The Big Ash forest, Wallaby Creek, Victoria— changes during one lifetime

Abstract

In 1949 the area of mature Eucalyptus regnans F.Muell¹ (the Big Ash) on the Hume Range, Victoria, was a largely even-aged 230-year-old forest with a component of the overstorey derived from a fire in 1851. Subsequent fires have resulted in patchy regeneration where suitable gaps in the overstorey were present. In 1949 three main types of the understorey were present: type A, mature Pomaderris aspera; type B, dense immature Pomaderris aspera; and type C, coppiced Olearia argophylla and Bedfordia arborescens. In type A, ground fern was patchy and statistically correlated with patches of lower density Pomaderris aspera. Over a period of 48 years the eucalypt overstorey has been depleted by death and windthrow while understorey trees and shrubs have been severely damaged by sporadic heavy snowfalls and insect and fungal attack. The type A understorey is now showing signs of changing to Olearia argophylla dominance and the cover of ground fern and tree fern strata has doubled to more than 80% over this period in spite of damage caused by infrequent, but severe, droughts. The type B understorey is now mature and resembles type A, while the type C understorey shows invasion by Pomaderris aspera and regeneration of Olearia argophylla. No successful establishment of E. regnans has occurred. The rainforest in the gullies consists of alternating patches of forest and tree fern groves, the latter, together with rotting logs and upthrown root balls, providing niches for rainforest tree establishment. In swampy flats of Leptospermum grandifolium on the plateau Atherosperma moschatum is becoming increasingly dominant. Atherosperma moschatum is also invading mature understorey adjacent to riparian communities. This species and Olearia argophylla may constitute the final stage of the long secondary succession after fire in the Big Ash area. However, the Hume Range is adjacent to drier foothills and plains to the north, west and south. Whether the Big Ash will be spared from fire in future centuries is very doubtful.