East Texas forests show strong resilience to exceptional drought

Abstract

Drought-induced tree mortality has increased in many parts of the world because of climate change, and in some regions, has altered forest structure, species composition and ecosystem functions. These developments have the potential to reduce forest resilience and push forests over a tipping point to an alternate state (i.e. a different forest type or a non-forest ecosystem). Texas experienced an exceptional drought in 2011, which killed an estimated 65.5 million trees in the heavily forested areas of the East Texas region. The objective of this study was to understand the effects of the 2011 drought on mortality, biomass and growth in this region and explore forest stability at species, forest and ecoregion levels. We categorized 19 years’ time-series data of 1455 Forest Inventory and Analysis plots into four periods, base (2001–2003), pre-drought (2004–2010), drought (2011–2016) and post-drought (2017–2019), and used repeated-measures analysis of variance to analyse annual mortality, biomass loss, growth rates and the Forest Stability Index to understand forest stability. Our results show that tree mortality and biomass loss increased significantly during the drought period and annual growth rates declined. During the post-drought period, mortality and biomass loss rates returned to the pre-drought level and growth partially recovered. During the drought period, FSI dropped at species, forest type and ecoregion levels but recovered during the post-drought period, except for the Oak Woods and Prairies ecoregion and for forests dominated by southern red oak. Our results indicate that East Texas forests are undergoing a reorganization and recovery stage (in terms of species composition and stand structure) but have yet to reach a tipping point. Given the increased frequency and severity of climate change-induced weather events, East Texas forests could approach a tipping point in the future if there is insufficient time between events for reorganization and recovery. Further analyses are needed to understand the fate of tree species and forests in East Texas under global climate change.