The past 40 years in Southeast Asia have seen about 50% of lowland rainforests converted to oil palm and other plantations, and much of the remaining forest heavily logged. Little is known about how fragmentation influences recovery and whether climate change will hamper restoration. Here, we use repeat airborne LiDAR surveys spanning the hot and dry 2015-16 El Niño Southern Oscillation event to measure canopy height growth across 3,300 ha of regenerating tropical forests spanning a logging intensity gradient in Malaysian Borneo. We show that the drought led to increased leaf shedding and branch fall. Short forest, regenerating after heavy logging, continued to grow despite higher evaporative demand, except when it was located close to oil palm plantations. Edge effects from the plantations extended over 300 metres into the forests. Forest growth on hilltops and slopes was particularly impacted by the combination of fragmentation and drought, but even riparian forests located within 40 m of oil palm plantations lost canopy height during the drought. Our results suggest that small patches of logged forest within plantation landscapes will be slow to recover, particularly as ENSO events are becoming more frequent.
Bibliographical noteFunding Information:
We thank Glen Reynolds for suggestions in the preliminary phase of the manuscript, Matthew Struebig for helpful comments and Sacha Khoury for help with image processing and analysis. We are grateful to Marion Pfeifer for providing us with the Pléiades imagery used to distinguish forested areas from oil palm and Sui Peng Heon for providing local precipitation data. MHN was supported by a PhD scholarship from the Conselho Nacional de Pesquisa e Desenvolvimento (CNPq, grant No. 201516/2014-4) from Brazil. D.A.C. and T.J. were supported by NERC’s Human-modified Tropical Forests Programme (Biodiversity And Land-use Impacts on tropical ecosystem function project; grant No. NE/K016377/1). T.J. is funded by a NERC Independent Research Fellowship (grant No. NE/S01537X/1). M.S., J.K., and M.R. were funded through a grant from the Ministry of Education, Youth and Sports of the Czech Republic (grant number: INTER-TRANSFER LTT17017). We are grateful to the former NERC Airborne Research Facility for the LiDAR survey and NERC’s data analysis node for completing the postprocessing stages. The Global Airborne Observatory flights and data processing were supported by the UN Development Programme, the Avatar Alliance Foundation, the Roundtable on Sustainable Palm Oil, the World Wildlife Fund and the Rainforest Trust. The Global Airborne Observatory is made possible by grants and gifts from private foundations, visionary individuals, and Arizona State University. We thank the Sime Darby Foundation, the Sabah Foundation, Benta Wawasan and the Sabah Forestry Department for their support of the SAFE Project. We thank the South East Asia Rainforest Research Partnership for logistical support in the field, and Yayasan Sabah, Maliau Basin Management Committee, the State Secretary, Sabah Chief Minister’s Departments, the Malaysian Economic Planning Unit and the Sabah Biodiversity Council for permission to conduct research in Sabah. Publishing fees were partially covered by the University of Helsinki (profit centre: H5101; WBS-number: 75101002).
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