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).

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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.

A Tale of Two Highlands Part II: Ankafobe, Madagascar

Leighton Reid, James Aronson, and Chris Birkinshaw all contributed to this post on restoration in one of Missouri Botanical Garden’s community-based conservation sites in Madagascar. They are currently travelling together discussing opportunities for ecological restoration in MBG’s Madagascar Program and more generally for the country as a whole.

Madagascar’s central highlands appear as a grassy sea – an undulating terrain with intermittent red gashes where heavy rain has dramatically eroded the landscape. Driving north along the national highway from the capital, Antananarivo, one sees Eucalpytus trees growing near villages, as fuel and firewood plantations, but there is almost no natural forest. The few natural communities that remain represent vestiges of a former world.

The view across the road from Ankafobe - nearly unbroken grassland.

The view across the road from Ankafobe – nearly unbroken grassland.

Our destination today is one such vestige – the Ankafobe reserve. Ankafobe is a tiny (33 hectare) strip of native forest growing near the headwaters of a highland stream. Water-loving Pandanus trees demarcate the stream bed and provide fruits for several lemur species. A Souimanga Sunbird (Cinnyris sovimanga) flitters from tree to tree. Just outside of the forest, highly flammable grassland stretches to every horizon.

Pandanus spikes stand out in this thin patch of gallery forest at Ankafobe.

Fragmented gallery forest at Ankafobe. Spikey Pandanus demarcate the streambed. Red strips in the background are incipient forest restoration plots, where the soil has been turned over prior to planting nitrogen-fixing shrubs and native trees.

MBG staff and local villagers are working to restore forest on these bare hills, but it is not an easy task. Between clumps of grass is baked, orange laterite – rock hard soil bereft of life and nutrients. Tree seedlings planted in it grow slowly, or not at all. To improve seedling growth, MBG scientists are testing several strategies. One method is to turn over the soil and seed hearty legumes, whose symbiotic bacteria replenish soil nitrogen – a key ingredient in DNA.

Last October, a wildfire jumped the double fire breaks surrounding Ankafobe and burned a piece of the forest. Two hundred people from the local village (with a population of 600) voluntarily and spontaneously fought the fire for three days. Their impressive response minimized damage to this small forest and raised hopes and excitement about working together on conservation going forward.

The wildfire highlighted this forest fragment’s vulnerability, but it also provided a unique opportunity to observe the response to fire by a natural biotic community that has almost disappeared from the world. A number of trees were completely burned up that had been growing in the savannah just outside of the forest. Unexpectedly, several of these resprouted from their base and from superficial roots at some distance from the main stem. Nearby, the burned grassland bloomed an interesting  array of geophytic plants – particularly orchids – that were rarely observed in unburned grassland. These observations seem to support the hypothesis that at least part of the highland flora may be adapted to fire – a controversial idea that complicates the already challenging task of managing Ankafobe.

Ankafobe is a rare gem; a green emerald that stands out from the surrounding countryside and supports at least one species found almost nowhere else. The reserve is also a special opportunity for ecological restoration. Hard-won lessons from this site could eventually be used to restore tens of thousands of square miles of Madagascar’s central highlands.

Chris Birkinshaw (center) and the Ankafobe restoration team after a rainy afternoon in the field.

Chris Birkinshaw (center) and the Ankafobe restoration team after a rainy afternoon in the field.

Tale of two Highlands Part I: Horton Plains, Sri Lanka

This post is contributed by Dr. James Aronson, a restoration ecologist at MBG’s Center for Conservation and Sustainable Development, and his son Thibaud Aronson. James is also a researcher with the CNRS (National Center for Scientific Research) in Montpellier, France.

In Sinhalese Sri Lanka means “Resplendent Isle”, a fine name indeed for this tear-shaped island off the coast of southeastern India, just north of the equator. Last month I travelled with my son on a self-guided Natural History + Ecological Restoration visit, we are finding and photographing cloud forests and birds galore, like the endangered endemic Sri Lanka whistling thrush, Myophonus blighi, and the Kashmir flycatcher, Ficedula subrubra, which over-winters exclusively in the Sri Lanka highlands, from its very restricted breeding grounds in Kashmir, northern India.

