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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: Modelling age- and density-related gas exchange of Picea abies canopies in the Fichtelgebirge, Germany. | 229 Ann. For. Sci. 57 2000 229-243 INRA EDP Sciences Original article Modelling age- and density-related gas exchange of Picea abies canopies in the Fichtelgebirge Germany Eva Falge John D. Tenhunen Ron Ryel Martina Alsheimer and Barbara Kostner Biometeorology ESPM Univ. of California Berkeley CA 94720 USA Received 22 July 1999 accepted 1 December 1999 Abstract - Differences in canopy exchange of water and carbon dioxide that occur due to changes in tree structure and density in montane Norway spruce stands of Central Germany were analyzed with a three dimensional microclimate and gas exchange model STANDFLUX. The model was used to calculate forest radiation absorption the net photosynthesis and transpiration of single trees and gas exchange of tree canopies. Model parameterizations were derived for six stands of Picea abies L. Karst. differing in age from 40 to 140 years and in density from 1680 to 320 trees per hectare. Parameterization included information on leaf area distribution from tree harvests tree positions and tree sizes. Gas exchange was modelled using a single species-specific set of physiological parameters and assuming no influence of soil water availability. For our humid montane stands these simplifying assumptions appeared to be acceptable. Comparisons of modelled daily tree transpiration with water use estimates from xylem sapflow measurements provided a test of the model. Estimates for canopy transpiration rate derived from the model and via xylem sapflow measurements agreed within 20 especially at moderate to high air vapor pressure deficits. The results suggest that age and density dependent changes in canopy structure changes in clumping of needles and their effect on light exposure of the average needle lead to shifts in canopy conductance and determine tree canopy transpiration in these managed montane forests. Modelled canopy net photosynthesis rates are presented but have not yet been verified at the canopy level. norway spruce xylem .
