State‐and‐Transition Successional Model for Bauxite Mining Rehabilitation in the Jarrah Forest of Western Australia

Abstract

Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah (Eucalyptus marginata) forest of western Australia for more than 35 years. Completion criteria were developed in the 1990s for native species rehabilitation, with various desirable characteristics described as the rehabilitation ages. Successional models can be useful in mining rehabilitation for predicting whether sites are developing along the desired trajectory toward the rehabilitation objective. The current rehabilitation objective is to establish a self-sustaining jarrah forest ecosystem, planned to enhance or maintain water, timber, recreation, and conservation values. The major objective of this study was to present a state-and-transition successional model that assists Alcoa to identify sites that will and will not meet identified completion criteria. Agreed completion criteria and vegetation data collected from native species rehabilitation from 9 months to 15 years old were used to construct a state-and-transition model. The model identified the various desired and deviated successional states and factors that cause transitions between these states. Five desirable and nine deviated states were identified and described in detail. Key indicators relating to desired and deviated states include eucalypt density, species richness, legume density, topsoil cover, vegetation structure, ripping depth, and tree health and form. Identified management manipulations to return deviated states to the desired successional trajectory include ripping, reseeding, replanting, weed control, and tree thinning. Some of the identified thresholds between desired and deviated states will require significant management input (e.g., reripping), whereas others require little or no input (e.g., recovery following wildfire). Of the 6,429 ha of native species rehabilitation undertaken between 1991 and 2002, 98% is on or above the desired successional trajectory. More than half of the rehabilitated area is regarded as being above the desired trajectory because of high tree density. Although these sites meet the existing completion criteria, management input may be required in the future, emphasizing the importance of identifying maximum and minimum completion criteria. The state-and-transition model of successional development is a practical but rigorous land management tool that has the potential to be applied in a wide variety of ecosystems and wide range of land uses.

Case Study: Some Lessons From the Early Development of Native Forest Rehabilitation at Three Surface Mine Complexes in Australia

“…In contrast, the bauxite rehabilitation examples of a similar age were displaying the anticipated trajectory traits towards the attainment of the target forest ecosystems irrespective of the use of the non-structural predictive criteria (Grant, 2006). It was evident from the monitoring data and a subsequent site visit in September 2014 that a forest structure was developing with the growth and development of the high-forest tree species, along with the persistence of the characteristic small shrub and ground flora associated with the target ecosystems.…”

“…For For the bauxite rehabilitation, there is greater confidence given that the structural development is towards a forest formation, so much so that the agreed predictive monitoring is currently only necessary after 9 and 15 months of establishment, thereby negating further long term commitment to monitor (Grant, 2006;Koch, 2007a). However, whilst this may account for the early stages of development, the longer term ecosystem processes of replacement cohorts remains to be demonstrated as discussed further below.…”

“…Earlier examples of bauxite rehabilitation had seemingly exhibited similar trends as the sand and coal examples referred to above. The later bauxite rehabilitation schemes had incorporated changes in rehabilitation practice whereby sowing density of competitive shrub/small tree species was reduced or the species excluded, along with an emphasis on establishing the characteristic species (Grant, 2006;Grigg, 2012). This approach has continued with further refinements.…”

Successional changes in feeding activity by threatened cockatoos in revegetated mine sites

“…Although revegetation prescriptions were not available for the other two mines, revegetation at BBM, and NBG in particular, contained even higher proportions of marri stems relative to jarrah. Longer persistence of a proteaceous understorey may be aided by lower eucalypt stem densities, which has been proposed as a climate-change adaptation strategy for the forest (Wardell-Johnson et al 2015), although minecompletion criteria for the establishment of certain numbers of potential sawlogs (Grant 2006) would need to be revised if such an approach were adopted. Regardless, revegetation practices are likely to play an important role in the future provision of cockatoo food resources in revegetated areas of jarrah forest.…”

Does habitat structure influence capture probabilities? A study of reptiles in a eucalypt forest

“…Succession at older restored sites has now progressed to the stage where active management of sites is being investigated to satisfy multiple land-use objectives (Grant 2006). Management objectives being explored include thinning and burning, which result in marked changes to habitat structure (Grant and Norman 2006).…”