In urbanized areas, wind disturbances can be intensified by anthropogenic stresses under which trees may become hazardous, creating serious threats and damages to nearby targets. Therefore, species with notably lower both wood mechanical properties and compartmentalization, such as pioneers, are considered to have higher wind damage risk if subjected to unfavorable growing conditions. Eurasian aspen (Populus tremula L.) and silver birch (Betula pendula Roth.), are frequently found in both urban and peri-urban forests in Northeastern and Central parts of Europe, which strengthen the necessity for the evaluation of mechanical stability of such species. Therefore, static pulling tests were performed to compare the mechanical stability of the studied species in both urban and peri-urban forests. The loading resistance of the studied species differed, with birch being more stable than aspen, indicating aspen to be more prone to wind damage. Additionally, the mechanical stability of birch did not differ between trees growing in urban and peri-urban forests, suggesting static pulling tests are a suitable method for comparing trees from completely different growing conditions.
Climate change manifests itself as a change in the probability of extreme weather events, and it is projected that windstorms will become more frequent and intense in Northern Europe. Additionally, the frequency and length of warm periods with wet, unfrozen soil in winter will rise in this region. These factors will lead to an increased risk of storm damages in forests. Factors affecting trees’ resistance to wind uprooting have been well quantified for some species but not for a common and economically important tree, the silver birch (Betula pendula Roth.). Therefore, this study aimed to assess the root-soil plate characteristics of silver birch on wet and dry mineral soils in hemiboreal forests. The root-soil plate and aboveground parameters were measured for 56 canopy trees uprooted in destructive, static-pulling experiments. The shape of the root-soil plate corresponds to the elliptic paraboloid. A decreasing yet slightly different trend was observed in root depth distribution with increasing distance from the stem in both soils. The main factors determining root-soil plate volume were width, which was notably larger on wet mineral soils, and tree diameter at breast height. Consequently, the root-soil plate volume was significantly larger for trees growing on wet mineral soils than for trees growing on dry soils, indicating a wind adaptation.
The interactions between wind damage and biotic agents, such as root-rot and cervids (bark-stripping), amplify the effects of storms on forests in Europe and Norway spruce (Picea abies (L.) Karst.) stands, in the Eastern Baltic region in particular. Due to uneven manageability of the biotic agents, the information about their effects on susceptibility to wind damage can aid the prioritization of management for sustaining spruce stands. This study compared the effect of root-rot and bark-stripping on the mechanical stability of Norway spruce via mixed covariance analysis of basal bending moments, based on static tree-pulling test data of 87 trees from five stands in Latvia. Bark-stripping caused a significantly stronger reduction in resistance against the intrinsic wood damages (primary failure) compared to root-rot, while showing a similar effect on resistance to fatal (secondary) failure. This suggests that bark-stripping damage increases the susceptibility of spruce to storm legacy effects, and, hence, is a higher priority risk factor in Norway spruce stands under the climate-smart management approach.
Climate change will cause winds to strengthen and storms to become more frequent in Northern Europe. Windstorms reduce the financial value of forests by bending, breaking, or uprooting trees, and wind-thrown trees cause additional economic losses. The resistance of trees to wind damage depends on tree species, tree- and stand-scale parameters, and root-soil plate characteristics such as root-plate size, weight, and rooting depth. The root-soil plate is a complex structure whose mechanical strength is dependent on root-plate width and depth, as the root system provides root attachment with soil and structural support. In Latvia, the common aspen (Populus tremula L.) root system has been studied to develop a belowground biomass model, because information about root system characteristics in relation to tree wind resistance is scarce. The aim of this study was to assess the root-plate dimensions of common aspen stands on fertile mineral soil (luvisol). Study material was collected in the central region of Latvia, where pure mature (41–60 years old) common aspen stands were randomly selected, and dominant trees within the stand were chosen. In total, ten sample trees from ten stands were uprooted. The diameter at breast height (DBH) and tree height (H) were measured for each sample tree, and their roots were excavated, divided into groups, washed, measured, and weighed. The highest naturally moist biomass values were observed for coarse roots, and fine root biomass was significantly lower compared to other root groups. All root group biomass values had a strong correlation with the tree DBH. The obtained results show that there is a close, negative relationship between the relative distance from the stem and the relative root-plate depth distribution.
Abstract. This study analyses spectral separability of Norway spruce (Picea abies (L.) Karst.) trees several months after induction of mechanical damage (a simulated wind damage), and one year after the damage – at the beginning of vegetation season and then following a period of drought. Experiment includes sample group of trees (Bent trees) over three plots that underwent static pulling test, therefore simulating survival after storm event. They were compared to a group of trees of the same dimensions that did not undergo static pulling test (Control trees). Spectral reflectance data was collected using unmanned aerial vehicle (UAV) and multispectral sensor. Reflectance of four bands were extracted, converted into indices, and analysed with statistical tests. There were differences in plot response to experiment, as one of the plots failed to show significant difference between groups. Overall, multiple indices proved great results for spectral separation between Control and Bent trees. MACI (Modified Anthocyanin Content Index) was the most consistent in differentiating between groups. Other indices that represent chlorophyll content and photosynthetic activity were also relatively sensitive for stress detection. However, on the contrary to what was expected, period of drought did not seem to affect spectral reflectance of canopies. There was a distinct difference of chlorophyll and anthocyanin content, and photosynthetic activity in sample trees, but these deviations did not manifest in larger scale post drought. Moreover, MACI and GNDVI (Green Normalized Difference Vegetation Index) even reduced mean value gap after the period of low precipitation.
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