Willow Sawfly Management Trials - Weeds Australia

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Willow Sawfly Management Trials - Weeds Australia

The tallest plants at this site in April 2010 were two blackwood plants (111 and 117 cm tall) andtwo wirilda plants (110 and 183 cm tall). Overall, blackwood and wirilda plants were taller thansilver wattle and swamp gum plants (Table ii, Appendix 1).A small number of plants which had been planted in the areas outside the plots had survivedintense weed competition and were growing strongly, in comparison to many of the plants withinthe plots which exhibited very poor health as a result of browsing. The average heights of theseplants ranged from 38 cm for swamp gum to 100 cm for wirilda (Table 4), with one wirilda planthaving a height of 182 cm.Table 4: Average Heights in April 2010 of Additional Tube-stock Planted Outside TrialPlots in Spring 2008 at Campaspe RiverSpeciesHeight inApril 2010 (cm)Number ofPlantsswamp gum 38 2manna gum 74 3silver wattle 57 8blackwood 70 6wirilda 100 913Although the heights of the tall sedge plants were not measured, those that were still alive inApril 2010 were in good health and growing strongly, indicating that they were well establishedat this site.1.3.4 Effect of Willow Tree Treatment on Heights and Relative Growth RatesWillow tree treatment did not affect seedling height of any species at any of the sites, indicatingthat the heights of seedlings under those willows which were stem-injected were not differentfrom the heights of those growing under untreated willows. The interaction between willow treetreatment and species was also non-significant at all sites (Table ii, Appendix 1).The relative growth rates (RGR) of the six species planted at Kiewa River were calculated toaccount for the difference between species in plant height at the time of planting. RGR were notaffected by willow tree treatment, nor was the interaction between willow tree treatment andspecies significant (Table iii, Appendix 1). However, there were highly significant differences inRGR between the species (Table iii, Appendix 1). The RGR of silver wattle, blackwood and riverbottlebrush, which ranged between 3.2 and 4.9, were significantly higher (Table iii, Appendix 1)than the RGR of river red gum, tree violet and sweet bursaria (range from 1.7 - 2.0).1.3.5 Light Environment for Tube-stockOne of the key impacts of willow sawfly defoliation of willow trees is the increase in the lightavailable to the understorey, which enhances recruitment opportunities for other riparian species.This trial was designed to test whether this change in light environment under defoliated willowswas sufficient to promote the growth of native riparian species.

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