Forest susceptibility to storm damage is affected by similar factors regardless of storm type: Comparison of thunder storms and autumn extra-tropical cyclones in Finland

- We compared forest susceptibility to damage in thunder storms and autumn cyclones.
- Study was based on empirical data collected at NFI plots after severe storms.
- Stand damage probability was affected by similar factors in the two storm types.
- Damage probability depended on stand characteristics, cuttings, soil and topography.
- Storm damage susceptibility map was created based on the autumn storm model.

Wind storms are a major source of disturbance in European forests and changes in climate are expected to further increase the amount of damage. The aim of this study was to compare the factors affecting forest susceptibility to storm damage between two storm types, autumn extra-tropical cyclones and thunder storms, to find out whether similar factors expose forests to damage in storms with different meteorological characteristics. We used two storm damage data sets collected after two autumn storms in November 2001 and four thunder storms in summer 2010 in Finland. The damage caused by these storms was documented after the storms on plots of the Finnish National Forest Inventory. We used generalized linear mixed models to study the probability of storm damage in different types of forest stands. Explanatory variables in the models described stand characteristics, recent forest management operations, soil type and topography. The models were able to discriminate between the damaged and non-damaged plots (AUCautumn = 0.724, AUCthunder = 0.808). The autumn storm model also had some discrimination power for predicting the storm damage in the thunder storm data set (AUCthunder2 = 0.675). These results suggest that similar factors affect stand susceptibility to storm damage in both storm types. The potential use of the models was demonstrated by using the autumn storm model to calculate damage probabilities for stand simulations and to create a forest storm damage susceptibility map for Southern Finland.

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