Legacy effects of drought on tree growth responses to hurricanes

Abstract

Natural perturbations, including hurricanes and severe droughts, are becoming more frequent and intense in the tropics, yet our understanding of forest responses to these events is still limited. While the relationships between extreme climatic events and tree mortality are frequently studied, responses of trees that survived such perturbations have been rarely reported. Perturbations and their effects can be quite variable, and trees can respond both positively and negatively to them, depending on their sensitivity and opportunistic behavior. Understanding the potential variation in responses both within and among species is important for building predictions of forest responses. We studied tree growth responses (i.e., changes relative to standard conditions) to hurricanes and drought events in Puerto Rico across six common and broadly distributed species. We examined whether there is a congruence in responses to these contrasting extreme climatic events. We show that trees are particularly susceptible to droughts but display a wide range of responses to hurricanes. Despite the high stochasticity in the impacts of hurricanes, trees that showed reduced growth during previous droughts tend to show reduced growth during the hurricanes as well. Our results demonstrate that trees subjected to different and successive major climatic stresses have consistent declines in their performance. Projected increases in the severity of droughts and tropical storms could have an accumulated, and possibly compound, impact on tree growth. Long-term demographic studies are necessary to understand legacy effects of species responses to extreme climatic perturbations.

Hydraulic traits are not robust predictors of tree species stem growth during a severe drought in a wet tropical forest

“…The majority of the species in our study, however, had lower growth during drought. A recent study at the site using four of the same species found a decline on growth during the 2015 drought at higher elevation sites in the LEF for C. schreberiana , C. borinquensis and S. berteroana —results that were largely consistent with our findings (Umaña & Arellano, 2021). However, drought did not result in lower growth for D. excelsa in their study whereas we found that this keystone species, one of the most important species in Puerto Rican wet forests, also experienced one of the highest declines in growth during the 2015 drought, particularly for larger individuals.…”

“…Increases in tree mortality and growth declines have been associated with severe drought across several neotropical forests (Bretfeld et al, 2018; Engelbrecht et al, 2006; Leitold et al, 2018; Powers et al, 2020; Umaña & Arellano, 2021; Uriarte et al, 2016), which are expected to be exposed to increasing drought frequency and severity (Kooperman et al, 2018; Neelin et al, 2006). Even relatively short periods of decreased rainfall (≥10 days with no rainfall) during the wet season can increase seedling mortality (Engelbrecht et al, 2006).…”

Hurricanes increase tropical forest vulnerability to drought

“…montana, which dominate post-disturbance communities (Uriarte et al, 2009(Uriarte et al, , 2019. Umaña & Arellano (2021) studied six tree species at the same location in Puerto Rico and found that C. schreberiana was the species that had the highest growth reduction during drought, consistent with our findings. In their study, D. excelsa was not affected by severe drought and responded favorably to moderate droughts (Umaña & Arellano, 2021).…”

“…Umaña & Arellano (2021) studied six tree species at the same location in Puerto Rico and found that C. schreberiana was the species that had the highest growth reduction during drought, consistent with our findings. In their study, D. excelsa was not affected by severe drought and responded favorably to moderate droughts (Umaña & Arellano, 2021). Dacryodes excelsa is known to have extensive root grafting (Basnet , 1993) that could allow trees to redistribute water and make them less susceptible to drought.…”

“…Forests recovering from hurricanes are expected to favor resource‐acquisitive species over conservative ones due to high light conditions in the understory (Carreño‐Rocabado et al ., 2012; Subedi et al ., 2019), potentially leading to an increase in the overall level of forest susceptibility to drough. Yet species‐level responses to drought, and how they align with their responses to disturbances, are extremely variable and poorly understood (Umaña & Arellano, 2021).…”