Our paper on dense stands and thinning has been accepted and is available on early view online:
Jones C.S., Duncan D.H., Rumpff L., Thomas F.M., Morris W.K. and Vesk P.A. (2015) Empirically validating a dense woody regrowth ‘problem’ and thinning ‘solution’ for understory vegetation. Forest Ecology and Management. doi:10.1016/j.foreco.2014.12.006
This paper is based on two separate field projects done to evaluate dense regrowth stands of eucalypts and the effect of thinning management. Dense regrowth stands are increasing in extent worldwide. They generally occur on cleared land where there is a reduction in the landuse (usually livestock grazing) pressure. In some places, this regrowth is considered a bad thing, such as in parts of Europe where the grasslands that may have been grazed for centuries are valuable in their own right. In Australia, this regrowth is generally considered a good thing for biodiversity as it represents a transition back to the pre-cleared vegetation state. However, the regrowth stand is often structurally simplistic with a high density of stems the same size. These stems grow more slowly than in natural systems due to competition between them. This competition also suppresses the understorey vegetation, which was the focus of our research.
We evaluated our results in relation to published benchmarks of stem density and understorey vegetation cover. We found that stands with stem density greater than benchmark levels (Gibbons et al. 2010) suppress native understorey vegetation cover below its benchmark levels. Thinning stems can restore native understorey vegetation in the short term, providing the soil seedbank has not been removed and there is no excessive grazing. This is the desired outcome from thinning, but the catch is that BOTH native and exotic species can recover following thinning. In places that were weedy prior to the dense stand forming, or are adjacent to highly weedy areas, this could result in a negative impact of thinning on the understorey. Land tenure and environmental factors also influence the response of stands to thinning treatments, so although some very positive outcomes can be achieved, much needs to be considered before thinning is applied to any particular stand.
We hope you enjoy the paper! Please feel free to contact me regarding any of this work.
Gibbons P., Briggs S. V., Murphy D. Y., Lindenmayer D. B., McElhinny C. & Brookhouse M. (2010) Benchmark stem densities for forests and woodlands in south-eastern Australia under conditions of relatively little modification by humans since European settlement. Forest Ecology and Management 260, 2125-33.