Too much of a good thing: phosphorus over-fertilisation in rehabilitated landscapes of high biodiversity value

Abstract

Fertilisers supply essential nutrients lacking in post-mining substrates in nearly all terrestrial rehabilitation schemes. Regulators typically require the rapid revegetation of post-mining lands as an indicator of early rehabilitation success, mapping to perceived pathways of successful ecosystem recovery. However, we will show how this approach can lead to poorer outcomes in terms of vegetation composition and potentially, long-term issues in ecosystem biogeochemistry. Many mines exist in remote areas and on highly weathered, ancient, nutrient poor soils. Examples of these are the Fynbos of South Africa, the western and northern forests of Australia, the Campos rupestres of South America, and many tropical areas. Typically, restoration requirements in these areas require the return of a native vegetation community that existed prior to mining. This is particularly common for surface strip mining where large areas of land are cleared of vegetation annually. In this paper, we show how, where, and why over-fertilisation can occur. Based on examples from western and northern Australia, we demonstrate that the application of phosphoruscontaining fertilisers to these nutrient depleted soils can result in long-term elevated soil phosphorus, with species-specific negative impacts on plant health and growth. We show the rehabilitation benefits that can be gained by judicious fertilisation in terms of vegetation community structure and ecosystem development. Finally, to assess where these findings may have wider applicability, we identify further global regions with nutrient depleted soils, high plant diversity, and current or prospective strip mining operations.

Phosphorus supply affects seedling growth of mycorrhizal but not cluster-root forming jarrah-forest species

“…This finding also demonstrates the importance of N:P ratio in forest ecosystem development (e.g. Amazonas et al 2011), which is often overlooked in the assessment of ecosystem nutrition for restoration (Tibbett et al 2019).…”

Phosphorus uptake and toxicity are delimited by mycorrhizal symbiosis in P-sensitive Eucalyptus marginata but not in P-tolerant Acacia celastrifolia

“…These results may have broader application to the use of fertilizer for rehabilitation of other biodiverse plant communities growing on P-deficient soils elsewhere (e.g. Tibbett et al . 2019 ).…”

Characteristics and gaps in the assessment of progress in mine restoration: insights from five decades of published literature relating to native ecosystem restoration after mining

“…However, several examples suggest this may not reflect restoration of nutrient cycling functions as rapid accumulation of soil macronutrients (and in some situations nonlinear trajectories with higher levels of macronutrients in restored sites in early restoration) may be due to use of fertilizers, unnatural technosols, weed cover, or dense cover of nitrogen fixers, which has been linked to poor restoration outcomes (e.g. Silva et al 2013; Masse et al 2017; Tibbett et al 2019; Daws et al 2021). Assessments of whether biotic interactions necessary for restoration of nutrient cycling are occurring may provide a better indication of the progress of restoration of desired processes.…”