Disturbance history and stand dynamics in tall open forest and riparian rainforest in the Central Highlands of Victoria

Abstract

Spatial heterogeneity in the intensity of past disturbances has directly influenced the structure and composition of present-day forests around the world. In south-eastern Australia infrequent, high-intensity wildfires are a major part of the historical disturbance regime. While these fires are often assumed to produce even-aged stands, spatial heterogeneity in fire intensity due to highly variable topography may lead to more complex forest age structures. Our study describes the influence of disturbance on the age structure and dynamics of a mosaic of tall, open eucalypt forest, cool temperate rainforest and mixed species forest surrounding Bellel Creek in the Central Highlands of Victoria using dendrochronological techniques. We were particularly interested in the impacts of the 1939 Black Friday fire and its effects on forest age structure and subsequent stand development patterns. Within our study site tall open forest displayed two distinct age cohorts: (i) trees that established immediately after the 1939 fire and accounted for the majority of individuals in the forest, and (ii) scattered groups of older trees estimated to be approximately 200-250 years old. Cool temperate rainforest and mixed forest were also dominated by the post-1939 fire age cohort. However, a greater proportion of trees in these forest types survived the 1939 fire relative to the tall open forest.The impact of the 1939 fire on the growth of surviving trees was highly variable but generally short-lived. In most cases growth decreased after the 1939 fire, but generally returned to prefire levels within 1-3 years. Non-fire disturbances were limited to small-scale branch-and tree-fall events, although the extreme snowstorm of 1977 appears to have caused extensive damage to rainforest communities. Our study demonstrates the opportunities for dendroecological studies to reconstruct historical dynamics and disturbance patterns in Australian forests and provides important insights into variation in landscape-scale fire impacts and their effect on subsequent forest development patterns.

Accounting for Biomass Carbon Stock Change Due to Wildfire in Temperate Forest Landscapes in Australia

“…However, wildfires are highly variable in extent and severity, which is reflected in current stand age structures of a mosaic of even-aged and multi-aged forests [26], [35], [36]. Even-aged stands result from widespread mortality and regeneration following high-severity wildfire.…”

Impacts of increased fire frequency and aridity on eucalypt forest structure, biomass and composition in southwest Australia

“…Eucalypt forests also exhibit multiple age cohorts of trees and distinct structural changes due to heterogeneity in fire history (Simkin and Baker, 2008). In climates where high winter rainfall is followed by a dry summer season, the distribution and abundance of tree species is primarily determined by their ability to tolerate water stress and to re-establish after disturbance (Pigott and Pigott, 1993;Zavala, 1999).…”

Age and growth of a fire prone Tasmanian temperate old-growth forest stand dominated by Eucalyptus regnans, the world's tallest angiosperm

“…In Tasmania, analyses of short term relationships between fire and climate revealed that summer rainfall and indices of the El Nino-Southern Oscillation are important climatic factors influencing the area burnt each summer (Nicholls and Lucas, 2007). Simkin and Baker (2008) demonstrated the use of dendrochronology for precisely deter- Fig. 9.…”

“…Hemstrom and Franklin, 1982;Silla et al, 2002;Winter et al, 2002). Old-growth Eucalyptus regnans forests appear to conform to the pattern of infrequent and intense stand replacing fires, yet the precise dates of pre-European fire events which are crucial for characterising the fire regimes of these forests remain largely unknown Simkin and Baker, 2008), reflecting an Australiawide paucity of dendrochronological studies (Pearson and Searson, 2002) and difficulties in applying classical dendrochronological techniques to eucalypts (Brookhouse, 2006). Understanding the return times of stand-replacing fires in E. regnans forests and their relationship with prevailing climatic conditions is critical for contextualising catastrophic fire events in south eastern Australia, such as the recent February 2009 'Black Saturday' fires that burnt vast areas of forest in Victoria, south eastern Australia, with the loss of 173 lives and more than 3000 homes.…”

“…Our approach is to estimate the age and growth rates of co-occurring cohorts of E. regnans and Phyllocladus aspleniifolius (an understorey rainforest conifer) in an old-growth forest stand by applying a range of mutually reinforcing and independent dating techniques, namely; cross-dating of both E. regnans and P. aspleniifolius tree-ring series using dendrochronological techniques (Fritts, 1976;Fritts and Swetnam, 1989) and radiocarbon dating of sections of these cross-dated tree-ring series (Hua, 2009). P. aspleniifolius has been shown to be suitable for dendrochronological reconstructions using classical cross-dating techniques (Allen et al, 2001) but previous attempts to cross-date E. regnans have not been successful (Brookhouse, 2006;Simkin and Baker, 2008). We then use our findings to (a) evaluate previous estimates of the age of old-growth E. regnans trees (b) consider the implications for the model of forest succession proposed for E. regnans-rainforest systems and (c) consider the implications for the fire regimes and carbon storage of E. regnans forests.…”