Data from: Importance of deep water uptake in tropical eucalypt forest

Climate models predict that the frequency, intensity and duration of
drought events will increase in tropical regions. Although water
withdrawal from deep soil layers is generally considered to be an
efficient adaptation to drought, there is little information on the role
played by deep roots in tropical forests. Tropical Eucalyptus plantations
managed in short rotation cycles are simple forest ecosystems that may
provide an insight into the water use by trees in tropical forests. The
contribution made by water withdrawn from deep soil layers to the water
required for evapotranspiration was quantified daily from planting to
harvesting age for a Eucalyptus grandis stand using a soil water transfer
model coupled with an ecophysiological forest model (MAESPA). The model
was parameterized using an extensive data set and validated using time
series of the soil water content down to a depth of 10 m and water-table
level, as well as evapotranspiration measured using eddy covariance. Fast
root growth after planting provided access to large quantities of water
stored in deep soil layers over the first 2 years. Eucalyptus roots
reached the water-table at a depth of 12 m after 2 years. Although the
mean water withdrawal from depths of over 10 m amounted to only 5% of
canopy transpiration from planting to a harvesting age of 5 years, the
proportion of water taken up near the water-table was much higher during
dry periods. The water-table rose from 18 to 12 m below-ground over 2
years after the harvest of the previous stand and then fell until
harvesting age as evapotranspiration rates exceeded the annual rainfall.
Deep rooting is an efficient strategy to increase the amount of water
available for the trees, allowing the uptake of transient gravitational
water and possibly giving access to a deep water-table. Deep soil layers
have an important buffer role for large amounts of water stored during the
wet season that is taken up by trees during dry periods. Our study
confirms that deep rooting could be a major mechanism explaining high
transpiration rates throughout the year in many tropical forests.