No abstract

Windstorms cause major disturbances in European forests. Forest management can play a key role in making forests more persistent to disturbances. However, better information is needed to support decision making that effectively accounts for wind disturbances. Here we show how empirical probability models of wind damage, combined with existing spatial data sets, can be used to provide fine-scale spatial information about disturbance probability over large areas. First, we created stand-level damage probability models using wind damage observations within 5-year time window in national forest inventory data (NFI). Model predictors described forest characteristics, forest management history, 10-year return-rate of maximum wind speed, and soil, site and climate conditions. We tested three different methods for creating the damage probability models -generalized linear models (GLM 1 ), 1 Abbreviations: AUCarea under curve, BRTboosted regression trees, dddegree days, GAMgeneralized additive model, GAMMgeneralized additive mixed model, GISgeographic information system, GLMgeneralized linear model, GLMMgeneralized linear mixed model, GTK -Geological Survey of Finland, GVIFgeneralized variance inflation factor, MS-NFImulti-source national forest inventory, NFI (NFI11, NFI12) generalized additive models (GAM) and boosted regression trees (BRT). Then, damage probability maps were calculated by combining the models with GIS data sets representing the model predictors. Finally, we demonstrated the predictive performance of the damage probability maps with a large, independent test data of over 33,000 NFI plots, which shows that the maps are able to identify vulnerable forests also in new wind damage events, with area under curve value (AUC) > 0.7. Use of the more complex methods (GAM and BRT) was not found to improve the performance of the map compared to GLM, and therefore we prefer using the simpler GLM method that can be more easily interpreted. The map allows identification of vulnerable forest areas in high spatial resolution (16 m x 16 m ), making it useful in assessing the vulnerability of individual forest stands when making management decisions. The map is also a powerful tool for communicating disturbance risks to forest owners and managers and it has the potential to steer forest management practices to a more disturbance-aware direction. Our study showed that in spite of the inherent stochasticity of the wind and damage phenomena at all spatial scales, it can be modelled with good accuracy across large spatial scales when existing ground and earth observation data sources are combined smartly. With improving data quality and availability, map-based risk assessments can be extended to other regions and other disturbance types.

Changing climate is expected to cause range shifts and reduced growth in Norway spruce (Picea abies (L.) Karst). In order to mitigate these changes, genetic variation between populations can be utilized in selecting alternative tree origins that are better suited to the new conditions. The aim of this study was to examine the intraspecific differences in the climatic drivers of radial growth in Norway spruce. We used tree-ring data from seven Norway spruce provenance experiments in Finland, located in different climatic conditions and including a large variety of provenances. The annual ring-width indices were studied with hierarchical clustering, correlation analysis with climate variables, pointer year analysis and linear models to identify the provenance differences in growth variation and its climatic control, and compare them on a latitudinal gradient. The cluster analysis revealed patterns of provenance differences in growth variation: north European and central European provenances were grouped in separate clusters within sites, although with some exceptions. Largest provenance differences in climate-growth responses were found in relation to winter and spring temperatures. In the southern provenances warm winters were typically associated with faster growth whereas for the northern provenances the correlations varied from nonsignificant to negative. In addition, the pointer year analysis showed negative growth anomalies only in the southern provenances for years with exceptionally cold winters. These patterns may reflect the physiological differences between the provenances relating to, for example, cold tolerance and the timing of spring phenology. As the climate warming in Europe is predicted to be strongest during the winter months, acknowledging the intraspecific growth responses to climate in Norway spruce becomes increasingly important.

Suvanto, S., le Roux, P.C., Luoto, M., 20xx. Arctic-alpine vegetation biomass is driven by fine scale abiotic heterogeneity. Geografiska Annaler, Series A: Physical Geography, 96, 549-560. Thus, we examine the effects of abiotic conditions (as measured by ten variables representing topography, soil properties and geomorphological processes) on variation in aboveground vascular plant biomass to understand the determinants of contemporary fine scale heterogeneity in this variable. We also compare the results from one destructive biomass estimation method (clipharvesting) to three non-destructive biomass estimates: vegetation cover, height and volume. To investigate the local drivers of biomass we analysed an extensive data set of 960 1 m 2 cells in arctic-alpine tundra using spatially-explicit generalized estimation equations to conduct variation partitioning. The abiotic environment had a clear impact on the fine scale distribution of biomass (variance explained 32.89 % with full model for sampled biomass). Soil properties (temperature, moisture, pH and calcium content) were most strongly related to aboveground biomass (independent effect in variation partitioning 7.03 % and combined effect including joined effects with topography and geomorphology 19.6 %). Topography had only a small influence after soil and geomorphology were taken into account (independent effect only 2.23 % and combined effect 18.73 %), implying that topography has only indirect effects on vegetation biomass. Of the three nondestructive biomass estimates, the results for vegetation volume were most similar to those for clipharvested biomass samples. Thus, we recommend utilizing vegetation volume as a cost-efficient and robust non-destructive biomass estimate in arctic-alpine areas. Our results indicate that the fine 2 scale environmental variation has to be taken into account more carefully when modelling vegetation biomass and carbon budget, especially under changing climatic conditions.

