Stephen Luntz in the December issue of Australiasian Science describes recent research by David Lindenmayer on the relationship between logging, fire and change in temperate forests. Unfortunately the Australiasian Science article is trapped behind a paywall, but Luntz summarizes on his blog, here.
Temperate forests can be divided into two sorts, there are those that are fire tolerant, and those that are not. – Stephen Luntz
Fire tolerant species have evolved to create a more fire prone environment. Fire destroys non fire tolerant trees, and the fire tolerant trees then colonize in the aftermath.
In contrast the non fire tolerant species have evolved to avoid the creation of fire prone situations, and large masses of these species can actually act as fire buffers.
This analysis of the relation between fire and fire tolerant species is hardly new. What is, is Lindenmayer analysis of the role of logging in the process of creating a “landscape trap”.
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 reburning 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. – Lindenmayer et al, 2011.
Lindenmayer goes on to describe the development of a Landscape Trap in Victoria’s mountain ash forests. Mountain ash forests like those in the Alpine National Park, near where I live. Mountain ash forests that have been severely burnt twice in the past decade.
Lindenmayer makes a number of suggestions for avoiding an irreversible change in the landscape. Most importantly concern logging, but of particular interest to me (I’ll explain why in a second) is this:
Given the extent of recently burned forest in Victoria, a third important strategy to reduce the risks for development of a landscape trap is to try to limit the amount of future ﬁre. Although mountain ash trees are dependent on ﬁre to promote regeneration, ﬁres have been extensive in the past 25–100 y; another ﬁre in the coming 20 y within currently young regenerating stands is likely to lead to a major regime shift.mountain ash forests is a signiﬁcant challenge.
Broad-area prescribed burning is not a viable management option because high levels of moisture in the vegetation and large quantities of biomass make planned ﬁres extremely difﬁcult to control. However, prescribed burning as part of a regime of ﬁre can be an appropriate management option in drier forest types that are adjacent to mountain ash forests. Carefully applied strategic burning in such drier environments may help to reduce the extent of spatial contagion in wildﬁre that occurs in these areas and, in turn, reduce the risk for adjacent stands of mountain ash forest being burned. – Lindenmayer et al, 2011
I grew up on a small farmlet in North East Victoria. We raised some cattle and for a short while, attempted market gardening.
Managing the fire risk of the adjacent bush land was a prominent concern for us in the lead up to each summer. We did this with yearly back burning.
It is now pretty clear that this was a mistake.
Over ten years we saw the immediate landscape change, and eventually decided to abandon the practice.
In the aftermath of the 2009 bush fires, there was a massive public clamour in rural communities for the regular burning of practically everything. In the autumn and spring that followed I saw how on private land and along roadsides of the community I grew up in, every that would burn was burnt.
I fear that the net effect of these attitudes to fire prevention among land holders could be to trade the long term possibility of a less fire prone landscape for the short term security of dust and ash.