Water budgets were constructed over a 22 month period for young uncut or coppiced (resprouting)
Eucalyptus kochii Maiden & Blakely subsp.
plenissima Gardner (Brooker) trees in twin-row belts through annual pasture at a deep sand site (320 mm yr
–1 mean rainfall) near Kalannie, Western Australia. Budgets were based on measurements of tree transpiration, canopy interception of incident rainfall, and neutron-based transects of soil water changes within and outside rooting catchments of trees. Transpiration of uncut 5- to 7-year-old trees sited over a fresh perched aquifer averaged 3.7 mm day
–1 across the 5 m wide tree belt, compared to 2.4 mm day
–1 for trees distant from the aquifer, and an average of 1.5 mm day
–1 for 0–2 year coppice. Rain incident upon canopies of uncut trees contributed only 8–14% of their transpiration after evaporation losses were accounted for. Trees away from the aquifer dried soil profiles down to a hardpan at 5–7 m depth and up to 12.5 m out from the canopy edge, while also obtaining an estimated 13–16% of their transpirational requirement from below the hardpan. The equivalent of one third of rain falling on tree-free areas away from the aquifer was lost in deep drainage, but with 17% tree cover present, net deep drainage was reduced to 21% of rainfall where trees were coppiced, or 5% where trees were left uncut. Taking also into account the additional drying of soil by trees, hydrologic balance would have been maintained with a 20% canopy cover of 0–2 year coppices or with 10% devoted to uncut trees.
alley farming - oil mallee - salinity - short-rotation coppice forestry - soil hardpan - tree water sources