Modeling shrub encroachment in subalpine grasslands under different environmental and management scenarios

Abstract

Woody plants are spreading in many alpine and subalpine ecosystems and are expected to continue increasing in response to land abandonment and global warming. This encroachment threatens species diversity, and considerable efforts have been deployed to control it. In this study, we combined a lattice model and field data to investigate the efficiency of different management strategies in controlling shrub encroachment in alpine grasslands. The model parameter values were estimated in the field based on the thorny shrub Echinospartum horridum (erizón) which is currently encroaching in central Spanish Pyrenees. Our study shows that encroachment could accelerate if climate warming continues. Different management scenarios consisting of a gradient of livestock pressures, fire events and mechanical removal were simulated to identify scenarios able to control the expansion of shrubs into grasslands. Our study shows that grazing alone cannot stop encroachment. Rather, a combination of grazing and shrub removal (either by fire or mechanical removal) is needed, and our model can help estimate the frequency and intensities of the shrub removal. This model can be used to investigate the consequences of different management scenarios and environmental variability which could be of practical value in the preservation of alpine grasslands.

Diversity of bumblebees, heteropteran bugs and grasshoppers maintained by both: abandonment and extensive management of mountain meadows in three regions across the Austrian and Swiss Alps

“…Changes in agriculture either by intensification or abandonment have resulted in a reduction of semi-natural grasslands in Europe (Baur et al 2006a;Graf et al 2014). After land-use abandonment, succession starts immediately (Tasser and Tappeiner 2002), leading to shrub encroachment and establishment of woody species in open grassland (Komac et al 2013;Wiezik et al 2013). The process of shrub encroachment depends on several factors such as proximity to forest, altitude and steepness of the slope (Tasser et al 2007).…”

Scrub encroachment into species-rich limestone grassland: recruitment, herbivory and the threat from incipient scrub

“…Changes in land use over the past five decades are the greatest threat owing to, on the one hand, the intensification of agriculture and, on the other, to abandonment followed by scrub encroachment. Several authors agree that heterogeneous vegetation mosaics of semi-natural grasslands, scrub and wood patches are of high biological and cultural value but recent land use changes have made them one of the most threatened landscapes in Europe (Mortimer et al 2000;Schmidt et al 2000;Vera 2000;Wallis et al 2002;Van Uytvanck et al 2008;Saiz and Alados 2012;Komac et al 2013). To reverse this trend we need a better understanding of the effects that domestic herbivores have on scrub encroachment, particularly where the grazing regime has been successful in preserving the semi-natural grassland and scrub-grassland mosaic.…”

“…In Britain and continental Europe, considerable effort has been made to prevent the expansion of scrub (i.e. shrubby vegetation) into highly valued habitats such as species-rich limestone grasslands (Hester and Miller 1995;Kollmann and Poschlod 1997), wetlands with meadows (Schmidt et al 2000), sub-alpine and semi-arid grasslands (Saiz and Alados 2012;Komac et al 2013) where site managers of different protected areas struggle to stop or reverse scrub encroachment (Mortimer et al 2000;Wallis De Vries et al 2002;Williams et al 2009). Recently, scrub by itself has been gaining recognition as a critical component of heterogeneous vegetation mosaics, such as the 'woodland-scrub-grassland' mosaic, which is very rich in both plant and wildlife species (Mortimer et al 2000;Vera 2000;Bello et al 2010).…”

High resistance of plant biodiversity to moderate native woody encroachment in loess steppe grassland fragments

“…The strong effects of woody encroachment on ecosystem structure and functioning have been well documented (Dullinger, Dirnböck, & Grabherr, ; Komac, Kefi, Nuche, Escós, & Alados, ). Woody encroachment often results in ecosystem degradation with related biodiversity decline, and has considerable effects on net primary production, the cycling of surface water and nutrients, and carbon balance (Lett & Knapp, ; Knapp et al, ; Kesting, Wrage, & Isselstein, ; Maestre et al, and literature cited therein).…”