Alien plants alter the growth form ratio and structure of Australian grasslands

Abstract

Questions Niche complementarity is often invoked to explain co‐existence between native and alien plant species in grasslands. However, positive correlations between native and alien plant diversity observed in recent studies could mask the displacement of particular native species and functional groups or the negative effects of particular alien species. We asked: do alien species alter the species composition or proportions of growth forms in grasslands? Do particular alien species decrease native plant diversity? Location South Australian grasslands. Methods We performed RDA ordination on growth form abundances or Hellinger‐transformed species abundances obtained from plot‐based surveys, constrained by alien species richness and cumulative cover. Control variables (climate, soil, land use and geographic space) were partialled out. We related individual alien species abundances to native richness, diversity and cover. We tested for functional differences between coexisting growth forms using trait hypervolumes. Results While alien richness and cover explained just 2% of variance in native species composition (control variables 17%), aliens explained 18% of variance in native growth form abundance (control variables 33%), and were associated with increased herb and grass cover. Few individual alien species were associated with strong negative or positive differences in native richness, diversity or cover: correlations followed a Gaussian distribution with near‐zero mean. Trait hypervolumes differed between native and alien herbs with an overlap of 0.44, indicating substantial, but not complete, functional differences. Conclusions Given environmental context, alien cover was a good predictor of native herb and grass abundance relative to woody growth forms, but not of species composition per se. While the direction of causality is equivocal, aliens may facilitate native grasses and herbs, and niche complementarity may be involved. Due to functional redundancy across the species pool, the resulting species composition appears to be spatially contingent. Importantly for management, we identify alien species associated with reduced native diversity.

Shifting hotspots: Climate change projected to drive contractions and expansions of invasive plant abundance habitats

“…Indeed, 91% (123 of 134) of the species in our study are ornamental species that were deliberately introduced to the U.S. (Lehan et al, 2013). With the growth of relatively unregulated online plant sales (Beaury, Patrick, & Bradley, 2021;Humair et al, 2015), coupled with inconsistent regulations of invasive plants across state borders (Beaury, Fusco, et al, 2021;Lakoba et al, 2020), human Invasion success varies across plant growth forms (Ni et al, 2021) and differential invasion success of growth forms alters the composition and structure of native invaded communities (Guerin et al, 2019). Forbs/herbs represent the dominant growth form of abundant invasive plants in the eastern U.S., making up 42% of our dataset.…”

Composition and phylogenetic structure of Pampean Grasslands under distinct land use and presence of alien species

“…2021). Closely related alien and native species with high trait overlap tend to compete for similar resources in moderate environmental conditions, and this can result in competitive exclusion, causing a shift in species composition in the community (Violle et al 2011;Guerin et al 2019). However, whether or not the relatedness between alien and native species facilitates or impedes invasion, also depends on the degree of trait similarity in evolutionary history (Strauss et al 2006), which was not evaluated in this study.…”

Assessment of global, national and regional‐level digital soil mapping products at different spatial supports

“…Using the SLGA as an example, there is a wide range of studies in which SLGA products have been used, such as ecology, hydrology, soil and crop modelling (Kidd et al, 2020). The current SLGA consists of 12 nationally mapped soil properties, which have been used in several ecological multivariate analyses, including the classification of rangeland vegetation by environmental factors (Baruch et al, 2018), an investigation into the effect of climate change on ant communities in rainforests (Nowrouzi et al, 2019), and determining the variance in native and introduced plant species composition (Guerin et al, 2019). In these examples, a fine-resolution product was not essential to the outcome of the study.…”