Root-soil Plate Research Articles

Mechanical vulnerability of beech (Fagus sylvatica L.) poles after thinning: Securing stem or roots is risk dependent

In this study, we analysed how the tree growth in stem and roots reacts to thinning, focusing on the consequences for mechanical stability of the root-soil plate quantified by field mechanical bending tests. In order to disentangle the role of the biomechanical control of growth (thigmomorphogenesis) from other factors, half of the studied trees were guyed to remove mechanical stimulation due to the wind of living cells. Surprisingly, our results show a decrease in the root-soil plate mechanical performances for a given stem biomass after thinning. This decrease was however explained by boosted biomass allocation to the stem at the expense of the root system. Further, relationship between the initial stiffness and the strength (overturning moment) of the root-soil plate was modified by thinning. It is suggested that at this development stage (poles), as stem break is the weakest point of tree resistance to wind loads, the biomechanical control of growth strengthens preferentially the stem and not the anchorage. Further developments should study the diversity of behaviours between development stages and between species for a unified theory on the role of the thigmomorphogenetic syndrome in tree resistance to wind risk, with synergies and trade-offs with other processes and functions.

Impact of Root Distribution Characteristics on the Overturning Resistance of Leucaena leucocephala Forest in Debris-Flow Accumulation Area, Dawazi Gully, Yunnan, China

Tree resistance to overturning is crucial in forestry hazard applications and management. Tree anchorage varies considerably with species, tree age, and site conditions. We investigate the relationship between the root characteristics of the overturning slip surface and the role of roots (regarding different diameters in overturning). Four Leucaena leucocephala were fully excavated by a quadrate monolith to establish root distribution characteristics, and 19 L. leucocephala were uprooted until the trees completely overturned to measure the anchoring resistance to overturning. A model was developed to improve the descriptions of root characteristics in the mechanical processes for tree overturning. The results show that the distribution characteristics of the root system were well described by the model. For the root–soil plate radius, the thickest root diameter and the root biomass of different diameters at the overturning slip surface increased with the diameter at the breast height. The root biomass affected the strength of the overturning slip surface; the root density may be a key factor in identifying the location of the overturning slip surface. The model could predict the overturning moment of most overturned trees; although it overestimated the overturning moment for small diameters at breast height trees, the results will be useful for understanding the influence of root distribution characteristics in overturning.

Root-Plate Characteristics of Common Aspen in Hemiboreal Forests of Latvia: A Case Study

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.

Root-Soil Plate Characteristics of Silver Birch on Wet and Dry Mineral Soils in Latvia

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.

A quantitative evaluation of soil mass held by tree roots

Tree roots hold soil that is dramatically heavier than the tree biomass, wet or dried. This soil might compensate for the imbalance between above- and belowground mass. Root–soil plates are recognized to play an important role in root anchorage of plate-like root system, however, actual measurements of their mass have rarely been reported. Even though the root–soil plate mass is often estimated using aboveground allometric indices, no research confirms the validity. Seven root–soil plates of Cryptomeria japonica fallen by Typhoon Jebi were divided into roots and soil, and their weights were directly measured. Mass of the seven plates ranged from 251 to 3070 kg on a dry basis. Roots accounted for 8% of total plate mass and soil for 92%. The mass of the soil held in the plates was 2.8 times greater than tree biomass. The root-to-shoot biomass ratio was 0.26, whereas the ratio of root–soil plate mass to shoot biomass was 3.9, meaning that the root–soil plate mass was much greater than aboveground biomass. These results suggest that the soil mass held in the plate is the main component of whole-tree mass including the plate. The root system holds soil weighing as much as 13 times the root system’s mass. The soil might balance the aboveground weight of the tree by adding mass. Aboveground allometric indices are good indicators of root–soil plate mass and allow the belowground mass to be estimated to understand tree anchorage without soil disturbance.

