Eighty-four mature Norway spruce (Picea abies L. Karst), silver fir (Abies alba Mill) and Scots pine (Pinus sylvestris L.) trees were winched over to determine the maximum resistive turning moment ...(M(a)) of the root-soil system, the root-soil plate geometry, the azimuthal orientation of root growth, and the occurrence of root rot. The calculation of M(a), based on digital image tracking of stem deflection, accounted not only for the force application and its changing geometry, but also for the weight of the overhanging tree, representing up to 42% of M(a). Root rot reduced M(a) significantly and was detected in 25% of the Norway spruce and 5% of the silver fir trees. Excluding trees with root rot, differences in M(a) between species were small and insignificant. About 75% of the variance in M(a) could be explained by one of the four variables-tree mass, stem mass, stem diameter at breast height squared times tree height, and stem diameter at breast height squared. Among the seven allometric variables assessed above ground, stem diameter at breast height best described the root-soil plate dimensions, but the correlations were weak and the differences between species were insignificant. The shape of the root-soil plate was well described by a depth-dependent taper model with an elliptical cross section. Roots displayed a preferred azimuthal orientation of growth in the axis of prevailing winds, and the direction of frequent weak winds matched the orientation of growth better than that of rare strong winds. The lack of difference in anchorage parameters among species probably reflects the similar belowground growth conditions of the mature trees.
The bending and growth characteristics of large fresh stems from four silver fir (Abies alba Mill.) and three Norway spruce (Picea abies (L.) Karst.) trees were studied. Twenty logs taken from ...different stem heights were subjected to four-point bending tests. From the bending test records, we calculated stress-strain curves, which accounted for detailed log taper, shear deformation and self weight. From these curves we determined, among other parameters, the modulus of elasticity (MOE), the modulus of rupture (MOR) and the work absorbed in bending (W). No significant differences were found between species for the wood properties examined. Values of MOE, MOR and W generally decreased with stem height, with MOR in the range of 43 to 59 MPa and MOE ranging from 10.6 to 15.6 GPa. These MOE values are twice or more those reported for stems of young Sitka spruce (Picea sitchensis (Bong.) Carr.) trees. Based on the radial growth properties measured in discs from the logs, we calculated predicted values of MOE and MOR for the stem cross section. The predictions of MOE were precise, whereas those of MOR were approximate because of a complex combination of different failure mechanisms. Methods to test and calculate MOE, MOR and W for the stems of living trees are discussed with the aim of improving analyses of tree biomechanics and assessments of forest stability protection.
To provide data and methods for analyzing stem mechanics, we investigated bending, density and growth characteristics of 207 specimens of fresh wood from different heights and radial positions of the ...stem of one mature Norway spruce (Picea abies L. Karst.) tree. From the shape of each stress-strain curve, which was calculated from bending tests that accounted for shear deformation, we determined the modulus of elasticity (MOE), the modulus of rupture (MOR), the completeness of the material, an idealized stress-strain curve and the work involved in bending. In general, all mechanical properties increased with distance from the pith, with values in the ranges of 5.7-18 GPa for MOE, 23-90 MPa for MOR and 370-630 and 430-1100 kg m(-3) for dry and fresh wood densities, respectively. The first three properties generally decreased with stem height, whereas fresh wood density increased. Multiple regression equations were calculated, relating MOR, MOE and dry wood density to growth properties. We applied these equations to the growth of the entire stem and considered the annual rings as superimposed cylindrical shells, resulting in stem-section values of MOE, MOR and dry and fresh densities as a function of stem height and cambial age. The standing tree exhibits an inner stem structure that is well designed for bending, especially at a mature stage.
In its latest report, the Intergovernmental Panel on Climate Change (IPCC) concludes that global climate change can still be slowed down if greenhouse gas emissions are rapidly and strongly reduced. ...We present a detailed regional CO2 budget for the Alpine tourist region of Davos, Switzerland, including emissions and potential sinks. The aim of the study was (1) to estimate the most important CO2 sources and sinks, (2) to identify the most efficient reduction measures and (3) to assess the feasibility of different reduction targets. The results show that the emissions due to heating contribute to a proportion of 86.3% to the total budget, which is mainly due to the harsh local climate and the tourism-focused local economy. They also show that the yearly CO2 emissions per capita in Davos exceed the Swiss average of 6 tonnes by 25%. The augmentation of the carbon pool through the natural environment compares to 10.3% of the total emissions, and further afforestation of the community forest can contribute to an improvement of the total budget by 2.6%. The reduction aim of -15% until 2015 (compared with 2004), as set by the municipality itself, could be easily reached through better building insulation and the use of renewable energy sources. More ambitious aims, such as a 2000 W-society or CO2 neutrality, however, will not be realised without major drawbacks in living standards.
