RECOVERY OF SNOW GUM FORESTS AND PEATLANDS
Large tracts of vegetation in Victoria have been burnt in one or more fires since 2003. Some mountains have been burnt in more than one fire, up to three, or even four times. By comparing frequently-burnt vegetation to unburnt or seldom-burnt vegetation, it is possible to estimate the impact of fire on the structure and composition of plant populations and communities and their likely rate of post-fire recovery.
For example, between the 2003 and 2009 fires, almost all snow gum forests in Victoria were burnt, to the extent that old growth stands are now rare. Recent work that I conducted while at DSE found that multi-burnt stands have high tree density and thin stems, and although post-fire seedling recruitment is high, seedlings are likely to be outcompeted and remain in a suppressed state, reducing their ability to compensate for the loss of mature adults. At some sites multi-or thin-stemmed architecture may have become entrenched, perhaps leading to irreversible changes in stand structure. Snow gum is a tenacious niche persistor but the current outlook is one of a radical demographic shift in population structure in sub-alpine landscapes.
The outloook for bogs that were burnt for the first time since 2009 at Lake Mountain is positive, compared to sites which have multiple fires over the last twenty years or so at Mt Buffalo which show increasing dominance by woody species. Continued high fire frequency and the risk of fire at Mt Baw Baw are of significant concern.
WETLANDS
Spring wetlands on the Strathbogie plateau were surveyed and mapped using recent aerial photography to estimate their current and former extent. More than half of the original wetland vegetation in the study area appears to have been lost, probably as a result of clearing for agriculture. Nine vegetation communities were identified, with one of these uniquely confined to spring-fed mounds, not previously described in Victoria. Floristic composition was correlated with climate and site disturbance but charcoal throughout sediment cores suggested that historical disturbance regimes included fire. Forested sites at higher elevations where grazing pressure appears to have been less intense were the least disturbed sites.
Approximately 60% of the wetlands surveyed were assessed as showing signs of soil moisture loss but there was no evidence that water extraction via dams and known bores was a significant driver of current vegetation composition. Threats requiring management were related to habitat destruction and degradation, dysfunction of physical and biological processes, and changes to disturbance regimes. Establishment of native vegetation buffers and biomass management are likely to be of benefit for future management of spring wetland vegetation.
THREATENED SPECIES
A range of rare or threatened species was surveyed after the 2003/2004, 2006/2007 and 2009 bushfires to assess whether populations were regenerating. Information recorded during the surveys included population size, habitat variables, an estimate of fire severity, threats and management requirements. Species included resprouters with no persistent seed bank, seeders able to recruit from a persistent seed bank, and species with the ability to resprout and regenerate from seed. Threats were recorded in a quarter of populations; however, most of these were relatively minor - with some exceptions - notably weeds and feral animals which required strategies for management. Rapid monitoring methods were developed to determine the rate of post-fire recovery over time.
The majority of populations of most species, regardless of regeneration type, were recovering successfully after the fires with many having benefited from the stimulus to regeneration. The fires presented a unique opportunity to acquire information on the population biology and dynamics of threatened flora and their response to fire.
Kohout M., Coates F., Downe J. and Duncan, M. J. (2009) Post-fire recovery of rare or threatened flora in Victoria after the 2006 Great Divide fires. Unpublished Report. Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, Melbourne.
