Does the removal of 'Lantana camara' influence eucalypt canopy health, soil nutrients and site occupancy of a despotic species?

Abstract

Weed removal experiments provide strong evidence for weed impacts, validating management techniques and demonstrating the means by which biodiversity can be maintained. We examined the effects of removing Lantana ('Lantana camara') through herbicide application in eucalypt-dominated sclerophyll forest and, then measured the response of soil carbon and nitrogen levels, tree canopy health and the density of Bell Miners ('Manorina melanophrys') a bird species thought to amplify the negative impacts of Lantana on tree health. Four sites in northern New South Wales were monitored for 2.5 years. We measured Lantana health, (index of height, number of stems and leaves present), soil nutrients (nitrogen and carbon at two depths: 0-10 cm and 20-30 cm), Bell Miner density (using acoustic methods) and eucalypt canopy health (5 trees/quadrat) in six 50 x 50 m quadrats per site (n = 24; 12 treated, 12 untreated). Lantana foliage in treated quadrats was sprayed with glyphosate. Lantana showed significant reductions in health within 6 months of treatment and remained in a debilitated state compared to control quadrats for the duration of the project. Despite this, soil nutrients, Bell Miner density and canopy health did not differ between intact and treated quadrats for up to 2 years after treatment. The lack of impact on soil nutrient level or tree canopy health despite large changes in Lantana abundance in treatment sites was unexpected, and may indicate that Lantana is unimportant in shaping these measures. However, a more likely explanation is that longer term monitoring is required before the full impact of Lantana removal can be detected. The level of habitat modification following herbicide application was insufficient to stimulate relocation of Bell Miner colonies. Further investigation is required into how Lantana removal affects Bell Miner density, soil nutrient levels and canopy health in the medium to long term.