New Forest Edges Facing West Nearly Quadruple Wind Damage Odds in Swedish Forests

Newly created forest edges, especially those facing the prevailing westerly winds, dramatically raise the risk of wind damage in Swedish forests, according to a nationwide analysis of more than two decades of inventory data. Stands with a fresh western-facing edge had nearly 3.6 times higher odds of wind-induced mortality than stands without a new edge, and the presence and orientation of edges emerged as the strongest determinants of vulnerability in the entire model. The finding, drawn from over 57,000 permanent monitoring plots across Sweden, suggests that the way foresters arrange harvests on the landscape may matter as much as the storms themselves.

The study, published in Annals of Forest Science, was led by Emily Viola Delin and colleagues at the Swedish University of Agricultural Sciences, working with Svetlana Saarela of the Natural Resources Institute Finland. The team set out to determine the relative importance of edge orientation, stand structure, and management history in explaining wind-induced mortality in Swedish forests. Previous Swedish studies of wind damage and forest attributes had relied on short time intervals and temporary plots, while studies elsewhere covered even shorter spans or smaller areas. By contrast, this analysis exploited the Swedish National Forest Inventory’s permanent sample plots, which have been re-measured at five-year intervals since their establishment in 1983, giving the researchers a temporally robust picture of forest conditions across the entire country.

The researchers compiled data from 57,756 observations on 8,817 unique subplots, covering inventory years from 2003 to 2022. The start year was constrained by the introduction of new inventory methods in 2003, which limited comparability with earlier data. To keep the analysis focused on forests where wind damage is a meaningful threat, the final dataset was restricted to stands with an average height greater than seven meters and a basal area of more than five square meters per hectare. Each ten-meter-radius permanent plot was characterized in detail: tree species composition, stand height and age, soil moisture class, ground slope and slope direction, and the history of harvesting operations both within and adjacent to the plot.

Wind mortality was identified through the inventory’s cause codes, which assign a specific code to trees killed by wind or snow. The researchers included trees recorded as both dead and removed by harvesting, since trees damaged by wind are often felled and taken away before the next survey. They acknowledged a caveat: the code used to identify damage encompasses both wind- and snow-induced mortality, so while wind was likely the dominant cause during the study period, a small proportion of events may reflect snow damage. Thinning history was reconstructed chronologically, with the cumulative percentage of basal area removed calculated separately for the last five years and for the previous six to ten years.

Edge characteristics were encoded with particular care. The inventory records whether a clear-cut is present within 25 meters of a plot, when that edge was created, and its orientation in degrees from the plot center. An edge was classified as western-facing if its direction fell between 210 and 330 degrees. The researchers then built a categorical variable distinguishing three situations: no new edge, a new edge not facing west, and a new edge facing west. The statistical framework was a generalized linear mixed-effects model with a logit link, in which the presence or absence of wind damage was the response variable, and the repeated measurements on each subplot were accounted for through a subplot-level random effect that also absorbed potential spatial autocorrelation.

The results were striking. Stands with a new western edge had an odds ratio of 3.59 for wind damage compared with stands lacking a new edge, corresponding to a 28 percent higher absolute probability of damage. New edges not facing west also raised risk, with an odds ratio of 1.99 and a 14 percent higher probability. In other words, any freshly exposed edge increased vulnerability, but a western-oriented one added roughly 15 percentage points more probability than a non-western edge. This pattern aligns with aerodynamic and field studies showing that windward stand margins experience localized acceleration of airflow, strong vertical deflection, and increased turbulence penetration into the canopy, concentrating mechanical loading precisely where trees have had no time to acclimate.

Stand structure also shaped vulnerability, though less powerfully than edges. Taller stands were more susceptible, with damage probability rising with height until an eventual leveling off indicated by a negative quadratic effect. A higher proportion of Norway spruce slightly increased risk, though the effect was modest. Latitude showed a consistent positive effect, with each degree north increasing the odds of damage by about five percent. That result ran counter to the expectation that damage probability would decline toward northern Sweden, where wind intensity is generally lower and landscapes less fragmented. A post-hoc test including an interaction between latitude and stand height did not improve model fit, and the authors refrained from further mechanistic speculation, noting they lack data on whether regional differences in stand structure, soil conditions, or management intensity vary systematically with latitude.

Management history left a clear temporal signature. Stands thinned within the previous five years showed a modest increase in damage risk with increasing thinning intensity, whereas stands thinned six to ten years earlier exhibited reduced risk. This pattern likely reflects short-term instability following canopy opening and the gradual re-establishment of mechanical stability as remaining trees acclimate to their newly exposed position. The finding echoes earlier work showing that higher thinning intensities were associated with greater storm damage in the seasons immediately following the operation. By contrast, slope and soil moisture did not show significant effects in this dataset, a result that aligns with some earlier Swedish findings but differs from studies in Norway, where steeper slopes increased damage probability.

The model’s explanatory power was limited but its discrimination was strong. The fixed predictors alone explained roughly five percent of the variance in wind damage occurrence, while including subplot-level variation accounted for about 42 percent, indicating that much of the unexplained variation likely reflects local wind conditions that the inventory does not capture. Tjur’s R-squared of 0.15 showed moderate discrimination between damaged and undamaged observations, and the area under the curve of 0.94 confirmed that fitted probabilities closely tracked observed responses. The authors noted larger deviations and wider confidence ranges in edge categories with fewer observations, and they cautioned that the five-year interval between surveys introduces temporal uncertainty, since damage occurring shortly after an inventory may not be detected until the next measurement.

The practical implications reach from individual stands to whole landscapes. Because the inventory only records adjacent clear-cuts within 25 meters, the analysis reflects the influence of very recent and immediate edges rather than longer-distance gradients in wind exposure. Even so, the authors argue that planning harvests to limit newly exposed windward edges, coordinating thinning timing, creating gradual and structurally diverse transition zones, retaining buffer strips, and avoiding extensive clearcuts oriented directly toward prevailing winds could substantially reduce storm damage under both current and future regimes. With windstorms having felled about 75 million cubic meters of stem-wood in Sweden in 2005 alone, and with forest vulnerability to wind likely to increase under changing growth rates, soil conditions, and management practices regardless of how storm climates evolve, the orientation of the next clear-cut may be one of the most consequential decisions a forest manager makes.

Subject of Research: Wind-induced mortality in Swedish forests and the influence of edge orientation, stand structure, and thinning history

Article Title: Edge presence and orientation drive wind-induced mortality in Swedish forests

Article References: Delin, E. V., Holmström, E., Saarela, S., Trubins, R., Johansson, U., & Nilsson, U. (2026). Edge presence and orientation drive wind-induced mortality in Swedish forests. Annals of Forest Science, 83(1), Article 38. https://doi.org/10.1186/s13595-026-01356-4

Image Credits: AI Generated

DOI: 10.1186/s13595-026-01356-4

Keywords: wind damage, forest edges, edge orientation, Sweden, National Forest Inventory, Norway spruce, thinning, clear-cut, forest management, storm risk, boreal forests, windthrow