Differences in maximum resistive bending moments of Pinus radiata trees grown on a range of soil types

https://doi.org/10.1016/S0378-1127(00)00298-XGet rights and content

Abstract

The maximum resistive bending moments (Mb) were measured for 164 Radiata pine (Pinus radiata D. Don) trees spanning a range of sizes and growing on six different New Zealand soil types. Mb was significantly and positively correlated with tree height, diameter at 1.4 m (DBH) and stem volume with the latter explaining the greatest proportion of the variation in Mb (R2=0.854). Trees with higher taper (lower ratio of tree height to DBH) had higher maximum resistive bending moments than trees with low taper. Both root plate diameter and root plate depth were significantly and positively associated with Mb. For trees which failed by uprooting, stem volume, height:DBH ratio and root plate width explain over 91% of the variation in Mb. Differences in Mb were also found between soil types. Trees growing on northern yellow-brown earths and southern yellow-grey earths had significantly greater values of Mb than those growing on yellow-brown pumice soils. A higher incidence of stem failure was also recorded on yellow-grey and yellow-brown earths. This type of failure could not be successfully modelled using elementary beam theory because of the breakdown of the uniform stress assumption and the presence of stem defects.

Introduction

The plantation forestry estate in New Zealand covers a total area of ≈1.63 million hectares (Ministry of Forestry, 1997) and is distributed over a wide range of soil types. Radiata pine (Pinus radiata D. Don) is the predominant species occupying ≈91% of this area. Since records began, wind damage in the form of stem breakage and uprooting has occurred throughout much of the country (Wendelken, 1955, Wendelken, 1966, Prior, 1959, Chandler, 1968, Irvine, 1970, Wilson, 1976, Somerville et al., 1989, Somerville, 1995).

Keeping in mind the threat posed by wind, a model which uses a combination of fundamental physics and empirical data is being developed to predict the risk of damage (Moore and Somerville, 1998). The model predicts the threshold wind speed necessary to damage the mean tree within a stand of given diameter at breast height (DBH), height and spacing, and which is growing at a particular location. Within the model a tree is assumed to fail if the applied overturning moment exceeds the maximum resistive bending moment (Mb) of the tree. Mb is defined as the maximum resistance of the tree stem to failure or the root system to overturning, with the relative strengths of these determining the mode of failure (Petty and Worrell, 1981).

In order to determine Mb for trees with certain characteristics and growing conditions, a number of authors have used winch and cable systems to apply artificial wind loads to trees. One of the first such studies was carried out by Fraser (1962) who found that a linear relationship existed between Mb and stem weight for Sitka spruce (Picea sitchensis Bong Carr.). Other authors (Fraser and Gardiner, 1967, Smith et al., 1987, Frederickson et al., 1993) have obtained similar results.

In New Zealand two previous tree winching studies have been performed (Somerville, 1979, Papesch et al., 1997). The latter found that strong linear relationships existed between Mb and both stem volume and DBH for the range (DBH=18.2–63.9 cm) of Radiata pine trees measured at Eyrewell Forest, Canterbury. In the same forest, Somerville (1979) investigated the effect of different site preparation techniques on Mb. He found that there was a tendency for trees growing in deep rips to fail by stem fracture rather than by uprooting but that this was not accompanied by a significant increase in Mb. This indicates that root architecture has an influence on the failure mode of a tree. Further observational evidence was provided by Wilson (1976) who observed that the incidence of stem breakage during the 1975 storm in Eyrewell Forest was higher where soils were deeper.

The wind forces acting on tree stems have been the subject of several studies (Petty and Swain, 1985, Milne, 1995, Wood, 1995) while Coutts, 1983, Coutts, 1986 performed some of the first work investigating the mechanics of tree root anchorage. He used static tree pulling tests to identify the four main components of the root anchorage of shallowly rooted Sitka spruce. These were (1) tensile strength of windward roots, (2) weight of the root–soil plate, (3) resistance of leeward roots to bending at the hinge region and (4) the resistance to failure of the soil underneath the root–soil plate. The shallow rooting of the trees in these studies was due to the presence of a high water table; a condition relatively uncommon in New Zealand. However, for hybrid larch (Larix europea×japonica) growing on a free draining soil, Crook and Ennos (1996) found that ≈75% of the anchorage strength was provided by the windward sinkers and tap root. Because the root–soil plate is a compound structure the material properties of the soil are also very important in determining overall root anchorage strength (Mattheck et al., 1997).

