Fragmentation, forest structure, and topography modulate impacts of drought in a tropical forest landscape

Abstract

Climate models predict increases in drought conditions in many parts of the tropics. Yet the response of tropical forests to drought remains highly uncertain, especially with regards to the factors that generate spatial heterogeneity in drought response across landscapes. In this study, we used Landsat imagery to assess the impacts of a severe drought in 2015 across an ~80,000‐ha landscape in Puerto Rico. Specifically, we asked whether drought effects varied systematically with topography and with forest age, height, and fragmentation. We quantified drought impacts using anomalies of two vegetation indices, the enhanced vegetation index (EVI) and normalized difference water index (NDWI), and fit random forest models of these metrics including slope, aspect, forest age, canopy height, and two indices of fragmentation as predictors. Drought effects were more severe on drier topographic positions, that is, steeper slopes and southwest‐facing aspects, and in second‐growth forests. Shorter and more fragmented forests were also more strongly affected by drought. We also assessed which factors were associated with stronger recovery from drought. Factors associated with more negative drought anomalies were also associated with more positive postdrought anomalies, suggesting that increased light availability as a result of drought led to high rates of recovery in forests more severely affected by drought. In general, recovery from drought was rapid across the landscape, with postdrought anomalies at or above average across the study area. This suggests that forests in Puerto Rico might be resilient to a single‐year drought, though vulnerability to drought varies depending on forest characteristics and landscape position.

Disentangling the effects of environment and ontogeny on tree functional dimensions for congeneric species in tropical forests

“…Despite our experimental design that purposefully limited phenotypic range by focusing on species within a single genus, species show strong trait differentiation along the two main functional dimensions, suggesting that they occupy distinct niche space both in terms of leaf physiology and leaf economics. As the four focal Micropholis species have contrasting habitat preferences, such strong trait differences between species may play a role in local biotic interactions and shape species distributions across environmental gradients (Fortunel et al , ; Schwartz et al , ).…”

“…An important challenge to strengthen predictions for how tropical forests will respond to climate change is to improve our understanding of how multiple factors shape tropical tree response to water and nutrient availability (Condit et al, 2013;Fortunel et al, 2016;Uriarte et al, 2018;Schwartz et al, 2019). Functional traits allow examining species distributions across broad environmental gradients only in that we assume traits to be tightly linked to the underlying key physiological processes driving species response to the environment (Violle et al, 2007).…”

Hurricane-Induced Rainfall is a Stronger Predictor of Tropical Forest Damage in Puerto Rico Than Maximum Wind Speeds

“…For this study, we limited our study area (312,319 ha) to forested areas in Puerto Rico [65][66][67] . Field plots [68][69][70][71] cover the rainfall distribution, elevation gradients and two dominant geologies (volcanic and limestone), that are reflected in the diversity of forest characteristics present in Puerto Rico (Fig. 1, Supplementary Fig.…”

Contrasting Trends of Forest Coverage between the Inland and Coastal Urban Groups of China over the Past Decades

“…The landscape diversity has also changed in areas where forests have changed significantly (e.g., Shanghai, Changzhi, and Jincheng). spatial patterns (such as patch fragmentation, landscape diversity, and spatial aggregation) [13][14][15][16] and the relationship between LUCC and ecological processes [17][18][19][20].Edurne et al used several Landsat TM images for different months of 1987 and 2010 to assess the forest cover change of the Natural Natural Park (Spain) based on remote sensing and landscape metrics. The results showed that the change of forest cover in the region leaded to the increase of landscape fragmentation, and they believed that the spatial and temporal changes of tree species distribution in forests were closely related to the landscape structure [21].…”

“…The landscape diversity has also changed in areas where forests have changed significantly (e.g., Shanghai, Changzhi, and Jincheng). spatial patterns (such as patch fragmentation, landscape diversity, and spatial aggregation) [13][14][15][16] and the relationship between LUCC and ecological processes [17][18][19][20].…”