Geoecological Zonation of Revegetation Enhances Biodiversity at Historic Mine Sites, Southern New Zealand

Abstract

Rocks exposed by mining can form physically, mineralogically, and geochemically diverse surface substrates. Engineered mine rehabilitation typically involves covering these rocks with a uniform layer of soil and vegetation. An alternative approach is to encourage the establishment of plant species that are tolerant of challenging geochemical settings. The zonation of geochemical parameters can therefore lead to geoecological zonation and enhanced biodiversity. Abandoned gold mines in southern New Zealand have developed such geoecological zonations that resulted from establishment of salt-tolerant ecosystems on substrates with evaporative NaCl. A salinity threshold equivalent to substrate electrical conductivity of 1000 µS separates this ecosystem from less salt-tolerant plant ecosystems. Acid mine drainage from pyrite-bearing waste rocks at an abandoned coal mine has caused variations in surface pH between 1 and 7. The resultant substrate pH gradients have led to differential plant colonisation and the establishment of distinctive ecological zones. Substrate pH <3 remained bare ground, whereas pH 3–4 substrates host two acid-tolerant shrubs. These shrubs are joined by a tree species between pH 4 and 5. At higher pH, all local species can become established. The geoecological zonation, and the intervening geochemical thresholds, in these examples involve New Zealand native plant species. However, the principle of enhancing biodiversity by the selection or encouragement of plant species tolerant of diverse geochemical conditions on exposed mine rocks is applicable for site rehabilitation anywhere in the world.

Success in restoring native plant communities on kimberlite mining dumps in the Afro‐alpine Drakensberg region of Lesotho

“…Furthermore, the observed plant species assemblage could have been a result of geoecological zonation (i.e. the influence of rocky mining material on vegetation patterns), as reported by Craw and Rufaut (2021) on the mine dumps in New Zealand, thus suggesting that other species will only colonise as the environment is ameliorated by these pioneer species over time. Generally, the natural post-disturbance recovery of vegetation in alpine ecosystems is slow owing to harsh environmental conditions, short growing seasons, and the slow rate of the biological processes (Krautzer et al, 2012;Mokotjomela et al, 2009;Ntloko et al, 2022).…”

Evolution of Alkaline Mine Drainage and Unique Biodiversity on Soil-Free Mine Substrates, Southern New Zealand

“…In our previous work on this topic, we outlined the general principles of this approach to biodiversity-enhanced rehabilitation for acid and circumneutral mine drainage (Craw and Rufaut 2021;Rufaut et al 2018). We also developed a regional scale understanding of the geochemical processes that lead to formation of alkaline saline substrates above a wide range of rock types (Craw et al 2022a(Craw et al , b, 2023).…”