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Abstract: In densely populated regions, forests can help protect communities and infrastructures from natural hazards such as avalanches and rockfall. To promote the protective function, substantial efforts are made to actively manage forest stands. In 2009 alone the Swiss government invested more than 60million sfr for the maintenance of protection forests. However, to date there has been no comprehensive evaluation of how the structural development of actively managed stands differs from that of passively managed stands in the Alps. Over the past century the structure of Norway-spruce dominated subalpine forests of the Swiss Alps has been changing and it is not clear how these changes affect the potential protective function of these forests, as well as other forest functions such as wildlife habitat. Furthermore, it is not clear how stand dynamics and structural changes differ between stands that are actively managed and those that are passively managed, and thus to what degree active efforts of forest management are contributing to stands that actually have a greater protective function than passively managed forests. In this study, we analyzed the dynamics of subalpine forests using time series of forest inventory data and examined the influence of active vs. passive management, exposition, distance to treeline, elevation and slope steepness on stand structure and dynamics. We analyzed data from 395 plots in dense, subalpine, spruce-dominated forests in the Swiss Alps. Data were collected during three distinct periods (1983–1985, 1993–1995 and 2004–2006) as part of the Swiss National Forest Inventory (NFI). Using regression trees and multivariate statistics, we investigated which factors have the most important influence on tree growth and stand development. Overall, forest density increased significantly over the last 20years and the predominance of dense forests increased at higher elevations. However, forest density has not increased in actively managed forests over the past 10years. In passively managed stands, density was higher on south-facing slopes than on north-facing slopes. The volume and density of dead wood has increased over the last 20years in both actively managed and passively managed forests. Active management over the last 20years has maintained forest conditions that adequately maintain stands’ protection functions in the Swiss Alps. However, stand development, especially increasing density, in the passively managed stands of the Swiss Alps suggests that the majority of passively managed stands also provide adequate protective functions against rock and avalanche hazards without the high costs of active management. [Copyright &y& Elsevier]

Abstract: To examine the speed of tree regeneration in lower subalpine forests (1300–1700m a.s.l.) of the European Alps after blowdown events, we developed a spatially explicit simulation model. Calibrated with data from 10 years of observation on extensive blowdown areas in Switzerland, the model incorporates the interactions between the changing herb layer and the growth of Norway spruce (Picea abies (L.) Karst.). The model consists of a vegetation model and a tree model: the vegetation model simulates spatial changes in the herb layer using a cellular automaton combined with a Markov transition matrix. Herb layer changes include the dispersal of tall herbs and raspberry (Rubus idaeus) on different microsite types, the growth of pioneer tree species (Sorbus aucuparia), the decay of fallen trunks, and their colonization by plants. The tree model simulates growth and demographic processes of spruce trees (P. abies) with an individual-based approach, including seed dispersal, germination, establishment, growth and mortality as a function of herb layer properties. The model was evaluated through sensitivity analysis along with stepwise multiple rank regression. As a measure of the goodness of fit, we compared the model results with independent field data. The sensitivity analysis showed that seed availability, seedling survival and the presence of advance regeneration are the key processes for successful reforestation. The model reliably simulated the observed tree height distributions after 8 and 10 years (R 2 between 0.81 and 0.93). Long-term simulations yielded initially sparse spruce regeneration, which is retarded by unfavourable microsite conditions. The results indicate that the recovery of the forest to protect against avalanches and landslides may not be achieved for several decades on blowdown sites with large distances to the nearest forest edge, and thus low seed supply. On sites where less than 10% of the surface was covered by logs and with higher seed supply, the protection against avalanches and landslides may be sufficient again about 50 years after a blowdown event. [Copyright &y& Elsevier]

Assesses structures in mountain forests for investigating the forests' dynamics and protective function. Number of plots surveyed in subalpine spruce dominated forests in various parts of Switzerland for the purpose of study; Forest structure types made in the forest area around Davos, Switzerland; Method used to calculate the transition probabilities between the different structure types in the period from 1930 to 1970.