Probability Of Wind Damage Research Articles

Diversification of forest management can mitigate wind damage risk and maintain biodiversity

Mitigating future forest risks, safeguarding timber revenues and improving biodiversity are key considerations for current boreal forest management. Alternatives to rotation forestry likely have an important role, but how they will perform under a changing climate remains unclear. We used a boreal forest growth simulator to explore how variations on traditional clear-cutting, in rotation length, thinning intensity, and increasing number of remaining trees after final harvest (green tree retention), and on extent of continuous cover forestry will affect stand-level probability of wind damage, timber production, deadwood volume, and habitats for forest species. We used business-as-usual rotation forestry as a baseline and compared alternative management adaptations under the reference and two climate change scenarios. Climate change increased overall timber production and had lower impacts on biodiversity compared to management adaptations. Shortening the rotation length reduced the probability of wind damage compared to business-as-usual, but also decreased both deadwood volume and suitable habitats for our focal species. Continuous cover forestry, and management with refraining from thinnings, and extension of rotation length represent complementary approaches benefiting biodiversity, with respective effects of improving timber revenues, reducing wind damage risk, and benefiting old-growth forest structures. However, extensive application of rotation length shortening to mitigate wind damage risk may be detrimental for forest biodiversity. To safeguard forest biodiversity over the landscape, shortening of the rotation length could be complemented with widespread application of regimes promoting old-growth forest structures.

Enhancing TreeMMoSys with a high-precision strain gauge to measure the wind-induced response of trees down to the ground

Measuring tree response to wind loads is fundamental for the process-based analysis of wind-tree interactions. Comprehensive knowledge of wind-tree interactions enables the further development of decision support tools available for estimating the probability of wind damage to trees. The assessment of critical wind loads that lead to damage is particularly important. This paper describes the inexpensive Tree Strain Sensor (TSS) suitable for precisely measuring the response of tree parts to external loads such as pulling tests and natural wind loading. It is an addition to the recently developed Tree Motion Monitoring System (TreeMMoSys) but can also be used as a standalone device, allowing measurements necessary to estimate effective wind loads on trees.

Tree- and stand-scale factors shape the probability of wind damage to birch in hemiboreal forests

Strong wind is the major natural disturbance in European forests, that periodically causes tremendous damages to forestry. Yet, factors that affect the probability of wind damage for birch ( Roth and Ehrh.), the most common deciduous tree species in hemiboreal forests, are studied scarcely. This study aimed to assess the effects of several tree- and stand-scale variables on the probability of wind damage to birch using data from the Latvian National Forest Inventory (2004–2018), and determine individual tree characteristics that affect the height of the stem breakage. The data analysis was done using the Bayesian binary logistic generalized linear mixed-effects model and a linear mixed-effects model. The probability of wind damage significantly increased by stand age, basal area, and slenderness ratio. Trees with prior damage had a significantly higher probability (odds ratio 4.32) for wind damage. For wind-damaged trees, the snapping height was significantly decreased by an increase in the slenderness ratio ( = 0.03) and prior damage ( = 0.003). Previously damaged trees were more frequently (73%) snapped in the lowest 40% of tree height than trees without prior damage (54%). The probability of wind damage is largely set by factors related to the selection of site, species composition, and rotation. The damage probability could be decreased by management measures that lower competition within the stand with particular regard to preserving intact remaining trees during these manipulations. Factors that reduce the probability of the damage simultaneously increase the snapping height, emphasizing their relevance for mitigation of the wind damages.Betula pendulaB. pubescenspp

Tree, stand, and landscape factors contributing to hurricane damage in a coastal plain forest: Post-hurricane assessment in a longleaf pine landscape

