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

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

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

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

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

Trees in the desert?

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

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

Saguaro and boojum

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

Boswellia Oman

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

Astrotricha hamptonii

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

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

jordan woods

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

What does a desert tree look like?

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

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

Where do desert trees grow?

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

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

*Endemic to the country or region indicated.

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

 

baobabs Mada - pete

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

spiny thicket - pete

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

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

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

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

 Where can one see living Desert Canopies today?

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

Great western woodlands

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

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

macuira stream

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

wayuu family

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

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

Prosopis cineraria

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

Prosopis pallida Peru

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

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

isla guadalupe

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

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

Things are not always better on the sunny side!

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

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

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

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

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

Ankafobe Forest South-facing on left.JPG

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

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

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

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

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

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

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.

 

Native tree seedlings grow best near existing forest and beneath shade in highland Madagascar

A team of MBG scientists describes a recent experiment to grow native trees in a degraded part of Madagascar’s central highlands.

Tampo_Raw

The dissected landscape of the Tampoketsa de Ankazobe in central Madagascar. Imagery: Google Earth (2018).

Seen from space, parts of Madagascar’s high plateau look like a wizened, grayish-pink brain drying in the sun. Thin, dark lines demarcate nooks and crannies – nearly the only places where bits of forest remain.

Formerly, the forests here covered more territory. Just how much territory is debated; ancient grasslands are also present in highland Madagascar. But in this area, about three hours northwest of the capital, many forests have been cleared, burned, and converted to new grassland within living memory.

To restore forests to their recent extent would benefit a range of species, including Schizolaena tampoketsana (a threatened, micro-endemic tree) and an undescribed species of fat-tailed dwarf lemur. However, restoration has been easier said than done so far. Natural forest regeneration is slow to non-existent, even near remnant forests where fire is excluded. Planted tree seedlings grow only millimeters each year, if they survive at all. Adding fertilizer seems to inhibit seedling growth. Inoculating seedlings with mycorrhizal fungi seems promising, but we are not yet sure if this will make a difference in the field.

Following a field trip in November 2016, we decided to test a couple of other tactics for growing native trees on this weathered plateau. First, we tested planting trees near existing forest. Being near the forest could help young seedlings by shading them from the hot sun or by sharing beneficial microorganisms. Second, we put shade structures over some of tree seedlings to test how much the bright, hot sunlight prevented tree growth.

We tested four tree species: Baronia taratana (Anacardiaceae), Nuxia capitata (Stilbaceae), Uapaca densifolia (Phyllanthaceae), and Eugenia pluricymosa (Myrtaceae).

ExpDesign

An experiment with native tree seedlings at Ankafobe, a small forest fragment on the highlands northwest of Madgascar’s capital, Antananarivo. Photo: Chris Birkinshaw.

Three of the tree species survived and grew more when we planted them next to the forest. The fourth, Nuxia capitata, was a super species and grew relatively well wherever it was planted.

Two of the four species also survived more often beneath shade structures. But interestingly, this shade effect did not completely account for the effect of proximity to forest. That suggests that shade is important for protecting young seedlings from the hot sun, but something else is going on too. Perhaps trees growing next to the forest get a boost of water, since remnant forests sit at the valley bottom where water collects. If this is true, then tree seedlings might do well in any valley bottom, not just ones with remnant forest in them.

Our study site, called Ankafobe, is only a small area, so it would be a stretch to generalize our observations to the entire region. However, we are not the only ones to have done such a test in this ecosystem. In 2000, Ingar Pareliussen led a study with the same basic elements as ours at a site ten kilometers away, at Ambohitantely. Like us, Pareliussen’s team found that seedlings planted near the edge of a remnant forest grew better than those planted further away. In contrast, shade structures did not improve seedling survival. In fact, one species grew worse in the shade.

Fig_TampoEdges

One vision for landscape-scale forest restoration on the Tampoketsa de Ankazobe. We used an edge-detection algorithm in Inkscape to highlight forest edges and valley bottoms, the places where trees grew best in our study. Imagery: Google Earth (2018).

Together, our two studies begin to suggest the outlines of a vision for landscape-scale forest restoration on the high Tampoketsa de Ankazobe. If native tree seedlings perform better along forest edges, it follows that a cost-effective strategy would be to focus on planting those areas first, leaving the higher, drier areas alone. Planting along edges would also be a conservative strategy given our hazy understanding of past landscapes. Some grasslands in highland Madagascar seem to be very old, and planting trees in such places could destroy habitat for grassland species, which are threatened in their own right.