The physical properties of forest soil types in New Zealand vary widely and it is therefore possible that the relationship between Mb and tree size will also differ between soil types. More than one function for Mb may therefore be necessary in the model to predict the risk of wind damage to forest stands. This paper investigates the relationship between Mb and tree size by performing a series of tree winching experiments on trees of different sizes growing on a range of New Zealand forest soils types. The effects of tree taper, root plate size and differences in Mb between modes of failure are also investigated.

Section snippets

Site and resource descriptions

Data were collected from seven sites in New Zealand which contained soils with widely varying physical properties (Table 1). Limited data were available on the physical properties of the soils at the seven sites. (DSIR Soil Bureau, 1954, DSIR Soil Bureau, 1968a, and unpublished data). No information was available on rooting depth in soils at Maramarua Forest; however the maximum penetration resistance of the nearby Naike clay soil is 2.54 MPa (DSIR Soil Bureau, 1968b). Radiata pine root

Prediction of Mb from tree characteristics

Since the variance of Mb increased with increasing predicted values, a logarithmic transformation was performed to stabilise this. In order to maintain linear relationships between Mb and each of the potential explanatory variables, logarithmic transformations were also applied to height, DBH and stem volume. Significant linear relationships (p<0.001) existed between Mb, and tree height, DBH and stem volume (Table 3, relations (1)–(3)). The H/DBH ratio of sampled trees ranged between 32 for the

Discussion and conclusions

Failure mode is closely linked to soil type. Ninety-two percent trees failed by uprooting on non-cohesive soils but only 11% failed by this mode on clay soils. Mergen (1954) stated that the distribution and anchoring ability of tree roots are affected by soil texture and consistency. Stronger root anchorage prevents a tree from uprooting and the force is transferred to the tree stem resulting in stem breakage (Coutts, 1986). The factors determining consistency are cohesive and adhesive strength

Acknowledgements

This study was funded by the Ministry of Research, Science and Technology under contract CO4302 and by the Forest Research/Industry Wind Risk Modelling Multi-Client Agreement which comprises CHH Forests Ltd., Fletcher Challenge Forests Ltd., Selwyn Plantation Board Ltd. and Wenita Forest Products Ltd. Todd Cheeseman, Marcel Griffiths and James McEwan helped with the tree winching. Drs. Douglas Maguire, Malcom Skinner, Mr. Piers McLaren and two anonymous reviewers provided useful comments on

References (42)

  • C. Mattheck et al.

    Mechanical control of root growth: a computer simulation

    J. Theor. Biol.

    (1997)
  • K.C. Chandler

    Climatic damage to the forests of the Tapanui district

    N.Z. J. For.

    (1968)
  • M.P. Coutts

    Root architecture and tree stability

    Plant Soil

    (1983)
  • M.P. Coutts

    Components of tree stability in Sitka spruce on peaty gley soil

    Forestry

    (1986)
  • Craig, R.F., 1990. Soil Mechanics, 4th Edition. Chapman and Hall, London, 410...
  • K.W. Cremer et al.

    Effects of stocking and thinning on wind damage in plantations

    N.Z. J. For. Sci.

    (1982)
  • M.J. Crook et al.

    The anchorage mechanics of deep rooted larch, Larix europea×japonica

    J. Exp. Bot.

    (1996)
  • DSIR Soil Bureau, 1954. General survey of the soils of North Island, New Zealand. Soil Bureau Bulletin 5, N.Z. Dept....
  • DSIR Soil Bureau, 1968a. General survey of the soils of South Island, New Zealand. Soil Bureau Bulletin 27, N.Z. Dept....
  • DSIR Soil Bureau, 1968b. Soils of New Zealand, Part 3. Soil Bureau Bulletin. N. Z. Dept. Sci. Ind. Res. 26(3)...
  • A.I. Fraser

    The soil and roots as factors in tree stability

    Forestry

    (1962)
  • Fraser, A.I., Gardiner, J.B.H., 1967. Rooting and stability in Sitka spruce. Forestry Commission Bulletin No. 40. HMSO,...
  • T.S. Frederickson et al.

