Anchorage of mature conifers: resistive turning moment, root-soil plate geometry and root growth orientation

Abstract

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.

Mortality of silver fir and Norway Spruce in the Western Alps — a semi-parametric approach combining size-dependent and growth-dependent mortality

“…This colonization advantage may be balanced by a lower competitive ability for P. abies than for A. alba when resources (typically light) are scarce (Schütz, 1969;Wasser and Frehner, 1996). In regard to our results, we can argue that P. abies colonization advantage can also be compensated by a higher mortality rate for high diameter which can be interpreted as a lower life-span due to lower resistance to external perturbations such as rockfall (Stokes et al, 2005), storms (Lundstrom et al, 2007) and insect attack (Zolubas, 2003) or to an earlier senescence.…”

Energy dissipation of rockfalls by coppice structures

“…Four different phenomena have been identified in the physical effect of forest structures on the dynamics of fallen boulders: (a) kinetic energy absorption through direct impact between a boulder and a trunk, Gsteiger (1989), Zinggeler (1989), Stokes et al (2005), Brauner (2005), , Lundström et al (2007Lundström et al ( , 2009 kinetic energy absorption through interaction between a rock and shrub vegetation, (c) increasing rugosity of slope and a consequent reduction of coefficient restitution, Jones et al (2000), (d) the positive effect of forest vegetation on geotechnical soil characteristics, Pfeiffer (1989). The theoretical energy dissipated by forest structures depends on the number of tree/boulder impacts and on the kinetic energy dissipated by a single impact.…”

“…Dorren et al (2007) summarised as follows the methods proposed in the literature to quantify energy absorption during tree/boulder impact: (a) Couvreur (1982) and Zinggeler (1989), this method derives the fracture energy from standard dynamics tests on a small sample; (b) Stokes et al (2005), this method is based on static winching experiments that calculate the energy required to cause a failure in the root system, (c) Brauner et al (2005), this method assumes that the banding energy is fully dissipated by the work expended to bend the tree stem to the point at which it breaks, (d) , derived the tree/boulder energy absorption capacity through real-size rockfall experiments on living trees, by measuring energy absorption as a function of tree diameter at breast height (DBH) and of rockfall impact eccentricity, (e) Lundström et al (2007Lundström et al ( , 2009, derived the energy absorption of trees subject to rockfall and root system anchorage mechanics, for many Alpine Conifer species, with a new approach and an experimental method, (f) Jonsson (2007), used full-scale impact test data to calibrating a numerical single tree impact model, using Finite Element Method (FEM), in this way the author can consider energy absorption of tree dependent on: DBH, tree/boulder impact height, angle and eccentricity, level of tree damage and material properties.…”

“…Many of these studies were predominantly conducted in the Alpine area using characteristic tree species, Berger et al (2001, Dorren et al (2004, Brauner et al (2005), Stokes et al (2005), Lundström et al (2007Lundström et al ( , 2009. Through these studies, numerous important steps have been made towards understanding the mitigation of rockfall risks.…”

“…Recent studies , Lundström et al, 2007, 2009) have made considerable progress towards understanding the mechanism of kinetic energy absorption during tree/boulder impact, through real-size tests. However, the results of these studies are not easily applicable to coppices, due to the differences in structure between the trees in a coppice and those in high forest areas (e.g., size of stems, root system/stem ratio, type of wood).…”