Victorian Box-Ironbark forests and woodlands have higher densities of small stems and a paucity of old-growth characteristics, such as large, hollow-bearing trees, in relation to pre-European forests.  Since old-growth vegetation provides high quality habitat for many vertebrate species, managers want to expedite the development of these characteristics.  Managers believe that a new management technique, “ecological thinning”, will decrease competition and assist in the restoration of Box-Ironbark forests and woodlands because retained stems should grow faster than stems in non-thinned stands.  However, thinning trial results will be inconclusive in the short term due to the slow growth of Eucalyptus species.

The primary aim of our study is to model the probabilities that management actions will change current stands into higher quality habitat.  To do this, our models predict how ecological thinning, current timber harvest practices, and natural disturbances affect vegetation structure over time.  Expert knowledge was used to construct models due to the dearth of relevant stand dynamics data.  We quantified stochastic variation, within-expert variation and between-expert variation to see how uncertainty affected model predictions.   

Results/Conclusions

We found that the majority of uncertainty in model predictions was due to between-expert variation.  We also found that model predictions for ecological thinning were far more uncertain than predictions for current management or natural disturbances.  As a result, our current models predict that ecological thinning could be detrimental to stand development.  Thus, we cannot recommend ecological thinning as a strategy to increase old-growth characteristics in Box-Ironbark forests and woodlands.  However, as monitoring data are collected, we can update our models and reduce the uncertainty in predictions of the long-term effects of ecological thinning on vegetation development.