Mulga (Acacia Aneura) death adjacent to haul roads in the Northern Goldfields, Western Australia
Faculty of Computing, Health and Science
School of Natural Sciences / Centre for Ecosystem Management
Increasing numbers of mulga (Acacia aneura) deaths have been observed adjacent to mine haul roads in the Northern Goldfields, Western Australia. Although there may be several causes of tree death, it is thought that increased soil salt levels, due to watering of the haul road with hypersaline water, and/or road shadow effect are the two most likely causes. This study compared treated roads (watered with hypersaline water) and control roads (not watered) and the upslope and downslope sides of the roads. Tree canopy decline was significantly greater at treated road sites than control sites. The proportion of old dead trees was significantly higher at control road sites than treated road sites. The downslope side of roads (treated and control) showed a significantly higher proportion of both dead trees and recently dead trees. The downslope side of the treated road had significantly greater soil conductivity than the control road (both upslope and downslope) and the upslope side of the treated road. This suggests that runoff from watered roads causes salinity increases downslope, which in turn results in tree death.