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Working in dense Mesquite
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Our knowledge of the ecology of mesquite is very poor. This
is surprising given the importance of mesquite as a weed in
many tropical parts of the world, and the role a sound knowledge
of ecology can provide in developing better management strategies.
Ecology can help in predicting potential spread and impact
through landscapes, an important step in developing management
strategies, optimising integrated control strategies, improving
management of dispersal, and selecting effective biological
control agents.
Key features
It is already known that mesquite is an exceptional plant,
with many adaptations that lend itself to being a highly effective
invasive. Stand out features include:
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long-lived adults: plants over 100 years old are common
in the native range
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long-lived seed banks: under the right conditions seeds
can remain viable under the soil for many years
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excellent disperser: pods are highly palatable to a
wide range of vertebrate herbivores including livestock
(horses, cattle, sheep, goats, etc), ferals (horses, goats,
pigs) and natives (emus, kangaroos, wallabies). Viable
seeds can subsequently pass through the gut and be dispersed
in the dung
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most extensive root system of any plant in the world:
can access water at depths up to 80 m, and up to 30 m
from the base of the tree, as well as upward growing roots
to capture small rainfall events.
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large carbohydrate stores: allows even seedlings to
regrow from multiple top-kill events, such as from fire
or mechanical control
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Mesquite seedlings sprouting
in horse dung
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New insights
Ecological research was initiated by CSIRO in the Pilbara
region in 1998, through the PMMC and in collaboration with
DAWA, and the University of WA. Research is ongoing, but important
findings to date include:
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mesquite is very long lived, with mortalities rare among
all size classes since 1998 despite prolonged drought
and defoliation by the leaf-tying moth. This will have
important consequences for management, and suggests that
any new biological control should aim to dramatically
reduce adult longevities.
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mesquite seed banks in the Pilbara are surprisingly
low, typically well under 50 seeds/ sq m, even around
cattle troughs and under dense mesquite. It is not yet
known whether low seed banks are typical of mesquite,
or the result of leaf-tier activity.
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mesquite seedlings can emerge and become established
after only a single rainfall event. Once they are over
ca 30 cm they are essentially drought-proofed.
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mesquite infestations can reach very high densities,
up to ca 20,000 plants per ha. A significant proportion
of those are juveniles that remain essentially quiescent
until the adult canopy is removed. This has important
consequences for management.
Current research
The ecology of different species or hybrids of mesquite in
Australia is likely to differ in important respects, such
as reproduction, seed bank dynamics and responses to stresses.
Comparative ecological research is commencing in 2004 in other
core infestations in Australia to test this. Study sites will
be located within hybrid infestations (north Queensland),
P. pallida infestations (north Queensland) and a P.
velutina infestations (south-west Queensland).
Ultimately predictive models will be developed to predict
spread and impact of different mesquite species and hybrids
through landscapes, and help optimise and cost management
strategies. It is intended that this research will assist
in mesquite management throughout the tropics.
References
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van Klinken, R.D. and Campbell, S. (2001). Australian
weeds series: Prosopis species. Plant Protection
Quarterly 16 (1), 1-20.
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Osmond, R., Campbell, S., and van Klinken, R.D. (2003).
Mesquite: ecology and threat. In Mesquite Best Practice
Manual.
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Gardner, G., Spafford Jacob, H., Steadman, K.J., and
van Klinken, R.D. (subm.). Effect of temperature, scarification
and light on germination of seeds of three mesquite (Leguminosae:
Prosopis spp.) hybrids naturalized in Australia.
The Fourteenth Australian Weeds Conference.
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Gardner, G., Spafford Jacob, H. and van Klinken, R.D.
(subm.). Seed bank of mesquite (Leguminosae: Prosopis
spp.) in the Pilbara Region of Australian rangelands.
The Fourteenth Australian Weeds Conference.
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Mesquite Best Practice Manual (2004)
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