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.

Dick Cove-Upland2

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.

Dick cove - cove bench1

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.

Sassafras

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.

Leighton & Callie

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.

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

*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.

Green Again: Restoring rain forests in eastern Madagascar

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 unique animals. 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.

RevisedExpansionMap

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.

Melaleuca quinquenervia Analalava

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.

MattQuant_Edit

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.

fire_03

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.

forest_06

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.

 

What can bat poop tell us about past tropical landscapes?

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.

Bat Food Chain

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.

Bat Guano Team by JF

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.

Taking a guano core by JF

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!

This pilot study was generously funded by grants from the Living Earth Collaborative and from the International Center for Energy, Environment and Sustainability.

How does fire affect ant-mediated seed dispersal?

Eva Colberg describes her ongoing research at Shaw Nature Reserve. She is a Ph.D. student in the Biology Department at the University of Missouri St. Louis.

In the late 1940s, Ohio-born entomologist Mary Talbot spent her days crouched in the woods of St. Charles, MO, tracking ant activity in painstaking detail through the seasons. Similarly, last summer I tried my hand at watching ants in the woodlands of Shaw Nature Reserve, with the addition of crumbled pecan shortbread cookies and the help of my field assistant, Dayane Reis. Foraging ants flocked to the buttery feast, the contrast of the crumbs’ sandy color against dark soil and leaf litter allowing us to easily follow the cookie thieves back to their nests.

EvaNHER20190301_Photo1

A plot of flagged ant nests (found by following cookie-bearing ants) in the Dana Brown Woods, one of the management units at Shaw Nature Reserve.

We watched at least seven different species of ants run off with the cookie crumbs, but I was most interested in the winnow ant (Aphaenogaster rudis). Reddish-brown, long-legged, and narrow-waisted due to a double-segmented petiole (the connection between the abdomen and thorax), the winnow ant worker is an elegant lady. She is also remarkably swift-footed and strong, adept at carrying chunks of pecan cookie or naturally occurring analogs.

EvaNHER20190301_Photo2

A winnow ant (Aphaenogaster rudis) worker, with the petiole and post-petiole that give the species its svelte waist. From her head to the end of her abdomen, this ant is about 4.5 mm long.

To an ant, a cookie more or less resembles an insect carcass, a staple of many ant diets. Chemically and nutritionally, the seeds of many of Missouri’s spring-flowering herbs also resemble a delicious dead insect (or cookie). From an ant’s point of view, this means food for larvae. From a seed’s point of view, this means dispersal. Hitchhiking to an ant’s nest gives the seed a new location to germinate and grow away from the parent plant, and potentially a multitude of other benefits such as escape from predation or better soil conditions. In any case, this is ant-mediated seed dispersal, or myrmecochory.

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A field ant (Formica subsericea) grabs a bloodroot (Sanguinaria canadensis) seed by its elaiosome, the oily, nutritious appendage that most resembles a dead insect and attracts ants.

In other parts of the world, benefits of myrmecochory include enhanced survival and germination after fire. In arid, fire-prone areas of both Australia and South Africa, ants bury seeds deep enough to buffer the intense heat of fire, but shallow enough that the heat weakens the seed coat and increases the odds of germination. Thus, the ants protect the seed from the flames while still providing exposure to a Goldilocks level of heat.

Just as in Australia and South Africa, fire is (or was, and with the help of land managers is once again becoming) also a frequent occurrence in Missouri. At Shaw Nature Reserve, managers use prescribed burns to restore an open structure to the reserve’s oak-hickory woodlands. But, is ant-mediated seed dispersal interacting with fire the same way here as in those other fire-adapted ecosystems?

This is a key question of my dissertation research at University of Missouri St. Louis. Using cookies to find winnow ant nests last summer helped me test methods and plan out my experiments for this coming year. Specifically, I will be tracking where the ants take their seeds, whether ants disperse seeds more or less in the year after a fire, and whether the presence and timing of surface fire affects the germination of the seeds after dispersal. Stay tuned!

You can keep up with Eva Colberg on Twitter (@ColbergEva) or by checking out her science communication initiative Science Distilled STL.

Virtual field trip to the Guajira desert and the Serranía de Macuira in northern Colombia

James and Thibaud Aronson describe the natural and cultural context of a little-known area of northern Colombia, home to the Wayuu people and a microcosm of arid lands worldwide.

