Tasman region forestry study important for the industry

A seven-year forestry study looking at the impact of sediment in rivers from harvesting and earthworks has entered its fifth year.

The $2.7 million study is jointly funded by Ministry for Primary Industries through its Sustainable Food and Fibre Futures fund and OneFortyOne New Zealand Forests. The work is being done in two forested catchments located in OneFortyOne’s Donald Creek Forest near Tadmor in the Tasman district.

Jo Field, OneFortyOne’s Environment Manager, said the study is exploring the effectiveness of current best practice in sediment control as well as looking at opportunities to improve practice.

“The current phase of the study is measuring post-harvest sediment load changes and impacts using current best practice sediment control techniques, alongside freshwater monitoring data collected throughout the study,” Jo said.

“This year we reached a significant milestone for the project. We were able to analyse and compare the data from a catchment that has been recently harvested with data from the control (unharvested) catchment.”

Interim results show that sediment loads are higher in the post-harvest catchment than in the control catchment. This is expected for the post-harvest area as there are extensive earthworks associated with roads and landings and it no longer has the tree canopy to reduce the impact of rain on the soils and stream, however the groundcover vegetation does develop rapidly.

Despite the sediment loads being higher after harvesting, there has been no quantitative or anecdotal evidence to suggest any impact on water quality or habitat in the Tadmor River downstream. Later in the project, we will be seeking input from industry and relevant experts to see if we can design better sediment control options than is current best practice.

This would then be tested in the currently unharvested catchment prior to it being harvested and compared with the existing methods. The data will help us understand the impacts of our business. It will help us learn what works well and where we might do better.

"This is a valuable opportunity to test the performance of current and new in-forest sediment management techniques - and we are grateful to work alongside Cawthron Institute, Envirolink, Manaaki Whenua - Landcare Research as well as the Ministry for Primary Industries,” Says Jo “This is important work, which we'll be able to share widely with the forestry sector and other stakeholders.”