Risk assessment of forest disturbance by typhoons with heavy precipitation in northern Japan

Under future climate regimes, the risk of typhoons accompanied by heavy rains is expected to increase. Although the risk of disturbance to forest stands by strong winds has long been of interest, we have little knowledge of how the process is mediated by storms and precipitation. Using machine learning, we assess the disturbance risk to cool-temperate forests by typhoons that landed in northern Japan in late August 2016 to determine the features of damage caused by typhoons accompanied by heavy precipitation, discuss how the process is mediated by precipitation as inferred from the modelling results, and delineate the effective solutions for forest management to decrease the future risk in silviculture. In the results, we confirmed two types of behaviours in the model: one represents the same process as that of forest disturbance by strong wind, which has been widely studied, and another represents a unique process mediated by storms and precipitation that has not been previously investigated. Specifically, the ridges that received strong wind from the front side had the highest risk of disturbance. Precipitation increased the probability of disturbance in forest stands, and its effect was dependent on the dominant species composition. Our hypothesis regarding treefall mediated by storms and precipitation is that rainwater flows into the gaps around the tree root systems during sway and the introduction of rainwater below the root-soil plate decreases the root anchorage. The species-specific vulnerability to rainfall may depend on the volume of lateral roots. Modelling the disturbance risk helped us to examine the kinds of factors that were related to exposure and vulnerability that should be managed to effectively decrease the risk of disturbance by typhoons during future uncontrollable hazards. It is recommended to avoid silviculture on the ridges of plateaus considering the high risk estimated in this area. In addition, species with dense lateral roots would be suitable for planting because they may have high resistance to typhoons with heavy precipitation.

Uprooting of tree induced by typhoon: a case study of super typhoon Mangkhut in university town of Shenzhen

Super typhoon Mangkhut resulted a large number of fallen tree in form of uprooting in university town of Shenzhen (UTSZ), which hadn't happened for years. This study conducted a survey about tree uprooting induced by super typhoon Mangkhut in UTSZ, aiming to reveal main reasons for tree uprooting in UTSZ. Species of fallen trees were recognized. Fallen direction and height of fallen tree were measured. Also depth and diameter of root-soil plate and dry density of soil beneath root-soil plate were measured. The results showed that many fallen trees with uprooting in UTSZ had relatively small volume of root-soil plate which was not able to offer sufficient anchorage to tree during typhoon. One of solutions to avoid this phenomenon is not to select tree species with shallow root depth. Ponding was found in many places where uprooting occurred in UTSZ. Increase of degree of saturation of soil induced by ponding can significantly decrease soil strength which is a major component of anchorage of tree. Thus we recommend to modify the poor drainage condition of soil in UTSZ. Degree of compaction of soil may not be a main factor related to tree uprooting in UTSZ.

Модели поведения лесных массивов при воздействии на них ветровых нагрузок

Проведен обзор двух механико-эмпирических моделей HWIND и GALES, используемых в настоящее время для определения ветровой нагрузки на деревья и скорости ветра, при которой произойдет выворот деревьев или повреждение стволов. В модели GALES вычисляется аэродинамическая шероховатость и смещение нулевой плоскости лесных насаждений. Обе величины позволяют подсчитать действующий на дерево изгибающий момент для любой скорости ветра и предсказать скорость ветра, при которой произойдет выворот дерева или повреждение его ствола. В модели HWIND момент, возникающий от ветровой нагрузки на крону дерева, вычисляется из предположения, что профиль скорости ветра имеет логарифмический характер. Прочность на изгиб ствола дерева и момент сопротивления корневой системы опрокидыванию дерева находятся на основании эксперимента, что позволяет рассчитать скорость ветра необходимую для выворота дерева и разрушения ствола. Проведено сравнение двух моделей и указано направление их усовершенствования.

