Assessing Tree Drought Resistance and Climate-Growth Relationships under Different Tree Age Classes in a Pinus nigra Arn. ssp. salzmannii Forest

Abstract

The magnitude of drought impact in forest ecosystems depends on which group of trees are more severely affected; greater mortality of smaller trees can modulate the trajectories of succession, while the mortality of larger trees can disproportionately offset the ecosystem’s carbon balance. Several studies have documented a greater vulnerability of large trees to extreme droughts while some other studies reported a greater growth reduction in smaller trees during droughts. We tested these hypotheses by comparing tree basal area increment (BAI), drought resistance (i.e., magnitude of growth decline during drought), and resilience (i.e., magnitude of growth recovery after drought) across five different age-classes in black pine (Pinus nigra Arn. Ssp salzmannii) forests in Spain. Our results showed that the BAI patterns, drought resistance, and resilience were strongly influenced by tree age-classes. In addition, the effect of climatic water balance (precipitation minus potential evapotranspiration) on BAI significantly varied among age-classes. The effect of water balance on BAI was lower for younger age-classes (1–39 years of age) compared to older age-classes. We observed a greater growth reduction (i.e., lower resistance) in older trees (>40 years of age) during droughts compared to younger trees (<40 years of age). However, all trees, irrespective of their ages, were able to recover the growth rates after the drought. In general, younger trees showed a greater capacity in recovering the growth rate (i.e., more resilient) than older trees. We detected no significant effects of stand basal area and stand density on BAI, drought resistance, and resilience. Overall, our results indicated that growth of older trees was more negatively affected during drought. Therefore, these older/larger trees can be selected for commercial thinning, or can be released from competition, which can minimize the potential impacts of future droughts in black pine forests in Spain.

New evidence for population-specific responses to drought events from tree ring chronologies of Pinus nigra ssp. laricio across the entire distribution range

“…Camarero et al (2018) observed that an extreme drought induced a marked growth reduction in declining black pine individuals when accounting for age effects on growth rates (younger declining and older non-declining individuals). Nevertheless, these results are in contrast with other studies conducted both on black pine (e.g., Lucas--Borja et al, 2021;Granda et al, 2018;Martin-Benito et al, 2008) and other tree species (e.g., Bose et al, 2021;Bennett et al, 2015;Dorman et al, 2015). In these studies, older trees were found to be less resistant to drought than younger trees and the impact of drought events on growth and mortality rates in larger trees was relatively greater than in smaller trees.…”

Did the 2018 megadrought change the partitioning of growth between tree sizes and species? A Swiss case‐study

“…Tree growth responses to drought can depend on tree sizes (D'Amato et al 2013;Schwarz & Bauhus 2019) and stand characteristics (Bottero et al 2017;Bose et al 2018;Andrews et al 2020). For example, small Pinus nigra trees were more drought sensitive, in terms of growth, in mixed conifer stands in Spain (Martı ´n-Benito et al 2008), while large trees were more sensitive in mixed Picea abies and Fagus sylvatica stands in Germany (Pretzsch et al 2018), as well as in pure Pinus nigra stands in Spain (Lucas-Borja et al 2021). Several studies reported higher mortality rates of large trees under drought stress (Bennett et al 2015;Olson et al 2018), while others documented higher mortality of smaller trees (van Mantgem et al 2009;Colangelo et al 2017).…”

“… 2018 ), as well as in pure Pinus nigra stands in Spain (Lucas‐Borja et al . 2021 ). Several studies reported higher mortality rates of large trees under drought stress (Bennett et al .…”

Screening for drought resistance among ornamental maples (Acer sp.). A field experiment in juvenile plants

“…Nevertheless, drought stress resistance can substantially change with the tree age. As referred by Lucas-Borja et al (2021), effect of water inbalance (precipitation minus evapotranspiration) on basal area increment was lower in younger age classes (1-39 years old) of black pine (Pinus nigra Arn. ssp.…”

“…Since conflicting results come from studies on aging effect in tree drought resistance (e.g. Li et al, 2012;Lucas-Borja et al, 2021;Unawong et al, 2022), a representative tree age seems to be an important issue in the species evaluation process. We suppose that juvenile plants, fully manifesting species differences, could meet this requirement.…”