Factors affecting stand structure in forests – are there climatic and topographic determinants?

Multi-aged stands are not a common structural type of mountain-ash forest in the Central Highlands of Victoria, southeastern Australia, but they are nevertheless important, particularly as habitat for wildlife. Extensive field data and information generated from spatial models of climate, topography and radiation regimes were examined to identify factors which related to the occurrence of stands of multi-aged mountain-ash forest. The probability of occurrence of multi-aged stands increased significantly ( p < 0.001) with the age of the forest. There also was evidence that multi-aged stands were more likely to occur on steeper slopes ( p = 0.01). When actual on-ground field measurements were ignored and program-generated climate, topography and radiation data only were modeled, a decrease in the shortwave radiation ratio (a measure of the estimated solar radiation budget) was associated with a significantly increased probability of occurrence ( p = 0.03) of multi-aged stands. Our analyses indicated there are particular parts of mountain-ash forest landscapes where complex multi-aged stand structures are more likely to develop. This has implications for the methods used to harvest mountain-ash forests for timber and pulpwood, particularly the need for increased retention of structural components of stands targeted for logging.