Sap flux simulation and tree transpiration depending on tree position within stand of different densities

Tree sap flow rate was measured using THB method in two trees of Picea abie s at the experimental forest study site in the Beskydy Mts. during two time periods of three days in the autumn 1997. Sampled trees were affected by t heir location within plots of different stand densities. An exponential rel ationship between diameter at breast height and sapwood area was applied to scale up the specific sap flux data to the whole stand transpiration. Rela tions of specific sap flux and different microclimate factors were used for simulations of whole stand transpiration as well. The specific sap flux data highly correlated with air temperature and relat ive air humidity measured at 5m height (canopy height equaled 6.6m), and in cident global radiation with one hour time lag. The best simulation was bas ed on multiple regression among all above mentioned factors (without the ti me lag) when constant night fluxes were presumed. The trees located in spar se plot transpired more than the trees in dense plot when incident global r adiation up to 500 W. m(-2). Thus, daily sum of transpiration was greater i n dense plot except sunny days when daily sum of incident global radiation overcome ca 14 MJ. m(-2). day(-1). The differences between experimental plo ts were 500 trees. ha(-1) in stand density.