Hurricanes occur regularly along the Atlantic and Gulf Coasts of the southern United States and can have intense ecological and economic impacts on forests. Frequent low-intensity fire plays a well-known role in many coastal plain upland forests, including longleaf pine (Pinus palustris). Hurricanes may also play a critical role in shaping these communities. Field studies investigating wind susceptibility of coastal tree species often rank longleaf pine among the most wind-resistant species. This assertion is usually based on analyses that evaluate whether the fraction of downed trees is greater than expected by chance. However, tree species’ associations with different soil types and landforms, and differences in tree size and spatial distribution can confound inferences. Accounting for tree, stand, and landscape factors can improve estimates of species differences in probability of wind damage. Following Hurricane Michael in 2018, we used observations from more than 3000 trees and generalized linear mixed models to investigate how tree-level factors (species and DBH), stand-level factors (stand density and soil type), and landscape-level factors (wind exposure and landscape configuration) affect tree vulnerability to hurricane winds in a longleaf pine-dominated landscape. Probability of damage varied between species, was dependent on soil type, and increased with increasing diameter for all species. Longleaf pine was in the lower range of treefall probability for all soil types and showed the lowest variability in wind susceptibility, confirming findings from other studies. However, we observed important interactions between species and soil types. Oak (Quercus spp.) species were more susceptible to treefall on drier soils, while pine (Pinus spp.) species were more resistant, suggesting that hurricanes, along with frequent fire, may play a role in shaping the landscape-scale structure of southeastern pine systems. Understanding the role of hurricanes in disturbance-prone forests can provide insight on the ecological processes structuring diverse coastal forest systems while informing activities critical for their management and conservation. Additionally, multi-aged silvicultural approaches may serve to increase the hurricane resilience of forests.

Stem Damage Modifies the Impact of Wind on Norway Spruces

Bark stripping caused by cervids can have a long-lasting negative effect on tree vitality. Such trees of low vitality might be more susceptible to other disturbances. The amplifying effects of disturbance interactions can cause significantly more damage to forest ecosystems than the individual effects of each disturbance. Therefore, this study aimed to assess the impact of bark stripping (stem damage) on the probability of wind damage and snapping height for Norway spruces (Picea Abies (L.) H. Karst.). In this study, we used the Latvian National Forest Inventory data from the period 2004–2018. In the analysis, we used data based on 32,856 trees. To analyse the data, we implemented a Bayesian binary logistic generalised linear mixed-effects model and the linear mixed-effects model. Our results showed that stem damage significantly increased the probability of wind damage and affected the snapping height of Norway spruces. Similarly, root damage, the slenderness ratio, the stand age, the stand density, the soil type, and the dominant tree species had a significant influence on the probability of wind damage. In both periods, trees with stem damage had significantly (p < 0.05) higher probability (odd ratio 1.68) to be wind damaged than trees without stem damage. The stem damaged Norway spruce trees snapped in the first 25% of the tree height, while trees without stem damage snapped around half (50%) of the tree height. Our results show that stem damage significantly alters the effect of wind damage on Norway spruces, suggesting that such damage must be incorporated into wind-risk assessment models.

A simple wind–tree interaction model predicting the probability of wind damage at stand level

Forest wind damage occurs under the passage of strong intermittent wind gusts at tree level. In order to predict the probability of tree damage of a forest, a simple statistical wind speed model was developed and coupled to a tree swaying model. The wind model is based on a stochastic approach and on some universal characters of normalized wind statistics at canopy top. This model aims at generating high frequency (10Hz) time series of the three wind velocity components at canopy top knowing only the wind intensity from a nearby meteorological station and the height and cumulative plant area index of the forest. Compared to field measurements and large-eddy simulations over different canopy structures and densities, the wind model was able to reproduce accurately the main features of canopy-top wind dynamics, in particular the signature of the mixing-layer type coherent eddy structures developing at canopy top. Coupled with a tree swaying model, the model has allowed to predict the probability of wind damage of forest following the windstorm intensity and duration, and following the main tree characteristics resulting from silvicultural scenarios. By responding to some weaknesses of existing mechanistic wind risk models, this simple wind–tree interaction model may represent the first step toward a new generation of mechanistic wind risk models based on a probabilistic approach.

