Contrasting response of native and non‐native plants to disturbance and herbivory in mountain environments

Abstract

Aim Climate warming and increasing human disturbance are expected to promote non‐native plant invasions in mountain ecosystems. Although biological invasions are also expected to be modulated by biotic interactions, it is still not clear how invertebrate herbivores can affect plant invasion dynamics. Using a large manipulative experiment, we aimed at testing: (1) the effect of soil disturbance and elevation on native and non‐native plant communities, and (2) the effect of plant‐herbivore interactions, nitrogen deposition, and elevation in driving plant establishment after soil disturbance. Location European Alps, NE Italy. Taxon Vascular plants. Methods We selected remote, uninvaded dry semi‐natural grasslands along the core elevational range of non‐native plants in the European Alps (c. 100–1300 m) and manipulated soil disturbance, nitrogen deposition, and invertebrate herbivory. Then, we followed the natural establishment under real field conditions of both native and non‐native plants over one growing season. We used generalized mixed‐effects models to test the effects of the experimental treatments. Results Native and non‐native species showed contrasting responses to soil disturbance and elevation. Low elevations and disturbance promoted non‐native success, while affecting native species diversity negatively. Two‐thirds of the experimental sites acquired novel non‐natives after disturbance. Most of the observed non‐natives were not present in the surrounding vegetation as mature plants, indicating that propagules were able to reach even remote natural areas. While current N deposition levels did not affect plant establishment, we found that after disturbance invertebrate herbivory might play an important role in facilitating non‐native invasions by reducing native cover. Main conclusions Our findings show that highly resistant ecosystems such as continuous grasslands can be easily invaded once the resident vegetation has been removed, and that natural herbivory pressure from invertebrates might amplify the negative effects of disturbance on resident native species irrespective of elevation. Together, these results indicate increasing risks of future plant invasions on mountains under global change.

Non-Native Herbivores Promote Plant Invasions Away From Mountain Roads in the Andes

“…Indeed, we found a positive effect of non-native herbivores on non-native cover in plots away from the road, highlighting their role in facilitating plant invasions into natural environments after their establishment in roadsides. These findings support previous research stating the importance of interacting effects, such as combined disturbance and climate, determining non-native plant invasions (Eschtruth & Battles, 2009;Geppert et al, 2021). Roads also positively affected non-native plant species richness, yet had a pervasive effect on native plants.…”

“…We found that non-native herbivores, using dung abundance as a proxy, interacted with distance to the road, promoting plant invasions at further distances from the road edge. The impact of non-native herbivores on non-native plant invasion has been widely documented before (Maron & Vilà, 2001;Parker & Hay, 2005;Bobadilla et al, 2020;Geppert et al, 2021). Habitat modification due to trampling disturbance from domestic livestock, for example, can damage vegetation and expose soils favouring non-native plants more tolerant to disturbances Farrell & Fehmi, 2018); selective browsing and grazing on natives over nonnative species can indirectly promote their abundance (Mack, 1989;Parker et al, 2006).…”

Different ways to success: Plant community trajectories over time and a soil moisture gradient in restored wetlands

“…Moreover, ruderal plants suffered more in flooded areas, as response to the lack of traits for moisture tolerance (Richards et al, 2020). In addition, alien species were found to be more common in dry grassland, confirming the sensitivity of these habitat to invasion as response to soil and landscape disturbances (Boscutti, Sigura, et al, 2018; Geppert et al, 2021). It is also plausible that the high diversity values found at the early stages of the succession might be sustained also by to the use of native seeds during restoration (Boscutti et al, 2016; Farrell et al, 2021).…”

Disturbance and indirect effects of climate warming support a plant invader in mountains

“…In fact, S. inaequidens is described as a weak competitor (Lachmuth et al 2011), which benefits from disturbance and thus release from competition (Scherber et al 2003, Caño et al 2007). The positive effect of disturbance is considered to be one of the most important factors supporting invasion success (Alpert et al 2000, Moles et al 2012), which holds also true in montane regions (Lembrechts et al 2016, Geppert et al 2021). For instance, disturbed habitats near mountain roads are more heavily colonized by exotic species when compared to less disturbed habitats only meters away (Haider et al 2018).…”