Canopy structure, defined by leaf area index (LAI), fractional vegetation cover (FCover) and fraction of absorbed photosynthetically active radiation (fAPAR), regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics.
Here, we introduce the Global LAI database: a global dataset of field-based canopy structure measurements spanning tropical forests in four continents (Africa, Asia, Australia and the Americas). We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences.
Using data collected from 887 tropical forest plots, we show that maximum water deficit, defined across the most arid months of the year, is an important predictor of canopy structure, with all three canopy attributes declining significantly with increasing water deficit. Canopy attributes also increase with minimum temperature, and with the protection of forests according to both active (within protected areas) and passive measures (through topography). Once protection and continent effects are accounted for, other anthropogenic measures (e.g. human population) do not improve the model.
We conclude that canopy structure in the tropics is primarily a consequence of forest adaptation to the maximum water deficits historically experienced within a given region. Climate change, and in particular changes in drought regimes may thus affect forest structure and function, but forest protection may offer some resilience against this effect.
We thank the students and research assistants involved in the various projects for their help in the field during data collection. We acknowledge the British Institute in Eastern Africa for logistic support during fieldwork campaigns in Kenya, Ethiopia and Tanzania. We thank the Stability of Altered Forest Ecosystems project for logistic support in Malaysian Borneo. RH, TM and AHM also thank Kementerian Negara Riset dan Teknologi (RISTEK) for permission to work in Indonesia under research permit number 178/SIP/FRP/SM/V1/2014.
CCM was supported by the ‘Uncovering the variable roles of fire in savannah ecosystems’ project, funded by Leverhulme Trust under grant IN-2014-022 and ‘Resilience in East African Landscapes’ project funded by European Commission Marie Curie Initial Training Network (FP7-PEOPLE-2013-ITN project number 606879). MP and AM collected data in Tanzania with funding from Australian Research Council, IUCN Sustain / African Wildlife Foundation and University of York Research Pump Priming Fund. MP and PO collected data in South Africa with funding through the European Research Council ERC-2011-StG_20101109 (project number 281986) and the British Ecological Society - Ecologists in Africa programme. MP, PP, ACS and RM collected data in Kenya, Ethiopia and Tanzania with support through the ‘Climate Change Impacts on Ecosystem Services and Food Security in Eastern Africa (CHIESA)’ project (2011–2015), which was funded by the Ministry for Foreign Affairs of Finland, and coordinated by the International Centre of Insect Physiology and Ecology (icipe) in Nairobi, Kenya. WWF-REDD provided funding to ND to collect data in Tanzania.
- Leaf area index
- Fractional vegetation cover
- Fraction of absorbed photosynthetically active radiation
- Human population pressure
- Protected areas
- Climate change