JARRAH FOREST RESTORATION IN WESTERN-AUSTRALIA - CANOPY AND TOPOGRAPHIC EFFECTS

The restoration of the northern jarrah (Eucalyptus marginata) forest a fter bauxite mining is a major objective of Alcoa of Australia Limited . The typically variable and sometimes low emergence of broadcast seed of jarrah-forest plant species may relate to microclimatic changes as sociated with mining disturbance. This study examined the effect of th e presence and absence of a canopy and topographic position in the pos t-mining landscape on the emergence of four canopy species (E. margina ta, E. calophylla, E. patens, and E. diversicolor) and related these p atterns to detailed measures of surface soil temperature and moisture. The absence of a canopy in the restoration appeared to result in adve rse microclimatic conditions for the successful early establishment of E marginata and E. calophylla from seed, particularly in the low topo graphic regions of the restoration. Emergence beneath a canopy compare d to that in the open was 17% and 6%, respectively, for E marginata an d 23% and 2%, respectively, for E. calophylla. For both species, emerg ence was also greater at upland than at lowland open restoration sites (9% and 3%, respectively, for E. marginata; 4% and 0.3%, respectively , for E. calophylla). In contrast, canopy removal and position on the topographic landscape did not reduce the early establishment success o f E. patens and E. diversicolor. Field measurements revealed that soil s were drier and that diurnal temperature fluctuations were wider in t he open restoration sites than beneath a canopy. Furthermore, cold con ditions were more frequent at lowland than at upland restoration sites , suggesting the occurrence of cold-air drainage to low-lying areas. I t is therefore possible that the field emergence patterns reflected th e lower tolerance of E marginata and E. calophylla than both E. divers icolor and E. patens to cold and dry surface-soil conditions. The ecol ogical significance and practical implications of the results are disc ussed.