high mortality, sometimes in excess of 40%. One of the strategies that local farmers recommended to improve survival was to erect small teepees over each seedling using the leaves of a common fern, Dicranopteris linearis. These structures are temporary – they eventually dry out and blow away – but GreenAgain’s experiment showed that they reduced transplant shock (i.e., mortality in the first few weeks) by 75% compared to seedlings that were left to bake in the hot sun. In contrast, many of the other treatments had no discernable effect.
To analyze and publish these findings, GreenAgain partnered with an award-winning undergraduate researcher, Chris Logan, in my lab at Virginia Tech, who led a peer-reviewed paper that is now available at Restoration Ecology.
Could technological solutions like hydrogels or irrigation systems produce greater improvements in dry season tree survival? Yes – they probably could for a certain price, but homegrown solutions like fern leaf shade tents are free and easily accessible to any person doing restoration across eastern Madagascar. They are also more likely to be used because they were developed by local people.
This study also showed that some native tree species are much better at coping with dry season stress than other species, so another possible solution for dry season plantings could be to plant only the tough survivors. Once those trees survive and begin to produce shade, fern leaf tents may not even be needed anymore to help more sensitive native species survive and grow.
To read more about ongoing restoration and ecological research in Madagascar, read our new review of how Madagascar’s evolutionary history limits forest recovery and our new open-access paper about strategies for dry season plantings in eastern Madagascar.
If you are in a position to support the work of local farmers restoring rain forests in eastern Madagascar, consider donating to GreenAgain at their website, greenagainmadagascar.org.
By Estefania P. Fernandez Barrancos, a PhD candidate in Biology at the University of Missouri – St. Louis and a fellow of the Whitney R. Harris World Ecology Center. Her most recent research paper in Forest Ecology and Management is freely available through March 9th.
When most people walk through a forest the last thing they probably look at is dead vegetation, and unless you are an avid mushroom harvester you probably don’t even notice dead logs. However, dead wood stores an important amount of carbon. An amount important enough that if dead wood disappeared it could promote more changes to our already rapidly changing climate.
Dead wood is also a crucial habitat for many organisms such as fungi, insects, and birds. Many insects and fungi use dead wood as a source of food and nutrients, and several species of birds are only able to nest in dead logs.
Anthropogenic disturbances, such as logging and deforestation, can significantly decrease the amounts of dead wood present on the forest floor, sometimes leading to losses of up to 98% of dead wood. The implications of dead wood loss are potentially warmer temperatures due to the release of carbon contained in dead wood as well as the loss of habitat that is critical to many forest organisms. Tropical ecosystems contain some of the most biodiverse habitats on Earth, yet they are among the ecosystems that suffer the most from anthropogenic disturbance. For example, most forests in the county of Coto Brus in Southern Costa Rica, our study area, were transformed into cattle pasture or coffee plantations in the 1950s-1980s. Today, the landscape consists of a mosaic of cattle pasture, coffee plantations, and small forest remnants.
Forest restoration is the process of assisting the recovery of an ecosystem that has been damaged or destroyed (SER International Standards) and it has a high potential to reverse the problem of dead wood loss through different strategies. In the Tropics, the most common restoration strategies are passive and active restoration. Passive restoration consists of allowing an ecosystem to recover with minimal to no human input. In contrast, active restoration consists of assisting the ecosystem in its recovery through actions such as tree planting.
Recently, I studied the pattern of dead wood re-accumulation through time after disturbance in southern Costa Rica as well as the effectiveness of passive and active restoration at recovering dead wood as it is found in undisturbed forests. To evaluate dead wood accumulation through time, my team and I surveyed dead wood volumes inside 35 forest patches of increasing ages (from 3 to over 100 years old) that were former coffee plantations. We evaluated the effectiveness of active vs. passive restoration at recovering dead wood by surveying dead wood volumes inside 17-year old passive and active restoration plots and inside nearby old-growth forests. Our passive restoration treatment was represented by natural regeneration plots around which fences were established to exclude cattle and where vegetation was allowed to re-establish naturally. Our active restoration treatment was represented by restoration plantations, where seedlings of two native (Terminalia amazonia and Vochysia guatemalensis) and two naturalized (Inga edulis and Erythrina poeppegiana) tree species were planted 17 years ago to facilitate the re-establishment of vegetation. Our reference ecosystem included nearby old-growth forests over 100 years old.
We found that dead wood recovers following a logistic shape through time in our study area: volumes are low initially, increase rapidly, and then plateau. The low volumes of dead wood at the beginning of succession could be explained by the fact that most of the wood remains are typically harvested by local inhabitants after lands are abandoned in our study area. As pioneer trees recolonize abandoned coffee plantations and subsequently die, they produce dead wood. As the forest grows older, there is a mix of short-lived pioneer trees and long-lived trees which contribute to large amounts of dead wood on the forest floor through branchfall and their own deaths.
