Water the odds? Spring rainfall and emergence‐related seed traits drive plant recruitment

Abstract

Recruitment of new individuals from seed is a critical component of plant community assembly and reassembly, especially in the context of ecosystem disturbance and recovery. While frameworks typically aim to predict how communities will be filtered on the basis of traits influencing established plant responses to the environment, assembly from seed is more complex: the responses of seeds (affected by dormancy and germination function) and establishing plants (affected by root and leaf function) can both influence outcomes within a single growing season. This creates a potential role for a more diverse set seed and seedling traits, and for environmental variability on shorter timescales (e.g. seasonal versus annual dynamics), than are typically considered. We followed thousands of individual seeds comprising eleven herbaceous grassland species through the first growing season, seeking to uncover critical environmental (precipitation amount and timing) and trait‐based filters on seedling emergence and survival in assembling communities. We saw the biggest recruitment limitation when seeds failed to emerge, driven independently by a dry spring and interspecific variation in seed mass (positive effect) and seed dormancy (negative effect). Seedling survival rates were higher than emergence, with weaker predictive roles for traits like seedling root mass allocation (positive effect) and seed mass (positive under spring drought), and lesser impacts of summer rainfall on soil moisture and survival. Interestingly, most trait relationships were not conditional on rainfall, suggesting water‐independent mechanisms of their respective advantages. Although recruitment is a complex process, our findings suggest that trait‐based assembly frameworks can be a useful way to anticipate outcomes, particularly if dynamic early‐stage conditions (e.g. spring rainfall) and attributes (e.g. seed dormancy) receive greater attention. Given the importance of recruitment for community turnover in the context of global change and land management efforts, this is an area ripe for continued expansion in trait‐based and applied ecology.

Integrating ontogeny and ontogenetic dependency into community assembly

“…Understanding what drives spatial variation in community assembly processes is a key goal in ecology (Myers et al, 2013; Weiher et al, 2011), with important implications for understanding the impact of anthropogenic climate change on biodiversity (Lavergne et al, 2010; Mokany & Ferrier, 2011) and informing ecosystem management (Wainwright et al, 2018). Recently, there has been a growing recognition that a community is the result of the differential growth and survival of organisms throughout their lifetimes (ontogeny; Larson & Funk, 2016; Máliš et al, 2016), and that therefore each ontogenetic stage is a pathway by which assembly processes may interact to influence overall community structure (Larson et al, 2021; Lasky et al, 2015). Despite decades of research on the role of ontogenetic variation in influencing forest diversity (Clark & Clark, 1984; Connell et al, 1984; Grubb, 1977), and advances in identifying relevant regeneration traits and filters (Larson & Funk, 2016), ontogeny has not been explicitly integrated into modern community assembly frameworks (e.g.…”

Fit by design: Developing substrate-specific seed mixtures for functional dike grasslands

“…This was unfortunate for at least some seedlings, and amplified by the intense drought in summer 2018 and 2019 (cf. Hari et al, 2020; Larson et al, 2021; Orrock et al, 2023). The lasting negative effect on persistence and FCS on the southern slope suggests a legacy effect of adverse weather conditions after sowing as observed by other studies (Groves et al, 2020; Stuble et al, 2017).…”

A recruitment niche framework for improving seed‐based restoration

“…B1B, middle panel). Both metrics were derived from experiments in Larson et al (2021), where seeds were buried in a protected area with minimal signs of seed loss to external factors.…”