What factors influence the extent of midstorey development in Mountain Ash forests?

The midstorey is a critical component of the structure of many kinds of forest globally. We constructed statistical models of the factors influencing the percentage cover of two dominant Acacia spp. (Montane Wattle [Acacia frigiscens]) and Silver Wattle [Acacia dealbata]) in the midstorey of Mountain Ash (Eucalyptus regnans) forests in mainland south-eastern Australia. We modelled the influence on the percentage cover of two these two species of Acacia of : (1) the age of the overstorey eucalypts (which corresponded to the time elapsed since the last major stand-replacing disturbance), and (2) environmental drivers (slope, aspect, elevation, and topographic wetness).

Stand age was an important factor influencing the percentage cover of both Montane Wattle and Silver Wattle. We found evidence of a non-linear, humped-shaped percentage cover-stand age relationship for the percentage cover of Montane Wattle, with the highest values in stands of Mountain Ash that were 30-60 years old. The...