Disturbance alters transience but nutrients determine equilibria during grassland succession with multiple global change drivers

Abstract

Disturbance and environmental change may cause communities to converge on a steady state, diverge towards multiple alternative states, or remain in long-term transience. Yet, empirical investigations of successional trajectories are rare, especially in systems experiencing multiple concurrent anthropogenic drivers of change. We examined succession in old field grassland communities subjected to disturbance and nitrogen fertilization using data from a long-term (22-year) experiment. Regardless of initial disturbance, after a decade communities converged on steady states largely determined by resource availability, where species turnover declined as communities approached dynamic equilibria. Species favored by the disturbance were those that eventually came to dominate the highly fertilized plots. Furthermore, disturbance made successional pathways more direct under low nutrients, revealing an important interaction effect between nutrients and disturbance as drivers of community change. Our results underscore the dynamical nature of grassland and old field succession, demonstrating how community properties such as beta-diversity change through transient and equilibrium states.

Local nutrient addition drives plant diversity losses but not biotic homogenization in global grasslands

“…To address the robustness of our results, we performed sensitivity tests including using longer-term time series and using subsets of sites with higher number of blocks. A few single-site experiments investigated scale-dependent plant diversity change over time ( 24, 25, 27, 39 ), and two studies from one single system show that nutrient addition may only cause vegetation homogenization in the longer term (> 3 years) but not short term ( 24, 25 ). Therefore, we test whether effects of nutrient addition on plant diversity across spatial scales would be consistent with the main results using 29 and 16 sites that have added nutrients for 10 and 14 years, respectively (Fig.…”

“…In this context, three independent meta-analyses show that grassland plant diversity decline are proportional at local and larger spatial scales under nutrient addition (20)(21)(22). Besides these three key studies, many single-site experiments and a few multi-site experiments have investigated scale-dependent plant diversity change but often found mixed results, with vegetation homogenization (23)(24)(25), differentiation (21,(26)(27)(28)(29)(30)(31), or no effects all reported (32,33). However, no study has so far integrated abundance-and trait-based plant diversity change (or lack thereof) seen at local scales to understand plant diversity change at larger spatial scales under nutrient addition.…”

Nothing lasts forever: Dominant species decline under rapid environmental change in global grasslands

“…Where perturbations cause changes to ecosystem functions that are dependent on species turnover, the lag in dominance loss may impede these changes (Von Holle et al, 2003). However, when disturbances overlap with perturbations, disturbances can eliminate any such lag, also interrupting system hysteresis and causing systems under pressure from global changes factors to rapidly approach new system equilibria (DeSiervo et al, 2023; Ratajczak et al, 2018). Absent from disturbance, we demonstrate that in global grasslands, the degree of dominance and lifespan of species differently influence the maintenance of dominance in current and future grasslands.…”

Short-term versus multi-decadal responses of community synchrony, biodiversity, and stability to multiple global change drivers

“…It is important to examine these interdependent changes in synchrony, biodiversity, and stability across long time series, as certain drivers, such as pulse disturbances (e.g., drought, fire, or tilling), can co-occur with ongoing press disturbance (e.g., atmospheric nitrogen deposition, warming). For example, long-term experiments show that disturbance may impact community composition (Valencia et al, 2020b;DeSiervo et al, 2023), while interactive e↵ects with other global change drivers could determine long-term competitive dominance and resilience (Komatsu et al, 2019).…”

“…We use data from a 22-year fully factorial grassland experiment at the Cedar Creek Ecosystem Reserve in Minnesota, USA. We build on previous work from Cedar Creek showing changes in species richness and community composition under disturbance and nitrogen addition (Seabloom et al, 2020), and that the system recovered to novel, nutrient-mediated equilibria after approximately a decade of transient dynamics (DeSiervo et al, 2023). We ask: (1) How do disturbance and nitrogen addition alter community synchrony?…”