Effects of coarse woody debris on understorey plants in a temperate Australian woodland

Question: Does coarse woody debris (CWD) modify adjacent understorey plant moisture content, growth and species composition in extensively cleared temperate woodlands? Location: Endangered Eucalyptus melliodora-E.blakelyi woodland in southeast Australia (149 degrees 18E, -35 degrees 20S). Methods: Total understorey plant moisture content, dry biomass, foliage cover as well as species composition and richness were compared between positions adjacent to and at a reference distance away from CWD of various decay states and large-end diameters. Pre-existing CWD and CWD added in 2007 were tested. A linear mixed model was used to test the effect of CWD, CWD decay class and large-end diameter. Results: Total plant moisture content, dry biomass and foliage cover were significantly higher near CWD compared to reference distances. Although CWD did not affect total species richness, native grass richness was significantly lower and cover by exotic forbs significantly higher near CWD than at reference distances. CWD decay state did not significantly affect the measured plant attributes. CWD large-end diameter was positively related to plant moisture content and foliage cover. Conclusions: This is the first study to quantitatively determine the effect of CWD on understorey plants in a cleared temperate woodland. The results indicate that CWD could be important for the survival and growth of understorey plants within ecosystems where trees have been removed. Higher plant moisture content near CWD suggests that CWD may also be effective in protecting plants from extreme moisture loss. This effect appears to be greater for large diameter CWD. Increases in total plant moisture content, dry biomass and foliage cover appear to be rapid and may be related to soil moisture availability as well as protection from solar radiation and soil nutrient enrichment near CWD. However, changes in growing conditions near CWD may also alter competitive interactions in favour of existing exotic species. In ecosystems similar to that examined here, the likelihood of reduced native grass richness along with an increase in exotic forbs near CWD should be taken into account given that CWD may persist for decades. This is particularly true in locations where invasive exotic weeds are present.