Interrelationships among dry season leaf fall, leaf flush and transpiration: insights from sap flux measurements in a tropical dry deciduous forest

Abstract

We measured the sap flux densities of 12 deciduous trees in a tropical dry deciduous forest with high seasonality of available water located in Cambodia and evaluated the seasonal trends in transpiration and leaf phenology. For all trees, the minimum transpiration was recorded in the middle of the dry season, and almost all trees restarted transpiration before the first monsoon rain. The occurrence of the 'paradox' of leaf phenology was confirmed. During the dry season, transpiration was controlled by leaf phenology and decreased with an increase in the duration of the leafless period. In contrast, during the wet season, daily changes in transpiration were determined by changes in evaporative demand. Transpiration during the dry season accounted for more than 30% of the annual total among trees, and at the stand scale, the dry season contribution was 38%. The dry season transpiration was not negligible for the water balance in this ecosystem. The soil water condition in the shallow layer, where the main root system is located, was not the source of transpiration during the dry season. This implied that the root probably extended to a deep layer and absorbed water. The relationships between the mean canopy stomatal conductance and vapour pressure deficit revealed that most trees were isohydric. Isohydric behaviour controlling stomatal openness to avoid xylem hydraulic failure was also confirmed at the stand scale and was advantageous for these trees, allowing them to continue transpiring under the high evaporative demand during the dry season.

Comparison of Wood Density and Water Content Between Dry Evergreen and Dry Deciduous Forest Trees in Central Cambodia

“…1500-1700 mm) and mean temperature (approx. 27°C) are similar between the provinces (Iida et al 2013(Iida et al , 2016. Most rainfall occurs during the rainy season from May to October (Iida et al 2013(Iida et al , 2016.…”

“…27°C) are similar between the provinces (Iida et al 2013(Iida et al , 2016. Most rainfall occurs during the rainy season from May to October (Iida et al 2013(Iida et al , 2016. The vegetation at the DEF sites primarily consisted of species from Clusiaceae, Dipterocarpaceae, Leguminosae, and Myristicaceae families (Kenzo et al 2012).…”

“…All tree species shed leaves during the dry season, although leaf phenology in canopy trees significantly varied according to species (Iida et al 2016). Most canopy trees were 12-20 m in height.…”

Effects of vegetation and soil on evapotranspiration, flow regime, and basin storage in three nearby catchments in northeast Japan

“…Kumagai et al, 2007;Iida et al, 2015). We estimated transpiration by evergreen conifers based on sapwood area (AS).…”

“…The water balance method as well as other methods (e.g. interception, sap flow, flux measurements) is effective for evaluating evapotranspiration quantitatively (Kosugi et al 2007;Shimizu et al 2015). The mean ratios of throughfall to rainfall over 570 days in each 5 NEW catchment were 82.1% (no.1), 80.1% (no.2), and 80.3% (no.3), respectively (Iwaya et al 2013).…”