Tropical forest canopies and their relationships with climate and disturbance： results from a global dataset of consistent field-based measurements

Background： 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. Methods： 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. Results： 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. Conclusions： 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.

Modeling vulnerability of protected areas to invasion by Chromolaena odorata under current and future climates

Invasive plant species and climate change are among the biggest threats to the ecological integrity of many ecosystems,including those of protected areas.Effective management of invasive plants requires information regarding their spatialdistributions Using maximum entropy,wemodeled habitat suitability for an invasive plant species Chromolaena odorata under current and future climatic conditions(HadGEM2-ESand MIROC5)in protected areas of four West African countries(Benin,Cote d'voire,Ghana,and Togo).Under current climatic conditions,approximately 73%of total land area within the protected areas was suitable for colonization by C.odorata.Under future climate projections,the total area of suitable habitats for this invasive plant was projected to decrease by 7-9%(HadGEM2-ES)and 12-14%(MIROC5).Country-specific patterns suggest that major protected areas in Cote d'Ivoire and Ghana will be more vulnerable to invasion by C.odorata than those in Benin and Togo under both current and future dimatic scenarios.To maintain normal ecosystem functioning and provisioning of ecosystem services within the protected areas studied here,locations that have been identified as most vulnerable to invasion by C.odorata should be accorded proportionately higher priority when formulating appropriate management strategies.