A simple and cost-effective method for cable root detection and extension measurement in estuary wetland forests

This work presents the development of a low-cost method to measure the length cable roots of black mangrove (Avicennia germinans) trees to define the boundaries of central part of the anchoring root system (CPRS) without the need to fully expose root systems. The method was tested to locate and measure the length shallow woody root systems. An ultrasonic Doppler fetal monitor (UD) and a stock of steel rods (SR) were used to probe root locations without removing sediments from the surface, measure their length and estimate root-soil plate dimensions. The method was validated by comparing measurements with root lengths taken through direct measurement of excavated cable roots and from root-soil plate radii (exposed root-soil material when a tree tips over) of five up-rooted trees with stem diameters (D130) ranging between 10 and 50 cm. The mean CPRS radius estimated with the use of the Doppler was directly correlated with tree stem diameter and was not significantly different from the root-soil plate mean radius measured from up-rooted trees or from CPRS approximated by digging trenches. Our method proved to be effective and reliable in following cable roots for large amounts of trees of both black and white mangrove trees. In a period of 40 days of work, three people were capable of measuring 648 roots belonging to 81 trees, out of which 37% were found grafted to other tree roots. This simple method can be helpful in following shallow root systems with minimal impact and help map root connection networks of grafted trees.

Impact of Tree Size and Container Volume at Planting, Mulch, and Irrigation on Acer rubrum L. Growth and Anchorage

Some trees uproot in storms apparently due to root deflections that occur during nursery production. Root deflection in a nursery container may lead to poor anchorage because of insufficient root growth into the landscape soil, and container volume/tree size at planting may influence root deflection. This study was designed to evaluate establishment, root growth, and anchorage six years after planting Acer rubrum L. trees of four different sizes from four corresponding container volumes and maintaining them with two irrigation regimes. Impact of mulch on establishment and root growth was also evaluated. Trees from the largest containers grew slowest in the first three years due primarily to water stress. Trunk tilt during winching tests increased due to greater root deflection, less mass of the root-soil plate, and reduced root growth into the landscape soil with increasing container volume and tree size. In contrast to the poorly anchored larger trees that had most of their large roots retained in the original planted root ball volume, the largest roots on trees from smaller containers grew freely into landscape soil. This resulted in stable trees with many stiff, straight roots pushing down against mineral landscape soil outside the root ball during winching. Trees planted from smaller containers appear to anchor sooner than trees from larger containers and would be more stable in a storm.

Evaluation of the root system resistance against failure of urban trees using principal component analysis

The resistance against failure is an important topic of recent arboricultural research. Trees in urban environments are particularly of interest because of the damage they can cause. Root system anchorage stiffness is the variable that allows the resistance of the root–soil plate against failure to be quantified repetitively and non-destructively. This study uses principal component analysis (PCA) to evaluate tree mechanical state, when the input parameters are the load parameters and suitable root–soil plate stiffness parameter. The PCA method allows the similarity of surveyed trees within a control group with known mechanical state to be identified. Thus, the mechanical stability of surveyed trees can be evaluated.

Improving statistical windthrow modeling of 2 Fagus sylvatica stand structures through mechanical analysis

In 1999, the major windstorm, Lothar, damaged many beech stands on the French Lorraine limestone plateau. Some of them were coppices with standards (CWS) while others were high forest (HF) stands. The use of statistical models to compare the wind firmness of different stand structures is often limited by poor estimates of the individual wind loading. Available knowledge about the mechanics of windthrow processes such as wind loading could improve statistical modeling. Our aim was to identify the main trees and site risk factors for beech and to compare wind firmness of both stand structures by fitting such a model. We developed a windthrow model with mixed effects, which is based on a simplified mechanical analysis of the wind-induced stresses and Weibull’s theory of fracture. This analysis revealed the relevancy of including the product of the crown diameter and the square of the tree height, known as the bending moment coefficient, in the model. The Weibull-based model was compared with multiple logistic regressions. Both models were fitted using tree and site factors on 384 dominant beeches (196 in CWS and 188 in HF) from 51 plots with comparable site conditions between the two stand structures.Damage mainly increased with tree height, although it also slightly increased with crown width. The bending moment coefficient used in the Weibull-based model more effectively accounted for tree size and tree shape effects than the logistic regressions.Stand structure showed an interesting second-order effect since the increase of risk with the increase of the bending moment coefficient was higher for HF. Including a random plot effect significantly improved the model likelihood and, therefore, took partly wind-induced spatial variability into account. To apply Weibull’s theory to windthrow, many assumptions that require further investigation must be made regarding the brittle behavior and the distribution of stresses in the root-soil plate.

