Theme: Effects of Wind on Forests
Moderator: D. DeWalle
11.8.1995 15:30 Room: U2
Studies show that certain indicators reflect stress symptoms in trees. Mostly parameters are measured in the crown (foliage) or in the soil-root system. by contrast, our approach linked the results from a multidisciplinary research team which includes analysis of trends in wood anatomy, wood chemistry and physico-mechanical integrity to find out: a) the reliability of certain parameters to reflect pollution stress; b) the well the parameters are linked; and c) how to develop a stress-response system for wood. Highly stressed spruce trees from the Erzgebirge in Germany were sampled. Ten trees were cut from a heavy SO2 polluted site and 10 trees from a less polluted site. 1 m long sections of boles sampled at 4 m above ground from which sufficient disks were cut for analysis by each working group on the research team. Trees were cross-dated to detection missing rings. Mean chronologies of trees on the most heavily polluted site reveal a decline in radial growth and their rings exhibit an increasing tendency for abrupt early-/latewood transition. SEM studies reveal slip planes in latewood tracheids and they are more likely to split along the compound middle lamella. More trabeculi and spirals in the tracheids were also found. Measurements of cell wall thicknesses and diameters in early- and latewood, fibrilar angles, number of resin ducts, latewood percentages and other parameters provide a good basis to assess possible changes. A variety of analytical methods were used to study wood chemistry. HPLC data show that, although free glucose and fructose in tree rings increases, beginning in the early 1960's, the rate of increase is different between the two sites. Examination of fragments of hemicelluloses show trends for arabinose and xylose. 13C spectra of wood extracts show free monosaccharides to be higher in the recent years and that peroxidase was more active at the heavy polluted site. Dendrochemical studies indicate shifts in elemental patterns. Studies of the anatomy and chemistry suggest adverse biomechanica
l behavior which may have decreased the resistance to damage by wind and ice storms. Biomechanical studies ranged from micro-tensile tests with specimens from early- and latewood, in association with acoustic-emission detection, and splitting tests to determine specific fracture energy and fracture toughness. SEM studies of fracture surfaces helped to interpret relationships between mechanical and ultrastructural characteristics.
Key words: wood anatomy, chemistry, air pollution, mechanical property.
Correspondence: Stefanie Stanzl-Tschegg, Universität für Bodenkultur Wien, Gregor Mendelstrasse 33, A-1180 Vienna, Austria