Continuous cover management reduces wind damage

Wind damage causes significant economic losses in boreal forests and elsewhere. Climate change may increase the occurrence of strong storms and decrease tree anchorage, making wind risk management an important aspect of future forest management. This study modeled the probability of wind throw as a function of thinning type, time since previous cutting, characteristics of the subject tree and stand, and shelter provided by adjacent upwind stands. The data were collected from two long-term silvicultural experiments, which experienced strong storm events during the past few years. The analyses showed that the most risky cutting was shelterwood cut, followed by even-aged silviculture characterized by repeated low thinnings. Cuttings where the probability of wind throw was lowest were selective high thinnings of uneven-sized stands, and dimension cutting. Very dense un-thinned stands had very low probability of wind damage. Increasing tree size, increasing height/diameter ratio, decreasing stand basal area, and decreasing basal area of adjacent upwind stands increased the probability of wind throw. Stands were most vulnerable to wind damage immediately after thinning. Uneven-sized stand structure was associated with low probability of wind throw. It was concluded that continuous cover management decreases wind damage, as compared to even-aged management.

Climate change and tree responses in Central European forests

Research on climate change effects concerns most eco-systems and species worldwide. There is strong evi-dence that forests in all parts of the world are affectedby changing temperatures and aggravating drought situ-ations (Allen et al. 2010). Marked range shifts of treespecies are projected as a consequence of extensive andlarge climatic changes (Hanewinkel et al. 2013). In thisframe, the International Conference on “Climate Changeand Tree Responses in Central Europe” held in Septem-ber 2013 in Zurich, Switzerland, invited research contri-butions with a special geographical focus on the coun-tries Austria, Czech Republic, France, Germany, Hunga-ry, Italy, Poland, Slovakia, Slovenia, and Switzerland.More than 250 participants attended the conference,and a total of 120 oral papers were presented in theframe of 13 thematic sessions (Table1). The conferencewas organized by the Swiss Federal Institute for Forest,Snow and Landscape Research WSL and the Swiss Fed-eral Institute of TechnologyZurichETH(Wohlgemuthand Priewasser 2013). The event aimed at bringing to-gether researchers from different disciplines and withexpertise on experiments, long-term survey, and model-ling (Table 1).In this special issue, five contributions are offeredand represent the variety of aspects related to climatechange effects.As one effect of climate change, extreme events such asEuropeanwinterstormsmaybecomemorefrequentoratleastmore disastrous (Seidl et al. 2014). In this context, Pasztoret al. (2015) used empirical models (generalized linear mixedmodels) to quantify wind damage in mountain forests of fourregions of the Austrian Alps (28,800 ha in total). The proba-bility of wind damage in these forests was best explained bythefactorstimberstockvolume,standage,elevation,previousdisturbances, wind gust speed, and frozen state of soil. WinddamagecanbemitigatedbydecreasingtheproportionofNor-way spruce (Picea abies), limiting stand age, and reducingtimber stock.Climate warming will result in more frequent drought ep-isodes (IPCC 2013) and hence, drought as a limiting factorwillaffectspeciesinalllifestages.Inthisrespect,Moseretal.(2015) studied the root architecture of Scots pine (Pinussylvestris) seedlings as well as the colonization rate of roottips by ectomycorrhizal fungi under experimental drought ina commongardenexperiment. While ectomycorrhizal coloni-zation did not increase under “dry” conditions compared to“wet’ or “seasonally variable” (Mediterranean) moisture con-ditions, root architecture clearly adapted to dry conditions byan increased root/shoot ratio under dry conditions. Plasticityinrootarchitectureissupposedtobeanimportantmechanismfor drought resistance of P. sylvestris during early seedlingestablishment.Global warming during the last century or during the lastdecadeshasbeenshowntocausespeciesrangeshiftsinalpineplants (e.g., Walther et al. 2005) or in forest species (e.g.,Lenoir et al. 2008). The paper of Kuchler et al. (2015)tested

