Succession secondaire et perte de diversité végétale après réduction du broutage dans un pâturage boisé des Alpes centrales suisses

Abstract

FrelØchoux F., Meisser M. and Gillet F. 2007. Secondary succession and loss in plant diversity following a grazing decrease in a wooded pasture of the central Swiss Alps. Bot. Helv. 117: 37 -56.Reduced cattle grazing pressure in the Alps has caused the reforestation of many subalpine pastures during the last decades. To understand the dynamics of natural reforestation and to evaluate how this change affects plant species diversity, we described the vegetation of a wooded pasture in the central Swiss Alps (Sembrancher, Valais) using the integrated synusial method. Based on stratified vegetation relevØs in 27 plots, we defined 11 community types at the synusial level (two tree-layer, five shrublayer, and four herb-layer synusiae), and four community types at the phytocoenosis level (pasture, tall forbs and scrub, wooded pasture and forest). The spatial distribution of these four phytocoenoses suggests that they represent successional stages after abandonment, and that the pathway of vegetation succession depends on the aspect. We suppose that on northern oriented, cool and shady locations, abandoned pastures first develop towards tall-forb meadows and scrub with Alnus viridis, and then to a preforested stage with Picea abies and Larix decidua. In contrast, on western oriented, warm and sunny location, Larix decidua (mainly) and Picea abies directly colonize the abandoned pastures, but further succession finally leads to the same pre-forested stage as on northern slopes. Plant species richness was highest in open areas and decreased by 25 % as tree cover increased from 6 % to 65 %. According to our successional model, plant species diversity is lost more rapidly on northern slopes (with species-poor green alder scrub) than on western slopes (with species-rich young larch forests), suggesting that northern slopes most urgently need an appropriate grazing management.

Shrub Encroachment Affects the Diversity of Plants, Butterflies, and Grasshoppers on Two Swiss Subalpine Pastures

“…Many reports suggest that encroachment is increasing in grassland and savanna ecosystems throughout the world because of changing land use and in response to climate change (Eldridge et al, 2011). The resulting transformation of grassland into woodland profoundly affects many ecosystem properties, including species diversity (Anthelme et al, 2001;Freléchoux et al, 2007), nutrient cycling (Archer et al, 2001;McKinley et al, 2008), and water balance (Huxman et al, 2005;Alewell and Bebi, 2011).…”

“…However, even here a dense cover can prevent trees from establishing, so that dwarf shrub vegetation persists for decades or even centuries (Connell and Slatyer, 1977;Putz and Canham, 1992;Niering, 2005). In addition, the speed and course of the succession may be affected by other factors such as altitude, local climate, aspect, and slope (Schütz et al, 2000;Freléchoux et al, 2007). One of the most abundant dwarf shrubs on Swiss alpine landscapes is Rhododendron ferrugineum, which is frequently accompanied by Vaccinium species to form the Rhododendro-Vaccinion association.…”

“…We recommend conservation actions that prevent extensive shrub encroachment but promote a mosaic of small areas at different successional stages. may form dense stands on pastures that have been abandoned or are little used (Cavallero et al, 2007;Freléchoux et al, 2007). Another limitation of previous studies of shrub encroachment is that they have rarely included both plant and insect taxa, even though this information would be very useful for management (Wallis de Vries et al, 2002).…”

Plant species selection by sheep in semi-natural dry grasslands extensively grazed in the south-western Italian Alps

“…After World War II, the decline in labour and in the number of stocked animals in human mountain habitats of Italy, such as semi-natural grasslands, favoured shrub and tree encroachment and led to a loss in plant and animal diversity (Falcucci et al 2007;Lonati et al 2014;Orlandi et al 2016) and to a decrease in the yield and nutritive value of forage (Freléchoux et al 2007). …”

Transition from traditional to modern forest management shaped the spatial extent of cattle pasturing in Białowieża Primeval Forest in the nineteenth and twentieth centuries

“…Nowadays, these landscapes are valued for their high biodiversity (Bokdam and Gleichman 2000; Frelechoux et al 2007; Bergmeier et al 2010; Hartel et al 2013; Öllerer 2013). Wood pastures are a well-researched topic but livestock grazing inside forests is little known.…”