Assessment criteria and successional pathways for rehabilitation after manganese mining on Groote Eylandt, Northern Territory

Abstract

Groote Eylandt Mining Company (GEMCO) operates a manganese mine on Groote Eylandt in the Gulf of Carpentaria in northern Australia. The land is rehabilitated after mining, the pre-existing eucalypt-dominated woodland being the target ecosystem and land use. The success of the rehabilitation has been variable, with many areas failing to develop toward a mature natural woodland ecosystem due to a number of factors. Issues have included varying rehabilitation goals over time; acacias, grasses and weeds out-competing the target eucalypt keystone species, and high grass biomass resulting in frequent intense fire, so that keystone juvenile, fire-susceptible plants are killed or suppressed. Vegetation monitoring was conducted over 2.5 years at 42 sites, including reference sites in natural woodland and rehabilitation ranging from 0.5 to 19 years of age. Univariate analysis of the vegetation data found that rehabilitation was somewhat similar to natural woodland in terms of species composition, but differed markedly in structure and the relative dominance of species. Multivariate classification and ordination analyses, based on a matrix of species composition and structural data, revealed that the 33 rehabilitated sites formed six distinct groups. These groups were ranked in decreasing similarity to woodland sites, based on location in the classification dendrogram as well as distance in ordination space. Three groups of rehabilitation sites were considered appropriate, transient states along the desired vegetation development or successional trajectory. The remaining groups were deemed 'undesirable' and unlikely to develop into the target eucalypt woodland, given the disturbance regime dominated by fire, without management intervention. ... A combination of a vital-attributes approach to the response of key species to time and disturbance by fire, with a state-and-transition (S&T) model of the identified rehabilitation groups, was used to develop a comprehensive S&T model of the observed and predicted rehabilitation at Groote Eylandt. ... The combination of vital attributes (VA) and state-and-transition (S&T) models in a VAST approach to defining successional development and assessment criteria in the rehabilitation of a natural ecosystem has considerable potential in ecological restoration elsewhere. It is applicable to a wide variety of ecosystems and land uses (e.g. mining, forestry and agriculture); it is practical, and valuable even in relatively simple, naïve form. It also has the virtue of being able to be refined and updated through repeated use and testing.