Linking ice accretion and crown structure: towards a model of the effect of freezing rain on tree canopies.
Despite a longstanding interest in variation in tree species vulnerability to ice storm damage, quantitative analyses of the influence of crown structure on within-crown variation in ice accretion are rare. In particular, the effect of prior interception by higher branches on lower branch accumulation remains unstudied. The aim of this study was to test the hypothesis that intra-crown ice accretion can be predicted by a measure of the degree of sheltering by neighbouring branches.



Freezing rain was artificially applied to Acer platanoides L., and in situ branch-ice thickness was measured directly and from LiDAR point clouds. Two models of freezing rain interception were developed: 'IceCube', which uses point clouds to relate ice accretion to a voxel-based index (sheltering factor; SF) of the sheltering effect of branch elements above a measurement point; and 'IceTree', a simulation model for in silico evaluation of the interception pattern of freezing rain in virtual tree crowns.



Intra-crown radial ice accretion varied strongly, declining from the tips to the bases of branches and from the top to the base of the crown. SF for branches varied strongly within the crown, and differences among branches were consistent for a range of model parameters. Intra-crown variation in ice accretion on branches was related to SF (R(2) = 0·46), with in silico results from IceTree supporting empirical relationships from IceCube.



Empirical results and simulations confirmed a key role for crown architecture in determining intra-crown patterns of ice accretion. As suspected, the concentration of freezing rain droplets is attenuated by passage through the upper crown, and thus higher branches accumulate more ice than lower branches. This is the first step in developing a model that can provide a quantitative basis for investigating intra-crown and inter-specific variation in freezing rain damage.
University of Freiburg, Faculty of Biology, Geobotany, Schaenzlestr. 1, D-79104 Freiburg, Germany charles.nock@biologie.uni-freiburg.de.
Charles A
CA
Nock
Department des Sciences Biologique, Université du Québec à Montréal, Centre-Ville Station, PO Box 8888, Montreal, Qc H3C 3P8, Canada.
Bastien
B
Lecigne
Department des Sciences Biologique, Université du Québec à Montréal, Centre-Ville Station, PO Box 8888, Montreal, Qc H3C 3P8, Canada.
Olivier
O
Taugourdeau
Department of Forestry and Wildland Resources, Humbolt State University, 1 Harpst Street, Arcata, CA 95521-8299, USA.
David F
DF
Greene
CIRAD, UMR AMAP, 34000 Montpellier, France.
Jean
J
Dauzat
Institute of Temperate Forest Sciences, Université du Québec en Outaouais, 58 Rue Principale, Ripon, Qc J0V1V0, Canada.
Sylvain
S
Delagrange
Department des Sciences Biologique, Université du Québec à Montréal, Centre-Ville Station, PO Box 8888, Montreal, Qc H3C 3P8, Canada Institute of Temperate Forest Sciences, Université du Québec en Outaouais, 58 Rue Principale, Ripon, Qc J0V1V0, Canada.
Christian
C
Messier
D031002:Acer / Q000033:anatomy & histology* / Q000502:physiology; D003198:Computer Simulation; D005615:Freezing; D007053:Ice; D008954:Models, Biological; D035261:Plant Components, Aerial / Q000033:anatomy & histology / Q000502:physiology; D011792:Quebec; D011891:Rain; D014197:Trees / Q000033:anatomy & histology* / Q000502:physiology
D007053:Ice
Acer platanoides L.; LiDAR; branch breakage; eastern North America; freezing rain; ice accretion; ice storm; modelling; temperate forest; terrestrial laser scanning; voxels