Disturbance is the key to plant invasions in cold environments

Abstract

Until now, nonnative plant species were rarely found at high elevations and latitudes. However, partly because of climate warming, biological invasions are now on the rise in these extremely cold environments. These plant invasions make it timely to undertake a thorough experimental assessment of what has previously been holding them back. This knowledge is key to developing efficient management of the increasing risks of cold-climate invasions. Here, we integrate human interventions (i.e., disturbance, nutrient addition, and propagule input) and climatic factors (i.e., temperature) into one seed-addition experiment across two continents: the subantarctic Andes and subarctic Scandinavian mountains (Scandes), to disentangle their roles in limiting or favoring plant invasions. Disturbance was found as the main determinant of plant invader success (i.e., establishment, growth, and flowering) along the entire cold-climate gradient, explaining 40-60% of the total variance in our models, with no indication of any facilitative effect from the native vegetation. Higher nutrient levels additionally stimulated biomass production and flowering. Establishment and flowering displayed a hump-shaped response with increasing elevation, suggesting that competition is the main limit on invader success at low elevations, as opposed to low-growing-season temperatures at high elevations. Our experiment showed, however, that nonnative plants can establish, grow, and flower well above their current elevational limits in high-latitude mountains. We thus argue that cold-climate ecosystems are likely to see rapid increases in plant invasions in the near future as a result of a synergistic interaction between increasing human-mediated disturbances and climate warming.

Microclimate variability in alpine ecosystems as stepping stones for non‐native plant establishment above their current elevational limit

“…Our results also suggest that this competition with standing biomass is more important than temperature for actual establishment, while temperature played a bigger role in biomass production after establishment. This decisive role of disturbance has been shown before at lower elevations (Lembrechts et al ), yet it was surprising that even this high in the alpine zone facilitation was still found to be subordinate to competition as the main biotic interaction determining invasion (Olofsson et al , Poll et al , Klanderud , Milbau et al ).…”

“…We follow the framework proposed by Burnham and Anderson (), using the function ‘model.sel’ from the R‐package ‘MuMIn’ (Barton ). In addition to the possible effects of all single factors, we hypothesized interactive effects between GDD or native biomass and disturbance, and between disturbance and nutrient addition (Lembrechts et al ). When models had a ΔAICc of less than 2, model coefficients were averaged using the function ‘model.avg’ (R‐package ‘MuMIn’, Barton ).…”

Lichens facilitate seedling recruitment in alpine heath

“…The increased importance of facilitation in stressful habitats could explain the lower recruitment observed on bare soils, as bare soils otherwise tend to promote seedling recruitment, also in arctic‐alpine vegetation (Lembrechts et al., ; Milbau, Shevtsova, Osler, Mooshammer, & Graae, ). However, recruitment is often better in small gaps, or for big gaps, close to the edge and not in the center, especially in harsh environments (Houle & Filion, ; Lembrechts, Milbau, & Nijs, ).…”

Establishment dynamics of native and exotic plants after disturbance along roadsides

“…Soil disturbance plays an important role in determining site invasibility (Chytrý et al, ; Boscutti, Sigura, Simone, & Marini, ; Seipel, Rew, Taylor, Maxwell, & Lehnhoff, ), and, independently of temperature, disturbed areas are more prone to establishment of exotic species than natural habitats (Parendes & Jones, ; Lembrechts et al, ; Sandoya et al, ; Haider et al, ). Soil disturbance facilitates plant invasions by providing colonization opportunities that allow the establishment of exotic species by seeds (Latzel, Mihulka, & Klimešová, ; Milbau, Shevtsova, Osler, Mooshammer, & Graae, ; McDougall et al, ; Seipel et al, ).…”

“…Soil disturbance facilitates plant invasions by providing colonization opportunities that allow the establishment of exotic species by seeds (Latzel, Mihulka, & Klimešová, ; Milbau, Shevtsova, Osler, Mooshammer, & Graae, ; McDougall et al, ; Seipel et al, ). Disturbance also reduces total plant biomass, facilitating exotic plants because of reduced competition with natives for light and resources (Lembrechts et al, ). At the same time, species‐rich communities have been shown to be generally less susceptible to invasion by exotic plants than frequently disturbed communities that are poor in native species (Oakley & Knox, ; Yannelli, Karrer, Hall, Kollmann, & Heger, ).…”