Genesis of an Inverted Treeline Associated With a Frost Hollow in South-Eastern Australia

A catastrophic frost in the Bonang valley, Victoria (alt. 660 m), during Aug. 1982 caused severe damage to naturally occurring trees growing within a contour-related inversion layer. All eucalypts and acacias on the valley floor and up to 6 m above it on the lowest slopes were either killed outright or suffered complete crown loss. Between 6 and 25 m above the valley floor, tall Eucalyptus viminalis. trees escaped damage if their crowns were positioned well above the inversion layer. Neighbouring trees of the slightly shorter original codominant E. radiata were so severely damaged that they were either killed or survived crown destruction only by production of trunk epicormics. Despite being wholly positioned within the inversion layer, the shorter trees of E. pauciflora generally survived without much damage, although leaf injury continued to develop for several years in some trees. Results of the final assessment 5 yr after the frost indicate that the lowest surviving E. viminalis trees, together with severely damaged E. radiata. trees, now constitute an inverted treeline separating forest above from dead trees and grassland below. This treeline is related to the 666 m contour, 6 m above the valley floor, and forms a very abrupt boundary because of the predominance of large undamaged trees of E. viminalis. The consequences of this rare catastrophic frost have implications for subalpine ecology in south-eastern Australia, especially the genesis and stability of inverted treelines.