Restoration thinning permits stems to capitalise on high-rainfall years in a regenerating endangered forest ecosystem

1. Passively regenerating native vegetation presents a cost-effective opportunity to sequester carbon and reinstate habitat in heavily cleared agricultural landscapes.

2. However, in some cases a few woody species recolonise in dense, low-diversity stands that are slow to self-thin.

3. Restoration thinning of over-dominant species has been proposed to accelerate ecosystem recovery, but its longer-term efficacy remains uncertain, and is likely to depend strongly on rainfall.

4. This study focuses on a restoration thinning experiment established in 2007 in dense brigalow (Acacia harpophylla) regrowth in Queensland, Australia. Using variation in rainfall between 2007 and 2017, we examined the interactive effects of neighbourhood density and moisture availability on the growth and survival of A. harpophylla.

5. We also compared the strength of A. harpophylla density effects on itself to its effects on a sparsely distributed co-occurring tree species (Casuarina cristata) that was codominant in the original forest.

6. Our results provide clear evidence that thinning permits A. harpophylla to grow rapidly during periods of high rainfall, and that interspecific competition between A. harpophylla and C. cristata is relatively weak. As such, thinning of dense A. harpophylla could be combined with seeding or planting of co-occurring tree species with complementary niches to further accelerate forest recovery in this extensive regrowth ecosystem.

Methods
See Towers, I. R. & Dwyer, J. M. (2020). Restoration thinning permits stems to capitalise on high-rainfall years in a regenerating endangered forest ecosystem. Ecological Solutions and Evidence for methods.