Frequency‐dependent tree growth depends on climate

Abstract

Climate and competition interact to affect species' performance, such as growth and survival, and help determine species distributions and coexistence. However, it is unclear how climatic conditions modulate frequency-dependent performance, that is, how performance changes as a species becomes locally rare or common. This is critical because declines in performance as a species becomes more common (negative frequency dependence) is a signature of niche differences among species that stabilize coexistence, whereas positive frequency dependence leads to priority effects and hampers species coexistence. Here, we used dendrochronology and hierarchical models to test whether frequency-dependent growth of sugar pine (Pinus lambertiana) depends on climatic conditions. We found that growth rates were strongly dependent on annual precipitation, but no frequency dependence was evident across all years. However, there was a strong interaction between precipitation and frequency dependence, revealing stabilizing niche differences in dry years but positive frequency dependence in wet years. These differences emerged because of precipitation-driven changes in the direction and strength of both con-and heterospecific competition. Overall, these results show how stabilizing and destabilizing effects can be temporally dynamic for long-lived species and interact with climate variation.

The competitive effect of neighbouring plants on the growth of two eucalypts is stronger in dry conditions

“…This finding contradicts predictions of the SGH (Bertness & Callaway, 1994) and contributes to an increasing body of evidence that in severely water‐limited environments, plant–plant interactions often become increasingly competitive, rather than facilitative (Barron‐Gafford et al., 2017; Maestre & Cortina, 2004; O'Brien et al., 2017; Tielbörger & Kadmon, 2000). Further, our finding that stronger competition was associated with reduced precipitation is supported by previous similar studies that assess how temporal variation in rainfall determines the nature of plant–plant interactions (Diez et al., 2021; Tielbörger & Kadmon, 2000) and by a recent study that found drought tended to increase competition‐induced tree mortality across parts of Europe (Kulha et al., 2023). Stronger competition in dry conditions has important implications for tree growth in future climatic conditions, in which drought frequency and severity is expected to increase (Dai, 2013; Reichstein et al., 2013).…”

“…Our hypothesis regarding neighbour identity is based on the fact that species-specific neighbour effects have been shown in this system previously (Britton et al, 2022). Finally, in contrast to the SGH (Bertness & Callaway, 1994), we expect the effect of neighbours to be strongest in the driest and hottest year when competition for water will be most intense, as seen in other tests of the SGH to temporal variation in rainfall (Diez et al, 2021;Tielbörger & Kadmon, 2000, but see Sthultz et al, 2007).…”

“…However, empirical support for the SGH in relation to temporal water stress gradients is mixed, whereby previous studies have found facilitation increased (Del Río et al., 2014; Sthultz et al., 2007), decreased (Tielbörger & Kadmon, 2000) or did not show clear differences (Soliveres et al., 2010) in lower rainfall (higher stress) periods compared to those with higher rainfall. Others have not directly tested the SGH but explored variation in neighbour effects on tree growth in response to temporal climate patterns, finding higher temperatures and reduced precipitation can either amplify (Diez et al., 2021) or reduce the strength of competitive neighbour effects (Luo et al., 2020). Thus, although there are clear indications that the neighbourhood effect varies temporally with climate, general patterns have not yet emerged.…”

“…Previous studies exploring temporal variation in neighbour effects on tree growth commonly focus on community‐level neighbourhood metrics (NMs) such as stand basal area (Gleason et al., 2017; Rollinson et al., 2016) or broad groupings such as conspecific and heterospecific neighbours (Diez et al., 2021). While community‐level metrics ignore the identity of neighbour species, con‐ and hetero‐specific groupings are based on the assumption that intraspecific competition should always be stronger than interspecific competition because of greater niche overlap (i.e.…”

Effects of population density and environmental conditions on life‐history prevalence in a migratory fish

“…According to this theory, as densities in the natal stream increase, juvenile salmonids should increasingly select habitats with lower densities to access the resources they need for growth prior to migration. Furthermore, the effects of population density on life‐history prevalence can be mediated by environmental factors (Brown, White, & Peet, 2021 ; Diez et al, 2021 ), and the effects of environmental drivers on life‐history prevalence may increase near carrying capacity (Jesmer et al, 2021 ).…”