Vulnerability of spruce (Picea abies) and beech (Fagus sylvatica) forest stands to storms and consequences for silviculture

Abstract

The form and magnitude of storm damage and stand disclosure patterns were assessed in 332 randomly chosen pure and regular stands of spruce (Picea abies L.) and beech (Fagus sylvatica L.) after storm LOTHAR, within a region of the Swiss Midlands. This data was analysed in relation to maximal wind speed, measured with Doppler radar techniques and other influential factors such as relief, allometric characteristics, silvicultural history, and neighbourhood. In addition, storm damage, assessed from aerial photographs over an extended perimeter (about 70,000 ha) was considered. A storm of the magnitude of LOTHAR (December 26 1999), with an average maximal wind speed of 45 m s À1 (160 km h À1 ) appears to have a highly chaotic wind field structure, with great spatial and temporal variation of wind gusts. Wind speeds were not a significant predictor for damage in spruce stands and only weakly influential for beech. The consequences of this high randomness were analysed to estimate the return time of such a storm at the stand level. It lies between 86 and 113 years for spruce, 357 and 408 for beech. Only a few independent variables were significant and the overall explanatory strength of the model was unexpectedly low (R 2 =0.07 for spruce and 0.30 for beech). Among the more reliable predisposing factors were mixture and aspect combined with gradient. An admixture of 10% or more broadleaved tree species or wind-firm conifers like Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] significantly reduced the vulnerability of spruce stands (by a factor of more than three). On wind-exposed aspects, damage was more than twice the average. Steeper slopes caused a significant reduction in susceptibility (by a factor of six for slopes over 50%, in comparison to gentle slopes <20%). Other factors such as height to diameter ratio of trees or time since last thinning did not appear to be significant predictors.

Improving estimations of maximal stand density by combining Reineke’s size-density rule and the yield level, using the example of spruce (Picea abies (L.) Karst.) and European Beech (Fagus sylvatica L.)

“…Thus yield models are generally not appropriate for projecting stand development, or only under certain conditions. The difficulty is that such mortality events from disturbances are stochastic (Drössler and Lüpke, 2005;Quine and Bell, 1998;Schütz et al 2006;Zeibig et al, 2005) and assessing the risk occurrence implies different methodological probabilistic from those used to estimate yield alone. For instance, it needs largely corresponding areas covering hundreds of hectares, way beyond the usual reference for yield plots.…”

Structural Diversity in a Mixed Spruce-Fir-Beech Old-Growth Forest Remnant of the Western Carpathians

“…The reduction of silver fir in the lower and middle layer observed in our study is the direct consequence of this lack of saplings and virtually no ingrowth into these layers. As for Norway spruce, the overall significant decrease of its proportion in all stand layers seems to be the result of multiple factors associated with the recent climate changes such as increasing temperature, lower precipitation rates, more frequent severe disturbances and a more intense impact of bark beetle [11,[62][63][64]. Despite the still relatively high proportion of Norway spruce (24% of the growing stock) in the locality investigated in our study, we recorded a low density of seedlings and saplings, indicating a serious problem for the maintenance of this tree species in studied stands.…”

The influences of forest stand management on biotic and abiotic risks of damage

“…In general, broadleaves are regarded as being more stable than conifers (Bryndum, 1986;Holmsgaard, 1986), probably because broadleaves are usually leafless in winter, the period where most storms occur. Several authors report a higher stability of mixed species stands as compared to monocultures (Grodzki et al, 1999;Lekes and Dandul, 2000;Schütz et al, 2006;Slodicak, 1995) but others argue that damage to a mixed species stand will only be reduced equal to the share of the stable species (Lüpke and Spellmann, 1997). Dhôte (2005) also concluded that tree species identity is more important in predicting wind damage to mixed stands than species richness.…”

“…This is because a thinned stand, at least for the first 3-5 y after thinning, has increased canopy roughness (Dhôte, 2005;Schutz et al, 2006), which allows the wind to penetrate the canopy, and less wind energy is dissipated by the mechanical contact between crowns (Milne, 1991). In addition, trees that have grown in dense stands are poorly adapted to wind movement and therefore have poor anchorage strength until they can respond to the increased loading by strengthening their stems and root systems (Nicoll and Ray, 1996;Schütz et al, 2006;Stokes et al, 1997). One of the principles of forest fuel reduction treatments is to decrease crown density to reduce crown fire potential.…”