The above–belowground functional space of tropical dry forest communities responds to local hydric habitats

Abstract

Tropical dry forests are environmentally complex ecosystems with highly heterogeneous water availability, such that distinctive plant communities are found in contrasting habitats in close proximity to each other. This leads to the question of how resource heterogeneity has led to functional heterogeneity among communities. One hypothesis is that the main trade-offs and the size of the functional space should diverge between communities that differ in their most limiting resource. To test this, we compared aboveground and belowground traits of saplings of 33 dominant species from the dry forest plant communities of two locations that differ in water and also in light availability. In the drier community, the major functional dimension described a tradeoff between drought tolerance and drought avoidance strategies. This dimension was also evident in the wetter community; however, traits related to the efficiency of resource capture were decoupled from the drought tolerance-drought avoidance tradeoff. Trees from the wetter community tended to develop more efficient fine roots for resource capture. The functional space of the drier and more heterogenous forest was larger than the wetter forest, and plant strategies to deal with drought accounted for a much larger portion of trait variation. Overall, functional differentiation may occur between systems that are close in proximity but differ in the availability of resources such as water and light. These environmental differences cause plant communities to differ in functional properties both aboveground and belowground, likely promoting heterogeneous responses to anthropogenic and natural disturbances at the landscape scale.

Lithological substrates influence tropical dry forest structure, diversity, and composition, but not its dynamics

“…However, the strong differences in structure and diversity, together with the soil differences observed by Sandoval-Granillo (2020), point to clearly different environmental conditions between substrates, as discussed earlier. As soils derived from phyllite seem drier and less fertile, one may reasonably assume that species in this substrate are better adapted to harsher environmental conditions (Díaz-Castellanos et al, 2022). For instance, communities in which conservative traits are prevalent in a Brazilian TDF showed higher productivity and biomass stocks than their counterparts with more acquisitive traits (Prado-Junior et al, 2016), which provides support to our hypothesis.…”

“…Empirical observations from sites on the two substrates also suggest that limestone environments are rockier and highly heterogeneous, with many small and irregular patches of developed soils, shallow soils, and bare rock (Miguel-Talonia, unpublished data). Thus, limestone environments may provide a wider variety of microhabitats than phyllite, thus allowing more species to establish on this TDF community (Ribeiro et al, 2007;Díaz-Castellanos et al, 2022).…”

“…Regarding (2), we hypothesized three alternative scenarios based on the two mechanisms of geological effects advanced earlier, i.e., direct effects on forest dynamics through soil conditions differentially affecting the same set of species (soil-effects mechanism) against indirect effects on forest dynamics through species composition, where different species respond differently to environmental factors (composition-effects mechanism). If phyllite represents a harsher environment for TDF growth than limestone, it is likely that trees growing on this substrate are better adapted to cope with water and nutrient limitations (Scholz et al, 2014;Díaz-Castellanos et al, 2022). In this case, the soil-effects mechanism would result in increased stability of limestone TDF by providing higher and more stable soil water content, regardless of interannual variation in precipitation.…”

Tropical forest dynamics in a changing world

“…However, for practical purposes, substrates are regarded as relatively stable elements of the abiotic environment in ecological literature. The role of substrates for vegetation is mostly seen at spatial scales, driving differences in species compositions and structure development across the landscape (Ribeiro et al, 2007;Peña-Claros et al, 2012;Díaz-Castellanos et al, 2022). Yet, they can influence forest dynamics by their interaction with climatic conditions (Vargas Gutiérrez et al, 2023).…”

“…Empirical observations from sites on the two substrates also suggest that limestone environments are rockier and highly heterogeneous, with many small and irregular patches of developed soils, shallow soils, and bare rock (C. Miguel-Talonia, unpublished data). Thus, limestone environments may provide a wider variety of microhabitats than phyllite, thus allowing more species to establish on this TDF community (Ribeiro et al, 2007;Díaz-Castellanos et al, 2022).…”