Growth and survival of riparian plantings in relation to Weeping Willow canopy in the Upper Hunter River

Revegetation presents many challenges to managers. This is especially true in riparian systems where their dynamic nature adds a further dimension to achieving successful revegetation. There are several options available to managers to help improve the success of revegetation initiatives. For example, the benefits of maintaining the existing canopy of exotic species for native seedling survival is being recognized in many terrestrial systems (Padilla & Pugnaire 2006). This is in contrast to the previously employed standard management practice of slashing, mowing or removing pre-existing exotic species. The retention of existing canopy is likely to be particularly useful in riparian systems where the maintenance of established vegetation cover is especially important to retain the structural integrity of the channel, as well as the biological integrity of the river itself (Richardson et al. 2007). However, an established canopy may have a detrimental effect on seedling survival and growth (Padilla & Pugnaire 2006). To date, much of the research that has dealt with revegetation in riparian systems in Australia has advocated the use of River Oak (Casuarina cunninghamiana) and Eucalyptus species (Woolfrey & Ladd 2001; Webb & Erskine 2003). Hicks et al. (1999) investigated the potential of longstem tubestock of four species, Weeping Bottlebrush (Callistemon viminalis), Weeping Lilly Pilly (Waterhousea floribunda), River Oak and Water Gum (Tristaniopsis laurina). However, despite the obvious ecological benefits of diverse plantings, few studies have examined the performance and therefore the suitability, of other Australian riparian species in their home range (Webb et al. 1999). This study examines the growth and survival of seedlings of five native riparian species in relation to the presence or absence of Weeping Willow (Salix babylonica) canopy cover in order to assess their suitability for revegetation and the role of canopy cover in seedling establishment. The following hypotheses were tested: (i) there is significant variation between species in seedling survival and growth, (ii) seedling survival and growth is greater under Weeping Willow canopy than in open areas