Extreme and Highly Heterogeneous Microclimates in Selectively Logged Tropical Forests

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.

A Research Agenda for Microclimate Ecology in Human-Modified Tropical Forests

“…The SAFE project is an ideal testbed for this work, as physiological and behavioral responses to temperature have already been characterized for a number of functionally important invertebrate groups, including ants, termites, dung beetles, leeches and mosquitos (Drinkwater et al, 2019;Gregory et al, 2019;Woon et al, 2019; see Case study 1). Moreover, these data can be coupled with existing long-term microclimate records and high-resolution landscape maps of understorey temperature and vapor pressure deficit (Hardwick et al, 2015;Blonder et al, 2018;Jucker et al, 2018).…”

“…But perhaps the most pervasive impact of logging is that by opening and thinning the canopy, it increases solar radiation and air flow in the understorey and decreases evapotranspiration-thereby altering the forest's microclimate (Breshears, 2006;Hardwick et al, 2015;Senior et al, 2017). As a result, not only do logged forests tend to be warmer, drier and brighter than old-growth ones (Hardwick et al, 2015;Fauset et al, 2017;Senior et al, 2017), but microclimatic conditions in these human-modified ecosystems are also more spatially and temporally heterogeneous (Hardwick et al, 2015;Blonder et al, 2018).…”

“…(B) Shows variation in below-canopy mean daily temperature across the SAFE project modeled by integrating data from a network of microclimate sensors with LiDAR . (C) Captures variation in near-surface mean daily temperature across a 1-ha logged forest plot within the SAFE landscape generated by interpolating data from a grid of 72 microclimate data loggers (Blonder et al, 2018). (D) Is a thermal image obtained using a FLIR model E40 camera in a selectively logged forest in Sabah (Senior et al, 2019). tropical forests have been attributed to changes in microclimate .…”

Microclimate buffering and thermal tolerance across elevations in a tropical butterfly

“…A similar scenario occurs in Western Ecuador, one of our study areas, where a large portion of the low and mid elevations have been converted to agricultural lands in the past three decades (Wasserstrom and Southgate, 2013). Any habitat change that affects forest heterogeneity could reduce its great temperature buffering potential (Blonder et al, 2018), and butterfly diversity as a whole (Montejo-Kovacevich et al, 2018). Nevertheless, microclimates have been shown to recover decades after low impact land-uses (González del Pliego et al, 2016; Mollinari et al, 2019; Senior et al, 2018), allowing for recolonization of biodiversity (Hethcoat et al, 2019).…”

“…This complexity is not fully captured by interpolated datasets often used in ecological modelling (e.g. WorldClim2, Fick and Hijmans 2017), with mean temperatures in some cases overestimated by 1.5°C (Blonder et al, 2018; Kearney and Porter, 2009; Storlie et al, 2014). Thus, the biological relevance of studies in the tropics using weather station data is limited, as they are positioned specifically to minimise habitat characteristics that can be crucial in determining the thermal tolerance of local organisms (Frenne and Verheyen, 2016; Jucker et al, 2018; Senior et al, 2017).…”