Intraspecific variability in growth response to environmental fluctuations modulates the stabilizing effect of species diversity on forest growth

Abstract

Summary Differences between species in their response to environmental fluctuations cause asynchronized growth series, suggesting that species diversity may help communities buffer the effects of environmental fluctuations. However, within‐species variability of responses may impact the stabilizing effect of growth asynchrony. We used tree ring data to investigate the diversity–stability relationship and its underlying mechanisms within the temperate and boreal mixed woods of Eastern Canada. We worked at the individual tree level to take into account the intraspecific variability of responses to environmental fluctuations. We found that species diversity stabilized growth in forest ecosystems. The asynchrony of species’ response to climatic fluctuations and to insect outbreaks explained this effect. We also found that the intraspecific variability of responses to environmental fluctuations was high, making the stabilizing effect of diversity highly variable. Synthesis. Our results are consistent with previous studies suggesting that the asynchrony of species’ response to environmental fluctuations drives the stabilizing effect of diversity. The intraspecific variability of these responses modulates the stabilizing effect of species diversity. Interactions between individuals, variation in tree size and spatial heterogeneity of environmental conditions could play a critical role in the stabilizing effect of diversity.

Interactions among trees: A key element in the stabilising effect of species diversity on forest growth

“…Empirical studies in forest ecosystems have mainly attributed the stabilising effect of diversity to species differences in their response to fluctuating environmental conditions (Aussenac et al., ; Jucker, Bouriaud, et al., ; Río et al., ), consistent with the insurance hypothesis. Environmental fluctuations increase the variance in growth, but interspecific differences generate growth asynchrony (i.e., low ) among individuals, which ultimately stabilises growth at the community level.…”

“…Species diversity (hereafter diversity) is a major driver of ecosystems functioning (Cardinale et al., ; Hooper et al., ). In particular, there is mounting evidence that diversity stabilises forest growth under fluctuating environmental conditions (Aussenac et al., ; Hutchison, Gravel, Guichard, & Potvin, ; Jucker, Bouriaud, Avacaritei, & Coomes, ; Morin, Fahse, Mazancourt, Scherer‐Lorenzen, & Bugmann, ; Río et al., ). However, although significant progress has been made in recent years, our understanding of the mechanisms underlying the diversity–stability relationship in forest ecosystems remains incomplete.…”

“…The mean of the total growth of a community may be decomposed as the sum of the mean growth of all its constituent individuals. Similarly, the variance of the total growth of a community may be decomposed as the sum of the growth variances and covariances of all individuals in the community (Aussenac et al., ). The TS of a community constituted of n individuals is therefore given by: where and are the mean and the variance of individuals growth, and cov, the growth covariance of individuals i and j .…”

“…Indeed, diversity has been found to increase tree mean growth (Chamagne et al., ; Chen et al., ; Fichtner et al., ; Jucker, Bouriaud, et al., ; Potvin & Gotelli, ), and to reduce the variance of tree growth by buffering tree response to climate fluctuations (Jucker, Bouriaud, et al., ; Lebourgeois, Gomez, Pinto, & Me′rian, ; Pretzsch, Schütze, & Uhl, ). In studies that have examined the stabilising effect of diversity in forest communities, these effects were attributed to favourable interactions among individuals (i.e., reduced competition and facilitation; Jucker, Bouriaud, et al., ; Río et al., ; Aussenac et al., )). However, in these studies, interactions were not directly measured.…”

Corrigendum

“…Aussenac, R., Bergeron, Y., Ghotsa Mekontchou, C., Gravel, D., Pilch, K. and Drobyshev, I. () Intraspecific variability in growth response to environmental fluctuations modulates the stabilizing effect of species diversity on forest growth. Journal of Ecology, 105, 1010–1020.…”