PARENT SESSION
Contributed Oral Session 95: Forest Ecology: Physiological Processes
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal
Decreasing scaling error on transpiration by accounting for individual variations and modifying the mensuration method of sapwood depth.
Quiñonez-Piñón, Rebeca*,1, Valeo, Caterina1, 1 University of Calgary, Calgary, Alberta, Canada
ABSTRACT- Transpiration is an ecohydrological process that is driven by the spatial and temporal heterogeneity of vegetation type and its physiological functions, as well as the variations in meteorological factors and energy/water availability. Thus spatial and temporal variability in the amount of transpired water is large even between individuals of the same species. Such wide variability makes spatial scaling a complex issue, and makes the development of scaling factors very difficult. The goal of this work is to decrease the error in estimated transpiration when scaling from an individual tree to a whole plot. This study was performed in five boreal species: Popolus tremuloides, Picea glauca, P. mariana, Pinus banksiana and P. contorta. Transpiration was measured by the thermal dissipation method. Mensurations were done on individuals of every species chosen based on their circumference at breast height in order to have a wide range of tree sizes. Before attempting any scaling, we analyzed how transpiration rates varied between individuals of the same species and how their transpiration trends are influenced by meteorological parameters. Individuals showed similar diurnal sap flow trends; however there are differences in amount of water transpired and hysteresis. Younger trees showed higher sap fluxes and water storage capacity than older trees. We considered sapwood area (SA) to be an adequate tree to plot scaling parameter; but the accuracy of SA estimations should be increased in order to obtain better correlation with other morphological characteristics. Microscopic methods were used to estimate the sapwood depth at the four different cardinal points of the trees sampled. For every species, sapwood depth and diameter at breast height showed a good correlation matched by a polynomial of second order (e.g. for pine species y = 0.1394x2 - 8.0037x + 139.86; r2=0.89). Transpiration values were estimated to plots of 60x60m using the indirect estimation of SA. Values were compared to ET estimated with the Penman-Monteith method.
Key words: transpiration, scaling error, sapwood area, boreal forest