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Pacific Conservation Biology Pacific Conservation Biology Society
A journal dedicated to conservation and wildlife management in the Pacific region.
RESEARCH ARTICLE

Effects of Opuntia stricta on floristic composition and diversity within Broughton Island Nature Reserve, North Coast, New South Wales

John T. Hunter https://orcid.org/0000-0001-5112-0465 A C , Briannon Hunter B and James Mitchell-Williams B
+ Author Affiliations
- Author Affiliations

A School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia.

B Hewlett Hunter Pty Ltd, Invergowrie, NSW 2350, Australia.

C Corresponding author. Email: jhunter8@bigpond.com

Pacific Conservation Biology - https://doi.org/10.1071/PC20062
Submitted: 21 August 2020  Accepted: 9 November 2020   Published online: 1 December 2020

Abstract

Aeolian sand dunes on the Broughton Island are heavily disturbed by nesting birds and invaded by Opuntia stricta (Prickly Pear). Biological control agents do not establish well on exposed coastal systems and thus herbicide treatment is currently the main control, but it is expensive in terms of resource allocation. Invasive species are generally considered by many to be controlled at all cost but in many situations, they are benign or even beneficial. We test if O. stricta causes significant change to the vegetation on aeolian sands on Broughton Island. 40100 m2 plots were placed randomly over areas of differing cover of O. stricta. Within these plots additional six subplots of 4 m2 were placed. All flora species were scored for cover. Univariate and multivariate analyses were performed testing the effects of O. stricta on floristic composition and species density and turnover. Regression models showed a non-significant (r2 = 0.95; P = 0.0557) negative effect of O. stricta cover on species density at the 100 m2 plot size and at the 4 m2 scale (r2 = 0.013; P = 0.0858). Global comparison of species density between plots with and without O. stricta at the 4 m2 scale was non-significant. Homogenisation occurred (lowered beta diversity) across plots with O. stricta presence at the 4 m2 scale. More species had their average cover reduced by O. stricta presence than those that were benefited. The scale at which the investigation was undertaken (4 or 100 m2; species density and beta diversity) affected the magnitude and significance of O. stricta on the results obtained. The scale at which investigations are made was found to be of importance. Overall, although negative changes were noted in flora species diversity and homogenisation was apparent the negative impact may not be sufficient to justify the costs and resources needed to control the species which is unlikely to be eradicated from the site.

Keywords: aeolian sand dunes, alien flora, biological control, Broughton Island, Cactoblastis cactorum, Dactylopius opuntiae, dunal communities, herbicide, invasive alien species, keystone species, Opuntia stricta, Prickly Pear.


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