Quantification of landform heterogeneity and its relationship with ecological patterns in broad-scale post-mine rehabilitation

Abstract

Broad-scale surface mining of minerals and quarrying for construction material is usually associated with significant alteration of topography and substantial disturbance to ecological systems. Post-mining ecological rehabilitation typically starts with reconstruction of topography. A fairly common industry practice has been to use landform elements such as plateaus, terraces, and gentle slopes to assist with stabilizing unconsolidated mine waste material. However, this approach often leads to the generation of uniform landform features that do not typically reflect those in natural landscapes. Previous research in undisturbed and agricultural landscapes shows that ecological attributes and diversity is positively correlated with landform heterogeneity. The objective of this thesis was to investigate if those findings were still valid in post-mining rehabilitated landscapes using information and knowledge captured from a history of sites mined for heavy mineral sands on North Stradbroke Island (NSI), in Southeast Queensland, Australia, as an example. Nine rehabilitation blocks varying in age, location and management practices were selected for study. Landform heterogeneity indices (LHIs) were identified and new indices were developed to quantify landform heterogeneity. LHIs were derived through analysis of three landform characteristics (relief, slope, aspect) using remote sensing data. The ecological indicators like native species richness, vegetation density, vegetation and soil cover represented the ecological patterns in rehabilitating landscapes and were measured through field surveys. The research hypothesis stated that greater heterogeneity in landform characteristics (relief, slope and aspect) positively influences ecological patterns across the post-mine rehabilitating landscapes. The underlying assumption is that greater landform heterogeneity may lead to qualitative and quantitative diversity of environmental parameters essential for the occurrence, establishment, sustenance and survival of different species, thereby improving the ecological recovery on post-mine lands. The results indicated that the LHIs proved to be very effective in quantifying even subtle differences in landform profiles. The analysis showed correlations between some combinations of landform heterogeneity indices and ecological variables with sensitivity to the spatial scale of investigation. These correlations varied both in direction and strength among the different rehabilitation blocks. In some blocks landform heterogeneity contributed up to 77% of the variance in particular ecological measures. When some of other dominant drivers of ecological patterns in rehabilitation, such as rehabilitation practices, soil characteristics and seed mix, were included in the analysis, landform heterogeneity stood out as a major significant contributor in explaining the variance case of all ecological variables. Thus, while some of the primary drivers of post-mining ecological development and success (for example, climate, substrate and rehabilitation practices) are difficult to control over extensive areas and extended time periods, landform heterogeneity may provide a tool to indirectly control the micro-environmental parameters that may encourage an improved ecological outcome. This theory can be further tested by conducting similar studies in different bio-geographic environments and post-mine landscapes to ascertain the degree to which these relationships between landform heterogeneity and ecological indicators identified in this study are generic, and the level to which relationships are sensitive to local bio-geographic conditions and substrates. The measurement and potential opportunity for manipulation of landform heterogeneity in post-mine landscapes may provide a simple and effective tool for improving ecological rehabilitation that will be of benefit to the industry, Government and local communities. Apart from the value that the insights from this study could bring to post-mining landscapes, this approach could also be applicable for other broad-scale ecological restoration projects where the capacity to influence landform shape and dynamics and hence micro-environments and micro-climates may exist.