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

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. © 2013 Elsevier Ltd.We gratefully acknowledge the support of the Spanish Science and Innovation Ministry (PN-MICINN) (CGL2008-00655/BOS) and Spanish Environmental Ministry (MMAMRM 002/2007). The Ordesa-Monte Perdido National Park (OMPNP) provided logistic support and access to the national park. We thank the AEMet for providing meteorological information. We thank Bruce MacWhirter and Sara Palacios and two anonymous referees for critically reading and providing helpful suggestions on the manuscript. SK's research is founded by a Humboldt fellowship from the Alexander von Humboldt foundation to S.K.Peer Reviewe