MAPPING THE RISK OF FOREST WIND DAMAGE USING AIRBORNE SCANNING LiDAR

Abstract. Wind damage is known for causing threats to sustainable forest management and yield value in boreal forests. Information about wind damage risk can aid forest managers in understanding and possibly mitigating damage impacts. The objective of this research was to better understand and quantify drivers of wind damage, and to map the probability of wind damage. To accomplish this, we used open-access airborne scanning light detection and ranging (LiDAR) data. The probability of wind-induced forest damage (PDAM) in southern Finland (61°N, 23°E) was modelled for a 173 km2 study area of mainly managed boreal forests (dominated by Norway spruce and Scots pine) and agricultural fields. Wind damage occurred in the study area in December 2011. LiDAR data were acquired prior to the damage in 2008. High spatial resolution aerial imagery, acquired after the damage event (January, 2012) provided a source of model calibration via expert interpretation. A systematic grid (16 m x 16 m) was established and 430 sample grid cells were identified systematically and classified as damaged or undamaged based on visual interpretation using the aerial images. Potential drivers associated with PDAM were examined using a multivariate logistic regression model. Risk model predictors were extracted from the LiDAR-derived surface models. Geographic information systems (GIS) supported spatial mapping and identification of areas of high PDAM across the study area. The risk model based on LiDAR data provided good agreement with detected risk areas (73 % with kappa-value 0,47). The strongest predictors in the risk model were mean canopy height and mean elevation. Our results indicate that open-access LiDAR data sets can be used to map the probability of wind damage risk without field data, providing valuable information for forest management planning.

Comparison and validation of three versions of a forest wind risk model

Predicting the probability of wind damage in both natural and managed forests is important for understanding forest ecosystem functioning, the environmental impact of storms and for forest risk management. We undertook a thorough validation of three versions of the hybrid-mechanistic wind risk model, ForestGALES, and a statistical logistic regression model, against observed damage in a Scottish upland conifer forest following a major storm. Statistical analysis demonstrated that increasing tree height and local wind speed during the storm were the main factors associated with increased damage levels. All models provided acceptable discrimination between damaged and undamaged forest stands but there were trade-offs between the accuracy of the mechanistic models and model bias. The two versions of the mechanistic model with the lowest bias gave very comparable overall results at the forest scale and could form part of a decision support system for managing forest wind damage risk.

Life-style services and yield from south-Swedish forests adaptively managed against the risk of wind damage: a simulation study

We estimated the effect of adapting forest management to reduce the risk of wind damage under climate change on life-style services and forest yield in a south-Swedish forest using an integrated modelling approach. The ECHAM5/CCLM models had been used to produce a reference climate and a climate change scenario for the A1B emission scenario. Using the FinnFor model we estimated the effect of the climate change scenario on the site index for three common commercial tree species for the period 2001–2100. The adjusted site index was applied in projections of the forest using the Forest Time Machine model. The WINDA-GALES model was used to calculate the probability of wind damage in simulated future states of the forest. Effects of increasing forest owner motivation to take measures to adapt to climate change were simulated by comparing the effects of introducing adaptive measures in years 2001 and 2051, respectively. These adaptive measures had been identified in consultation with stakeholders. In the simulations, adaptive regimes resulted in generally increased yield, increased hunting potential and a higher number of forest management operations to be carried out, although other aspects of recreation services were reduced. The net return remained unaffected by most of the adaptive forest management regimes. The simulations were made without accounting for effects of predicted wind damage on the states of the forest. Forest owners perceiving increased risk of wind damage but also risk to their life-style would have to balance adaptive measures between these risks. We conclude that adapting forest management to reduce the risk of wind damage may impact on life-style services. Hence, this may affect the process of adaptation to an increasing risk of wind damage in southern Sweden.

