Impact threshold for an alien plant invader, Lantana camara L., on native plant communities

Alien plant invaders significantly threaten native community diversity, although it is poorly understood whether invasion initiates a linear or non-linear loss of resident species. Where low abundances of an invader have little impact on native species diversity, then a threshold level may exist, above which native communities rapidly decline. Our aim was to assess the broadscale effects of an alien thicket-forming shrub, lantana (Lantana camara L.), on wet sclerophyll forest in southeastern Australia. Vascular plant species richness, abundance and composition were measured and compared along a gradient of lantana invasion. There was a strong negative non-linear relationship between native species richness and lantana cover, indicative of an impact threshold. Native species richness remained stable below 75% lantana cover, but declined rapidly above this threshold level, leading to compositional change. Thus, sparse lantana infestations had evidently little effect on the resident community, with impacts elicited at an advanced stage of invasion. The impact of lantana was pervasive, with all major structural groups (i.e. ferns, herbs, shrubs, trees and vines) exhibiting significant species losses; however, the rate of species loss was relatively greater for tree and shrub species, signalling a shift in vegetation structure from tall open forest to low, dense lantana-dominated shrubland. Potentially, broadscale conservation of species diversity could be achieved by maintaining lantana infestations below the 75% cover impact threshold at sites containing regionally common species that are also widely represented in non-invaded vegetation. This would enable targeted invader eradication at sites of high conservation value (i.e. those containing regionally rare species or endangered ecological communities). Disciplines Life Sciences | Physical Sciences and Mathematics | Social and Behavioral Sciences Publication Details Gooden, B., French, K. O., Turner, P. & Downey, P. O. (2009). Impact threshold for an alien plant invader, Lantana camara L., on native plant communities. Biological Conservation, 142 (11), 2631-2641. This journal article is available at Research Online: http://ro.uow.edu.au/scipapers/4978 1 Impact threshold for an alien plant invader, Lantana camara L., on native plant 1 communities 2 3 Running Head: Impact threshold for an alien plant invader 4 5 Ben GOODEN, Kris FRENCH, Peter J. TURNER and Paul DOWNEY 6 School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia 7 Pest Management Unit, Parks and Wildlife Group, Department of Environment and Climate 8 Change (NSW), PO Box 1967, Hurstville, NSW, 1481, Australia 9 Author contacts: Ben Gooden email: [email protected]; Kris French email: 10 [email protected], ph: +61 2 4221 3655, fax: +61 2 4221 4135; Peter Turner email: 11 [email protected]; Paul Downey email: 12 [email protected]. 13 Corresponding authors: Ben Gooden, Kris French. 14 15 Abstract 16 Alien plant invaders significantly threaten native community diversity, although it is 17 poorly understood whether invasion initiates a linear or non-linear loss of resident species. 1816 Alien plant invaders significantly threaten native community diversity, although it is 17 poorly understood whether invasion initiates a linear or non-linear loss of resident species. 18 Where low abundances of an invader have little impact on native species diversity, then a 19 threshold level may exist, above which native communities rapidly decline. Our aim was to 20 assess the broadscale effects of an alien thicket-forming shrub, lantana (Lantana camara 21 L.), on wet sclerophyll forest, southeastern Australia. Vascular plant species richness, 22 abundance and composition were measured and compared along a gradient of lantana 23