Climatic distribution of tree species in the Atlantic Forest

Abstract

Species under milder climates (e.g., warm and wet) tend to experience lower variability in temperature and rainfall regimes and might occur in narrower climatic ranges than species that tolerate harsher conditions (e.g., cold or dry climates). Thus, tree species that occur under harsh conditions should have a broader climatic range, being a small subset of the flora. Here, we assess the influence of climate on species distribution of 1138 tree species from the Atlantic Forest biodiversity hotspot. We investigate their range (or niche breadth), and the "center of gravity" index (or niche optima), along with gradients of mean annual temperature and climatic water deficit (CWD). We further identified those species associated with conditions on different ends of temperature and moisture gradients. We found a small subset of species occurring under colder temperatures or under drier conditions, and these species had a wider niche breadth.The warm or wet-affiliated species had narrower ranges along with the temperature and the CWD gradients, respectively. Moreover, species affiliated to warm and those to moister conditions had greater densities near their occurrence limits, thus they may be more susceptible to climate changes. We conclude that global climate changes will affect the incidence and abundance distribution patterns of tree species along this threatened biodiversity hotspot, mainly those with narrow niches and within the limit of its distribution.

Multi-dimensional temperature sensitivity of protected tropical mountain rain forests

“…Our study and that of Klipel et al (2022) nevertheless show that the dominant tree species of montane forests have broad, not narrow, climate envelopes, and the weighted mean niche breadths are therefore also broad. The optimum temperatures of the dominant species of our montane forests are > 15 • C unpublished data, even though current MAT in the forests they dominate is in the 10-11 • C range -this is also the reason why values of the community thermal capital index are positive in the montane forest plots, as we discuss below.…”

“…Our hypothesis is supported and the CWM thermal niche breadth is therefore substantially sensitive to the spatial temperature gradient (Table 3). In line with the climate variability hypothesis, broad thermal niches may arise in montane species due to the need to tolerate a broader inter-and intra-annual range of environmental conditions than is the case for lowland tropical species (as proposed by Stevens, 1992, among others, and verified for 1,138 tree species of Brazilian Atlantic Forest by Klipel et al, 2022). Among the key elements of the broad range of environmental conditions in montane environments could be chilling temperatures and frost, Rehm and Feeley (2015).…”

“…Finally, we calculate the community weighted mean (CWM) thermal niche breadth for each sample plot and determine its relationship to mean annual temperature. This index permits an indirect test of the climate variability hypothesis, that lowland locations with reduced seasonal temperature variation select for species with narrower thermal ranges (Stevens, 1992;Cuesta et al, 2020) than montane areas with wider ranges of temperature variation, as found by Klipel et al (2022) for the Brazilian Atlantic Forest biome. We therefore hypothesize that CWM thermal niche breadth has a negative relationship to temperature, so that the mean thermal niche breadth should decrease with increasing mean annual temperature.…”