Long-Term Dynamics and Hotspots of Change in a Desert Grassland Plant Community

Abstract

Natural and anthropogenic disturbances are key drivers of vegetation dynamics. The hierarchical-response framework proposes that directional change in communities is driven by chronic resource alterations resulting from global environmental change in the absence of disturbance. Because vegetation is spatially heterogeneous, some local areas within a larger community may be more dynamic than others. Thus, the average rate of change may mask dynamic hotspots and local areas where vegetation remains stable. We used long-term data from two line-intercept transects in undisturbed desert grassland to quantify large-scale community dynamics, small-scale local dynamics, and boundary dynamics of grass patches in the absence of disturbance. We found that directional change in species composition was evident but that the overall rate of change varied spatially. Cover of both dominant grasses, Bouteloua eriopoda and Bouteloua gracilis, increased over the full transects, but most change occurred in localized hotspots. Patch boundaries of the dominant grasses exhibited both stability and local dynamics. Overall, the increasing abundance of B. eriopoda may predispose this grassland to shrub encroachment, whereas locally stable areas may prove resistant to state transition. More generally, global environmental change may be a pervasive driver of vegetation dynamics through localized hotspots of temporal change and spatially varying changes in patch boundaries in the absence of disturbance.

Quantifying long‐term plant community dynamics with movement models: implications for ecological resilience

“…No slope (zero) represents stability. Rather, TLA offers a summary of whether directional changes are occurring at a site; it can also enable assessments of variation in behaviors among replicates at a site in a comparative framework (Collins and Xia 2015). More recent methods include principal coordinate of neighborhood matrices combined with redundancy analysis (PCNM-RDA; Angeler et al 2009).…”

A Multiscale, Hierarchical Model of Pulse Dynamics in Arid-Land Ecosystems

“…Species-specific responses in leaf-level photosynthesis to pulses and different rooting depths (two-layer hypothesis) are well documented but may not necessarily predict competitive outcomes nor explain patterns of dominance or changes in species composition. For example, Thomey et al (2014) showed that the photosynthetic response of B. gracilis to water pulses outperformed that of B. eriopoda, despite the fact that abundance of B. eriopoda is increasing faster than B. gracilis across a desert-grassland ecotone (Collins & Xia 2015). Mechanistic models that directly incorporate resource exchanges into competition coefficients could be developed to mechanistically link these two levels of the HPDF.…”

Plant–soil feedbacks promote negative frequency dependence in the coexistence of two aridland grasses

“…B. gracilis and B. eriopoda are perennial, C4 grasses that naturally co-occur in the ecotone between Chihuahuan desert grasslands and the short-grass steppe [21]. Their co-occurrence has been documented for more than 25 years [22] at the Sevilleta National Wildlife Refuge (Sevilleta hereafter), where our field collections occurred. Although prior work shows that the two grass species compete and their coexistence may be facilitated through recruitment niche partitioning [23,24], the mechanisms promoting their long-term coexistence remain elusive.…”

“…In the Chihuahuan desert grasslands of New Mexico, USA, where their ranges overlap and field collections for this study took place, B. gracilis and B. eriopoda are the dominant species and are known to coexist based on long-term monitoring [22]. Results of experimental removals at this site suggest that it is probably competitive dominance of B. gracilis that results in B. eriopoda subordination, whereas other factors, such as the abiotic environment, may determine areas where B. eriopoda dominates and B. gracilis is subordinate [24].…”