Developing predictive models of wind damage in Austrian forests

Among natural disturbances, wind storms cause the greatest damage to forests in Austria. The aim of this study is to quantify the effects of site, stand and meteorological attributes on the wind disturbance regime at the operational scale of forest stands. We used binomial generalized linear mixed models (GLMMs) to quantify the probability of damage events and linear mixed models (LMMs) to explain the damage intensity at the forest stand level in four management units with a total forest area of approximately 28,800 ha. Timber stock volume, stand age, elevation, previous disturbances, wind gust speed and frozen state of soil contributed in explaining probability of wind damage. While the model of disturbance probability correctly classified 90 % of all cases in the data set (specificity 95 %, sensitivity 26 %), the model for damage intensity explained only low percentages of the variation in the observed damage data (full model R 2 = 0.38, fixed effects-only model R 2 = 0.09; cross-validation in the four forest management units yielded similar R 2 values). The developed models indicated that decreasing the proportion of Norway spruce (Picea abies [L.] Karst), limiting stand age and reducing the timber stock in course of tending treatments in stands exposed to wind disturbance can mitigate the risk and the expected damage intensity. High gust speeds and salvage cuts after earlier damage increase the probability of further wind disturbance events.

Analysis of wind damage caused by multiple tropical storm events in Japanese Cryptomeria japonica forests

This study analyzed wind damage caused by tropical storms from 1991 to 2007 to Japanese forests mainly consisting of Cryptomeria japonica. Statistical analyses based on logistic regression and Cox regression models were conducted in relation to conditions at the forest and stand level. Known damage to forests managed by Kyusyu Rinsan Corporation (KR forests), located on the Kyushu Island, was analyzed at the forest level, using tropical storm characteristics such as air pressure, precipitation and periods when the forests were within the storm zone as predictors. Wind damage was also examined at the stand level (150 analysis points) using Cox regression models, according to stand age, site index, terrain conditions, management practices and wind velocity indicators (horizontal and vertical velocity vectors). The results indicated that at the forest level, higher maximum hourly wind speed and longer periods of >15 m s−1 of wind speed were significantly correlated to damage occurrence. At the stand level, indicators of upward vertical velocity, thinning treatments and site index were positively associated with the probability of wind damage. For instance, stands receiving higher upward vertical velocities and thinning treatment within 2 years were more likely to have reduced stability against tropical storms. Stands with higher and lower site index than average also showed lower stability in our analysis.

Potential climate change impacts on the probability of wind damage in a south Swedish forest

We estimated how the possible changes in wind climate and state of the forest due to climate change may affect the probability of exceeding critical wind speeds expected to cause wind damage within a forest management unit located in Southern Sweden. The topography of the management unit was relatively gentle and the forests were dominated by Norway spruce (Picea abies (L.) Karst.). We incorporated a model relating the site index (SI) to the site productivity into the forest projection model FTM. Using estimated changes in the net primary production (NPP) due to climate change and assuming a relative change in NPP equal to a relative change in the site productivity, we simulated possible future states of the forest under gradual adjustment of SI in response to climate change. We estimated changes in NPP by combining the boreal-adapted BIOMASS model with four regional climate change scenarios calculated using the RCAO model for the period 2071–2100 and two control period scenarios for the period 1961–1990. The modified WINDA model was used to calculate the probability of wind damage for individual forest stands in simulated future states of the forest. The climate change scenarios used represent non-extreme projections on a 100-year time scale in terms of global mean warming. A 15–40% increase in NPP was estimated to result from climate change until the period 2071–2100. Increasing sensitivity of the forest to wind was indicated when the management rules of today were applied. A greater proportion of the calculated change in probability of wind damage was due to changes in wind climate than to changes in the sensitivity of the forest to wind. While regional climate scenarios based on the HadAM3H general circulation model (GCM) indicated no change (SRES A2 emission scenario) or a slightly reduced (SRES B2 emission scenario) probability of wind damage, scenarios based on the ECHAM4/OPYC3 GCM indicated increased probability of wind damage. The assessment should, however, be reviewed as the simulation of forest growth under climate change as well as climate change scenarios are refined.

