Re: Bushfires everywhere
Trevor Nottle wrote:
>
> Dear All
> Among the most interesting results were the studies of the way the fires
> travelled, the fuel loads and the burn rates of different plants and trees.
> One suggestion put forward was that broad leaved deciduous trees were far
> less likely to ignite or burn than evergreen trees, esp. pines, with high
> levels of combustible saps and resins.
Hi Trevor
One interesting thing about the NZ bush is the number of _broad-leaved_
evergreens (we have almost no native deciduous trees) and where these
predominate, such as in areas regenerating after clearence by early
settlers, they do seem to be quite effectively fire resistant. This is
very evident around Wellington, where many hills too steep for
agriculture were actually cleared in early colonial times in such places
as the Hutt valley simply to discourage suprise attacks by the local
Maori. Unfortunately intial regeneration was hampered by the spread of
imported gorse plants (used initially on the farms in the valley bottoms
as hedge plants).
Gorse is hideously inflammable and for the best part of a century the
frequent fires in it prevented almost all re-establishment of a proper
bush cover on the denuded hills. However in the last thirty or forty
years more drastic measures have been taken to curb the fires and in
many cases the bush is becoming thoroughly re-established. The early
part of the succession is almost entirely broad-leaved species, some
individuals of which have often survived juat in gullies, especialy
south-facing ones, and even where fires still occur, these little
"islands" do come through burns with little damage beyond marginal
scorching.
If they manage go for an appreciable number of years unburnt, even the
intervening ridges get invaded by broad leaved species coming up among
the gorse. In fact, if one can only keep fire out, gorse is an excellent
nurse crop, providing shade and shelter and very good N-rich mulch.
Moreover, as the bush gets higher it begins to be shaded which it can't
tolerate, and eventually just dies out naturally leaving only the
fire-resistant species behind..
Where natural or quasi-natural areas of bush still exist, fire damage is
very rare. presumably the evergreens act as a damper and protect the
more vulnerable gymnosperm species where these predominate. Those of our
forests mainly at risk are the huge acreages of pine plantations, where
constant surveillance is carried out to catch any outbreak and nip it in
the bud before serious damage can be done.
Moira
--
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata (near Wellington, capital city of New Zealand)