    Testing loblolly pine windfirmness with a simulated wind stress

    Can. J. For. Res.

    (1993)
  • A.I. Irvine

    The significance of wind throw for Pinus radiata management in the Nelson district

    N.Z. J. For.

    (1970)
  • J.P. McLaren et al.

    Height growth of Pinus radiata as affected by stocking

    N.Z. J. For. Sci.

    (1995)
  • F. Mergen

    Mechanical aspects of wind-breakage and windfirmness

    J. For.

    (1954)
  • K. Metzger

    Der Wind als massgeblicher Faktor für das Wachstum der Baume

    Mundener Forstliche Hefte

    (1893)
  • Milne, R., 1995. Modelling mechanical stresses in living Sitka spruce stems. In: Coutts, M.P., Grace, J. (Eds.), Wind...
  • Ministry of Forestry, 1997. A national exotic forest description as at 1 April 1996. Ministry of Forestry, Wellington,...
  • J.R. Moore et al.

    Assessing the risk of wind damage to plantation forests in New Zealand

    N.Z. For.

    (1998)
  • J. Morgan et al.

    Shape of tree stems: a re-examination of the uniform stress hypothesis

    Tree Physiol.

    (1994)
  • Cited by (119)

    • Overturning resistance of large diameter Norway spruce (Picea abies (L.) Karst) on sloped conditions

      2022, Forest Ecology and Management
      Citation Excerpt :

      Moreover, pulling tests data are available for peaty gley soils(Coutts, 1986), Podzols (Gardiner et al., 2000) and mixed Cambisols and Pozsols (Lundström et al., 2007). There is scarce information on the stability of Norway spruce growing on freely draining mineral soil which is a typical configuration of the Central European alpine and subalpine context, given the fact that anchorage strength appears to be scarcer for this soil condition (Dupuy et al., 2005; Moore, 2000). Lastly, some interest has been placed on analysing the influence of a sloped terrain on the overall stability of trees.

    • Mechanical behavior of trees with structural defects under lateral load: A numerical modeling approach

      2021, Urban Forestry and Urban Greening
      Citation Excerpt :

      Climatic and environmental conditions affect tree growth and tree stability (Rahardjo et al., 2009; Khalilnejad et al., 2013; Harnas et al., 2015). Several studies have been undertaken to develop devices and procedures for the detection of the presence of decay (Wang and Allison, 2008; Johnstone et al., 2010; Arciniegas et al., 2014), to measure the strength of tree components (e.g., bending moments) (Kane and Clouston, 2008), to model wind load dynamics (James et al., 2006; Li et al., 2018, 2019), to perform an assessment of mechanical stability of root architecture (Smiley, 2008; Bartens et al., 2010; Ow et al., 2010; Gilman et al. 2013; Lee, 2016), and to conduct tree pulling tests (Moore, 2000; Peltola et al., 2000; Koizumi et al., 2010; Ow et al., 2010; Kim et al., 2020). The most common types of tree failures are tipping and fractures.

    • Stability analysis of laterally loaded trees based on tree-root-soil interaction

      2020, Urban Forestry and Urban Greening
      Citation Excerpt :

      Assessing the potential of tree failures has been hampered by a lack of empirical data with respect to the assessment of structural defects. Tree pulling tests have been conducted by applying a load with a winch to pull forest trees until they are uprooted, or the stem failed in determining the resistance of trees against rupture and uprooting (Papesch et al., 1997; Moore, 2000; Peltola et al., 2000). These tests are designed to cause ultimate failure to predict the critical turning or bending moment of the tree and therefore lead to the destruction of the subjected trees.

    View all citing articles on Scopus
    1

    Present address: Department of Forest Resources, Oregon State University, Corvallis, OR 97331, USA.

    View full text