River Red Gum Ecological Thinning Trial Monitoring Report 2021 210249

Abstract

This report presents results from the fourth year of post-treatment monitoring of an ecological thinning trial in River Red Gum forests within Murray Valley National Park, NSW. The trial aims to evaluate whether reducing stem density through ecological thinning can improve biodiversity, canopy condition and forest resilience. Monitoring was conducted across 22 sites representing different initial stem densities and water availability levels (Site Quality 1 and 2). Key findings show that thinning had varying effects depending on site conditions and thinning intensity. Thinning increased growth rates of smaller trees (20cm diameter) by 30-100% while decreasing growth of larger trees (100cm diameter) by 75-80%. Tree mortality doubled on moderately thinned Site Quality 1 plots. Coppice regeneration increased substantially, particularly in Site Quality 2 plots. While thinning initially promoted seedling recruitment, it later reduced germinant occurrence by 18-40% in most Site Quality 1 plots. Heavy thinning reduced native plant species richness in some plots but increased exotic species richness by 55-130%. Canopy cover decreased by 14-35% in thinned Site Quality 1 plots. No significant effects were found on bird species richness or fuel hazard levels. The results demonstrate complex interactions between thinning treatments and site conditions, providing important insights for adaptive management of River Red Gum forests.