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Objective
To establish reasons for failure of trees to regenerate in the Belah-Rosewood country of western New South Wales and hence to devise strategies to ensure tree regeneration on pastoral leases.
Research
The study concentrated on the following arid woodland
tree species: Callitris glaucophylla, Cypress pine, Casuarina
pauper, Belah, Geijera parviflora, Wilga, Hakea
leucoptera, Needlewood, Acacia loderi, Nelie, Acacia
melvilei, Yarran, and Alectryon oleifolius ssp. canescens,
Rosewood.
For these species the natural composition of the associated communities were determined by reference to relatively undisturbed examples and their regeneration characteristics were determined through:
Outcome
Assessment of reproductive strategies in the field
indicate that despite the age and senescence of many of the remaining
trees, flowering and fruiting is prolific with large quantities
of seed produced in most years.
This seed viability and high production ensure the
availability of viable seed when soil conditions are suitable
for germination. Simulated grazing trials under glasshouse conditions
showed that young seedlings were reasonably tolerant of grazing
pressure and persistent defoliation was needed to kill them.
Indications are that the communities at 250 sites
across the study area have been severely depleted due to harvesting
of timber and clearing of overstorey trees in an attempt to increase
growth of grasses. The form of trees has been severely modified
through lopping for fodder and high browsing by stock and goats.
Assessment of stem diameter histograms from sites with a varied grazing history indicate that areas subjected to heavy long-term grazing have shown little or no regeneration for the past 100 years. Regeneration is particularly prolific where there has been major soil disturbance prior to good rains.
Implications
The long term survival of these communities is under
threat unless steps are taken to modify grazing levels to allow
regeneration when there is suitable climatic events such as occurred
in 1973-75. Regeneration can take place alongside moderate stock
grazing provided grazing pressure from rabbits, goats and kangaroos
can be kept at a low level.
It is too soon for exclusion plots established in
north-west Victoria and south-west New South Wales to show clear-cut
results, but there is evidence of recovery of tree dominants and
associated woody species when protected from grazing. The study
is an ongoing one.
RIRDC Project No: ULA-5A
RESEARCHER: Dr R F Parsons
ORGANISATION: La Trobe University
BUNDOORA VIC 3083PHONE: 03 479 2216
FAX: 03 479 1188PUBLICATIONS:
Batty, A I and Parsons, R F, 1992, Regeneration of Acacia melvillei in part of semi- arid south-eastern Australia. Proc. R. Soc. Vic. 104, pp89-97.
Scriven, R N, Westbrooke, M E and Bath, R K, 1992, Regrowth status and strategies for regeneration of Rosewood, Alectryon oleifolius, in western New South Wales. In Australian Rangelands in a Changing Environment. Proceedings of 7th Biennial Conference Australian Rangeland Society, Cobar.
Westbrooke, M E and Parsons, R F, 1994, Prospects for the regeneration of arid woodland trees in the semi-arid woodlands of south east Australia. Proceedings Australian Rangeland Conference, Katherine, July 1995.
Last updated: 10 October 1996
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