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Restoring Jarrah Forest Trees after Bauxite Mining in Western Australia

Authors


  • Conflict of Interest Statement: J. M. Koch is a paid employee of Alcoa. G. P. Samsa has declared no conflict of interest.

Address correspondence to J. M. Koch, email john.koch@alcoa.com.au

Abstract

The overstory of the jarrah forest is dominated by Jarrah (Eucalyptus marginata) with a smaller proportion of Marri (Corymbia calophylla). There are also several smaller tree species in the areas where Alcoa mines. Alcoa’s restoration aims to restore all these species at densities similar to the unmined forest. This paper describes the establishment, survival, and growth of these trees with particular focus on Jarrah. Factors affecting the growth and form of Jarrah are also discussed. Establishment of Jarrah from seed in restored sites is variable (mean 10%), and once established, survival is high over two summer droughts (96%) and still high (mean 83%) after about a decade regardless of the presence of the Jarrah dieback disease Phytophthora cinnamomi. High establishment densities (10,000 stems/ha) show mortality rates of 22% after a decade. Growth rates of Jarrah trees are high (1.5–2.7 m2·ha−1·yr−1 basal area), similar to tree growth in unmined forest following clear-fell operations. Jarrah responds to both N and P fertilizers when very young but the response to early N application is not significant after approximately one decade. Between one- and two-thirds of Jarrahs established from seed grow into saplings, but this proportion decreases with increasing tree density. Closer tree spacing results in more single-stemmed Jarrah trees at the expense of growth. Tree seed used for restoration should be sourced from northern Jarrah forest areas with similar soil type and rainfall. Seed from outlier populations and coastal plain vegetation types should not be used.

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