Effects of root architecture, physical tree characteristics, and soil shear strength on maximum resistive bending moment for overturning Salix babylonica and Juglans ailanthifolia

Effects of root architecture, physical tree characteristics, and soil shear strength on overturning moment due to flooding were investigated using Salix babylonica and Juglans ailanthifolia, exotic and invasive plants in Japanese rivers. Tree-pulling experiments that simulated flood action were conducted, and the resulting damage was examined to assess the effects of physical tree characteristics and root architecture on the maximum resistive bending moment (M max) for overturning. In situ soil shear strength tests were conducted to measure soil strength parameters. The effects of species differences on the M max were examined by analyzing root architecture. S. babylonica has a heart-root system that produces a greater overturning moment due to the strong root anchorage and the large amount of substrate that must be mobilized during overturning. J. ailanthifolia has a plate-root system that produces a smaller overturning moment. However, trees with the plate-root system may withstand overturning better due to an increased root:shoot ratio. The results of the study show that the M max of a tree for overturning had significant (P < 0.05) correlations with a tree’s physical characteristics, including height (H), trunk diameter at breast height (D bh), D bh 2 , height multiplied by the second power of D bh (trunk volume index H × D bh 2 ), and root–soil plate depth (R d), and root–soil plate radius (R r). Considering the strategy of J. ailanthifolia to increase the root:shoot ratio for anchoring in the substrate, the trunk volume index (H × D bh 2 ) is a better parameter than D bh 2 because it indirectly involves the difference in below-ground volume and surface area. Different soil cohesion values were found at different experimental sites, and the average M max for overturning each species decreased linearly with increasing soil cohesion.

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

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.

Understanding the impact of root morphology on overturning mechanisms: a modelling approach.

The Finite Element Method (FEM) has been used in recent years to simulate overturning processes in trees. This study aimed at using FEM to determine the role of individual roots in tree anchorage with regard to different rooting patterns, and to estimate stress distribution in the soil and roots during overturning. The FEM was used to carry out 2-D simulations of tree uprooting in saturated soft clay and loamy sand-like soil. The anchorage model consisted of a root system embedded in a soil block. Two root patterns were used and individual roots removed to determine their contribution to anchorage. In clay-like soil the size of the root-soil plate formed during overturning was defined by the longest roots. Consequently, all other roots localized within this plate had no influence on anchorage strength. In sand-like soil, removing individual root elements altered anchorage resistance. This result was due to a modification of the shape and size of the root-soil plate, as well as the location of the rotation axis. The tap root and deeper roots had more influence on overturning resistance in sand-like soil compared with clay-like soil. Mechanical stresses were higher in the most superficial roots and also in leeward roots in sand-like soil. The relative difference in stresses between the upper and lower sides of lateral roots was sensitive to root insertion angle. Assuming that root eccentricity is a response to mechanical stresses, these results explain why eccentricity differs depending on root architecture. A simple 2-D Finite Element model was developed to better understand the mechanisms involved during tree overturning. It has been shown how root system morphology and soil mechanical properties can modify the shape of the root plate slip surface as well as the position of the rotation axis, which are major components of tree anchorage.

Root-soil rotation stiffness of Norway spruce (Picea abies (L.) Karst) growing on subalpine forested slopes

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.

Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador

Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50� ). Three tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m, 48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased significantly from 6.1 � 10 )3 m 2 m )1 at 1900 m to 3.2 � 10 )3 m 2 m )1 at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently. Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide anchorage in soils with low bulk density and in environments with high wind speeds. Abbreviations: AR – aspect ratio; CSA – cross sectional area; DBH – diameter at breast height; ZRT – zone of rapid taper

Comparison of two models for predicting the critical wind speeds required to damage coniferous trees

Two independently developed mathematical models (GALES and HWIND) for predicting the critical wind speed and turning moment needed to uproot and break the stems of coniferous trees were compared and the results tested against field data on the forces experienced by forest trees and the wind speeds required to damage them. The GALES model calculates the aerodynamic roughness and zero-plane displacement of a forest stand. The aerodynamic roughness provides a measure of the stress (force/unit area) imposed on the canopy as a function of wind speed and the zero-plane displacement provides a measure of the average height on the tree at which the wind acts. Together they allow a calculation of the bending moment imposed on the tree for any wind speed. Data from almost 2000 trees uprooted during pulling experiments and destructive sampling of green wood then allow the model to make predictions of the wind speed at which the tree will be overturned and at which the tree will break for a number of coniferous species. The model assumes a linear relationship between tree stem weight and the maximum resistive moment that can be provided by the root system and it assumes that the stress in the outer fibres of the stem induced by the wind is constant with height. In the HWIND model the turning moment arising from the wind drag on the crown is calculated assuming a logarithmic upwind profile. Together with the contribution from the overhanging weight of the stem and branches caused by bending of the stem this provides the total bending moment. The angle of stem bend is explicitly calculated from the stiffness of the stem. The breaking strength of the stem and the support given by the root-soil plate are calculated from previous experiments on timber strength, and tree resistance to overturning by using root-soil plate mass to derive the resistive moment. This allows calculation of the wind speed required to break and overturn the tree. Model comparisons were performed for individual Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies L.) with varying tree height and stem taper (dbh/height). Tree location was at the forest stand edge on a podzolic soil. Model comparisons gave good agreement for the critical wind speeds at the forest edge required to break and overturn trees with a maximum difference in prediction of 26%. Slightly better agreement was obtained for Norway spruce (mean difference of 10.8%) than Scots pine (mean difference of 12.3%) and the best agreement was for trees with a taper of 100. At higher taper the GALES model generally predicted higher critical wind speeds than the HWIND model whereas at lower taper the reverse applied.

A mechanistic model for assessing the risk of wind and snow damage to single trees and stands of Scots pine, Norway spruce, and birch

A mechanistic model for assessing the risk of wind and snow damage to single trees and stands of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and birch (Betula spp.) is presented. The model predicts the critical turning moment and wind speed at which the trees will be uprooted or break at forest margins. The resistance to uprooting is predicted using the estimate of the root-soil plate weight to derive a resistive moment, while the resistance to stem breakage relies on values for the modulus of rupture determined for different species of timber. A tree is assumed to be uprooted if the total turning moment exceeds the support provided by the root-soil plate anchorage. Similarly, a tree is assumed to break if the breaking stress acting on the stem exceeds a critical value of the modulus of rupture. The model is in general quite sensitive to parameter changes, which partly results from the location in the forest to which it was designed to apply (the stand edge). The predictions of the critical turning moments needed to uproot and break trees nevertheless give a good agreement on average with the Finnish tree-pulling data for Scots pine, Norway spruce, and birch.

Development of structural root architecture and allometry of Quercus petraea

Root growth direction, radial distribution of roots, and biomass partitioning within the root system were examined on fifty-five 20 and 28-year-old sessile oak (Quercus petraea (Matt.) Liebl.) trees. The root systems were spatially subdivided into three concentric cylinders. Diameters and compass direction of roots were recorded at each point where they crossed one of the cylinders. Analysis of the distribution of root cross-sectional area (Ar) at 30 cm radius from the stem showed clustering in a preferred direction only for 10 small trees (diameter at breast height (DBH) &lt; 9 cm). A classification of four incline growth types was used to describe differences in root architecture associated with the different age stands. Approximately 75% of all roots kept their orientation throughout the root-soil plate on both plots. Equations were developed to describe allometric relationships between basal area, DBH, sum of Ar, and root biomass. With increasing stem diameter, the root biomass was allocated predominantly to and evenly distributed within the surface root system, effectively increasing tree stability. Results from this study support the idea that root system architecture is inherently determined and that DBH or proximal root diameter measurements are sufficient to predict root biomass of young sessile oak when soil properties are nonrestrictive.