For more information about this experiment, you can read our open access paper in Plant Diversity. We have also published several other blog posts about Ankafobe.

Homemade mycorrhizal inoculum improves seedling growth for some native Malagasy trees

MBG Madagascar’s Chris Birkinshaw and Dinasoa Tahirinirainy describe exciting, preliminary results from a forest restoration experiment in highland Madagascar.

 

Ankafobe Forest on Malagasy highlands - experiment located on grassy ridges

This sliver of riparian forest is one of the last vestiges of Madagascar’s highland forests. Decades of Missouri Botanical Garden research in Madagascar have shown that more than 80% of all plant species on the island exist nowhere else. Many are threatened with extinction due to habitat loss. Several previous posts have described forest restoration efforts at this site, home to the largest population of the endemic sohisika tree (Schizolaena tampoketsana) – a species that belongs to a family (Sarcolanaceae) that only exists on Madagascar.

A small number of forest restoration projects in Madagascar routinely inoculate the tree seedlings in their nurseries with a homemade mycorrhizal inoculum. While the nurserymen are convinced that this technique promotes growth and survival of tree seedlings, there seems to be no published data objectively demonstrating these positive outcomes. In an effort to provide the evidence to justify investment in this technique, we designed a simple experiment that will compare the survival and growth under four treatments of young plants of six native trees planted in grassland adjacent to the Ankafobe Forest on the central Malagasy highlands.

Table – Four experimental treatments to test the effects of mulch and mycorrhizal inoculum on native tree seedling growth in highland Madagascar

  Inoculated Not inoculated
Mulched Treatment 1 Treatment 2
Not mulched Treatment 3 Treatment 4 (control)

In our experiment, fifteen seedlings of each of six native tree species will be grown under each of the four treatments listed above. The mycorrhizal inoculum was made by filling a pit (150 cm long × 50 cm wide × 30 cm deep) lined with sacks with topsoil collected from around the roots of three native tree species, then growing maize and beans in this soil for three months before cutting these plants down and letting the substrate dry out for two weeks. The substrate remaining in the pit is the inoculum and was used by adding one tablespoon to each seedling container.

Making the inoculum

Beans and maize are grown in topsoil collected from a remnant forest to amplify local mycorrhizae populations. This enriched soil (i.e., inoculum) is then added to seedling containers.

The tree seedlings that received mycorrhizal enrichment were inoculated in November 2017, and all of the seedlings were otherwise grown under the same conditions in the nursery until January 2018 when they were planted out into an experimental plot at Ankafobe. Half of the tree seedlings were surrounded by a thick layer of grass-based mulch (~30-cm deep). The comparison of seedling performance with and without the addition of mulch is interesting because of the possibility that mulch helps to maintain a relatively cool and moist environment in which the mycorrhizae can flourish.

Table – Mean difference in tree seedling height (cm) between seedlings inoculated versus not inoculated with homemade mycorrhizae, after two months in the nursery (N = 30 seedlings per species).

Species Inoculated seedling height Non-inoculated seedling height t p1
Aphloia theiformis 29.5 ± 10.2 33.4 ± 6.5 -1.75 1.0000
Baronia tarantana 18.1 ± 6.1 11.4 ± 3.5 5.21 <0.0001
Brachylaena ramiflora 27.2 ± 6.0 31.8 ± 6.5 -2.87 1.0000
Craspidospermum verticillatum 43.0 ± 5.9 42.6 ± 3.7 0.37 1.0000
Macaranga alnifolia 34.8 ± 8.6 39.2 ± 5.2 -2.43 1.0000
Uapaca densifolia 23.0 ± 7.9 11.5 ± 2.6 7.58 <0.0001

1 t and p values are from a one-tailed student’s t-test asking whether inoculated seedling height was greater than non-inoculated seedling height. P values are adjusted for multiple comparisons with Bonferroni correction.

Although we plan to measure seedling survival and growth 12 months from the time when they were planted (i.e., in January 2019), we were interested to see that for two of the species the height of inoculated seedlings was significantly greater than the height of non-inoculated seedlings after a mere two months in the nursery. On average, inoculated seedlings of Baronia tarantana are 1.6× taller than non-inoculated seedlings; while the seedlings of Uapaca densifolia are a full 2× taller. For the other species there was no significant difference between the height of the inoculated and non-inoculated plants.

