Poster: Ecophysiology

Abs # 51: Transpiration in a red pine stand based on sap flow measurements

Presenter:	Reid, Nathan L, reid_n@denison.edu
Authors	Reid, Nathan L (A)   Firooznia, Fardad  (A)
Affiliations:	(A): Denison University

The objective of this research is to scale sap flow measurements from individual red pine trees (Pinus resinosa Ait.) to an entire red pine stand. Sap flow in tree trunks can be estimated using temperature dissipation probes (TDP). Thirty-mm-long probes were inserted at the four cardinal azimuths (N, S, E, and W) in each tree. Temperature differentials were measured every 10 seconds and means were recorded every 30 minutes using a Campbell 10X datalogger. Sapwood width was measured using 4 stem cores per tree. Sap flux density is estimated through the temperature differentials, and sap flow is calculated through multiplying sap flux density by sapwood area. Sap flux density was measured in three trees for the whole summer of 2002, while six other sets of probes were moved among different trees every 10 days (24 trees). Trees with larger diameters had higher sap flow rates partly due to larger sapwood areas, and partly due to higher sap flux densities. The variation in sap flux density was analyzed within and among trees on 10-day intervals. The sap flux variability measured at different azimuth locations was not consistent between trees. The variability within a tree ranged from 1% to 100%. We used the sap flux density averaged among the four azimuth locations as an estimate of the actual sap flux density of each tree, and used these averages to calculate daily sap flow. There was good correlation between daily sap flow of the three constant trees and those of the others: R² values range from 80-98%, with one exception with R² = 64%. Therefore, we believe we can reasonably scale the daily sap flow to the level of the stand given knowledge of tree diameter distribution within the stand.