Responses of young trees to wind : effects on root architecture and anchorage strength.

Since the Great Storm of October 1987, public and political interest in wind damage to trees has heightened, resulting in increased research efforts to reduce windthrow.This thesis examines the responses of young Sitka spruce (Picea sitchensis (Bong) Carr.) and European larch (Larix decidua (Mill.)) to wind stress.Two laboratory experiments were performed in which Sitka spruce and European larch were grown in wind tunnels.Trees responded to wind stress by increasing the number and altering the morphogenesis of windward woody lateral roots which provide the most resistance to overturning.Responses of shoot growth to wind stress were small, however, uneven irradiance levels appeared to cause asymmetric growth.The distribution of root biomass around the tree was related spatially to the distribution of shoot growth.A third experiment investigated the translocation pathway in Sitka spruce by feeding one root per plant with dye.The dye ascended spirally, reaching branches at many points around the stem.It was concluded that a different mechanism, such as an increase in stem cambial activity, must be occurring to stimulate asymmetric root growth.Trees with characteristics likely to promote stability, such as increased root growth, could be selected for in breeding programmes.Clones of Sitka spruce were examined for their response to mechanical stimulation by flexing.Flexed trees increased biomass allocation and branching in woody roots under the most stress.Anchorage tests showed that some flexed clones of Sitka spruce had an increased resistance to overturning.In order to identify whether changes in architecture can affect pull-out resistance of roots, a model which simulates the uprooting of a root system with different branching patterns was designed, allowing predictions of anchorage abilities with regard to architecture.If features which enhance tree stability are identified, foresters may utilize that knowledge when selecting trees to plant in the field.the production of this thesis is to Alastair, who, with much patience, has struggled through many drafts of chapters and somewhat embarrassing first attempts at statistics.However, without those stimulating and enthusiastic discussions with Mike, this line of research may never have even been pursued.Many thanks to Keith Partridge and Colin Abbot in York and to Keith Clifford and Dave Clark in Roslin for looking after all my plants, and to the latter pair for building that wind tunnel and making all those temperature measurements.Thanks are due to James (Jaaaaaaames) Perrins and Tim Stickland for their invaluable guidance as I learned to operate the image analyzer.Bruce Nicoll has indulged in many post-lunch provocative arguments regarding roots, and has provided some of the data presented in Chapter 5. I would like to thank especially Jonathan Ball for his support during the months of writing up and for his and Andy Sedman's help with the modelling of root anchorage presented in Chapter 6.Many thanks are due to all members of F2, both past and present, especially Julie Watson and James Merryweather, for everything.Finally, I would like to thank my parents for their moral (and fmancial!)support during my years as a student.