Efeito da exclusão parcial da chuva na transpiração de espécies vegetais da flona de Caxiuanã (projeto Esecaflor/LBA), Pará.

Abstract

The data used in this work were obtained during the “Long-term drought impact on water and carbon dioxide fluxes in Amazonian Tropical Rainforest Experiment” (ESECAFLOR) which is subproject of Large Scale Biosphere Atmosphere Experiment in Amazônia (LBA). This study was carried out at Ferreira Penna Scientific Station (FPSS) into the Caxiuanã National Forest (CNF) in Pará State (1o 42’ 30’’ S; 51o 31’45’’ W; 62 m a.s.l.). The region has a wellpreserved forest with a canopy of 35 m high. The predominates trees species in the landscape are Eschweilera coriacea (White Matá-matá), Voucapoua americana (Acapu) and Protium pallidum (White Pitch). Sap flow measures were made between the years of 2000 and 2003, aiming to determinate the transpiration of many different trees in normal situation of water availibility and the effects of the drought long term induced. The ESECAFLOR site consist of two different areas with 1 ha each. Plot A (control) and Plot B (rainfall exclusion). The Trunk Heat Balance (THB) method based on Sap Flow Meter P4.1 system was used for measuring sap flow predominates trees species in Amazônia. Results show that the big trees on the tropical rainforest are susceptible at long term droght stress. The transpiration and rainfall relation showed how important is the vegetaton function on the forest hidrological cicle and the climate. Redutions of the soil water content available in the plot B were obseerved during all the study period. For two analysed periods, the mean transpiration in Eschweilera Coriacea increased 56% in the tree A237 (control plot), and decreased 68% in the tree B381 (drought plot). The transpiration in three trees of Couratari Multiflora showed a similar behavior during the period from December 2002 to November 2003, with shorts variations because of climate factors impacts like a vapor pressure deficit and high solar radiation availability. The transpiration obtained by model in 524 and 499 trees in the plots A and B, respectively, reached 1,228.3 mm year-1 and 401.0 mm year-1 in the B plot. These values represent 58.5% and 19.1% of rainfall registrered in the plots A and B, respectively, and also 76.4% and 24.9% of evapotranspiration, from December 2002 to November 2003. The estimated transpiration was regularly distributed during the year, around 45.4% in the winter (rainy season), and 54.5% in the summer (dry season) to plot A, and 43.1% (winter), and 56.9% (summer) in the plot B.