Re: Some musings on current local tree diseases/Pinus radiata
- Subject: Re: Some musings on current local tree diseases/Pinus radiata
- From: T* &* M* R*
- Date: Mon, 14 Jan 2002 19:44:30 +1300
david feix wrote:
> The case wtih many of California's native oaks is more
> threatening. Many species are not regenerating well
> due to changes in land use, heavy grazing pressures
> and rodents are also a major cause of young seedling
> oaks nonsurvival for species such as Valley
> Oaks(Quercus lobata), in particular.
This failure to regenerate is a major concern for NZ conservationists
also. Grazing is as you say a serious problem. We have friends who
bought a costal property with a pretty extensive natural stand of
Totatra trees (Podocarpus totara). They let much of their property out
for grazing for the first few years and the Totara grove at that time
was a bit of pleasent open parkland with short turf between the trees.
However our friends gradually became aware the trees were rather scruffy
and definitely ageing and there were just no replacements developing
anywhere in the grove.
They decided to simply fence the trees off from the animals and the
results, with no extra help, have been dramatic. The change of policy
must have occurred around ten years ago I think and by now the grass has
been shaded out or smothered by litter, the trees are growing again and
the undergrowth, not only of young Totara but of other native species as
well, is quite dramatic.
Such fencing of bush remants is becoming quite common on farms and is
encourage both by the Conservation Department and also by our leading
conservation society, Forest and Bird. If they can achieve continuous
patches running across adjacent farms, or at least only short gaps in
between groves, it helps the replenishment of native bird species as
well, as it creates corridors across country to counteract the serious
shrinkage of the natural ranges of threatened species. Some of the
rarest NZ birds are
very limited in their flight and unable to migrate overland to a new
area if their home territory shrinks below survival size.
You also mention rodents as enemies of regeneration and we have
certainly found this problem here also even though the species which
occur here (all introduced) are limited to three rats and a single mouse
(the English field mouse). Although they must take some fruit and seeds,
the major problem with the rats is their effect on the bird popoulation
as they are extremely able nest robbers and often also kill the female
as she tries to defend her eggs or brood..
The impact of the mice on the other hand is a direct threat to the
survival of plants and seed-eating birds, as they eat so much of the
seed each year.
They also greatly reduce the insect population which has its own
peculiar effects, especially in the case of rare native species. In any
areas such a offshore islands where major conservation projects are in
progress getting rid of rats and mice have made remarkable diferences to
the vegetation and
wildlife in general, so its not just enough to fence out the stock.
Moira
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata, New Zealand, SW Pacific. 12 hours ahead of Greenwich Time
