[permaculture] Prairies and Forests

Bob Howard rmhoward at omninet.net.au
Wed Jul 10 04:54:21 EDT 2002


the following abstract was published in Nature 2 May 2002 - i've copied it as you
would need to register to read it from the web address.

[start Nature]
Feedback with soil biota contributes to plant rarity and
invasiveness in communities

JOHN N. KLIRONOMOS

Department of Botany, University of Guelph, Guelph, Ontario, Canada N1G 2W1

Correspondence and requests for materials should be addressed to J.N.K. (e-mail:
jklirono at uoguelph.ca).


Understanding the relative abundance of species in plant communities is an
unsolved problem.
Mechanisms such as competition, resource partitioning, dispersal ability and
predation
tolerance do not adequately explain relative abundance under field conditions.
Recent work
suggests that interactions between plants and soil microbes is important. Here I
show that such
interaction explains a significant proportion of the variance in the relative
abundance of species
in plant communities. Rare plants exhibited a relative decrease in growth on
'home' soil in
which pathogens had had a chance to accumulate, whereas invasive plants benefited
from
interactions with mycorrhizal fungi. Some plant species accumulate pathogens
quickly and
maintain low densities as a result of the accumulation of species-specific
pathogens, whereas
others accumulate species-specific pathogens more slowly and do not experience
negative
feedback until plant densities reach high levels. These results indicate that
plants have different
abilities to influence their abundance by changing the structure of their soil
communities, and
that this is an important regulator of plant community structure.

[finish Nature]

As this suggests soil biota may be a determining factor. Fire it has been noted
has a marked affect on Australian soils - consider that in W.A. the dibbler
(antechinus sp)  today exists only in an unburnt patch of the Two People's Bay
National Park because it lives on the fungus that grows in the soil.

the change in burning patterns from those used by Noongar people to those
practiced by whitefellas is basically the cause of its decline along side of
clearing for agriculture.

I do really think that one needs to discuss the inseparability of habitat and
species in a discussion about species extinction - also there are no general rules
about fire versus other ways of clearing. As the dibbler demonstrates - it
coexisted with a fire regime practiced for 30,000 years - within 200 years of
subtle but significant changes in the fire regime and the fragmentation of it''s
habitat and it's now dependent upon a regime that is quite artificial compared to
the previous 30,000 years i.e no fires at all.

regards

Bob Howard





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