Novel insights into how the mean and heterogeneity of abiotic conditions together shape forb species richness patterns in the Allegheny plateau ecoregion

Abstract

While plant community theory tends to emphasize the importance of abiotic heterogeneity along niche axes, much empirical work seeks to characterize the influence of the absolute magnitude of key abiotic variables on diversity. Both magnitude (as reflected, e.g., by a mean) and heterogeneity (variance) in abiotic conditions likely contribute to biodiversity patterns in plant communities, but given the large number of putative abiotic drivers and the fact that each may vary at different spatiotemporal scales, the challenge of linking observed biotic patterns with the underlying environment remains acute. Using monitoring data from a natural resource agency, we compared how well statistical models of the mean, heterogeneity, and both the mean and heterogeneity combined of 17 abiotic factor variables explained patterns of forb species richness in Northeast Ohio, USA. We performed our analyses at two spatial scales, repeated in spring and summer across four forest types. Although all models explained a great deal of the variance in species richness, models including both the mean and heterogeneity of different abiotic factors together outperformed models including either the mean or the heterogeneity of abiotic factors alone. Variability in forb species richness was mostly due to changes in mean calcium levels regardless of forest type. After accounting for forest type, we were able to attribute variation in forb species richness to changes in the heterogeneity of different abiotic factors as well. Our results suggest that multiple mechanisms act simultaneously according to different aspects of the abiotic environment to structure forb communities, and this underscores the importance of considering both the magnitude of and heterogeneity in multiple abiotic factors when looking for links between the abiotic environment and plant community patterns. Finally, we identify novel patterns across spatial scales, forest types, and seasons that can guide future research in this vein.OPEN RESEARCH BADGES This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.kp3cb17.

Fine‐scale environmental heterogeneity and spatial niche partitioning among spring‐flowering forest herbs

“…We show that local species‐environment relationships are predictable based on morphological, physiological, and phenological characteristics and that heterospecific individuals remain spatially segregated as environmental sorting, competition, and dispersal play out at local scales. This study advances our understanding of how environmental heterogeneity could maintain high local plant diversity in temperate forest understories (Bratton, 1976; Beatty, 1984, 2014; Vellend et al, 2000; Peet et al, 2014; Catella et al, 2019), the spatial scale at which forest herbs can partition habitat (Amarasekare, 2003; Hart et al, 2017), and, more generally points to the importance of spatial resource partitioning in promoting local plant diversity (Amarasekare, 2003; Silvertown, 2004; Lundholm, 2009; Bartels and Chen, 2010; Stein et al, 2014).…”

“…This environmental variation is positively associated with species richness and has been implicated as an important factor maintaining regional diversity (Ricklefs, 1977; Kreft and Jetz, 2007; Stein et al, 2014). Environmental heterogeneity can also influence plant distributions at finer scales (Lundholm, 2009; Bartels and Chen, 2010; Costanza et al, 2011; Catella et al, 2019). Yet, few empirical studies carefully consider the physiological differences and competitive interactions underlying differential species responses to local environmental heterogeneity (Silvertown, 2004) or the spatial scales at which this local heterogeneity could facilitate coexistence (Amarasekare, 2003; Kneitel and Chase, 2004; Lundholm, 2009; Tamme et al, 2010; Hart et al, 2017).…”

“…Understory plant species also respond sensitively to environmental variation at finer spatial scales. Within forest stands, herbaceous plant species often exhibit highly heterogeneous spatial distributions and these local distributions reflect, in part, fine‐scale variation in the environment (Struik and Curtis, 1962; Anderson et al, 1969; Burton et al, 2011; Sabatini et al, 2014; Chudomelová et al, 2017; Catella et al, 2019). For example, fallen trees create light gaps in otherwise closed canopy forests, which favor the growth of certain herbaceous species (Thompson, 1980).…”

Asymmetrical pegs in square holes? Functional and phylogenetic determinants of plant community assembly in temperate forest understories

“…Static co-occurrence patterns could also obscure relevant community dynamics. There is, however, little evidence for complementary resource usage among temperate forest herbs in the absence of spatial or temporal environmental heterogeneity (Amarasekare 2003, Silvertown 2004, Costanza et al 2011, Beatty 2014, Catella et al 2019. In contrast, differential plant responses to spatial environmental heterogeneity strongly influence local plant distributions (Beatty 2014).…”

“…For example, herb distributions respond sensitively to edaphic conditions and light availability (Curtis 1959, Givnish 1982, 1987, Gilliam 2014. Species turnover along these environmental gradients reflect physiological tradeoffs suggesting that environmental sorting and competitive hierarchies structure herb distributions at both local scales (Bratton 1976, Beatty 1984, Gilbert & Lechowicz 2004, Catella et al 2019) and across landscapes (Curtis 1959, Amatangelo et al 2014, Beatty 2014, Peet et al 2014. The potential for trait differences to stabilize local coexistence among forest herbs has received less attention.…”