Colombia is one of the world’s seventeen megadiverse countries.  In a few hours of travel, one can go from the sweltering Amazonian lowlands to the snow-capped peaks of the Andes. It even has a true desert, a small peninsula called la Guajira, shared with Venezuela, which constitutes the northernmost point of South America.

For most of the last 50 years, the Guajira was notoriously dangerous, principally because of drug trafficking, but things have improved in recent years. We traveled there last month, shortly after the first big rains the region had received in several years. ​ And we found that it’s a poignant example of the plight of drylands globally and their peoples.

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The Guajira peninsula, in northern Colombia, including the authors’ itinerary.

Our trip actually began in Panama, which was part of Colombia until 1903. While much smaller, Panama is also a country of contrasts. Much of the Pacific coast used to be covered in seasonally dry tropical forest, and some fragments persist today in and around Panama City itself, while the forests of the Caribbean slope, a mere 50 km away, are much wetter. A curious switch occurs near the Colombian border, where the wet forests then extend down the Pacific coast of Colombia and Ecuador – the famous Chocó-Darien rainforest, one of the wettest and most diverse tropical forests on Earth.

Meanwhile, the seasonally dry forests continue along the 1,000 km long Caribbean coast of Colombia and give way to semi-desert and then true desert (annual rainfall < 250 mm), lined by a coast with mangrove forests, and a series of lagoons and bays where flamingos and ibises add a shock of color.

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Mangroves in Bahia Hundita, Alta Guajira, showing desert woodland with tree cacti (Stenocereus griseus) and various legume trees growing on the sandstone bluffs in the background.

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Roseate spoonbills, great egrets, and a white ibis sharing a coastal wetland near Uribia.

As if this wasn’t enough contrast, halfway along the Caribbean coast rises the Sierra Nevada de Santa Marta, Colombia’s tallest mountain range, reaching 5,700 meters (18,700 feet) above sea level at the highest peak. It takes only about two hours to drive from its foothills, where toucans and monkeys chatter in the majestic trees, to Riohacha, the gateway to the desert.

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A brown-throated three-toed sloth (Bradypus variegatus) hanging by one arm in a Cecropia tree in Tayrona National Park, at the base of the Santa Marta mountains.

Alta Guajira’s desert trees and woodlands

The Alta Guajira is arid indeed, but it hosts trees, remarkable both in their exuberant diversity and their abundance, considering the high temperatures and meager rainfall. We saw what we consider true desert canopies, such as we have described in other posts. However, no desert flora exists in isolation, and indeed the kinship to the ecosystem type known as Seasonal Dry Tropical Forest (SDTF; see map above) seems to be strong.

The dominant trees of the Guajira are species of Prosopis, Caesalpinia, Vachellia (formerly part of Acacia s.l.), Parkinsonia and other legume genera, accompanied by Bursera, Capparis relatives, Bignoniaceae, and other species common in the dry forests of Central and South America, and 3 kinds of tree cacti (Stenocereus, Pilocereus, and Pereskia), growing close together, often covered in climbing vines. In particular, it was interesting to see bona fide desert woodlands dominated by two well-known legume trees, Prosopis juliflora and Vachellia farnesiana, which are widespread and often strongly invasive in other parts of the world, but not here! Fascinating biogeographical and ecological questions abound in this poorly explored region, many of which are relevant to conservation and restoration.

Regarding  landscape ecology in the region, the vegetation is curiously like a patchwork, alternating between dense desert woodlands, nearly pure tree cacti stands, sometimes with a dense grass cover, and sometimes not, and frequent saline flats where nothing grows. In our opinion, the human element, namely land and resource use history, is paramount to understanding what one sees when travelling here and trying to ‘read’ the landscapes.

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Mixed patch of tree cacti and spiny legume trees with a surprising amount of grass understory. Elsewhere under similar stands, for no clear reason, there is no grass cover at all.

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A track of the Alta Guajira, near Nazareth, at the base of the Macuira hills where the notorious Prosopis juliflora, known in Colombia as Trupillo, is so exuberant and long-lived it forms a natural tunnel above this track.

 

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Prosopis juliflora colonizes newly exposed beach dunes, in areas where the shoreline is receding. Here, at Camarones, it occurs alongside Calotropis procera, a woody weed of the Apocynaceae known in English as giant milkweed, and familiar throughout the Caribbean islands, the Middle East and drylands of Africa. It survives because of its toxic milky latex where most other plants get eaten out by livestock.

