The effectiveness of plastic fences and tree guards for reducing browsing damage: A case study from East Gippsland.  J. Di Stefano and L. Mazzer.  April 2002.  15pp. (unpubl.)

SUMMARY

Browsing of hand-planted Eucalyptus seedlings can be a serious problem in south-eastern Australia. The effectiveness of one type of plastic fence and one type of tree guard to protect seedlings from browsing was trialled at two native forest coupes in Victoria's East Gippsland. Treatment effects on browsing damage and seedling height were compared statistically 32 weeks after planting at one site (Delegate) and 38 weeks after planting at the other (Brodribb).

Seedlings in tree guards were significantly taller than control seedlings at the Delegate site (mean ± se = 66.9 ± 6.6 cm versus 36.5 ± 4.6 cm). None of the other statistical comparisons were significant, although graphical displays showed marked treatment effects in some cases. Previous studies, however, have shown that some types of fences and tree guards provide effective protection from browsing animals. It is likely that the inability of the fence and tree guard designs tested in this study to consistently protect seedlings from browsing was due to their particular construction, and not a failing of these general strategies. Consequently, appropriately designed fences and tree guards could be useful for reducing browsing damage in Victorian native forests.

Assuming a critical effect size of 50%, retrospective power analysis indicated that the number of replicates used in this study (3 per treatment) was inadequate. Consequently, all non-significant results should be considered inconclusive. A priori power analyses using estimates of population variance derived from the existing data indicated that the number of replicates per treatment (95% CI) required to detect an experimental effect of 50% with a power of 0.80 was 58 (32-137) for browsing data and 43 (23-115) for height data. It is recommended that if possible, a priori power analysis should be used in the planning phase of ecological field experiments.