High resilience, but low viability, of pine plantations in the face of a shift towards a drier climate

Abstract

Plantations of Mediterranean pines will face warmer and drier climate conditions during the 21st century. However, we lack field assessments of how severe droughts could threaten the viability of many of these plantations, often located at xeric sites and lacking adaptive management measures such as thinning. In this work, we related radial-growth variability to recent defoliation, to evaluate the resilience and vulnerability of Maritime pine (Pinus pinaster) plantations from xeric sites in south-eastern Spain to three recent droughts (1995, 2005, and 2012). Tree diameter and growth resistance after the most severe drought, which occurred in 1995, were positively related to growth. In addition, the current defoliation level, a proxy for tree vigor, was related to growth, decreasing as tree-to-tree competition increased. These findings indicate that increasing drought will reduce growth and increase the needle loss and mortality rate across many dense pine plantations in the Mediterranean Basin, suggesting that they are more prone to die. Thus, limited resilience of plantations may explain their higher defoliation and indicate that future severe droughts could lead to widespread dieback and high mortality at marginal sites. Therefore, if effective management is not implemented, warmer and drier conditions will likely threaten the viability of many of these drought-prone plantations and their ability to deliver key ecosystem services.