We also found that restoration plantations contain 41% of dead wood amounts found in old-growth forests, whereas natural regeneration only contained 1.7% of dead wood volumes found in old-growth forests. The extremely low recovery of dead wood in natural regeneration might be explained by the fact that our natural regeneration plots were dominated by exotic grasses which typically hamper tree colonization. If there are no trees growing in the plots, there cannot be dead wood either. This is an important finding, because it shows that restoration plantations area a faster and more efficient way to recover dead wood in this fragmented, pasture-dominated landscape, even though this restoration strategy might be more time consuming and expensive due to the costs and time of planting seedlings.
Overall, our study unveils an important forest process, showing that dead wood carbon pools recover following a dynamic logistic pattern through time in this Neotropical forest region. Knowing that dead wood is 50% carbon, our findings allow us to predict carbon stocks in Neotropical forests more accurately. Our study also shows that restoration plantations accelerate the recovery of dead wood carbon pools in this Neotropical ecosystem, and potentially promote the preservation of dead wood-associated biodiversity.
For more information, see our recent paper in Forest Ecology and Management, which is freely available online through March 8th, 2022.
Rakan “Zak” Zahawi is the executive director of the Charles Darwin Foundation in Galápagos, Ecuador. He and his collaborator, Rebecca Cole, partnered with a coffee processing plant to repurpose farm waste and help restore a rainforest. Read more about the project in an open access article in Ecological Solutions and Evidence.
From the very first time I saw the results of the orange peel project on the ground back in 2004 I was sold! What a brilliant idea I thought – use the waste products generated from the production of orange juice (and any related citrus products) to regenerate degraded habitats where expansive dry forests were once found. The idea was Dan Janzen’s, an ecologist at the University of Pennsylvania who has worked in northern Costa Rica for the better part of 50 years. At the time I was working for the Organization for Tropical Studies (OTS) and given that I work as an ecologist in forest restoration, a colleague thought I might be interested.
The idea is simple, take truckloads of agricultural waste (in this case orange peels) and spread them in a layer ~0.5 m thick across hectares of extremely degraded land dominated by forage grasses. Under the tropical sun this layer generates an enormous amount of heat, and in the process of ‘cooking’ down it asphyxiates and kills the forage grass that is notoriously difficult to eradicate. At the same time, birds and other seed dispersers visit the site, attracted by the abundant larvae helping to decompose the material. The net result is a lot of organic material and nutrients and many seeds dispersed combining to help jump-start the recovery of a degraded habitat and return it to a forested state.
I never forgot that visit and over the years that I worked in southern Costa Rica as Director of the Las Cruces Biological Station (a field station run by OTS) I always thought of trying the study there. The difference was that there was no orange production in the region but another agricultural byproduct was widely available – coffee pulp waste! I wondered – could the results of the orange project be replicated with another agricultural waste product? While the idea was always on my mind, it took more than a decade for me to actually test it after Rebecca Cole, a long-term research colleague who was based at the University of Hawaii expressed interest in collaborating.
With funds secured from the March Conservation Fund, we setup a modest pilot study with a 35 × 45 m plot buried half a meter deep. That’s 30 dump trucks – or 360 m3 of material! As with the orange peel study, this land was primarily degraded pasture and would have been slow to recover on its own. We monitored this and an adjacent similar-sized plot for 2 years and the results were nothing short of spectacular. While the control treatment languished with overgrown grasses with a few shrubs, the coffee waste plot was completely transformed. The grass was smothered and in its place a patch of young trees. All species were pioneers but they are nonetheless critical to the recovery process – and the fact that they dominated the entire plot was really promising. With time it is hoped that more mature forest species will come into this system and establish – and with a young canopy of pioneers providing a little shade, the conditions are perfect for this to happen!
This study is a small pilot project, but the results speak for themselves. So does the coffee industry! Every year, millions of tons of coffee pulp waste are generated and finding a way to not only dispose of this waste in an ecologically sound manner, but also use it for habitat recovery is a win-win for everybody. It is exceedingly rare for industry to be able to pair up so seamlessly with conservation and restoration that it is hard to believe. Of course, there are hurdles – such as governmental regulations that manage such waste products, but the potential here is enormous. And the next challenge before us is to see if we can bring this idea to scale and test the methodology across big areas of degraded habitat in the tropics. We will keep you posted!
Read more about this project in a recent open-access article published in Ecological Solutions and Evidence.
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.
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.
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%.
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.
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.
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?
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.
Is the amount of land a country pledged to restore related to their past record of restoring forested landscapes and implementing sustainable development?
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?
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.
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.
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.
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.
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.”
