Pan-Tropical Analysis of Climate Effects on Seasonal Tree Growth

Abstract

Climate models predict a range of changes in tropical forest regions, including increased average temperatures, decreased total precipitation, reduced soil moisture and alterations in seasonal climate variations. These changes are directly related to the increase in anthropogenic greenhouse gas concentrations, primarily CO2. Assessing seasonal forest growth responses to climate is of utmost importance because woody tissues, produced by photosynthesis from atmospheric CO2, water and light, constitute the main component of carbon sequestration in the forest ecosystem. In this paper, we combine intra-annual tree growth measurements from published tree growth data and the corresponding monthly climate data for 25 pan-tropical forest sites. This meta-analysis is designed to find the shared climate drivers of tree growth and their relative importance across pan-tropical forests in order to improve carbon uptake models in a global change context. Tree growth reveals significant intra-annual seasonality at seasonally dry sites or in wet tropical forests. Of the overall variation in tree growth, 28.7% was explained by the site effect, i.e. the tree growth average per site. The best predictive model included four climate variables: precipitation, solar radiation (estimated with extrasolar radiation reaching the atmosphere), temperature amplitude and relative soil water content. This model explained more than 50% of the tree growth variations across tropical forests. Precipitation and solar radiation are the main seasonal drivers of tree growth, causing 19.8% and 16.3% of the tree growth variations. Both have a significant positive association with tree growth. These findings suggest that forest productivity due to tropical tree growth will be reduced in the future if climate extremes, such as droughts, become more frequent.

Key drivers of ecosystem recovery after disturbance in a neotropical forest

“…The main difference between the 3 scenarios lies in the absolute values of the Survivors' ACS loss, with very high values for the wet scenario. This result may look strange given that drought has often been identified as one of the main climate drivers of tropical forest dynamics Wagner et al 2012Wagner et al , 2013Wagner et al , 2014Wagner et al , 2016, with large mortality events among tropical trees during El Nino years for instance (Phillips et al 2009) that have not only immediate but also long-term and cumulative impacts on the carbon cycle (Doughty et al 2015). Those large mortality events are associated with tree hydraulic traits, the most susceptible species being those having a low hydraulic safety margin (Anderegg et al 2016).…”

Vulnerability of Commercial Tree Species to Water Stress in Logged Forests of the Guiana Shield

“…Moreover, the variability of the dry season length in Amazonia [6] has been underestimated in the climate models used for the IPCC 5th assessment report so that the projected changes of the dry-season length are likely to be the lower bound of the ongoing changes [7]. Recent studies have tried to understand the potential impact of this increase in water stress on tropical forests [8][9][10][11][12].…”

Tree growth over three years in response to monthly rainfall in central Amazonia

“…In tropical forests, high rainfall intensity in the rainy season is often associated with reduction in the levels of irradiance in response to cloudiness (Mulkey et al, 1996;Wagner et al, 2014). Therefore, it can be expected that an increase in irradiance leads to increase in tree growth (Graham et al, 2003;Stark et al, 2015).…”

“…Some studies have shown that in central Amazonia carbon gains tend to be higher in the rainy season (Malhi et al, 1998;Vieira et al, 2004;Wagner et al, 2014). However, there is not conclusive evidence that soil water content is a limiting factor in the dry season, as somehow gross primary production starts to increase at the end of the dry season (Restrepo-Coupe et al, 2013), when soil water content is still at its lower levels (42% v/v, Malhi et al, 1998).…”