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Accueil du site → Doctorat → États-Unis → 1995 → Vegetation responses under goat stocking strategies to control hopbush (Dodonaea Viscosa subsp. Angustissima) in the semi-arid woodlands of eastern Australia

New Mexico State University (1995)

Vegetation responses under goat stocking strategies to control hopbush (Dodonaea Viscosa subsp. Angustissima) in the semi-arid woodlands of eastern Australia

Muir, Susan Jean

Titre : Vegetation responses under goat stocking strategies to control hopbush (Dodonaea Viscosa subsp. Angustissima) in the semi-arid woodlands of eastern Australia

Auteur : Muir, Susan Jean

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) 1995

Résumé
Hopbush (Dodonaea viscosa subsp. angustissima) is a widespread woody weed that limits pastoral viability in the semi-arid woodlands of eastern Australia. Rainfall in these communities averages 350 mm year$\sp-1,$ and soils are loamy sands. The effectiveness of goats to control hopbush was evaluated by comparing the impact of several goat and sheep stocking strategies on hopbushes and the herbage layer. The most effective goat strategy to control hopbush was the High Goat treatment, with 90% hopbush mortality under persistent heavy stocking at 1 goat ha$\sp-1$ for 33 months. Lighter browsing pressure in the Medium Goat treatment was less successful, with 30% hopbush mortality after stocking at 0.7 goat ha$\sp-1$ for 3 years. The Repeat Goat treatment, which aimed to rapidly defoliate hopbushes and then maintain browsing pressure on resprouting shrubs, killed 60% of hopbushes in 18 months. This strategy commenced stocking at 4 goats ha$\sp-1$ but rates were adjusted as forage availability declined during the next 12 months. Repeat Goat paddocks were then spelled for 3 months, until herbage growth permitted a second period of stocking at 1 goat ha$\sp-1$ for less than 2 months. Natural hopbush mortality under conventional sheep grazing was about 3% year$\sp-1.$ Severe depletion of the herbage layer during goat stocking was an unavoidable consequence for successful hopbush control, with levels $<$20 kg ha$\sp-1$ in all treatments. Herbage responses to exceptional rainfall during spelling, however, were double in High Goat and Repeat Goat treatments compared to the Sheep treatments. Hence, restricted periods of heavy goat stocking did not deleteriously affect key components of the herbage layer. Therefore, successful hopbush control depends on using a heavy goat grazing pressure, obtained by stocking at least three times conventional sheep rates for several years to promote extensive hopbush consumption. Higher stocking rates, such as the Repeat Goat treatment, causes comparable hopbush mortality within a shorter period, but also involves more complex management. In this study, goat stocking coincided with a prolonged drought, which enhanced hopbush consumption and minimized the impact on quiescent herbages. Judicious adjustment of goat stocking rates could be necessary after effective rain to maintain herbage vigor.

Mots Clés : Goats, Ecology, biological control, weeds, Biological sciences, Range management

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