Thermally buffered microhabitats recovery in tropical secondary forests following land abandonment

Abstract

Given the dramatic loss of tropical forests and accelerating climate change, secondary forest regeneration is increasingly recognised as being an important method for reversing losses in biodiversity and carbon stocks. The recolonisation of biodiversity within secondary forests depends upon the recovery of forest structure, including the range of microhabitats used by diverse communities. Here, we investigate the return of critical microhabitats along a successional gradient of secondary forest in the Tropical Andes of Colombia. We measured the abundance of live (bromeliads, tree ferns and moss) and dead (deadwood and leaf litter) microhabitats across three landscapes, each encompassing primary, and young and old secondary forests. Considering the increasing rate of climate warming in the region, we also explored whether these microhabitats provide thermally buffered microclimates. We found that secondary forests have different composition and lower complexity of microhabitats than primary forests, but that the abundance of bromeliads and deadwood recover towards primary levels. Each microhabitat reduces exposure to extreme temperatures, serving as thermal buffers by reducing maximum and increasing minimum temperatures among all forest types. These benefits exist despite ambient temperatures in secondary forests surpassing those of primary forests by 1-2⁰C on average. The protection of secondary forest and promotion of further forest regrowth in the Tropical Andes should represent an urgent investment for conservation, and the value of these secondary forests for offering critical microhabitats and buffered microclimates under climate change should not be overlooked.

Tropical forests are thermally buffered despite intensive selective logging

“…Many ectotherms, such as amphibians, spend some or all of their time exploiting cool microclimates inside microhabitats, which thermal images are unable to capture. We selected three types of microhabitat known to provide cool microclimates (González del Pliego et al., ; Scheffers, Brett et al., ; Scheffers, Evans et al., ), and placed one temperature datalogger (HOBO pendant datalogger, Onset, model UA‐001‐64K or model UA‐002‐64K) per plot in each microhabitat type: deadwood (>10 cm stem diameter), tree holes (>2 cm at widest point of entrance hole, <2 m above the ground) and leaf litter (1.5 m left of the plot centre). The hygrometer measurements of macroclimate temperature were not always synchronized with the dataloggers inside microhabitats, hence we additionally measured macroclimate temperature using a datalogger suspended 1.5 m above the ground at the centre of each plot, shielded against direct radiation and precipitation by an inverted plastic funnel (Scheffers, Brett et al., ; Shoo, Storlie, Williams, & Williams, ).…”

“…In primary forests and secondary forests re‐growing on abandoned farmland, previous studies found that organisms—particularly ectotherms—avoid suboptimal temperatures in the wider “macroclimate” (climate at a spatial scale of m to ha) by moving locally into “microclimates”: climate at a fine‐scale, mm to m, that is distinct from the macroclimate (González del Pliego et al., ; Scheffers, Brett, Diesmos, Williams, & Evans, ; Scheffers, Evans, Williams, & Edwards, ). Climate at this fine‐scale is more relevant for the majority of terrestrial biodiversity, which primarily consists of small‐bodied ectotherms (Nadeau, Urban, & Bridle, ; Potter, Arthur Woods, & Pincebourde, ; Suggitt et al., ).…”

“…The most informative fine‐scale temperature data are derived from point measurements that are highly replicated in both space and time, and demonstrate that loss of vegetation cover causes local daytime warming (Ewers & Banks‐Leite, ; González del Pliego et al., ; Hardwick et al., ; Senior, Hill, González del Pliego, Goode, & Edwards, ). Selective logging affects vegetation by lowering and thinning the canopy, reducing leaf area index (Ewers et al., ; Hardwick et al., ) and the number of vegetation strata, and creating large forest gaps (Kumar & Shahabuddin, ; Okuda et al., ).…”

“…Conversely, enhanced air‐mixing in more open logged forests might create cooler and less variable microclimates. Previous evidence suggests that the availability of cool “microhabitats” (localized environments within which cool microclimates are contained; González del Pliego et al., ; Scheffers, Brett et al., ; Shi, Wen, Paull, & Guo, ) can be reduced (e.g. leaf litter; Saner et al., ) or increased (e.g.…”

“…We focused on cool microclimates in the understorey only (climate at mm to m scale that is cooler than the macroclimate and located within ~2 m of the forest floor). Microclimates on the surface of the forest floor were captured by a thermal camera, while dataloggers were used to capture microclimates within cool understorey microhabitats: leaf litter, tree holes and deadwood (González del Pliego et al., ; Scheffers, Brett et al., ; Scheffers, Evans et al., ). We determined thermal buffering potential according to: (i) the microclimate temperature relative to that of the macroclimate; (ii) the daily variation in microclimate temperature; and (iii) the availability of microclimates in space.…”