Abstract
Microclimate within forests influences ecosystem fluxes and demographic rates. Anthropogenic disturbances such as selective logging can affect within-forest microclimate through effects on forest structure, leading to indirect effects on forests beyond the immediate impact of logging. However, the scope and predictability of these effects remains poorly understood. Here we use a microclimate thermal proxy (sensitive to radiative, convective, and conductive heat fluxes) measured at the forest floor in three 1-ha forest plots spanning a logging intensity gradient in Malaysian Borneo. We show 1) that thermal proxy ranges and spatiotemporal heterogeneity are doubled between old growth and heavily logged forests, with extremes often exceeding 45°C, 2) that nearby weather station air temperatures provide estimates of maximum thermal proxy values that are biased down by 5-10°C, and 3) that lower canopy density, higher canopy height, and higher biomass removal are associated with higher maximum temperatures. Thus, logged forests are less buffered from regional climate change than old growth forests, and experience much higher microclimate extremes and heterogeneity. Better predicting the linkages between regional climate and its effects on within-forest microclimate will be critical for understanding the wide range of conditions experienced within tropical forests.
Highlights
Tropical forests host the majority of terrestrial species diversity, and generate the majority of terrestrial nutrient and water fluxes (Malhi et al, 1999)
We found that selectively logged forests experienced more heterogeneous, hotter, and consistently extreme microclimate thermal proxy values than old growth forest
We found consistent differences of >10◦C occurring at 1–5 meter spatial scales. These ranges of variation are consistent with prior studies of air temperature heterogeneity within forests (Scheffers et al, 2017) and have broad implications for climate change responses: the environments experienced by organisms may potentially expose individuals to extreme conditions not predicted in fine-scale air temperature data or in broader-scale climate data (Baraloto and Couteron, 2010; Scherrer and Körner, 2010; Stark et al, 2017)
Summary
Tropical forests host the majority of terrestrial species diversity, and generate the majority of terrestrial nutrient and water fluxes (Malhi et al, 1999) They are being increasingly affected by fire, clearance, selective logging, and urbanization (Chazdon, 2003; Newbold et al, 2015) which all contribute to a highly heterogeneous mosaic of disturbed patches. Selective logging may cause reductions in canopy closure that in turn drive increased radiation and airflow, which lead to decreased broad-scale climate buffering and higher variation in microclimate (Fauset et al, 2017). The extent of these effects remains controversial (Senior et al, 2017b). Other studies have shown that fire (Didham and Lawton, 1999) and logging (Fetcher et al, 1985; Senior et al, 2017b) have similar effects on reducing buffering of forest microclimate from broadscale climate variation
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