Experiment showing line of seedlings some with and some without mulch (1)

Tree seedlings are planted out in a field experiment at Ankafobe in January 2018. These seedlings are planted adjacent to a line of “green manure” (i.e., nitrogen-fixing Tephrosia shrubs planted to improve the degraded highland soil prior to planting native tree seedlings).

 

Hill of Honey: Forest Recovery on Madagascar’s Central Highlands

This post was co-written by Leighton Reid and Chris Birkinshaw after a three-day field trip in the tampoketsa with Cyprien Mandriamanana and Jeannie Raharimampionona.

A narrow, paved road winds north from Antananarivo through a high, windswept plain. It is the wet season, and the hills are green and close-cropped, but in the long dry season the landscape burns black. Orange rivers wind through the valleys, muddied by massive erosion. Here and there are thin strips of riparian forest, chock full of endemic species.

The biggest chunk of remaining forest is Ambohitantely, Malagasy for “hill of honey”. Ambohitantely encompasses 1,800 ha of humid forest (about three times the size of Saint Louis’s Forest Park). We visited the reserve to observe natural forest recovery in one of the few places it can still be seen on Madagascar’s Central Highlands.

Ambohitantely map

Ambohitantely: the last large tract of forest on Madagascar’s Central Highlands. Ten kilometers to the northwest is Ankafobe, a much smaller forest fragment managed by a local community with assistance from Missouri Botanical Garden.

Forest transition feedback

Why is forest recovery so rare in the Malagasy highlands? Madagascar’s Central Highlands are currently undergoing a complete ecological transition, from forest and wooded savanna to grassland. The degradation cycle often starts when people cut forest trees to extract wood for timber and charcoal production. Small-scale cutting opens the canopy, dries the forest floor, and creates debris, all of which increase forest vulnerability to annual wildfires that sweep across the grasslands during the eight month dry season. C4 grasses quickly colonize the burned land, inhibiting forest recovery, and creating ideal conditions for future fires. The reason that Ambohitantely has natural forest recovery for us to observe is because reserve staff maintain a wide fire break for more than thirty kilometers around the reserve.

Our guide at Ambohitantely took us on a hike through several areas where forest had once been cleared and burned but where fire had been excluded for 15 or 25 years, allowing the forest to begin to recover. Frankly, the vegetation was uninspiring. Low shrubs and forbs were scattered through a matrix of C4 grass (mostly Aristida), but trees and tree seedlings were nowhere to be seen outside of the forest (where they were abundant). By tropical forest standards, this looked slow. But for natural forest recovery on the Central Highlands, it’s hard to imagine a better situation than being protected from fire and immediately adjacent to the largest remaining tract of forest.

Ambohitantely forest edge

After 25 years of recovery, forest edges were sharp. Tree seedlings were almost totally restricted to forest, and grasses dominated the ground layer just outside.

Our main interest in Ambohitantely was to compare natural forest recovery there to our observations at another forest fragment, Ankafobe, 10 km northwest. For the last decade, MBG has partnered with a local community to preserve a thin, riparian forest containing several critically endangered plant species. Community members constructed a fire break and have begun to restore the surrounding hillsides by turning over the orange clay and planting fast-growing legumes to develop the soil.

Ankafobe hillside with Schizolaena

A degraded hillside at Ankafobe; the remnant forest is down the hill to the right, near the edge of the photo. The tree at the top of the hill is Schizolaena tampoketsana, a critically endangered microendemic in an endemic Malagasy plant family (Sarcolaenaceae). It is a remnant forest tree that likely escaped repeated fires by being nestled in a deep, protective gully. The multi-stemmed shrub in the foreground is actually a large tree species, Brexia montana, which has likely resprouted many times from a well-developed root system.

Some of our comparative observations were promising. We were happy to find examples at Ambohitantely where recovering land dominated by heather and blueberry seemed to have continued developing into a more diverse thicket, including Nuxia capitata, Psiadia altissima, and Razafimandimbisonia minor. At Ankafobe, we had worried that the heather growing in some areas signified poor soil conditions and possibly arrested development.

Overall our visit left us with more questions than answers. We hope to answer at least a couple of them over the coming years.