Trees bend and break when exposed to external forces such as wind, rockfall, and avalanches. A common simplification when modelling the tree response to these forces is to simplify the system as a ...clamped beam which means that the stem deflection is related to the stem flexibility only. However, a certain part of the stem deflection originates from rotation of the root-soil plate. In this paper, we investigate this contribution to the overall stem deflection. Norway spruce (Picea abies (L.) Karst) trees were subjected to winching tests to analyse the anchorage mechanics of the tree. The tests were performed at two experimental sites with an average slope of 32 and 34° and one site with a nearly flat ground in subalpine forests near Davos, Switzerland, during the vegetation periods of 2003 and 2004. The trees were pulled downslope with a winch and the applied force, stem base rotation, and the angle of the applied force relative to the stem were recorded. After the tree had fallen over, stem diameter and branch mass were measured for every meter segment. These data were used to model the tree in the finite element software ANSYS®, which was used for calculating the rotational stem base moment as a function of stem base rotation. The root-soil rotation stiffness k root was defined as the secant stiffness calculated at 0.5° root-soil plate rotation. Young's modulus of elasticity E of the stem was iteratively changed until the correct stem rotation was obtained. The best correlation between k root and different tree characteristics was the squared diameter at breast height, DBH². Not incorporating the normal forces due to weight of the overhanging masses from crown and stem resulted in a maximum underestimation for k root of approximately 14%. Thus, also the acting moment on the stem base will be underestimated causing the safety factor against uprooting to be overestimated.
The damage caused by snow avalanches to property and human lives is underestimated in many regions around the world, especially where this natural hazard remains poorly documented. One such region is ...the Argentinean Andes, where numerous settlements are threatened almost every winter by large snow avalanches. On 1 September 2002, the largest tragedy in the history of Argentinean mountaineering took place at Cerro Ventana, Northern Patagonia: nine persons were killed and seven others injured by a snow avalanche. In this paper, we combine both numerical modeling and dendrochronological investigations to reconstruct this event. Using information released by local governmental authorities and compiled in the field, the avalanche event was numerically simulated using the avalanche dynamics programs AVAL-1D and RAMMS. Avalanche characteristics, such as extent and date were determined using dendrochronological techniques. Model simulation results were compared with documentary and tree-ring evidences for the 2002 event. Our results show a good agreement between the simulated projection of the avalanche and its reconstructed extent using tree-ring records. Differences between the observed and the simulated avalanche, principally related to the snow height deposition in the run-out zone, are mostly attributed to the low resolution of the digital elevation model used to represent the valley topography. The main contributions of this study are (1) to provide the first calibration of numerical avalanche models for the Patagonian Andes and (2) to highlight the potential of Nothofagus pumilio tree-ring records to reconstruct past snow-avalanche events in time and space. Future research should focus on testing this combined approach in other forested regions of the Andes.
In the Swiss Alps, 15% of Swiss mountain forests are grazed during summer, mainly by cattle. The forest laws of various Swiss cantons characterise forest grazing as a detrimental form of land use and ...stipulate that this grazing practice should be restricted. However, little is known about tree damage actually caused by cattle. Seven subalpine ranges in the Swiss Canton Grisons, grazed by cattle at different stocking rates, were investigated. The condition of naturally regenerated young trees (Picea abies (L.) Karst.) was assessed before and after the cattle grazing period. In order to characterise the influence of wild ungulates on the young trees during winter, the assessment of tree condition was repeated in the proximate spring. In total, 4% of the young trees were browsed on the apical shoot, 10% were browsed on lateral shoots, 13% of the trees showed other damage. The variation among ranges could almost completely be explained by the cattle stocking rate (livestock units per hectare). During winter, wild ungulates browsed 3 times as many young trees as the cattle during summer. The results suggest that cattle stocking rates on subalpine wood pastures should not exceed one livestock unit per hectare in order to avoid intensive browsing and other damage by cattle on young Norway spruces.PUBLICATION ABSTRACT
Abstract
A simple center-of-mass avalanche model that accounts for avalanche flow in forests is presented. The model applies the principle of conservation of energy to calculate the deceleration of ...avalanches caused by tree fracture, overturning and debris entrainment. The model relates the physical properties of forests (tree spacing, tree age, tree type, soil conditions) to avalanche flow. Modified dry-Coulomb and velocity-dependent friction parameters commonly used in avalanche runout calculations are derived. Example calculations demonstrate how the model can be applied to back-calculate observed avalanche events. The model
quantitatively
explains why large avalanches can destroy forests without significant deceleration. Furthermore, it shows why tree fracture consume/little of the avalanche’s energy. Finally, the model reveals how protective forests in avalanche tracks can be maintained over time to provide the best protective capacity against snow avalanches.
We investigated the natural frequencies and damping ratios of 24 Norway spruce trees (Picea abies (L.) Karst) growing on subalpine forested slopes using swaying experiments. Trees were winched to the ...release position using a manually operated cable winch. Before release, the stem base rotation was approximately 2 degrees. All trees were tested in both fall-line and cross-slope direction if possible to reveal the difference between the two perpendicular directions. A new method based upon the Hilbert transformation for evaluating the damping ratio for trees was used. It enabled us to investigate the damping ratio for all excited modes of vibration in the tree structure during the swaying experiments and to study if velocity proportional damping (viscous damping) is a reasonable assumption when predicting the tree response to different external actions using mechanical models. No difference in first natural frequency and damping ratio was found between the fall-line and cross-slope direction for all tested trees. The first natural frequencies correlated best with the diameter at breast height and squared total tree height DBH/H ². For the damping ratio, no significant correlation with different tree characteristics could be found. A non-velocity proportional damping ratio was observed for two trees. This indicates that using a viscous damping for all frequencies is an appropriate simplification when modelling the wind-tree interaction.
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