This study identified the factors influencing the presence, stocking rate and basal area of the southern Australian cool temperate rain forest tree myrtle beech (Nothofagus cunninghamii).
This investigation was conducted in the montane ash forests of the Central Highlands of Victoria, south-eastern Australia.
The occurrence of N. cunninghamii was measured as part of field surveys of 474 sites (2844 plots) distributed widely throughout mountain ash (Eucalyptus regnans), alpine ash (E. delegatensis) and shining gum (E. nitens) forests. Statistical analysis was employed to examine relationships between the occurrence of N. cunninghamii and measured site attributes and interpolated and derived environmental variables.
The presence of N. cunninghamii was significantly related to five variables: the age of the overstorey eucalypt stand, dominant species of overstorey eucalypt tree, topographic position in the landscape, slope and the estimated quantity of precipitation in the warmest quarter of the year. N. cunninghamii was more likely to occur in old growth eucalypt stands, in gullies and locations with high values for rainfall in the warmest quarter. In addition, there was an interaction between slope and dominant eucalypt tree species—in forests dominated by E. regnans, N. cunninghamii was more likely to occur on steep slopes whereas in E. nitens and E. delegatensis-dominated stands, N. cunninghamii was more likely to occur on flatter terrain. Statistical modelling also showed a significant positive effect of slope on both the stocking rate and basal area of the species. The stocking rate of N. cunninghamii also was significantly higher in old growth eucalypt stands.
The study demonstrated that the patterns of distribution of N. cunninghamii may be more complex than recognized previously and it illustrated the importance of multiple factors including climatic conditions, disturbance processes (as reflected through the age of the dominant overstorey eucalypt stands) and topography. Our work also shows there can be complex interactions between age cohorts of different tree species in the same stand—in this case, the dominant overstorey eucalypts and the understorey which includes N. cunninghamii stems.