Mountain protective forests under threat? an in-depth review of global change impacts on their protective effect against natural hazards

Abstract

Forests in mountain areas provide an indispensable ecosystem service by protecting people and infrastructure against natural hazards. As forests are increasingly affected by global change, including climate change, more frequent and severe natural disturbances, and shifts in land use, open questions remain regarding the long-term and sustainable provision of this crucial protective service. To improve our understanding of the various effects of global change on protective forests, we summarized the current knowledge based on a systematic review. Focusing on changes in mountain forests’ protective effect against snow avalanches, landslides, rockfall, torrential floods and debris flow, we assessed 72 peer-reviewed, English publications. Overall, climate-induced changes are expected to increase forests’ protective effect at higher elevations but reduce it at lower elevations mainly due to increased drought. Natural disturbances usually decrease the protective effect of forests, and their impact is often further exacerbated by salvage logging. Different forest management strategies are often studied using forest simulation models, and their impacts on protective forests strongly depend on the local context and interactions with climate change. While clearcuts consistently reduce the protective effect, other forest management interventions such as thinning can have either positive or negative effects. Most of the reviewed studies were case studies based on forest simulation or process-based hazard models (but rarely combining the two), while empirical evidence was scarce. Forests’ protective effect is often assessed using (diverse) indicators of forest structure, but evaluations of resulting risks are less common. More consistent modeling approaches linking forest structure to hazard and risk, as well as consistent indicators across different case studies, are needed for a better understanding of changes in protective forests and the service they provide under global change.

Ecosystem services at risk from disturbance in Europe's forests

“…A loss of soil erosion control could have severe and long-lasting consequences, as soil formation takes centuries to millennia, and tree growth depends on soil conditions (Lévesque et al, 2016;Wieder et al, 2015). Losing this service could thus lead to a loss in forest cover, which could have detrimental secondary effects on other ecosystem services, particularly in mountain areas where humans depend strongly on the protective effect of forests (Moos et al, 2023). The recreational value of forests and their contribution to human well-being has recently increased during the Covid19 pandemic (Muro et al, 2022;Pichlerová et al, 2023).…”

Management recommendations for Alpine protection forests: the importance of regeneration quality and initial stand composition

“…We derived short-and long-term management recommenda<ons under the as-sump<ons of (1) a constant climate and (2) the absence of large disturbances. Many simula-<on studies have inves<gated similar aspects regarding the protec<ve effect of mountain forests (Moos et al (2023) provide a good overview), but to our knowledge an extensive comparison of management strategies for protec<on forests at the stand scale has not been done to date, and this is the gap we are filling with the present analyses.…”

“…In most cases, the net change in protec<ve quality resulted from simultaneous improvements (or deteriora<ons) of the indices of protec<ve quality. Hence, suitable management regimes in protec<on forests always have to be tailored to the current stand composi<on and the site-specific growth condi<ons, and there is no silver bullet for a suitable management approach (Moos et al, 2023). This is in line with the approach of NaiS (Frehner et al, 2005), where (a) target states are indicated, rather than prescribing management regimes, thus requiring local foresters to adjust the management interven<ons to the current stand characteris<cs, and (b) target states are differen<ated by groups of site types, i.e., site condi<ons.…”

The Swiss common garden network: testing assisted migration of tree species in Europe

“…For Switzerland, however, it is not sufficient to limit trials to the warmest and driest sites, because important ecosystem services, such as the protection against natural hazards, are also required at higher elevations. The climatic suitability of the current tree species is likely to become an issue in these regions as well (Moos et al, 2023). Other tree species already present at lower elevations in Switzerland may be suitable candidates for replacing tree species at higher elevations.…”