Climate change and the probability of wind damage in two Swedish forests

We simulated how possible changes in wind and ground-frost climate and state of the forest due to changes in the future climate may affect the probability of exceeding critical wind speeds expected to cause wind damage within one northern and one southern study area in Sweden, respectively. The topography of the study areas was relatively gentle and the forests were dominated by Norway spruce ( Picea abies (L.) Karst.) and Scots pine ( Pinus sylvestris L.). Using estimated changes in the net primary production (NPP) due to climate change and assuming a relative change in the site productivity equal to a relative change in NPP, we simulated possible future states of the forest under gradual adjustment of the site index in response to climate change using the model The Forest Time Machine. Global climate change scenarios based on two emission scenarios and one general circulation model were downscaled to the regional level. The modified WINDA model was used to calculate the sensitivity of the forest to wind and the probability of wind damage for individual forest stands for the periods 2011–2041 and 2071–2100 and for a control period 1961–1990. This was done while taking into account effects on stability of the forest from expected changes in the occurrence of ground frost. Increasing sensitivity of the forest to wind was indicated for both study areas when adhering to recommended management rules of today. Adding also a changed wind climate further increased the probability of wind damage. Calculated probabilities of wind damage were generally higher in the southern study area than in the northern one and were explained by differences in wind climate and the state of the forests, for example with respect to tree species composition. The indicated increase in sensitivity of the forest to wind under the current management regime, and possibly increasing windiness, motivate further analysis of the effects of different management options on the probability of wind damage and what modifications of Swedish forest management are possibly warranted.

A review of mechanistic modelling of wind damage risk to forests

Summary This paper reviews the current status of mechanistic models for wind damage risk assessment, describing model structure, applicability, validation and current limitations. We focus particularly on the hybrid mechanistic/empirical models GALES and HWIND, which have been designed for calculating wind damage risk at the stand level within uniform forests and which are the most widely adopted models within the research community. These models have been integrated with different methods for predicting the local wind climate in order to calculate the probability of wind damage in a number of different countries. We also discuss ongoing modelling work and proposals for future development in order to deal with complex forest structures and to predict the wind damage risk of individual trees within stands through the integration of mechanistic risk models with forest growth and yield models within a geographical information system framework. This kind of model integration will enable spatial representation of tree lists and damage propagation and allow managers to evaluate the effect of different harvesting and thinning scenarios on the risk of windthrow of both stands and individual trees within a stand.

The probability of wind damage in forestry under a changed wind climate

We (1) estimated how the possible changes in wind climate due to climatic change may affect the probability of exceeding critical wind speeds (CWS) expected to cause significant wind damage within a forest management unit located in southern Sweden, (2) analysed how the probability of exceeding an approximate CWS as observed in the management unit would change in different regions in Sweden if expecting a similar kind of forested area to occur in different geographical locations. The topography of the management unit was relatively gentle and the forests were dominated by Norway spruce (Picea abies (L.) Karst.). Seven regions across Sweden were selected for comparison of possible future probability of damaging wind speed. The model-system WINDA was modified and used for calculations of the probability of wind damage together with regionally downscaled climate change scenario (CCS) data. In total, two climate scenarios downscaled using the RCAO model for the control period 1961–1990 and four for the period 2071–2100 were used. The CCSs represent fairly central projections on a 100-year time scale in terms of global mean warming. Although there is ambiguity between different CCSs, the results indicated that the present pattern of more windy conditions in southern than in northern Sweden will remain. For most sites the probability of exceeding the CWS from westerly to south-westerly directions was indicated to remain comparatively high and the probability of damaging wind from south-westerly to south-easterly directions was indicated to increase in many places. For southernmost Sweden increasing probability of exceeding the CWS from the north-westerly to south-easterly wind directions were indicated for all but one CCS. The results were discussed with respect to spatial planning in forestry under a changing wind climate.

