The Sabah Biodiversity Experiment: a long-term test of the role of tree diversity in restoring tropical forest structure and functioning

Abstract

Relatively, little is known about the relationship between biodiversity and ecosystem functioning in forests, especially in the tropics. We describe the Sabah Biodiversity Experiment: a large-scale, longterm field study on the island of Borneo. The project aims at understanding the relationship between tree species diversity and the functioning of lowland dipterocarp rainforest during restoration following selective logging. The experiment is planned to run for several decades (from seed to adult tree), so here we focus on introducing the project and its experimental design and on assessing initial conditions and the potential for restoration of the structure and functioning of the study system, the Malua Forest Reserve. We estimate residual impacts 22 years after selective logging by comparison with an appropriate neighbouring area of primary forest in Danum Valley of similar conditions. There was no difference in the alpha or beta species diversity of transect plots in the two forest types, probably owing to the selective nature of the logging and potential effects of competitive release. However, despite equal total stem density, forest structure differed as expected with a deficit of large trees and a surfeit of saplings in selectively logged areas. These impacts on structure have the potential to influence ecosystem functioning. In particular, above-ground biomass and carbon pools in selectively logged areas were only 60 per cent of those in the primary forest even after 22 years of recovery. Our results establish the initial conditions for the Sabah Biodiversity Experiment and confirm the potential to accelerate restoration by using enrichment planting of dipterocarps to overcome recruitment limitation. What role dipterocarp diversity plays in restoration only will become clear with long-term results.

Establishing the evidence base for maintaining biodiversity and ecosystem function in the oil palm landscapes of South East Asia

“…Once-logged forest appears to retain a reasonable proportion of the species present in old-growth forest [42,43], although it is likely that further rounds of logging will be more detrimental [44]. It is therefore not surprising that comparisons of species richness and composition between logged forest and oil palm plantations show a similar pattern to that for old-growth forest, with extensive species losses occurring [10].…”

Changes in forest land use and management in Sabah, Malaysian Borneo, 1990–2010, with a focus on the Danum Valley region

“…In collaboration with its local partners, particularly Yayasan Sabah, the Sabah Forestry Department and Universiti Malaysia Sabah, and a number of leading international universities and research institutions, SEARRP has established a suite of three major projects intended to address these issues: (i) the Stability of Altered Forest Ecosystems Project [12] that focuses on forest fragmentation and ecosystem functioning and resilience within agricultural landscapes (www.safeproject.net), (ii) a 50 ha permanent plot in the primary forest at Danum Valley, to be managed as part of the Smithsonian Tropical Research Institute's global network of plots of this type (www. ctfs.si.e.du/site/Danum+Valley), and (iii) the Sabah Biodiversity Experiment [13]-a large-scale enrichment planting project that aims to examine the links between the regime of forest restoration, productivity, biodiversity and ecosystem functioning (www.sabahbiodiversityexperiment.net).…”

Conclusion: applying South East Asia Rainforest Research Programme science to land-use management policy and practice in a changing landscape and climate

“…The SAFE Project thus involves and potentially integrates the breadth of science covered by SEARRP and directly addresses some of the key needs identified by Foster et al [10] regarding the ecosystem functioning of part-forest, part-oil palm landscapes (see above). In their article on the Sabah Biodiversity Experiment, Hector et al [12], by comparing a regenerating forest 22 years after selective logging with primary forest, demonstrate the scale of total carbon gain (100 tonnes of carbon per hectare or 40% of primary rainforest values) and biodiversity and other ecosystem services that could be obtained if enrichment planting is employed. These data will potentially be of direct value in assessing the carbonoffset value of restoration forest stands in REDDþ proposals and negotiations.…”

“…(e) The policy orientation and potential of current projects to underpin forest restoration of forest and the ecological functioning of part-forest/part-plantation landscapes The large-scale experiments described by Hector et al [12] (the Sabah Biodiversity Experiment) and Ewers et al [13] (the Stability of Altered Forest Ecosystems (SAFE) Project) in their articles represent the current direction of SEARRP science in seeking to provide the science directly to underpin two key land management issues of South East Asia, namely (i) the design and use of enrichment planting strategies with native canopy-tree seedlings to rehabilitate logged-over or repeatedly logged rainforest; and (ii) the effectiveness of forest fragments of different size and riparian forest zones of different width within oil palm landscapes in retaining biodiversity and ecosystem functioning, mitigating effects of oil palm on local air quality, global climate change and water pollution and reducing downstream effects on sedimentation and runoff. The SAFE Project thus involves and potentially integrates the breadth of science covered by SEARRP and directly addresses some of the key needs identified by Foster et al [10] regarding the ecosystem functioning of part-forest, part-oil palm landscapes (see above).…”