The ecological thinning trial aims to learn about the effectiveness of ecological thinning for addressing a range of conservation concerns associated with widespread high stem density stands and canopy dieback in Eucalyptus camaldulensis (river red gum) forests.

Conservation concerns tend to be highest in forest stands that are experiencing strong competition for water and other resources. This is because competition impacts plant occurrence, growth and health, with negative consequences for fauna habitat. Competition increases with increasing tree density and is greatest in high density stands with lower water availability. Ecological thinning aims to reduce competition by reducing the density of some small trees while retaining and enhancing biodiversity and habitat features.

The trial was conducted in the Millewa precinct of Murray Valley National Park in New South Wales. Prior to implementation, potential impacts to threatened entities were evaluated in a Public Environment Report and assessed under the Commonwealth Environmental Protection and Biodiversity Conservation Act 1995. The experimental design and monitoring plan for the trial was also approved by an independent scientific advisory committee.

There were a total of 22 study sites in the trial, located in a range of pre-thinning tree densities and spread between two levels of water availability (Site Quality). Within each study site, there were three 9 ha plots which were allocated to one of three ecological thinning treatments: control (no action), moderate thinning and heavy thinning. Thinning removed some trees <40 cm diameter at breast height. The intensity of thinning is best described by the proportion of trees that were removed, rather than the three thinning treatment categories.

Thinning was implemented between April 2016 and August 2017 and a range of ecological indicators were monitored before and after thinning. Baseline pre-thinning data was collected in the 2015-16 survey year and annual post-thinning monitoring was undertaken for five years, from the 2017-18 survey year until the 2021-22 survey year. Monitoring data was collected at a spatial and temporal scale appropriate to each ecological indicator.

Further details are provided within the datasets for each type of ecological indicator surveyed:

• River Red Gum Tree Size and Growth Data

• River Red Gum Tree Recruitment Data

• River Red Gum Tree Canopy Cover and Health Data

• River Red Gum Floristic Composition and Structure Data

• River Red Gum Fauna Data

• River Red Gum Litter and Woody Debris Data

• River Red Gum Fuel Hazard Data

Further information about the study design, data collection methods, and findings of the ecological thinning trial can be found within the documents below.