Decision support for identifying spruce forest stand edges with high probability of wind damage

In multiple-purpose forestry, windstorms affect both the ecological and economic values that forest stands represent. Silvicultural treatments and forest planning can reduce the probability of wind damage. A tool for the identification of spruce stands with a high probability of wind damage, aimed at helping forestry practitioners target such measures, is presented. Initial assessments of the annual probability of wind damage of exposed stand edges were made for a landscape of about 1200 ha in southern Sweden, using the WINDA system of models. In the calculations, each edge was classified as having either a high or a low annual probability of wind damage. Decision tree methodology using easily accessible variables was employed for identifying the edges classified as having a high probability of wind damage. Since in a multiple-use situation, the risk preferences of decision makers differ, one decision tree was constructed for each of three threshold probabilities of wind damage: 5, 10, and 20%. This corresponds to disturbance intervals of 20, 10, and 5 years or less in each case. The decision trees were found to correctly classify 64–71% of the high-probability stand edges, the misclassification rate for the low-probability stand edges being 12–26%. Alternative cost-matrices were used to take account of user-preferences regarding misclassification rates in the model output. Among the most important predictor variables used in the decision trees were stem taper, gap size in front of the stand edge, and the direction of wind exposure. In an evaluation landscape located 250 km from the parameterization landscape, the decision trees were found to correctly classify 44–50% and 0–83% of the high-probability stand edges with and without use of cost-matrices, respectively. For the evaluation landscape, a statistically significant difference between classifications produced by the decision tree approach and a set of randomly classified stand edges was obtained just for four of the decision trees. This result was explained in terms of the high degree of complexity of the underlying processes, limitations in the parameterization data set, and differences between the landscapes involved. Decision trees of the type described can thus provide help in practical forestry within and nearby the landscape used for constructing the decision trees. In general, the presented methodology appears to be suitable for developing management decision support tools.

WINDA—a system of models for assessing the probability of wind damage to forest stands within a landscape

An integrated system of models, WINDA, is presented for calculating the stand-wise probabilities of wind damage, uprooting and breakage of trees within a landscape. The calculations are made point-wise at exposed stand edges. WINDA integrates a modified version of the dose/response model HWIND [Can. J. For. Res. 29 (1999) 647], the airflow model WASP [Wind Atlas Analysis and Application Program (WASP), Risø National Laboratory, Roskilde, Denmark], and a component for calculating the zero-plane displacement and surface roughness and uses a GIS for geographical computations. The likelihood of damage is calculated using extreme value theory. WINDA was able to predict damage that compared well with observed extensive damage within 6.7 km 2 large landscape in southern Sweden. Output from the system of models was most sensitive to modifications in the input variables tree height and diameter at breast height and to the internal parameter critical friction velocity. The mechanistic modelling approach makes WINDA useful for evaluating effects on the probability of wind damage of silvicultural treatments and forestry activities as well as of a changed climate.

Effects of thinning on wind damage inPinus thunbergii plantation

Based on paper of “Theoretical derivation of risk-ratios for assessing wind damage in coastal forest”, wind damage in the pine coastal forest, which was thinned at four levels in December of 1997, was investigated for four successive growing seasons. Besides wind damage, the wind profiles outside and inside the coastal forest stand and the distributions of optical stratification porosity (OSP) were also observed. Based on these data, risk-ratios of wind damage for both individual trees and stands were estimated according to the methods developed in “Theoretical derivation of risk-ratios for assessing wind damage in a coastal forest”. The results showed that risk-ratios of wind damage, which were calculated from the mean height and diameter only and from the combination of wind and stand structure profiles, accurately predicted wind damage in the plantation. Relationships between different thinning ratios and incidence of wind damage showed that stand stability decreased soon after the thinning. This was due to the immediate effects of thinning on increasing the canopy roughness and wind load, and on decreasing the sheltering effects from surrounding trees. However, thinning strategies could improve the stability by long-term effects on growth and development of trees against extreme wind. Only canopy damage was recorded during the experimental period, no stem damage was found, even though the maximum 10-min wind speed outside the coastal forest attained 30.2 m s−1. The results obtained in this study indicate that thinning is the most effective silvicultural strategy available for managing coastal forest despite the increased probability of wind damage soon after thinning.