Research sheds new light on water catchments

CONTROLLING forest density can help maintain stream flow levels, according to research findings presented at a recent Forestry Tasmania seminar.
The findings were outlined to FT staff by University of Melbourne Department of Forest and Ecosystem Science associate professor Leon Bren, who has undertaken research into Melbourne’s forested water catchments.
Dr Bren told FT staff the research had generated doubt about the ongoing, widely held and bitterly debated view that water flows dropped immediately following harvesting and fires.
Dr Bren presented an updated analysis of data gathered from 1954-2007 for the Coranderrk paired catchment project 70 kilometres east of Melbourne.
The project compared rainfall and water flows in an area at Picaninny Creek that had been clearfelled, with a similar oldgrowth area at Slip Creek that had not been touched.
“Analysis of the data showed there was a net increase in stream flow in the clearfelled area compared with the control area for seven years after logging took place,” Dr Bren said.
Dr Bren said the initial increase was followed by a gradual decline in flow, presumably due to the roots of the regenerating trees taking up more water. However he also said trees take up considerable amounts of water regardless of whether they are regrowth or old growth trees.
Dr Bren said the second major finding was that the decline in water flow during forest regrowth was less than people had claimed and research showed that controlling forest density through thinning could help manage stream flows for the most beneficial results.
“Forest management and manipulation of forest density can modify water yields, giving either increased or decreased flows,” he said.
The research is ongoing, and Dr Bren is keen to link up with similar research projects being undertaken at the Warra Long-Term Ecological Research Site managed by Forestry Tasmania.