Other standouts are the beautiful Palo de Brasil, Haematoxylum brasiletto, with its unusual fluted trunks and Pereskia guamacho, an enigmatic ‘primitive’ tree cactus with true leaves and one of the most exquisite tasting fruits we know. This is one of the least well-known but most intriguing of all desert trees to our minds.

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Typical landscape of the northern Guajira desert woodlands, with an even-aged stand of one of the several neotropical legume trees known as Brazilwood: Haematoxylum brasiletto, or Palo de Brasil in Spanish.

Despite those common names, this species is in fact only found wild along Caribbean coastlines from Colombia and Venezeula, all the way north to both coasts of Mexico. The scientific name is thus a misnomer. The most famous Brazilwood tree is another legume, Paubrasilia echinata (= Caesalpinia echinata) that once grew abundantly along the Atlantic coast of Brazil, as a large tree with a massive trunk, reaching up to 15 meters tall. Today, it’s almost entirely gone in the wild, and mostly planted in gardens and along roadsides. It was prized for the bright red dye obtained from the resin that oozes from cut branches or trunks. The dye was widely used by textile weavers in the Americas and Europe in the 17th-19th centuries. The tree also provided the wood of choice for high quality bows for stringed instruments and was widely used for furniture making as well. So important was its economic value that the country was named after it, originally Terra do Brasil (Land of the Brazilwood), later shortened to Brazil. Recently it was designated as sole member of a new genus, as part of a comprehensive revision of the entire genus Caesalpinia, carried out by an international team of experts.

It’s curious that H. brasiletto bears the same common name as P. echinata, since the two trees are nothing alike, apart from their red sap and heartwood. Little literature exists for H. brasiletto, and we are embarking on some detective work to shed some light on this puzzle. We go into detail as these are both relatively fast-growing trees with great economic as well as ecological value. They would both be excellent candidates for inclusion in ecological restoration work and are both in dire need of conservation efforts.

Wayuu: Alta Guajira’s Indigenous People

This desert also hosts a fairly large human population. The Guajira is the home of the Wayuu, Colombia’s largest surviving indigenous group and, along with the Navajo, one of the last desert-dwelling peoples in the New World. These fiercely independent people, organized in 17 matrilineal clans, were never subjugated by the Spanish, and even today the Guajira region functions mostly in isolation from the rest of the country. As we were heading well off the beaten track, we needed a guide, a 4 x 4 jeep in good condition, and a skilled driver to navigate the meandering and unmarked desert paths.

Despite an ancient history of human presence, and some periods of intensive exploitation and intervention (such as a pearl harvesting boom that took place soon after European explorers arrived), the ecological condition of the region at the landscape scale is remarkably good. Indeed, apart from the salt works in the small town of Manaure, which produce two thirds of Colombia’s salt, and El Cerrejón, South America’s largest open-pit coal mine, in the south of the Guajira, there is no major industry.

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Typical traditional salt works at Manaure worked by hand by local men and women just as they have for generations.

And the isolated people who dwell here – fishermen, shepherds, and weavers – are right out of a Gabriel García Márquez story. Indeed the author, most famous for One Hundred Years of Solitude, grew up on Colombia’s northern coast, speaking both Spanish and the Wayuu language, Wayuunaiki. As we traveled deeper into the desert, we traversed small settlements with simple houses made of wood and yards surrounded by tree cacti hedges.

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The Wayuu village of Boca de Camarones, in the south of the Guajira peninsula, showing the living hedgerows of columnar cacti produced from tall stanchions. In the background, surrounding the homes, are Trupillos, and good specimens of Dividivi Libidibia coriaria (formerly called Caesalpinia coriaria).

This third caesalpinoid legume tree, closely related to the two Brazilwoods mentioned above, is the source of another lovely red dye, derived in this case from its pods. Until recently, there was an annual festival in Camarones, in honor of this formerly major economic plant product. The tree was also used as an important source of tannins. Like Paubrasilia echinata, it deserves more ethnobotanical and biogeographical studies.

Here, as in many other arid lands, goats and sheep are important for the Wayuu people, as a source of food and social currency. For example bride price during arranged weddings, and gifts for guests attending vigils of important elders and healers, are paid to this day in heads of live goats or sheep. Historically, mules and donkeys were very common as well, but now they are increasingly replaced by motorcycles.

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Small children following a flock of desert-hardy sheep in Boca de Camarones. The peaks of the Sierra Nevada de Santa Marta are visible in the background.

