Van Walt Environmental Connect Issue Two

Studying Soil Properties to Help Conserve Orangutans

and was bursting at the seams, as was the river bank on occasions (torrential downpours led to the camp being flooded waist-deep in water more than once!). After initial explorations of the area and inspection of satellite images, we established survey locations within the three main forest types that we encountered in the area; i.e. heath, peat and riverine forest. These forest types were visibly different, with apparent differences in tree size, tree stem density and species composition, which we aimed to demonstrate empirically through collection of field data. To do this, we established a series of 30 x 30 m tree plots in each forest type, within which we measured tree size and density, which can be used to estimate above-ground tree biomass. We also established transects to survey orangutan

population density in each forest type, which we do through counting their “nests” (sleeping platforms that they construct in the trees each night – orangutans are rarely encountered in the forest and so counting their nests is much easier!). Alongside this, we also measured selected soil properties in 20 locations within each tree plot. This included pH using a field tester kit, plus a soil moisture metre (Pico HD2 metre plus Pico 64 TDR soil probe) and auger generously loaned to us by Van Walt. Unlike a lot of field equipment in Borneo (!), this kit survived the long flight out, and humid and generally technologically very unfriendly jungle conditions, to provide some very useful data. The kit was easy to use and had the additional advantage of a very long battery life,

which was particularly useful in our electrically- starved forest camp. All students and volunteers that joined the expedition were provided with an opportunity to learn how to use the kit, which was particularly useful for the local Indonesian students, who had never had opportunity to use advanced soil testing apparatus like this before. At the time of writing, some field data collection is still ongoing and all data has not yet been entered into our electronic database, so our impressions at this stage are preliminary. Our initial soil moisture results are striking, however, with large differences observed between the different forest types. Specifically, soil moisture content in the peat and riverine areas was much higher than in the sandier heath soils on the slopes. Variation also appears to exist within the heath soils, with areas with a thicker layer of peat above the white-sand soil showing higher soil moisture contents than those areas with thinner surface peat layers (the depth of this surface peat layer varied between around 2-20 cm). We believe that these differences in soil moisture between forest types are likely to be driving force behind the variations in tree size, density and species composition between these forest types. The saturated peat areas exhibit very small tree size and high tree densities; the very dry heath areas also have small trees and fairly high tree density, but less extremely so. Both of these conditions are likely to create water and nutrient stresses for trees, resulting in their relatively low tree size, compared to riverine areas and patches of heath with thicker peat. Interestingly, because the sand layer in the heath forest areas is both coarse and very pure, heightened drainage appears likely to cause water stress even in this forest, which experiences around 2,000 mm of rain annually. Indeed, this forest exhibited some of the most marked transitions in forest types that our experienced research staff have seen, with the slightest changes in slope (and therefore drainage) leading to changes in forest types over the course of less than 50 m. We believe that this is another consequence of the incredibly sandy soils and their rapid drainage, which exaggerates the impacts of changes in drainage resulting from changes in slope, thereby producing these rapid changes in forest type. What does this mean in relation to orangutan conservation? Preliminary assessment of our orangutan population density data indicate that densities are highest in the riverine forest, variable/ intermediate in the heath forest and very low in the

peat forest. This fits with the observations described above, suggesting that orangutan abundance is likely driven by tree size and species composition in an area, which in turn is impacted by soil moisture (and nutrient availability, which we have unfortunately not yet been able to test, but which is likely closely tied to soil moisture contents). Once data collection and analyses are complete, we aim to use these data in our reports and publications, to highlight the unique nature of this forest, its ecological interactions and importance for wildlife conservation. This evidence will be important for justifying conservation efforts in the region and obtaining the necessary local and international support for these. We would like to thank Van Walt for loaning this equipment to us and contributing towards this effort.

Mark E. Harrison PhD. The Borneo Nature Foundation /

Wild Bornean orangutan mother and infant. Photo by Erik Perlett / Borneo Nature Foundation

Flooded research camp and volunteers. Photo by Bernat Ripoll Capilla / Borneo Nature Foundation 21


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