Adaptive growth of tree root systems in response to wind action and site conditions

Abstract

Soil-root plate dimensions and structural root architecture were examined on 46-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) trees that had been mechanically uprooted. Rooting depth was restricted by a water table, and root system morphology had adapted to resist the wind movement associated with shallow rooting. The spread of the root system and the ratio of root mass to shoot mass (root/shoot ratio) were both negatively related to soil-root plate depth. Root systems had more structural root mass on the leeward side than the windward side of the tree relative to the prevailing wind direction. Cross sections of structural roots were obtained at distances of 0.5, 0.75, 1.0, and 1.25 m from the tree center. Buttressed parts of roots had greater lateral and vertical secondary thickening above rather than below the biological center. This uneven growth, which produced a shape similar in cross section to a T-beam, was greater on the leeward side of the tree, and was greatest at 0.5 m from the tree center of shallow rooted trees. Further from the tree, particularly on the windward side, many roots developed eccentric cross-sectional shapes comparable to I-beams, which would efficiently resist vertical flexing. Roots became more ovoid in shape with increasing distance from the tree, especially on deep rooted trees where lateral roots tapered rapidly to a small diameter. We conclude that these forms of adaptive growth in response to wind movement improve the rigidity of the soil-root plate and counteract the increasing vulnerability to windthrow as the tree grows.

Influences de la sylviculture sur le risque de dégâts biotiques et abiotiques dans les peuplements forestiers

“…Any factor that decreases rooting depth, such as frequent waterlogging (Laiho, 1987;Offergeld, 1986;Poeppel, 1994;Schreiner et al, 1996;Van Nispen tot Sevenaer, 1975) or soil compaction (Andersen, 1954) can negatively affect anchorage (Nicoll et al, 2006). The effect of such adverse conditions on stand stability varies with the tree species, as well as the rooting system's ability of adaptation (Nicoll and Ray, 1996;Xu et al, 1997). Forest stability is also affected by the previous land use of a site, as conifer stands on former arable land are especially susceptible to Heterobasidion root rot (van Soest, 1954).…”

“…This is because a thinned stand, at least for the first 3-5 y after thinning, has increased canopy roughness (Dhôte, 2005;Schutz et al, 2006), which allows the wind to penetrate the canopy, and less wind energy is dissipated by the mechanical contact between crowns (Milne, 1991). In addition, trees that have grown in dense stands are poorly adapted to wind movement and therefore have poor anchorage strength until they can respond to the increased loading by strengthening their stems and root systems (Nicoll and Ray, 1996;Schütz et al, 2006;Stokes et al, 1997). One of the principles of forest fuel reduction treatments is to decrease crown density to reduce crown fire potential.…”

Comparison of the root system architecture between windthrown and undamaged spruces growing in poorly drained sites

“…No correlation between the width and the thickness of root plates indicates that root plates of spruces growing in poorly drained sites spread only in the horizontal direction. Nicoll and Ray (1996) found a direct relationship between the root-soil plate area and depth in 46-years-old Sitka spruce on peaty gley soil, with the shallowest plates having the largest areas.…”

Investigation of Root Distribution and Tensile Strength of Acacia mangium Willd (Fabaceae) in the Rainforest

“…Soil reinforcement increased by the presence of vegetation roots (Makarova et al, 1998) due to the fact that soil cohesion, increase with the presence of vegetation as well as the increase in soil shear strength (Cazzuffi et al, 2006) Plant root affords further cohesion to the soil and root-permeated soils are hence much stronger than soils alone to survive soil damage procedures such as mass movements. Soil reinforcement due to the roots are influenced by numerous variables, including root systems such as root distribution with depth, root distribution over different root diameter classes and root tensile strength (Nicoll and Ray, 1996;Li et al, 2007;De Baets et al, 2008;Sun et al, 2008;Stokes et al, 2009;Loades et al, 2010;Burylo et al, 2011), root number, root diameter (Wu et al, 1979), root architecture (Duputy et al, 2005) and pullout resistance (Nilaweera and Nutalaya, 1999). Nilaweera and Nutalaya (1999) compared root mechanical properties of some tropical plantsin rainforest in Thailand.…”