Regional and local determinants of drought resilience in tropical forests

Abstract

The increase in severity of droughts associated with greater mortality and reduced vegetation growth is one of the main threats to tropical forests. Drought resilience of tropical forests is affected by multiple biotic and abiotic factors varying at different scales. Identifying those factors can help understanding the resilience to ongoing and future climate change. Altitude leads to high climate variation and to different forest formations, principally moist or dry tropical forests with contrasted vegetation structure. Each tropical forest can show distinct responses to droughts. Locally, topography is also a key factor controlling biotic and abiotic factors related to drought resilience in each forest type. Here, we show that topography has key roles controlling biotic and abiotic factors in each forest type. The most important abiotic factors are soil nutrients, water availability, and microclimate. The most important biotic factors are leaf economic and hydraulic plant traits, and vegetation structure. Both dry tropical forests and ridges (steeper and drier habitats) are more sensitive to droughts than moist tropical forest and valleys (flatter and wetter habitats). The higher mortality in ridges suggests that conservative traits are not sufficient to protect plants from drought in drier steeper habitats. Our synthesis highlights that altitude and topography gradients are essential to understand mechanisms of tropical forest's resilience to future drought events. We described important factors related to drought resilience, however, many important knowledge gaps remain. Filling those gaps will help improve future practices and studies about mitigation capacity, conservation, and restoration of tropical ecosystems.

Vapor pressure deficit drives the mortality of understorey woody plants during drought recovery in the Atlantic Forest

“…HOLLUNDER et al Hollunder et al, 2021Hollunder et al, , 2022Schwartz et al, 2020). Therefore, our study shows a different perspective on the role of the acquisitive-conservative trait spectrum and the importance of considering vegetation gradients to predict tree mortality caused by droughts.…”

“…Species with acquisitive attributes and higher carbon gains decrease community drought resistance (Reich, 2014) while species with conservative attributes and lower carbon gains usually increase community drought resistance (Poorter & Bongers, 2006). Plants in dry habitats are expected to be more exposed to drought effects since these habitats have fewer resources and warmer temperatures (Nakagawa et al, 2000;Potts, 2003;Hollunder et al, 2021Hollunder et al, , 2022, and are characterized by species presenting conservative attributes (Apaza-Quevedo et al, 2015). Although lower carbon gain is strongly correlated with drought resistance, it is not yet clear whether those traits also mean drought protection under a warmer and drier climate.…”

Past human‐induced ecological legacies as a driver of modern Amazonian resilience

“…groundwater), soil moisture and fertility, modern anthropogenic activity, the basal area of trees and the traits of those trees (e.g. Costa et al, 2022; Flores et al, 2017; Flores & Holmgren, 2021; Köpp Hollunder et al, 2022; Oliveira et al, 2019; Sousa et al, 2020; Sullivan et al, 2020). The field‐based estimates of forest resilience have been compared with those based on remotely sensed data, and the two do not always align (Flores et al, 2017; Verbesselt et al, 2016).…”

“…Sakschewski et al, 2016). Abiotic factors such as water‐table depth, topography, moisture availability and soil nutrient levels can determine resistance and recovery to drought events (Costa et al, 2022; Köpp Hollunder et al, 2022). Leaf area, plant size, wood density and hydraulic trait diversity are plant functional traits that have also been linked to drought resistance and recovery, though results are not always in agreement (e.g.…”

Rainfall and topographic position determine tree embolism resistance in Amazônia and Cerrado sites

“…Understanding the vulnerability of trees to drought is critical to understand the response of tropical ecosystems to projected drier and warmer conditions [1][2][3][4]. While reduced rainfall and increased vapor pressure deficit are key drivers of tree mortality [5][6][7], topography creates spatial heterogeneity in plant groundwater access and mediates contrasting vegetation response to droughts [8][9][10][11][12]. Field observations show that trees in valleys are often less affected by droughts than their upland counterparts, with Conceptual diagram of the hydrologic gradient from hill to valley and its possible effect on vulnerability to drought [36][37][38].…”