Invasive species cover, soil type, and grazing interact to predict long‐term grassland restoration success

Abstract

Grasslands are undergoing tremendous degradation as a result of climate change, land use, and invasion by non‐native plants. However, understanding of the factors responsible for driving reestablishment of grassland plant communities is largely derived from short‐term studies. In order to develop an understanding of the factors responsible for longer term restoration outcomes in California annual grasslands, we surveyed 12 fields in Davis, CA, U.S.A., in 2015 that were seeded with native species mixtures starting in 2004. Using field surveys, we investigated how invasive plant richness and cover, native plant richness and cover, aboveground biomass, grazing, soil type, and restoration species identity might provide utility for explaining patterns of restoration success. We found a negative relationship between invasive cover and restoration cover, which was attributed to the slow establishment of seeded species and subsequent dominance by weeds. The relationship between invasive cover and restoration cover was modified by grazing, likely due to a change in the dominance of exotic forbs, which have a more similar growing season to restoration species, and therefore compete more strongly for late season moisture. Finally, we found that soil type was responsible for differences in the identity and abundance of invasive plants, subsequently affecting restoration cover. This work highlights the value of focusing resources on reducing invasive species cover, limiting grazing to periods of adequate moisture, and considering soil type for successful long‐term restoration in California annual grasslands. Moreover, observations of long‐term restoration outcomes can provide insight into the way mechanisms driving restoration outcomes might differ through time.

Comparison of Methods for Restoring Meadows Invaded by Solidago Species

“…are mowing, hand pulling, mulching, and ploughing the soil [24][25][26][27]. Herbicides produce rapid effects [28][29][30].Eradicating invasive species is insufficient to restore a semi-natural grassland, as propagules of target meadow plants must be provided to regenerate the sward and compete effectively with any remaining invasive species [31]. A successful way to provide meadow species seeds is transferring fresh hay.…”

The early response of subtropical tussock grasslands to restoration treatments

“…Clearing tussock grasslands for crop agriculture is also widespread as they are often found on nutrient rich soils (Fensham ). Many of Australia's tussock grasslands are biodiversity rich, economically valuable pasturelands, and their restoration offers considerable economic, social, and practical benefits to land managers (Gornish & Ambrozio dos Santos ). Grassland degradation generally causes gradual declines of stocking rates, soil stability, soil quality, resilience to drought, native biodiversity, and resistance to exotic invasion (Fensham , ; Fensham et al ).…”

Exotic Plant Species in the Mediterranean Biome: A Reflection of Cultural and Historical Relationships

“…However, a publication bias towards studies focusing on biologi-cal invasions by exotic species with negative impacts [125], especially in ecological terms, has been common within the scientific community. For example, in Mediterranean grasslands, invasion by exotic species has been frequently cited as a key threat responsible for decreased native abundance, richness, growth and regeneration [126][127][128], and altered species composition [128]. Although the scientific community is aware of reports about serious negative impacts in ecology [129,130], economy [34,35], and society [131], studies focusing on the possible benefits that exotic species can provide have been overlooked receiving much less attention [132][133][134].…”

“…Therefore, eradication programmes to re-establish the original vegetation might provoke severe local extinction of endemic species [127,154], population bottlenecks, and cascading effects across trophic levels [126,155], as well as on pollinator communities [150]. Some exotic species can contribute to achieve native species conservation policies [133]; sometimes, even the employment of exotic species has been proposed as an effective action for ecological restoration [156,157].…”

“…In fact, it has been reported that the perception of the consequences that exotic species have varies among different stakeholders [160]. Stakeholders with different socio-cultural contexts have very different opinions about exotic species; some of them recognise the benefits of exotic species not only on the native flora at local scale but also on other species they have established relationships with [154], on the ecosystem services [124], on the human wellbeing [161], on the local and global economy [127], and so on. Thus, the crucial importance of adopting a more balanced view of exotic species and understanding their presence in a new area as a holistic process [162] need to be highlighted.…”