  • Why is natural forest recovery so slow on the Central Highlands?
  • Has it always been this slow?
  • Are Malagasy tree species poor pioneers because of their long, relatively stable evolutionary ecological history?
  • Is there any way to make Malagasy trees grow any faster on the degraded grasslands?1
  • Are the fire-stoking C4 grasses introduced from east Africa rather than being native species?
  • If so, when?
  • Is the soil too far gone to ever recover?
  • How important were now-extinct seed dispersers and grazers, like 200-kg lemurs and elephant birds?
Ambohitantely cloud cover

Although Ambohitantely is the only remnant forest fragment of any size, we learned recently that it may not be a perfect reference system for Ankafobe. For one thing, Ambohitantely is slightly higher and farther east, which results in considerably greater cloud cover during the dry season. This probably ameliorates the harsh conditions outside of the forest, at least a little. Shown here is cloud frequency from May – October, taken from NOAA MODIS satellite imagery. Thanks, Michael Douglas!

References

Goodman, S.M. & Jungers, W.L. 2014. Extinct Madagascar: Picturing the Island’s Past. University of Chicago Press, Chicago, IL.

Pareliussen, I., Olsson, E.G.A. & Armbruster, W.S. 2006. Factors Limiting the Survival of Native Tree Seedlings Used in Conservation Efforts at the Edges of Forest Fragments in Upland Madagascar. Restoration Ecology 14: 196-203.

1Two datasets (one from our team and one from Pareliussen et al’s [2006]) suggest that NPK fertilizer, even in relatively small doses, reduces native tree seedling performance. It is unclear whether this is because of toxicity (a direct effect) or because other plants, like shrubs, are better able to utilize the nutrient pulse and then compete more strongly against the native tree seedlings (an indirect effect).

Can fungus help grow trees in Madagascar?

Thomas Timberlake and Cyprien Miandrimanana write from Madagascar about a field experiment using fungus to help tree seedlings survive.

One of the problems that has long bedeviled ecological restoration efforts in Madagascar is persuading young seedlings to grow at a pace of more than just a few centimetres per year. The site of Ankafobe in the central highlands is a prime example, with many five year old individuals, planted in the anthropogenic grassland surrounding the remaining forest fragments, still no taller than waist height. Clearly, the environment into which the seedlings are planted is in some way inhospitable.  One hypothesis to explain seedling underperformance  is that they are not managing to establish their normal symbiotic relationships with vesicular arbuscular mycorrhizae (VAM) fungi on which most higher plants depend.

Scaled visual comparison of VAM and VAM-less seedlings at Mitsinjo in Andasibe, Madagascar.

Scaled visual comparison of VAM and VAM-less seedlings at Mitsinjo in Andasibe, Madagascar.

In a VAM symbiosis, plants exchange a significant carbohydrate donation to the fungus in return for important nutrients, particularly phosphorus, and often increased drought tolerance. So if mycorrhizae propagules are absent in the savanna soil, this could well explain the slow growth rates and high mortality observed among planted tree seedlings at sites like Ankafobe.

In response to concern about poor seedling performance, various restoration projects in Madagascar have begun inoculating their nursery seedlings with VAM using a simple protocol pioneered by Mitsinjo, a restoration project in the eastern rain forest of Andasibe. Soil (presumed to contain mycorrhizal fungus) is gathered from underneath forest trees, mixed with sand in a sack-lined pit and then sown with rice and beans to act as hosts for the developing VAM. After three months of maturation, you have a sack-full of VAM inoculum, ready to be applied to the young germinating seedlings – one teaspoon per plant.

Many groups in Madagascar swear by the VAM protocol and the visual results can be compelling, but as yet there have been no experiments in the country to rigorously test whether this method is actually effective. This lack of clear evidence is what prompted us to work on a series of experiments testing and perhaps refining the VAM protocol.

We planted 480 native tree seedlings with and without VAM inoculation to test whether this method increases seedling survival and growth in the degraded savanna around Ankafobe. Digging into the solid laterite and planting the experimental seedlings was hard work but our efforts were rewarded one day with the sighting of a family of 10 young Tenrecs (Tenrec ecaudatus) who ventured bravely out of the security of the forest to observe the progress.

Planting complete, we took our “Time Zero” measurements and then a small sample of roots from both VAM and control seedlings to return to Antananarivo and check for the presence of mycorrhizae vesicles. The process of staining involved cooking up some rather nasty chemicals in our improvised laboratory – the kitchen – back in Tana.

Our next project will be to replicate our VAM study in Ananalava, a humid site on the east coast that contrasts with the drier climate of the Malagasy Highlands. Repeating our study in different environments will help generalize our results and recommendations for people working across this heterogeneous island.

Cyprien in our kitchen laboratory preparing an improvised stain to look for VAM vesicles.

Cyprien in our kitchen laboratory preparing an improvised stain to look for VAM vesicles.