We were also looking at the mosaic of grasslands, cloud forests, and lowland forests we find here from a restoration ecology perspective.  That means we’re trying to “read” the landscapes we see in terms of known transformations carried out during the British colonial era (1815 and 1948, when Sri Lanka was known as Ceylon), and since independence. The remarkable Horton Plains National Park is a mosaic of montane grassland (ca. 35%) and cloud forest (ca. 65%), encompassing the headwaters of three major rivers. It was declared a sanctuary in 1969 and elevated to national park status in 1988; it became part of a large UNESCO World Heritage site in 2010. In the central highlands of Madagascar, grasslands appear to occupy about 99% and most people assume they are anthropogenic…. This month, I’m travelling with Leighton Reid in the Central Highlands of Madagascar, and we will be blogging about this soon.

But, the history of preservation in the highlands here goes back a lot further, to the days when the Isle was part of the British empire, along with all of India. According to information we gathered at the extraordinary, and poorly known Hakgala Botanic Gardens, the great English botanist and explorer Joseph Dalton Hooker had advised the British government to leave all montane forests above 5000 ft. (ca. 1300 m) above sea level “undisturbed” and after 1873 the administration prohibited clearing and felling of forests throughout the central highlands. What a great idea that was! It is too bad there were not enlightened laws on hunting of wild animals as well. One Scottish officer in colonial service in Sri Lanka bragged he had shot and killed over 1400 elephants in Horton Plains and nearby. Today, there are none left there and, so far as we could determine, no plans to reintroduce them from the other remarkable parks, including Yalla and Uda Walawe….

So, what is the significance of the absence of elephants in this park? And, what else can we learn from past regimes and historic periods in Sri Lanka? For starters, we discover that conservation, and respect for other organisms goes back much further than the 19th century. Consider the sign at the entrance to Udawattakele Forest Reserve, near Kandy, one of the historic capitals from the long period of successive kingdoms the island had known prior to the European colonial chapter in Sri Lanka’s history:

O Great King, the birds of the air and the beasts have an equal right to live and move about in any part of this land as thou. The land belongs to the peoples and the other beings and thou are only the guardian of it.”

-Arahath Mahinda (a son of the emperor Asoka the Great, who brought Buddhism to Sri Lanka)

How would it be if we could revive that approach to the Web of Life in our own day and age?

So, what has Horton Plains National Park, with its grassland-forest mosaic, its tourists, and its absent elephants got to do with the Central highlands of Madagascar? For one thing, we can see that fire is a big ecological driver in both areas. The abundant arborescent Rhododendrons in Horton Plains tell a vivid tale in this regard.

Rhododendron arboreum subsp. zeylanicum at Horton Plains National Park. It appears to be fire-resistant and is the only tree species present in large areas of grasslands subject to fire.

Rhododendron arboreum subsp. zeylanicum at Horton Plains National Park. It appears to be fire-resistant and is the only tree species present in large areas of grasslands subject to fire.

On the grand scale of things, Sri Lanka’s Central highlands also resemble those of Madagascar’s since both are the crowns of a poor, emerging tropical island with small and very similar human population size (21 million vs. 24 million), despite being much nearly ten times smaller, and with over 30,000 years of human history, as compared to merely two millennia for Madagascar.

Horton Plains also has remarkable conservation value both for its biodiversity and the ecosystem services it provides to people. Also, as I said, it’s a mosaic of grasslands and cloud forest, that in the past was certainly much affected by both elephants and fire.

Finally, both Sri Lanka (along with the Western Ghats of southern India) and Madagascar count among the world’s biodiversity hotspots, easily visible in their fauna and flora, which is one of the main reasons why MBG researchers, and many others travel and work in Madagascar.

Now, let’s turn back to fires. A big fire hit Horton Plains in 1998, and there are serious invasions of two noxious, cosmopolitan weeds, namely Gorse and Bracken fern. Some control work is underway on the Gorse, but the Bracken fern is apparently not seen as being a problem. Rainbow trout were introduced in the 19th c. and apparently have displaced all native fish, and are taking a toll on native shrimp and no doubt other fauna.