Smaller conifers are more resilient to drought

Abstract

Warmer and drier climate conditions are negatively impacting conifers, which show different mechanisms to withstand drought stress including growth resilience. However, it is unclear which traits make trees and shrubs more resilient to drought in terms of growth recovery. We addressed this question by measuring and collecting from the literature several functional traits in 19 conifers of nine genera (Abies, Pinus, Pseudotsuga, Cedrus, Picea, Juniperus, Cupressus, Tetraclinis and Taxus) from three families (Pinaceae, Cupressaceae, Taxaceae) inhabiting sites of contrasting climate conditions in Spain. These traits were correlated with three growth resilience indices derived from ring-width data (Rt, resistance; Rc, recovery; Rs, resilience) with and without accounting for their phylogenetic signal. Growth resistance (Rt) was negatively related to plant height (r = -0.52, p = 0.04). Growth resilience (Rs) was negatively related to plant height (r = -0.93, p < 0.001) and leaf life span (r = -0.51, p = 0.03), but positively related to the thickness-to-span ratio (r = 0.80, p < 0.001). However, the relationship between Rs and leaf life span was not significant (p = 0.155) after accounting for phylogenetic signals. Lastly, growth recovery was positively related to the growth responsiveness to climate, assessed as the correlation between ring-width indices and water balance (r = 0.66, p = 0.002). Height and the thickness-to-span ratio, a surrogate of xylem resistance to cavitation, are linked to post-drought growth recovery in conifers subjected to seasonal dry conditions.