The Protective Role of Forests to Reduce Rockfall Risks and Impacts in the Alps Under a Climate Change Perspective

Abstract

Among the functions provided by forests, protection has always been considered one of the preeminent in mountain areas. In order to fulfil, maximize, and sustain this function, specific forest structures should be obtained and maintained through properly designed forest management. A specific management goal should be defined with a well-defined forest target against each natural hazard, based on the protection potentially provided by the forest stands, in either an active (e.g. against avalanches) or passive way (e.g. against rockfall). Climate change is forecast to affect both disturbance regimes and forest ecosystems, leading to new challenging issues concerning protection forest management. This paper describes how a forest stand exerts its protective role against rockfalls and the target profile to be reached for sustaining this function. Potential consequences of climate change on forest ecosystems that management will have to face in the near future are also addressed. New perspectives are provided taking into account the knowledge coming from recent research studies and specifically the results obtained in the RockTheAlps project (ASP462), dealing with the assessment of protection forests against rockfall in the Alps.

The influence of land abandonment on forest disturbance regimes: a global review

“…An increase in rockfall occurrences has already been observed in years with weather anomalies (Berger et al 2017); triggering factors (e.g. long and highintensity precipitations, freeze-thaw processes, hightemperature variations over a short period) are related to weather conditions (Lingua et al 2020). If climate change will most likely lead to an increase in rockfall occurrence (Berger et al 2017), possible interactions with land-use and land cover changes should be also taken into account (Lopez-Saez et al 2016), in order to better understand changes in rockfall regimes.…”

“…Very few papers (n = 4) were found dealing with this disturbance and land abandonment, whereas several studies dealt with the impact of climate change on rock instability and rockfall hazard (Lopez-Saez et al 2016;Berger et al 2017;Lingua et al 2020). An increase in rockfall occurrences has already been observed in years with weather anomalies (Berger et al 2017); triggering factors (e.g.…”

“…In these areas, the widespread increase in forest cover since the abandonment of marginal crops and pastures should provide increased protection against rockfall propagations (Berger et al 2017). If trees in the release zone can sometimes influence the start of a rockfall event (by speeding up weathering and cracking processes with their roots), in the path of the rocks rolling down the slope their mitigation effect can be significant and particularly effective if the rock size is smaller than 5 m 3 (Lingua et al 2020).…”

“…Rockfall is a site-specific phenomenon, but interactive effects of climate and land-use change bring about a general reduction at least in its severity, mostly due to the increased protective effects of forests, resulting from longer forested slopes, larger basal area and higher density of stands, and higher broadleaves proportion (Lingua et al 2020).…”

“…Post-abandonment forest expansion has been commonly observed on steep slopes of mountainous regions all over the world (e.g. MacDonald et al 2000;Fukamachi et al 2001;Southworth and Tucker 2001;Gehrig-Fasel et al 2007;Gellrich et al 2007;Kuemmerle et al 2008;Meyfroidt and Lambin 2008;Hartter et al 2010;Cao et al 2011;Aide et al 2012;Brown et al 2012;Garbarino et al 2020). This 'forest transition' (a reversal from net deforestation to reforestation in a region; Munroe et al 2013) may be favoured by national or international policies integrating environmental concerns and promoting ecosystem restoration (see for instance the Common Agricultural Policy (CAP) in the European Union; Pointereau et al 2008).…”