Crown jewel of the Alta Guajira

The crown jewel of this desert, its best kept secret, is the Serranía de la Macuira, a small mountain range (serranía meaning “small sierra” in Spanish) in the northeast of the peninsula. This miniature sky island is almost impossibly lush, thanks to moisture-bearing clouds that shroud its upper reaches. They feed streams that flow year-round, and sustain many kinds of trees that grow to well over 10 meters tall.

As one climbs the slopes of the Macuira, the humidity dramatically increases and the parched lowlands, with their desert woodlands, blend perceptibly into a seasonally dry tropical forest reminiscent of those we had seen in Panama. A little-known fact: seasonally dry tropical forests are the most endangered of all tropical forest types, and those in La Guajira are worthy of much greater research, conservation, and restoration.

Climbing higher still, the mid- and upper ranges of the Macuira seem like another world. Most astonishing of all, there is apparently an abrupt transition above 550 meters, and the higher reaches are covered in true cloud forest, with mosses, epiphytic orchids, tree ferns, and dozens of tree species that otherwise occur hundreds of kilometers away! This is probably the only place in the world where cloud forest is found less than 5 km from true desert. Fortunately – from a conservation point of view, but unfortunately for us – the upper peaks of all three peaks of the Macuira are sacred to the Wayuu, and completely off-limits, to native people and visitors alike. Try as we might, we were unable to get permission to hike up there.

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Seasonally dry tropical forest on the northeastern facing slope of the Macuira, where precipitation is much higher than in the surrounding lowlands occupied by desert woodlands.

Even though the whole Macuira is officially protected as a national park, the reality is more complicated. While walking inside the park, we encountered recently cut trees, the ubiquitous goats, and even a Wayuu man hunting birds with a slingshot in broad daylight. The beautiful continuous tree canopy covering most of the slopes stands in stark contrast to the severely eroded, nearly bare hilltops, on which stand small Wayuu homesteads. Still, the presence of clear ecotones speaks to mostly healthy landscapes.

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The severe erosion around a small Wayuu farm inside the Macuira National Park.

Alta Guajira’s ecological future

The pressures on the Guajira’s ecosystem health include a large mine (El Cerrejón, mentioned above), overgrazing by domestic livestock, and stark poverty facing the native people and more recent immigrants. But there are positive factors as well. There are progressive laws in Colombia related to ecological restoration. Moreover, since 2012, Colombia has a National Restoration and Rehabilitation Plans (pdf), as well as a Law of Remediation, which imposes large environmental offset payments from large-scale development projects (like hydroelectric dams) to underwrite conservation and restoration work. Moreover, the national park system, within its network of 56 protected areas, harbors populations of almost half of the 102 indigenous peoples in the country, and in the case of Macuira, this is clearly not just a paper park idea.

Still, the national park (25,000 ha in size; officially designated in 1977), operates with a skeleton staff attempting to carry out an ambitious management plan (pdf) despite an insufficient budget. Staff and volunteers provide short tours to day-visitors, and maintain some fenced-off livestock exclosure plots, where they are studying natural regeneration. Daily interaction with the Wayuu living in the park appear to be harmonious, and indeed there is a clear sense that part of the Park’s mission is to restore and protect the Wayuu people’s natural and cultural heritage. Recently, the Instituto Humboldt, Colombia’s stellar national research institute, has established permanent plots in the Macuira range as part of a series of 17 plots including all the tropical dry forest types in Colombia. In the Macuira, this work is done in collaboration with botanists from the Universidad de Antioquia, in Medellin. Furthermore, researchers at Kew, the Smithsonian Institute, and many conservation NGOs are all developing collaborations with the Colombian government to explore and help the country move forward with green development.  The Missouri Botanical Garden also has long-standing MoUs for joint research with 3 different institutions in Colombia, with bright prospects for deepening cooperation in the future.

Like many indigenous peoples around the world, the Wayuu are at a crossroads. Their language and some of their traditions are still alive and well, but others have already faded. There are few legal sources of income in the harsh desert, the ancestral Wayuu land. How will they manage in the future? What can they do to adapt?  Some, like our guide, José Luis, are trying to change mentalities, but they clearly need more help.  As throughout Colombia, there is clear and urgent need to build on the alpha-level studies already underway, and move onto applied ecology, agroforestry and land management programs, including community-based restoration programs and ecotourism in conjunction with the national parks.

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Our Wayuu guide José Luis Pushaina Epiayu (on the right) and Macuira park ranger Ricardo Brito Baez-Uriana (on the left), talking about birds with a local Wayuu family.