Impacts of enhanced storm water infiltration on urban Melia azedarach functioning in dry season

In the face of ongoing climate change and rising human populations, the health of urban green spaces and management of natural resources have become increasingly important. To help to mitigate urban heat islands and enhance the quality of urban forests, Water Sensitive Urban Design (WSUD) projects are being implemented around the world. One WSUD device, the TREENET Inlet, diverts stormwater from roads to the subsurface soil via leaky well soakage systems to provide passive irrigation for kerbside vegetation. This study in suburban Hawthorn in South Australia investigated the effects of these inlet systems on water-use and productivity of white cedar (Melia azedarach) street trees. Water use of mature white cedar trees was investigated by measuring sap flow using the heat-pulse method. Height, diameter at breast height, stomatal conductance and photosynthesis (CO2 release) of actively growing young trees were measured.

The results of this study revealed that mature white cedar street trees have a high night-time water uptake, with ~34% of the total water uptake from the project occurring during the night. The secondary finding was that TREENET Inlets provided ~21% more water for each tree to transpire during the dry season. The TREENET Inlets were also found to have significant benefits to young white cedar trees, with a 50% increase in tree height and a 25% increase in diameter at breast height over a three year period. TREENET Inlets also supported greater leaf functionality during the dry season with ~100% higher conductance and ~94% increase in photosynthesis rates observed in young trees with the inlets compared to those without. This one year study shows that TREENET Inlets provide significant benefit to white cedar street trees however more studies need to be conducted on more tree species in order to determine if the inlets provide the same benefits to other common urban tree species.

This project was funded by the Adelaide and Mount Lofty Ranges NRM Board, Mitcham Council and Flinders University.