Nitrogen and phosphorus fertilizer regime affect jarrah forest restoration after bauxite mining in Western Australia

Question: Removal of vegetation and disturbance of the soil profile during mining reduce nutrient pools available for plants during mine site restoration. Thus, fertilizer is needed to replace the loss of nutrients available to support vegetation establishment. Yet the application of fertilizer can promote the establishment of competitively dominant species to the exclusion of others, particularly in low-fertility ecosystems. Here, we test effects of fertilizer application rates on the establishment of jarrah forest. Location: Five restored mine pits in the jarrah forest that grows on low-fertility soils in southwest Western Australia. Methods: Nitrogen (0 and 20kg elemental N center dot ha(-1)) and phosphorus (0, 10, 20 and 40kg elemental P center dot ha(-1)) were applied factorially to 20mx20m field plots at five sites restored after bauxite mining with seeds and seedlings of jarrah forest species. Results: Two and a half years after the experiment was established, there were no effects of N application rates on species richness, percentage vegetation cover or community composition of the restored jarrah forest. In contrast, P application had a number of effects on the restored jarrah forest. Species richness was highest at intermediate P application rates (10-20kg center dot ha(-1)) and lowest at the two extreme treatments (0 and 40kg center dot ha(-1)). Higher rates of P application resulted in a higher seedling density (2.5 vs 5.0m(-2) for 0 and 40kg P center dot ha(-1), respectively) and increased plant cover. Fertilizer P also significantly affected community composition, favouring ephemerals and weeds at high application rates and re-sprouting species at lower application rates. Community composition was more similar to the restoration target (unmined jarrah forest) at 0kg center dot P center dot ha(-1) (similarity value of 36%) than at higher P application rates. Conclusions: The data suggest that, in terms of maximizing species richness and percentage cover, a P application rate of between 10kg center dot P center dot ha(-1)and 20kg center dot P center dot ha(-1)is optimal for jarrah forest restoration after bauxite mining. Additionally, the data suggest no benefit of N application at a rate of 20kg center dot N center dot ha(-1).