Neighborhood effects explain increasing asynchronous seedling survival in a subtropical forest

Abstract

Biotic interactions play a critical role in mediating community responses to temporal environmental variation, but the importance of these effects relative to the direct effects of environmental change remains poorly understood, particularly in diverse forest communities. Here we combine a neighborhood modeling approach with insights from coexistence theory to assess the effects of temporal variation in species interactions and environmental conditions (e.g., precipitation, temperature, and understory light availability) on seedling survival over nine census years in a subtropical forest. We find significant temporal shifts in the magnitude of neighborhood effects on both community‐wide and species‐level seedling survival (statistically significant random effects of neighborhood × year and neighborhood × species × year interactions). These results are consistent with the idea that environmental change will play a fundamental role on forest regeneration dynamics by altering biotic interactions at the neighborhood scale. Moreover, differences among species in response to neighbors over time contribute to a pattern of temporal decoupling of seedling survival between species, which can help to promote diversity in certain contexts. In separate analyses of multiple regression on distance matrices (MRM), altered interactions with neighbors are much stronger predictors of asynchronous seedling survival among species than the pure effects of climate and plant functional traits, explaining twice as much variation (43.9% vs. 22.2%). In sum, these results reveal that divergent species responses to interannual environmental variability detected are driven primarily by indirect effects mediated by changing biotic environments. This highlights the importance of including indirect effects from local biotic (neighborhood) interactions in forecasts of forest community responses to global change.

Biodiversity in changing environments: An external‐driver internal‐topology framework to guide intervention

“…The influence of internal dynamics is widely viewed as a key reason for the difficulty in predicting local diversity change (Chen et al, 2019; McGill et al, 2015). The four types of interaction topologies detailed above—dominance, facilitation, negative frequency, and positive feedback—are common expectations for contrasting structures that can enable generalization of internal dynamics.…”

Closing the life cycle of forest trees: The difficult dynamics of seedling‐to‐sapling transitions in a subtropical rainforest

“…Although biotic interactions also can have important impacts on seedling demography (e.g. competition, herbivory or plant–pathogen associations [Alexander et al., 2015; Chen, Swenson, et al., 2019; Chen, Wang, et al., 2019; Ibáñez et al., 2013; Uriarte et al., 2018]), these effects are largely negative (but see Corrales et al. (2018) on mycorrhizal associations).…”

“…Important mechanisms, such as ontogenetic variations in trait‐mediated demography (Green & Harms, 2018) and episodic recruitment events driven by climatic oscillations (Brown & Wu, 2005; Pederson et al., 2014), have been identified that may determine both the percentage of survivors of the seedling phase and the amount of time it takes to pass through this phase, critical to how we anticipate the temporal scales in forest regeneration. These life‐history processes make the demographic behaviour of species' seedling populations an important focus for explaining species coexistence and forest dynamics (Comita et al., 2010; Green et al., 2014), density‐dependent processes (Comita et al., 2014), the role of pests and pathogens in defining tree communities (Bagchi et al., 2014; Chen, Swenson, et al., 2019; Chen, Wang, et al., 2019), the spatial influence of forest structure on populations (Comita & Engelbrecht, 2009; Johnson et al., 2017) and trait‐based life‐history strategies (Jia et al., 2020; Umaña et al., 2017).…”

“…This is because most seedlings are in deep shade, and are in competition for nutrients and water with each other and adult trees. They have also been shown to be more vulnerable to herbivores, pests and pathogens than later life‐cycle stages (Bagchi et al., 2014; Barton & Hanley, 2013; Chen, Swenson, et al., 2019; Chen, Wang, et al., 2019). Rare access to resources, such as light through openings in canopy or understorey vegetation can substantially increase the growth rates of a relatively small number of seedlings for brief periods in their lives (Brokaw & Busing, 2000; Denslow et al., 1990; George & Bazzaz, 1999).…”

Asynchronous range shifts drive alpine plant–pollinator interactions and reduce plant fitness

“…These novel interactions have the potential to affect species' performance in surprising ways. For example, experimental range expansion of Florida mangrove seedlings into mature mangrove habitat showed species‐specific direct effects of canopy microclimate on seedling survival and indirect effects of herbivore damage, driven by microclimate (Chen et al, 2019).…”