Large and old trees have a vital role in preserving biodiversity in forest ecosystems. We used National Forest Inventory data from to2013 for studying changes in densities (stems per ha) of large trees (diameter ≥40 cm) in Finland. In addition, densities of old trees (age ≥150 years) are reported from 1971 to 2013. We present results separately for the three subzones of the boreal biogeographical zone. Large trees have increased as much as 325%. The change has occurred mainly since the 1970s. On country level, old trees have become slightly less common (-4%) since the 1970s, although a decrease was actually observed only in the northern boreal subzone. The large majority of old trees in Finland are quite small in diameter, however. Trees that are both large and old show a notable increase from 1971 to 2013. During the 2010s, densities of large trees were higher in the southern boreal subzone than in the northern boreal subzone, but in the 1920s the opposite was true. Densities of old trees have been much higher in the northern boreal subzone. The observed densities of large trees are still considerably smaller than those observed in unmanaged old-growth forests in Scandinavia. High densities of large and/or old trees were observed in areas with restrictions on wood production emphasizing their role in maintaining biodiversity. The results reflect the destructive effects of former land use and the transition from dimensional cuttings to clear cuts and thinning from below after the 1940s. Proportionally larger changes were observed for southern Finland, where a higher human population density and the resulting more intensive land use had more severe detrimental effects on forests. As the densities of large trees and old trees have developed in a completely different manner in Finland, our results suggest that monitoring only the size distribution of trees will not sufficiently describe the role of old trees as constituents of biodiversity. Thereagainst, densities of large trees and large old trees developed in a similar manner.

Abstract. Latitudinal and altitudinal gradients can be utilized to forecast the impact of climate change on forests. To improve the understanding of how these gradients impact forest dynamics, we tested two hypotheses: (1) the change of the tree growth-climate relationship is similar along both latitudinal and altitudinal gradients, and (2) the time periods during which climate affects growth the most occur later towards higher latitudes and altitudes. To address this, we utilized tree-ring data from a latitudinal gradient in Finland and from two altitudinal gradients on the Tibetan Plateau. We analysed the latitudinal and altitudinal growth patterns in tree rings and investigated the growth-climate relationship of trees by correlating ring-width index chronologies with climate variables, calculating with flexible time windows, and using daily-resolution climate data. High latitude and altitude plots showed higher correlations between tree-ring chronologies and growing season temperature. However, the effects of winter temperature showed contrasting patterns for the gradients. The timing of the highest correlation with temperatures during the growing season at southern sites was approximately 1 month ahead of that at northern sites in the latitudinal gradient. In one out of two altitudinal gradients, the timing for the strongest negative correlation with temperature at low-altitude sites was ahead of treeline sites during the growing season, possibly due to differences in moisture limitation. Mean values and the standard deviation of treering width increased with increasing mean July temperatures on both types of gradients. Our results showed similarities of tree growth responses to increasing seasonal temperature between latitudinal and altitudinal gradients. However, differences in climate-growth relationships were also found between gradients due to differences in other factors such as moisture conditions. Changes in the timing of the most critical climate variables demonstrated the necessity for the use of daily-resolution climate data in environmental gradient studies.

17Storms cause major forest disturbances in Europe. The aim of this study was to model tree-level 18 storm damage probability based on the properties of tree and its environment and to examine 19 whether fine-scale topographic information is connected to the damage probability. We used data 20 documenting effects of two autumn storms on over 17000 trees on permanent Finnish National 21Forest Inventory plots. The first storm was associated with wet snow fall that damaged trees, 22 while exceptionally strong winds and gusts characterized the second storm. During the storms 23 soils were unfrozen and deciduous trees without leaves. Generalized linear mixed models were 24 used to study how topographical variables calculated from digital elevation models (DEM) with 25 resolutions of 2 and 10 m (TOPO2 and TOPO10) were related to damage probability, in addition 26 to variable groups for tree (TREE) and stand (STAND) characteristics. We compared models 27 containing different variable groups with Akaike Information Criteria. The best model contained 28 variable groups TREE, STAND and TOPO2. Increase in slope steepness calculated from the 29 high-resolution DEM decreased tree-level damage probability significantly in the model. This 30 suggests that the local topography affects the tree-level damage probability and that high-31 resolution topographical data improves the tree-level damage probability models. 32

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