Long‐term experimental loss of foundation species: consequences for dynamics at ecotones across heterogeneous landscapes

Abstract

Abstract. Biome transition zones where species co-exist near their geographic limits are expected to be among the most responsive to changes in climate that result in mortality of foundation species. Long-term (.13 years) patterns in dominance and cover of functional types were examined following the annual experimental removal of one of three foundation species at an arid-semiarid biome transition zone. Objectives were to identify key processes influencing these patterns, and to predict future landscape-scale dynamics following mortality of different foundation species. Aboveground biomass of dominant species was removed from 3 3 4 m plots. Cover by species on control and removal plots was estimated annually in communities with a single dominant species, and in ecotonal communities with two dominant species across two types of ecotones (semiarid grassland-arid grassland, arid grassland-arid shrubland).For most species and functional types, trends in cover through time were related to the remaining species assemblages rather than to variable climatic conditions. In ecotonal communities, resident co-dominant species increased to dominance following the loss of a foundation species with little change in community composition. In mono-dominated communities, dominant species loss resulted in a shift to species that are currently sub-dominants of the same functional type as the species that was removed. Subdominant perennial grass and shrub species increased rapidly following removals in most grassland locations. Annuals and perennial forbs had variable cover values through time that were not clearly related to pulses in precipitation and were not synchronized across locations. The most common response regardless of the identity of the foundation species removed or the community type was an increase in cover by subdominant grasses and by the arid grass species (Bouteloua eriopoda). The rate of increase by B. eriopoda depended on initial cover, and resulted from both vegetative growth and seedling recruitment from other locations. Seed dispersal and seedling recruitment from other locations were not found for the semiarid grass, Bouteloua gracilis or the arid shrub, Larrea tridentata. Because B. eriopoda is more susceptible to shrub invasion, drought, and livestock grazing than the other two foundation species, widespread loss of either of the other species and subsequent increase in B. eriopoda is expected to result in an increase in landscapescale vulnerability to these environmental drivers. The extent and magnitude of this change in vulnerability will depend on the ability of B. eriopoda to respond based on the micro-environmental conditions of the site regardless of which species (B. gracilis, L. tridentata) is lost.

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

“…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]. Our greenhouse experiment uncovered a competitive hierarchy similar to that demonstrated experimentally at our field site, which lends confidence that it is applicable to this ecosystem.…”

“…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.…”

Chihuahuan Desert Grassland Responds Similarly to Fall, Spring, and Summer Fires During Prolonged Drought

“…In water-stressed systems, grass cover frequently decreases during the first year postfire (Scheintaub et al 2009), increasing resource availability for forbs. Also, forb abundance increased in a B. eriopoda removal experiment, suggesting a general competitive interaction between these dominant grasses and forbs (Peters and Yao 2012). Indeed, forb cover peaked initially following fire while grasses required several years to recover, leading to different recovery trajectories for fall and spring communities.…”

Towards an integration of scale and complexity in marine ecology

“…It is the practice of conducting manipulative experiments in a system that is also monitored for long time periods. Although the early focus was on monitoring, ecologists working at sites in the United States Long Term Ecological Network (LTER) are using this combined approach by conducting experimental manipulations (Byrnes et al 2011, Peters andYao 2012). If mechanistic insight is available from experimental manipulations performed in the same system for which long term data are available, then the consequences of altered species abundances, distributions, and diversities for the resilience of the system may be predicted.…”