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Acta Amazonica

Print version ISSN 0044-5967On-line version ISSN 1809-4392

Acta Amaz. vol.20  Manaus  1990

http://dx.doi.org/10.1590/1809-43921990201038 

BOTÂNICA

Transpiration rates for several woody successional species and for a pasture in the upper Amazon basin in Venezuela

Jeffrey C. Luvall *  

Christopher Uhl **  

*NASA, Marshall Space Flight Center, ES43, MSFC, AL. 35812

**202 Buckhout Lab. Department of Biology, Pennsylvania State University, University Park, PA 16802

ABSTRACT

Evapotranspiration rates for a eight month old tropical pasture were estimated using the Penman-Monteith equation. Transpiration rates for several woody secondary successional species and stump sprous in the pasture and conucos (farm sites) were measured using the tritiated water technique.

The stuty area was located near the village of San Carlos de Rio Negro (1° 56' N, 67° 03' W) in southern Venezuela, near the confluence of the Casiquiare and the Rio Guania wich forms the Rio Negro. The terrain was gently rolling with the areas between the small ridges supporting Amazon caatina forests on spodosols, and higher never flooded areas (tierra firma) supporting a mixed species forest.

Results indicated that for a one month period, ET loss (0.46 cm/day) from the pasture, including soil and root mat evaporation, was about 0.43 cm/day less than estimated from the adjacent undisturbed forest (0.89 cm/day). Pan A evaporation for the same time period was 0.64 cm/day. Transpiration rates for seed established species were significantly less (0.38 cm/day) than for stump sprouts (1.09 cm/day) of the primary forest in the pasture.

RESUMO

As taxas de evapotranspiração de uma pastagem de oito meses foram estimadas usando a equação Penman-Monteith. As taxas de transpiração de várias espécies lenhosas sucessionais e rebrotos na pastagem e canucos (fazendas) foram medidas com o uso de água radiada com tritio. O local de estudo estava localizado perto do vilarejo de São Casrlos do Rio Negro (1° 56' N, 67° 03' W) na parte sul da Venezuela, próximo a confluência do Casiquiare e Rio Gania, que formam o Rio Negro. O terreno era levemente ondulado com as áreas entre os pequenos cumes que sustentam uma mata de espécies mistas. Os resultados mostraram que durante o período de um mês, a perda de ET (0.46 cm/dia) da pastagem, incluindo a evaporação do solo e da camada das raízes, foi de cerca de 0.43 cm/dia menos que a estimada para a mata adjacente não-perturbada (0.89 cm/dia). A evaporação Pan A para o mesmo período foi de 0.64 cm/dia. As taxas de transpiração para as espécies estabelecidas através de sementes foram significativamente menores (0.38 cm/dia) do que para os rebrotos (1.09 cm/dia) das espécies da mata primária na pastagem.

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