Logging of Victorian mountain ash forests increases bushfire risk

New scientific research published in September 2011 highlights that logging in Victoria’s mountain ash forests is increasing the risk of catastrophic wildfires. The cycling of logging and wildfire is creating a landscape trap where the wet forest ecosystem is being permanently converted to a new landscape replaced by other species, particularly wattle, increasing the frequency and intensity of bushfire risk.

"These changes will significantly impair ecological functions like carbon storage, water production and biodiversity conservation," said Professor Lindenmayer. "This is historically unprecedented and is beginning to dominate the mountain ash landscapes we see today."

I wrote recently about Bush fire risk and climate change. Research published in July 2011 showed that Forests play a major role as carbon sinks. In June 2009 Scientists called for protection of Victorian forests - world’s most carbon-dense. This most recent research adds greater weight to the demands of many people to cease logging of native old growth forests, particularly in the Victorian Central Highlands where over 400,000 Hectares were burnt in the 2009 Black Saturday bushfires, with the remaining intact old growth stands important as refugia for wildlife.

Professor David Lindenmayer from the ANU Fenner School of Environment and Society lead a team of world-renowned ecologists in analysing Victoria’s mountain ash forests after the 2009 Black Saturday bushfires as well as examining decades of ecological data. The researchers found that in the past century large areas of mountain ash forests have been subject to timber and pulpwood harvesting. This has created an area dominated by young fire-prone trees and increases the risk of "mega fires".

The study was peer reviewed and published in the prestiguous Proceedings of the National Academy of Sciences of the USA (PNAS) in September 2011. The paper identifies that landscape traps exist in many ecosystems and have been identified in the destruction of tropical rainforests, while examining in particular the case for Victoria's wet temperate forests.

"The interacting effects of wildfire, logging, and the combination of wildfire and logging (i.e., salvage logging) are creating a previously unrecognized landscape trap in which the disturbance dynamics of “trapped” mountain ash forest landscapes are markedly different from those before European settlement. The core process underlying this landscape trap is a positive feedback loop between fire frequency/severity and a reduction in forest age at the stand and landscape levels, leading to an increased risk for dense young regenerating stands repeatedly re-burning before they reach a more mature state. The landscape trap will potentially create irreversible changes in disturbance dynamics, forest cover, landscape pattern, and vegetation structure, and thereby lead to a major regime shift or alternative state." says the research paper.

Fig 3 Development of a landscape trap in the mountain ash forests of the central highlands of Victoria. - PNAS September 20, 2011 vol. 108 no. 38 15887-15891

"Once a mountain ash forest landscape is dominated by widespread areas of young fire-prone forest, the elevated risk for high-severity spatially contagious fire decreases the probability that the landscape can return to its former mature state, particularly under the drier and warmer conditions associated with climate change." the paper says.

A change in the forest landscape will result in significant impairment of ecological functions like carbon storage, water production and biodiversity conservation. We are also likely to see a loss in biodiversity. Without old growth trees as part of the mountain ash forests the cavities that are crucial to nesting and denning sites for many species of animals will not be available in younger trees. Younger trees also do not provide features like extensive bark streamers which are key foraging micro-habitats for wildlife. Such changes in the vegetation age range will lead to irreversible losses in habitat suitability for about 40 species of vertebrates in mountain ash forests that are dependent on large 120 to 150+-year old trees with hollows, contends the scientists.

Professor David Lindenmayer explains: "Before European settlement, the fire regime was dominated by an infrequent severe wildfire that occurred in late summer. Young seedlings germinate from seed released from the crowns of burned mature trees to produce a new even-aged stand. The researchers examined the specific example of a Landscape Trap: the Mountain Ash Forests of Victoria, Southeastern Australia."

"What we are now realising is the combination of wildfire and logging is creating a previously unrecognised landscape trap in which the behaviour of the ash forest landscapes is markedly different from that which would have occurred before European settlement.

"The core process underlying this landscape trap is a positive feedback loop between fire frequency and severity and a reduction in forest age at the stand and landscape levels caused by logging."

"Individual patches of logged forest are becoming more fire-prone and when these are taken together the whole landscape is at risk of being consumed by mega fires," he said.

Professor Lindenmayer added that the increasing prevalence of dense young regenerating stands will lead to an increased risk of severe wildfires happening more often.

"Detailed on-site measurements following the 2009 wildfires have revealed that young forest burns at higher severity than mature forest, and their analysis suggest we will see more of these severe wildfires in the future." he said. "Once a mountain ash forest landscape is dominated by widespread areas of young fire-prone forest, the increased risk for high severity widespread fire decreases the probability that the landscape can return to its former mature state – particularly under the drier and warmer conditions associated with climate change. That’s why it’s described as a landscape trap; it’s self sustaining." concluded Professor Lindenmayer.

The research paper concludes with suggestions including management interventions to reduce the probability of landscape traps developing by identifying:

• unsustainable levels of harvesting;
  
• modifications to the frequency and severity of ecological disturbances;
  
• feedbacks between altered environmental conditions and other major human factors; and
  
• severely impaired landscape processes and functions.
  

Alternatively, it was suggested human caused stressors (such as logging) should be reduced and negative interactions between both man made and natural stressors in these forest systems also be reduced where possible. This would equate to a more conservative approach to logging practices. After catastrophic events like bushfires sustained yields of natural resources (logging) would need to be reassessed to avoid creating conditions for a landscape trap.

Sources:

• Adapted from Media Releases, ANU News, 12 September 2011 - Forest logging increases risk of mega fires
  
• PNAS September 20, 2011 vol. 108 no. 38 15887-15891 - Newly discovered landscape traps produce regime shifts in wet forests - Full article available via Open Access
  
• Image - Logging coupe in the forests of the Central Highlands of Victoria October 18, 2009 - from Flickr Creative Commons (CC BY-NC-SA 2.0)
  
• Image - Mountain Ash with cars from Wikipedia (Public Domain)