A regrowing forest in central Costa Rica, showing the promise of restoration. Photo credit: Matthew Fagan.
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 (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 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).
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?
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.
Average growth (cm)
Average growth (cm)
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.
Green Again Madagascar is a young non-profit aiming to reconnect rain forests in eastern Madagascar and collecting heaps of data in the process. Disclosure: Leighton Reid wrote this blog and is on Green Again’s board of directors.
Matt Hill is trying to restore a rainforest corridor across eastern Madagascar. His motivation is that Madagascar’s wet, eastern flank was once blanketed by a dark, rich forest festooned by bizarre plants and teeming with uniqueanimals. No longer. Over the last 70 years humans cleared almost half of what was there in the 1950s – mostly for farming. Although the farming is often temporary, the forest rarely grows back. Weedy ferns and exotic trees find their way onto the abandoned farms and take hold – boxing out the Malagasy species.
Some tropical rain forests can recover swiftly on their own, but not these. Eastern Madagascar is a strong candidate for hands-on ecological restoration.
Madagascar (left) and the region of eastern Madagascar where Green Again Madagascar operates (right). Dark green areas are intact rain forest. Colored ovals show the expanding project scope of Green Again over the past four years. Green Again hopes to one day reforest a longer corridor across the northeastern side of the island. Imagery is from Google Earth.
In the landscape around Foulpointe, native forest was replaced by shifting agriculture, which was replaced by a forest of invasive Melaleuca quinquenervia, a tree native to Australia. Photo by L. Reid.
Matt is a middle-aged ex-pat and a self-described “quant”. His father was a math professor, and Matt followed in his footsteps, earning a degree in mathematics from the University of Chicago and subsequently a masters from UCLA. Before landing in Madagascar, Matt had a career on Wall Street analyzing large databases for Putnam. He retired early seeking a simpler and more natural lifestyle, which he found in abundance in rural northeastern Madagascar.
I first met Matt in 2015 at Parc Ivoloina – a zoo and forestry station near the port city of Toamasina. Clad in gym shorts and flip flops, Matt was buzzing between nursery beds shaded with bamboo slats and a laptop powered by a portable solar panel, where a local was entering data about tree survival and growth. Matt explained his tree planting system to me. At each stage, from seed to tree, he and his team measure plant performance – including survival, height, and diameter. Matt’s team uses these data to quickly adopt methods that work and discard methods that don’t.
As he explained his tree planting system to me, I was impressed by Matt’s attention to rigorous data collection – a preadaptation from his Wall Street career that serves him well in his new pursuit of tropical forest restoration.
Matt Hill (left) explains database management to a local community member.
Starting a forest restoration program in eastern Madagascar
Matt was introduced to forest restoration by accident when he was stranded for several days in Toamasina waiting for the wild, muddy road to Maroantsetra to become passable. He visited Parc Ivoloina on a whim and learned about a recent wildfire. A local man had been making charcoal when his fire got out of hand and burned his own farm and 20 acres of a nearby forest. The experience moved Matt to begin growing and planting native trees on the burned land. This effort congealed into an NGO called Green Again Madagascar.
From the start, Green Again has been a collaborative effort involving a team of local people. Jean François Solofo Niaina Fidy is the head forester at Parc Ivoloina and president of a nearby village association. He initially advised Matt on the project and helped build local support. Many community members joined the restoration effort – growing trees in the nursery and planting them in the burned area. It is a steep learning curve. Many local people have only a few years of school and may not have held a pencil for some time. Matt teaches them to use GPS units, record data on datasheets, and enter it into an Excel spreadsheet. When the data do not make sense, they return to the field to take repeated measurements.
The work is hard but good by local standards. Many locals make their living by breaking large boulders into gravel by hand, with a hammer. Others spend their days shoveling sand from the river into dugout canoes and paddling it to shore where it is picked up by road construction trucks. In contrast, locals who get involved in these forest restoration projects pick up transferable skills in horticulture, computing, and business management.
Coping with wildfire (and learning from it)
In early November 2016, Matt called me in a panic. There was a wildfire. His plantings had burnt to a crisp.
Fires are common in eastern Madagascar, but this was a tragedy. To make a bad situation worse, the plantings that burned were an experiment that Matt was doing for a master’s thesis at the University of Minnesota.
A wildfire in 2016 that swept through a forest restoration site, destroying Matt’s master’s thesis experiment.
In the ashes of his ruined experiment, Matt found a few survivors. He discovered that some native trees are resistant to fire. These survivors may lose their leaves and stem to fire, but they can resprout from roots.
Importantly, Matt also learned that trees planted near the edge of plantings were more vulnerable to fire than trees planted in the center of a plantation. This is because the landscape outside of the tree plantations was more flammable than the trees inside the plantations. In particular, the thatch from a common fern (Dicranopteris linearis) would catch fire and burn for quite a long time.
