Australian plants adapted to wildfire regimes extreme in space, time, and complexity

 (writing in progress)
 
Wildfires of various kinds occur in many ecosystems, worldwide. I realise that my experience of this phenomenon is limited, and restricted to only a few landmasses.

However, I propose the following as a conceptual framework, within which readers from various parts of the world can further educate me.

It is well-known that certain Australian plants can be extremely flammable, and that these dominate extensive types of vegetation.

As far as I know, no plants indigenous to e.g. South America even remotely qualify as ecological counterparts for Eucalyptus and Triodia.

So, it seems reasonable to generalise that wildfire is a major ecological factor over much of Australia, whereas it is a minor factor in South America. On the latter continent, even the most fire-prone ecosystems - such as the cerrado and the llanos - fall short of Australia in terms of adaptation to wildfire by the dominant plants.

When it comes to the following ecosystems on other continents, the distinctions from Australia are harder to establish:

• the taiga biome in Eurasia and North America (https://en.wikipedia.org/wiki/Taiga), and
• coniferous forest and non-coniferous thicket (chaparral, https://en.wikipedia.org/wiki/Chaparral) under a mediterranean-type climate in California.

Canopy-consuming wildfires are extreme, because the living foliage of the dominant trees and tall shrubs ignites and explodes on a rapidly-moving front, which generates its own, self-propagating winds.

These canopy-consuming wildfires occur not only in forest and tall shrubland dominated by eucalypts in Australia, but also in comparable vegetation dominated by conifers, Adenostoma (https://en.wikipedia.org/wiki/Adenostoma), Arctostaphylos (https://en.wikipedia.org/wiki/Arctostaphylos), and Ceanothus (https://en.wikipedia.org/wiki/Ceanothus)

However, it seems that Australia excels in canopy-consuming wildfires spatially. This is partly because the tallest trees on Earth occurred in Australia. The species concerned (particularly Eucalyptus regnans, https://en.wikipedia.org/wiki/Eucalyptus_regnans) burns catastrophically from top to bottom as part of its normal life-cycle.

Although conifers (particularly Pseudotsuga, https://en.wikipedia.org/wiki/Pseudotsuga) in the Northern Hemisphere also have canopy-consuming fires, and grow extremely tall, the eucalypts exceed them in terms of record ‘depths’ of the canopy fire, viz > 100 m in some instances. (Of course the flames will spike far higher above ground than 100 m, possibly >150 m, but I refer to the height of the actual burning biomass.)

Wildfires in grassy strata occur on all vegetated continents - whether in savannas or in grass-dominated vegetation types.

However, hummock grasses (Triodia, https://en.wikipedia.org/wiki/Triodia_(plant)) seem without peer in terms of
I now realise that fires in Australia also set records in terms of the time dimension.

This is because the areas of hummock grassland in areas such as the Great Sandy Desert (https://en.wikipedia.org/wiki/Great_Sandy_Desert) are so vast that, once a fire starts in the east of this area and the wind then swings to easterly, the fire can burn continually/progressively for months (https://indaily.com.au/opinion/2021/12/08/the-burning-issue-of-fires-raging-in-remote-australia/ and https://www.preventionweb.net/news/we-are-professional-fire-watchers-and-were-astounded-scale-fires-remote-australia-right-now and https://www.uwa.edu.au/news/Article/2021/December/Professional-fire-watchers-astounded-by-the-scale-of-fires-in-remote-Australia).
 
I am unsure if any one fire has ever burnt across the Australian landscape for >100 days. It is possible, but I am unsure how we could confirm this. Anyway, it is a strange thought that, in fire-prone Australia, some fires burn > 100 m deep, and others burn for ?> 100 days.

Jarrah forest (https://en.wikipedia.org/wiki/Jarrah_Forest), in southwestern Australia seems to be more complex in its fire regime than any other gestation on Earth. The concurrent regimes are

• canopy-consuming fires, about once per century, that lead to cohort-replacement of the tallest trees
• fires restricted to the short, heathy understorey, more than once per decade,
• fires restricted to the understorey (including tall shrubs and low trees) and merely scorching the canopy of the tall trees, about once per two decades,
• fires continuing to burn individual trees, from the basal boles upward, for weeks, and
• fires (deliberately lit by indigenous people) restricted to 'grass-trees' of Xanthorrhoea (https://en.wikipedia.org/wiki/Xanthorrhoea).

Is there any vegetation in the western USA, Canada, or Siberia that can match such complexity in the fire regime?

https://www.tern.org.au/fire-giant-eucalypts-and-the-evolution-of-australian-forests/
https://www.sciencedaily.com/releases/2012/10/121031214005.htm
https://www.abc.net.au/science/articles/2012/11/01/3623363.htm

(writing in progress)

Publicado el julio 23, 2022 10:36 MAÑANA por milewski