Abstract

Anthropogenic activities have modified vegetation on subalpine belts for a long time, lowering the treeline ecotone and influencing the landscape mainly through grazing and fire. The abandonment of these traditional land use practices during the last decades and global warming are contributing largely to the colonization of woody species in subalpine grasslands, causing irreversible changes in ecosystem functioning. A variety of management strategies requiring the use of fire and/or clear-cutting are carried out to prevent the expansion of highly encroaching shrubs and improve the conservation status of subhumid high-productive grasslands ecosystems. However, it is still poorly understood how different management strategies affect the recovery of subalpine grasslands, which is influenced concurrently by the vegetation community involved. In this study we used field experiments to test the impact of management treatments on soil properties and vegetation responses in subalpine Bromion erecti grassland communities colonized by the pyrophyte shrub Echinospartum horridum (Vahl) Rothm. on the southern Pyrenees. Vegetation was monitored for 5 years in E. horridum plots (two plots per treatment) where the vegetation was removed by prescribed fire (Burnt treatment) or by mechanical removal (Clear-cut treatment). Undisturbed E. horridum plots were used as a control (C-Erizón) for shrub removal treatments and a Bromion erecti grassland community regularly grazed (C-Grass) was used as a control for subalpine grassland. Clear-cut treatment of E. horridum community was more effective to control E. horridum colonization than Burnt treatment and contributed to a higher extent to recover original grassland vegetation, because E. horridum seedling performed worse (lower germination rates) and plant species were more similar to the original grassland (legumes, non-legume forbs, and grasses). Shrubs and sub-shrubs cover in Burnt areas increased faster than in Clear-cut areas during the 5 years following the treatment, although it did not reach the level of C-Erizón. Species richness and diversity increased in comparison with C-Erizón in both treatments, but they were significantly lower than those in the C-Grass. Network connectivity was larger in well preserved grasslands, i.e, C-Grass, than in any other treatments, mainly dominated by negative plant-plant association. Soils nutrients declined in Burnt sites 4 years after the fire treatment and no difference was observed between Clear-cut and C-Erizón sites, although they did not reach the soil fertility values of C-Grass in terms of organic matter and C/N ratio. This study showed that grazing favors plant diversity and community complexity in subalpine grasslands. It also demonstrated that clearing is a better strategy than burning to restore grasslands after shrub encroachment because burning entails deeper soil degradation and faster recovering of the pyrophyte shrub, E. horridum.

Highlights

  • The subhumid grassland communities in mountain regions are shifting from productive grasslands to high competitive shrubland communities as reported in several alpine and subalpine zones (Anthelme et al, 2002; Tasser and Tappeiner, 2002; Gellrich et al, 2007; Gartzia et al, 2014)

  • E. horridum cover was significantly higher in C-Erizón in comparison with control grasslands (C-Grass), Burnt and Clear-cut treatments

  • Our results reveal that Burnt and Clear-cut treatments may control E. horridum expansion and improve pasture quality in terms of species diversity and species composition, they are not enough to return vegetation to the original well preserved grassland

Read more

Summary

Introduction

The subhumid grassland communities in mountain regions are shifting from productive grasslands to high competitive shrubland communities as reported in several alpine and subalpine zones (Anthelme et al, 2002; Tasser and Tappeiner, 2002; Gellrich et al, 2007; Gartzia et al, 2014). Shrub encroachment has profound effects on natural ecosystems: produces irreversible changes in ecosystem functioning (Knapp et al, 2008) and services (Metzger et al, 2006), modifies landscape net primary production patterns (Moreno-de-las-Heras et al, 2015), reduces biodiversity (Price and Morgan, 2008) and changes soil and vegetation properties towards an increase of resistance to runoff related erosion processes, but a decrease of slope stability against shallow landslides (Caviezel et al, 2014) This vegetation shift is not constant across mountain regions and will depend upon different factors, such as land management history (Milchunas et al, 1988), climate conditions (Sankaran et al, 2005), or vegetation structure (Theurillat and Guisan, 2001). Large herbivores such as reindeer enhance nutrient cycling and productivity, reduce shrub cover and promote graminoid vegetation in the Arctic tundra (van der Wal, 2006)

Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call