Green Again’s recent projects have taken this new information on board. Now, new plantings are designed with the fire survivor species on the outside and the delicate species on the inside. Some new plantings are also more extensive, so that the edge-to-interior ratio is lower and less of the trees are placed in the riskiest spots.
For good measure, Matt’s team also includes some “vulnerable” tree plantings using the earlier techniques so that the next time a fire sweeps through one of the sites, Green Again will have tangible evidence about which strategy is the most fire-proof.
A pristine rainforest in eastern Madagascar.
Green Again Madagascar has a small operating budget based on charitable donations and memberships. To learn more, visit the Green Again Madagascar website or write to Matt at GreenAgainMadagascar@gmail.com.
Photos: All photos are by Matt Hill unless otherwise noted.
Rachel Reid is a postdoctoral researcher at Washington University in St. Louis. She uses isotope chemistry to answer questions about ecology, geology, and conservation – including questions that can help build reference models for ecological restoration. Note: This blog is republished with permission from Amigos (No. 91 May 2019), the newsletter of Las Cruces Biological Station.
Many people head to Costa Rica for spring break to see monkeys and sloths at Manuel Antonio National Park or to try their hand at surfing in the Pacific. While we did stop to gawk at the crocodiles that hang out under the bridge over the Tárcoles River with a busload of tourists, the goal of our trip diverged significantly from the spring break crowd – we were heading off the beaten path to southern Costa Rica to collect samples of modern and ancient bat guano (aka poop).
Bats sometimes visit the same caves over thousands of years, and the accumulated piles of guano offer a unique opportunity to study past environments. Just like a core of sediment from the bottom of a lake or the ocean, a core of bat guano collected from a cave contains useful information about the past, both recent and distant. The material at the bottom of the core is the oldest and that at the top is the youngest, so by sampling the length of a core, we can essentially take a short, stinky walk back in time.
We are interested in detecting changes in bat guano chemistry (particularly the carbon isotope values) through time as a way of evaluating what type of vegetation would have been on the landscape in the past. This works because information about the plants at the base of the food chain gets propagated up to the plant-eating insects and then to the insect-eating bats whose guano we’re sampling.
Like other animals, bats and insects both gain carbon and nitrogen through the food they eat. Bats eat insects, which are in turn eating the local vegetation. Different types of plants have different carbon isotope values, such that most trees and shrubs (C3 plants) have much lower carbon isotope values than most grasses (C4 plants). Shifts in tropical bat guano carbon isotope values, therefore, are indicative of landscape-level changes in vegetation between more open, grassland plants and tropical forest.
How does bat poop inform conservation?
In the late 1940s, southern Costa Rica was nearly 100% forested. We know this from aerial photos – the earliest ones are from 1948. In later years, aerial photos show that most of that forest was cleared for coffee plantations; two thirds of it was cleared by 1980, for example.
This recent deforestation has motivated forest restoration efforts such as the creation of biological corridors and international scientific studies. Nonetheless, several studies (such as this and this) suggest that extinction rates in this region may be lower than would be predicted from recent habitat loss. One explanation for this could be that the regional flora and fauna evolved for several thousand years in a mixed forest and non-forest landscape managed by humans. By piecing together records of past vegetation from bat guano cores, we’ll be able to gain a better picture of what the landscape would have looked like in the past and potentially refine landscape-scale conservation and restoration targets.
For this first trip, our goals were to visit several caves to collect samples and to scout out future sampling opportunities. Southwestern Costa Rica has the highest concentration of karst caves in the country, so we were in the right place. In four days of fieldwork we visited three different caves (two of them twice!), collected 77 cm of core material, and took dozens of samples of modern bat poop.
At Bajo los Indios Cave, also known as Corredores, along the Rio Corredor, we ventured into a restricted, elevated chamber in hopes of finding deeper, more protected accumulations of guano. We were disappointed to find that even in this higher chamber, the cave was very wet and muddy and any significant guano accumulations appeared to have washed away. We collected a guano/mud core anyway and we’ll see what we can learn from it.
The bat guano team. From left to right: Leighton Reid & Christy Edwards (Missouri Botanical Garden), Rachel Reid & Alice Xu (Washington University in St. Louis), and Jeisson Figueroa (Organization for Tropical Studies). Photo by Jeisson Figueroa.
Leighton Reid uses a peat corer to extract a sample of bat guano from a karst cave. Photo by Jeisson Figueroa.
One additional important piece to our project is to try to get a better idea of what modern insectivorous bats, such as the mesoamerican mustached bat (Pteronotus parnellii mesoamericanas), are eating. We’ll then use that information to better interpret our results back in time. We’re excited to start analyzing samples!