Land‐use change and subalpine tree dynamics: colonization of Larix decidua in French subalpine grasslands

Abstract

Summary 1.In many places in Europe, trees are currently far below their theoretical altitudinal limit because of past land use. However, under the current crisis affecting mountain agriculture, trees are likely to recolonize the subalpine belt. Addressing the societal issues associated with such landscape change requires predictive tools to assess vegetation dynamics in relation to management strategies. This study aims to analyse the factors determining tree dynamics at the subalpine ecotone and to evaluate the impact of land-use change on landscape vegetation patterns. 2. We developed a hierarchical scaling approach and applied it to a European larch ( Larix decidua Mill.) colonization in the French Alps. Our landscape case study focused on subalpine south-facing grasslands of Villar d'Arêne (France). First, we used a habitat-suitability model to delineate the climatic suitability habitats of larch in the French Alps. Then we used a landscape model (LaMoS) to determine whether larch is able to colonize these grasslands predicted to be climatically suitable, considering land use and local vegetation. The sensitivity of landscape colonization patterns to land-use scenarios (abandonment, delayed mowing or traditional mowing) and biological attributes of larch were analysed with a factorial simulation experiment. 3. The accuracy of the habitat-suitability model at the French Alps scale allowed for the prediction that the grasslands of Villar d'Arêne were highly suitable for larch. 4. Simulations highlighted the effect of land use on larch establishment at the local but not at the landscape scale. On the other hand, larch attributes such as dispersal capacity, juvenile tolerance to light interaction (competition and facilitation) and its capacity to survive on infertile soil were shown as essential for tree spatial dynamics. 5. Synthesis and applications . Combining a habitat-suitability model with a spatially and temporally explicit landscape model enhances the capacity to account for environmental factors acting at different overlapping scales. This modelling strategy increases the robustness and accuracy of predictions, a prerequisite for landscape management in a global change context. We conclude that ongoing and future agri-environmental policies have to be quickly adapted to protect biodiversity and ecosystem services provided by subalpine grasslands.

Recent forest limit changes in south-east Norway: Effects of climate change or regrowth after abandoned utilisation?

“…Abandonment of felling, mowing and outfield scything, and also the reduction in domestic grazing is believed to explain much of the large-scale expansion of mountain birch, Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) in many subalpine areas of Norway (Aas & Faarlund 1995;Wehberg et al 2005;Wielgolaski 2005;Bryn 2006). The same processes have taken place in the European Alps and other populated mountain regions, although with other tree species (Bowen et al 2007;Tasser et al 2007;Albert et al 2008).…”

“…Recently, however, a number of studies have attempted to separate the effects of recent climate change from those of regrowth following the abandonment of human encroachment on the upper forest limit expansion in regions of previously extensive human outfield land-use (e.g. Motta et al 2006;Bolli et al 2007;Gehrig-Fasel et al 2007;Albert et al 2008;Gellrich et al 2008;Rutherford et al 2008). The results of these studies are less contrasting, although the emphasis on the driving forces behind the forest expansion of sub-and low-alpine areas varies.…”

The larch wood pasture: structure and dynamics of a cultural landscape

“…The needs for conservation of such environments has been outlined by several European and American authors (Grossmann and Mladenoff 2007;Manning et al 2006;Piussi 2000) as having paramount importance in order to prevent the disappearance of their diversity and cultural aspects. Open areas should be maintained by the processes that created them (Albert et al 2008). The balance between trees and herbivores is a fundamental issue in wood pasture management and grazing must be controlled as to limit damage to trees (Adams 1975).…”

“…Subalpine wood pastures are heterogeneous areas where wooded, half-open and open areas constitute a rich feeding source for large herbivores. In the past these forests were managed as open woodlands, with sparse (< 300 trees/ha) larch trees on grasslands that were generally over-used for grazing or mowing and secondary forest products, such as tar, litter and fire wood (Albert et al 2008;Bürgi and Gimmi 2007;Didier 2001;Gimmi et al 2008;Schulze et al 2007). Larch was favored by humans for livestock herding, because its light canopy permits the growth of suitable foraging ground cover (Motta and Lingua 2005).…”

Land-use and climate change effects in forest compositional trajectories in a dry Central-Alpine valley

“…Disentangling the effects of climate from land-use change is needed to better understand current forest composition and to evaluate future trajectories of forest dynamics. Whereas climate change slowly impacts nature at all scales continuously, changes of land-use affect forests quicker though at limited scales (Albert et al, 2008;Motta et al, 2006).…”