Comparisons of vegetation recovery post-fire, logging and salvage logging in the Victorian Central Highlands

Abstract

ABSTRACT

Disturbance is an important ecological driver of plant community composition and adaption. My research was in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands in Victoria where the primary forms of disturbance are wildfire and clearfell logging. Three large conflagrations in 1939, 1983 and 2009 resulted in uniformly aged stands of Eucalyptus regnans. My research, comprising four interrelated studies, uses these major fire events and recent logging, to compare the recovery attributes of the plants in Mountain Ash forest.

Chapter one compares plant species richness and functional group responses to logging and fire of different intensities. I found species richness declined across a 'disturbance gradient' of low severity fire (30.1species/site), high severity fire (28.9spp/site), clearfell logging (25.1spp/site) and salvage logging (21.7spp/site). The greatest differences between the effects of fire and logging are on sprouting species including ferns and midstorey trees, with logging causing a simplification of the forest biota. Species losses are attributed to the mechanical disturbance of harvesting and the fire/logging disturbance sequence.

Chapter two studies growth rates of tree ferns, Cyathea australis and Dicksonia antarctica. Five years after the 2009 fires, I measured the new growth of 335 tree ferns and found Cyathea australis averaged 73(+/- 22)mm/year of growth, while Dicksonia antarctica averaged 33(+/- 13)mm/year. An unexpected finding was higher growth rates in taller tree ferns, increasing with height by 5-6mm/yr/m in both species. The non-linear growth is explained by the taller ferns being exposed to greater amounts of sunlight as the dense regeneration progressively shaded the shorter ferns.

In Chapter three, I use a chronosequence from the major fire events of 2009, 1983, 1939 and 1851 to determine how species richness and functional groups differ in forests of different ages. Species richness is highest in the youngest cohort (17.1species/plot) when many early successional species are still present. The 1983 and 1939 cohorts have the lowest species richness (12.9 and 12.5 species/plot respectively) while the 1851 cohort has 13.4spp/plot. Sprouting species such as ferns and midstorey trees were most common in the older cohorts, while seeding species dominated the youngest. The presence of 12 species unique to the two oldest cohorts suggests Relay Floristics may best describe the successional pathway of this forest.

Chapter four examined how forest age prior to a disturbance affects subsequent regeneration cohorts. Using forest burned in 2009 that was 26, 70 and 158+ years of age at the time of the fire, I found species richness decreased with forest age (25.7, 22.7 and 20.7 species/site respectively). The diverse seeding species group, was most abundant in the youngest cohort, while sprouting species including ferns were the only functional group to increase with forest age.

My research concludes that Mountain Ash forests are resilient to fire, however, keystone species that resprout, like tree ferns and midstorey trees are susceptible to logging. Sprouting species increase with time since disturbance and as with other biological legacies, sprouting species need to be carefully managed for during logging operations.