Eucalyptus decline linked to fire suppression

7 05 2010

Earlier this year I was contacted by Vic Jurskis, a scientist with Forests NSW (Australia), alerting me to the work he has been doing on fire suppression and eucalyptus decline. He shared with me several of his scientific papers that document the pre-settlement burning of eucalyptus forests by the aboriginal people, and the critical effects that fire suppression is now having on those forests. (Reprints of these papers are available. Contact me about obtaining a reprint.)

In his most recent paper Jurskis writes –

“Exclusion of fire and/or grazing has contributed to shrub or sapling encroachment, weed invasion, loss of herbal diversity and tree decline compounded by pests, parasites and diseases. The ancient trees that were established before European settlement are especially vulnerable because they have become weaker competitors for water and nutrients, whilst they are more vulnerable to fires because they typically have exposed dry wood that is easily ignited and burns readily.”

(from Jurskis, V. 2009. River red gum and white cypress forests in south-western New South Wales, Australia: Ecological history and implications for conservation of grassy woodlands. Forest Ecology and Management 258: 2593–2601.)

In another paper Jurskis states –

“Natural fire regimes stabilised eucalypt ecosystems so that they were self sustaining, whereas post-European interference has substantially changed the environment, initiating unnatural ecosystem processes. Eucalypts are declining whilst many of their arbivores and competitors are proliferating.”

And under the heading “Implications for nature conservation”, Jurskis tells it straight –

“A realistic view of ecology would recognise the imposition of unnatural fire regimes as a disturbance, and distinguish true biodiversity from an unnaturally high biomass of a few native weeds or pest animals (Jurskis 2003; Jurskis et al. 2003). Many ecological imbalances could be remedied at a landscape scale by reintroduction of more natural fire regimes (Jurskis 2005). Unfortunately ecologists and ‘environmentalists’ adhering to philosophies of ‘non intervention’ or passive management have supported misconceptions and confusion based on traditional concepts of disturbance and succession (Attiwill 1994), as well as regulation of populations by predators (White 1993). They have opposed any reinvigoration of prescribed burning in the landscape (Jurskis 2000, 2003, 2005; Jurskis et al. 2003). This, together with controversies resulting from the recent widespread and disastrous fires resulting from ‘non intervention’ (e.g. Cheney 2005), will make it difficult to implement practical solutions to decline of eucalypt forests. “

(from Jurskis, V. 2005. Decline of eucalypt forests as a consequence of unnatural fire regimes. Australian Forestry  68:. 257–262.)

In a paper that Jurskis co-authored, which examined the differences in soil chemistry between burnt and unburnt eucalyptus forests the authors report –

“The pH of the surface soil (4.4 in 1:1water) in the regularly burnt area was higher than in the unburnt area (pH 4.1) and the exchangeable aluminium also differed (0.62cmol-1 in the burnt area and 1.3cmol-1 in the unburnt).”

(from Turner, J., M. Lambert, V. Jurskis, H. Bi. 2008. Long term accumulation of nitrogen in soils of dry mixed eucalypt forest in the absence of fire. Forest Ecology and Management 256: 1133–1142.)

And in recent review paper on fire suppression and eucalyptus decline, a separate group of researchers have come to a similar conclusion –

“The main conclusions drawn from this review . . . are: (1) low fire frequencies since European settlement have promoted the development of dense, shade-tolerant midstorey vegetation (ecological drift) and the decline of overstorey eucalypts in particular areas across a wide range of forest types in temperate Australia. Where this occurs, the developed midstorey vegetation (2) competes with overstorey eucalypts for soil water, and (3) alters soil microclimate conditions that deleteriously affect overstorey eucalypt-ectomycorrhizal interactions. Thus, (4) fire plays a crucial role in controlling tree nutrient-availability by increasing soil pH and the availability of P and cations.”

(from Close, D.C. et al. 2009. Premature Decline of Eucalyptus and Altered Ecosystem Processes in the Absence of Fire in Some Australian Forests. Bot. Rev. 75:191–202.)

Unfortunately, none of these studies consider the role of mosses or lichens in the ecosystem. I asked Vic Jurskis if he knew of any studies that quantified mosses or lichens in the eucalyptus forests he was working on and he replied that he was not aware of any measurements. But there is an interesting hint, in one of this papers he mentions that –

“Trees growing low in the landscape on soils with poor drainage and aeration were especially predisposed to decline.”

(from Jurskis, V. 2005. Eucalypt decline in Australia, and a general concept of tree decline and dieback. Forest Ecology and Management 215: 1–20.)

Interesting, as these are precisely the places you tend to find lots of mosses and lichens.

So there seems to be pretty compelling story coming out of Australia that eucalyptus decline, like oak decline here in California, is linked to fire suppression. Doesn’t it make you wonder why researchers aren’t looking more closely at fire suppression effects on Sudden Oak Death disease or Oak Wilt disease?

These studies together make a solid case for implementing fire mimicry practices in tending our fire-adapted forests here in California.

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