Forest management and silviculture
In the face of a drying climate and streamflow declines in south-west Western Australia, maintaining streams in forested areas has become a critical management challenge. Changes in runoff from multiple-use state forests, conservation reserves, and other lands vested in the Conservation Commission and managed by Department of Parks and Wildlife have implications for public water supplies, stream ecosystems, and the biodiversity that they support.
In particular, most of the remaining northern jarrah forest has experienced some form of silviculture since European settlement and regrowth forests, which tend to be denser than old-growth forests, use more water than their old-growth counterparts. This higher water use exacerbates declines in groundwater levels, reductions in streamflows, and the shift in some streams from perennial (i.e. flow all year round) to intermittent (i.e. they stop flowing over the drier months). Such changes have drastic ramifications for both stream ecosystems (including dependent species), and water availability for human uses.
The Department of Water works with the Department of Parks and Wildlife to achieve the following:
- Provide scientific input into forest management, including in the preparation of Forest Management Plans silvicultural guidelines.
- Assess and revise key performance indicators (KPIs) for the forest management plan that related to forested streams, and report on these assessments to the Conservation Commission. In the Forest Management Plan 2004–13 these were KPI 19 and 22, which dealt with salinity and water production respectively. In the current Forest Management Plan 2014–23, the relevant Key Performance Indicators (KPI) are KPI 10 and 11, which relate to stream condition (flow and salinity) and groundwater level, and the effectiveness of silviculture for water production.
The department's work has contributed to a significant change to forest management planning, with the high-level recognition of the dire state of many forested streams under the drying climate, and the inclusion of a policy framework to facilitate the implementation of silviculture for ecosystem health and silviculture for water production.
The review of Silviculture in Forests of south-west Western Australia commented that:
"Forest management to achieve a better water balance in a drying climate is a most critical issue facing forest managers now and in the future. As a consequence of a drying and warming trend since the 1970s, and a legacy of predominantly heavily stocked regrowth forests, these ecosystems are experiencing acute water stress.
If this issue is not addressed as a matter of priority, then the consequences will be undesirable, probably irreversible, and will likely compromise efforts to achieve ecologically sustainable forest management. Silviculture has a pivotal role in addressing this issue."
The department also works with the Department of Parks and Wildlife to ensure that any activities in water supply catchments don't contaminate, or otherwise adversely affect water quality.