Abstract

Many ecosystems around the world are vulnerable to competitive expansion by cosmopolitan colonisers (e.g. Phragmites australis, common reed) where human-mediated disturbance increases nutrient levels. Yet our understanding of the long-term dynamics within vegetation communities once this disturbance has been excluded, and how best to reduce the residual negative effects, is limited. The Great Artesian Basin (GAB) springs in South Australia offer a useful case study of vegetation responses post-disturbance because they form a collection of semi-independent ecosystems with a rich management history, from burning by Aboriginal people to pastoralism and stock exclusion from some springs since the 1980s. This paper presents a case study based on 35 years of observational data on the response of P. australis and other wetland vegetation at protected GAB springs of the Lake Eyre supergroup. The case study aims to understand how naturally present P. australis performs within GAB spring communities following stock exclusion. Where P. australis was present at the time of stock exclusion, it became monodominant across the main pool of several springs within the first decade, and expanded throughout the spring tail during the second and third decades. The endangered salt pipewort (Eriocaulon carsonii) appears to have been reduced in distribution and abundance where P. australis became monodominant. However, in two promising cases, P. australis dominance waned after 30+ years of stock exclusion and, in another, has not colonised a spring free of P. australis at the time of de-stocking despite the presence of source populations in a neighbouring spring. These findings suggest that decadal cycles of above-ground dominance followed by decline may occur in some GAB springs where P. australis was present at the time of stock exclusion. Active management of P. australis may be required, particularly where its dominant expansion phase poses a threat to species of conservation significance.