Differential climatic conditions drive Acacia tortilis tree growth in its opposite range edges in Africa and Asia.

Abstract

Tree growth is a fundamental biological process that is essential to ecosystem functioning, as well as water and element cycling. Climate exerts a major impact on tree growth, with tree species often requiring a unique set of conditions to initiate growth and maintain it throughout a growing season. Still, little is known about the specific climatic factors that determine tree growth in savannah and desert tree species. Among global tree species, Acacia tortilis occupies one of the largest distribution ranges (crossing 6,500 km and 54 latitudes), spanning across large parts of Africa and into the Middle East and Asia. Here we measured climate and Acacia tortilis tree growth (continuous measurements of stem circumference) in its southern and northern range edges in South Africa (SA) and Israel (IL), respectively, aiming to elucidate whether the growth-climate interactions were similar in both edges. Growth occurred during the SA summer (between December and March), and in IL during early summer, and autumn (April-June and October-November, respectively). Surprisingly, annual growth was 40% higher in IL than in SA. Within the wide distribution range of Acacia tortilis, our statistical model showed that climatic drivers for tree growth differed between the two sites. High temperatures facilitated growth in the hot and arid IL site, while high humidity permitted growth in the more humid SA site. Our results confer an additional understanding of tree growth adaptation to extreme conditions in Acacia's world range edges, a major point of interest with ongoing climate change. This article is protected by copyright. All rights reserved.