Stem sap flow at a secondary forest and its difference between dry and rainy seasons

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  • Tsuchiya Akio
    Graduate School of Integrated Sciences for Life, Hiroshima University
  • Tanaka Akira
    Centro de Estudo Integrados da Biodiversidade Amazônica, Instituto Nacional de Pesquisas da Amazônia

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  • 再生林のサップフローと乾期と雨期の差異

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<p>The stem sap flow (SF) of pioneer species was measured in a 15-year-old secondary forest in a suburb of Manaus, Amazonas, by means of the Granier Method. The hydraulic conductivity was converted into the stand-level evapotranspiration in combination with the sapwood area of stem transection in order to compare the conditions between dry and rainy seasons (30 days each). It was found that the SF had the same phase as the vapor pressure deficit (VPD) in both seasons, but the daily amount in rainy season was larger than that in dry season (dry season: 12.4 l/day, rainy season: 14.9 l/day), which was inverse to VPD. When comparing the periods with similar downward short-wave radiation (dry season: 597W/m2, rainy season: 609W/m2), it was found that the SF was larger in rainy season (36.9 l/day) than in dry season (27.7 l/day). It is well-known that the SF basically depends on VPD, but an inverse relationship was found in this study. The relationship resulted from the differences in soil water content (e.g. 0.28m3/m3 in dry season, 0.37m3/m3 in rainy season at a depth of 80cm in soil), and it influenced the sap flow of juvenile trees with shallow roots. Because the aboveground biomass was still small, the amount of evapotranspiration remained to be 1.0mm/day in dry season and 1.2mm/day in rainy season, which was smaller than that in savanna regions.</p>

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