Hydraulic redistribution (HR) in karite´ (Vitellaria paradoxa) and ne´re´ (Parkia biglobosa) tree
species was studied by monitoring the soil water potential (js) using thermocouple
psychrometers at four compass directions, various distances from trees and at different
soil depths (max depth 80 cm) during the dry seasons of 2004 and 2005. A modified WaNuLCAS
model was then used to infer the amount of water redistribued based on js values.
Tree transpiration rate was also estimated from sap velocity using thermal dissipative
probes (TDP) and sapwood area, and the contribution of hydraulically redistributed water
in tree transpiration was determined. The results revealed on average that 46% of the
psychrometer readings under karite´ and 33% under ne´re´ showed the occurrence of HR
for the two years. Soil under ne´re´ displayed significantly lower fluctuations of js
(0.16 MPa) compared to soil under karite´ (0.21 MPa). The results of this study indicated
that the existence of HR leads to a higher js in the plant rhizosphere and hence is important
for soil water dynamics and plant nutrition by making more accessible the soluble
elements. The simulation showed that the amount of water redistributed would be approximately
73.0 L and 247.1 L per tree per day in 2005 for karite´ and ne´re´ , and would represent
respectively 60% and 53% of the amount transpired a day. Even though the model has
certainly overestimated the volume of water hydraulically redistributed by the two species,
this water may play a key role in maintaining fine root viability and ensuring the well
adaptation of these species to the dry areas. Therefore, knowledge of the extent of such
transfers and of the seasonal patterns is required and is of paramount importance in parkland
systems both for trees and associated crops