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Australian National University (2016)

Managing kangaroo grazing for the conservation of grassland and grassy woodland fauna

Howland, Brett William Allen

Titre : Managing kangaroo grazing for the conservation of grassland and grassy woodland fauna

Auteur : Howland, Brett William Allen

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 2016

Résumé
Large mammalian grazers are ecosystem engineers that alter the resources available to other species through selective consumption of plant matter, redistribution of nutrients and trampling. While some level of grazing is considered critical for maintaining species diversity, alteration to natural grazing regimes can have a severe impact on native biodiversity. Restoration of grazing regimes which promote conservation of biodiversity is a priority in many protected areas. However, the ability to achieve this goal is limited by a lack of understanding of what ‘appropriate’ grazing regimes for conservation of biodiversity are. In south-eastern Australia, high intensity grazing by the native eastern grey kangaroo (Macropus giganteus) has been linked to the decline of multiple taxa. While efforts to manage the impact of kangaroo grazing on other taxa have been undertaken, the effectiveness of these interventions are limited by a lack of knowledge of what constitutes optimal grazing levels. In this thesis, I used kangaroo population counts, tree canopy cover maps, ground vegetation structure, and reptile and birds counts to investigate the relationship between kangaroos, grass structure, and fauna. I found that : 1) there was a strong negative relationship between the abundance of kangaroos and grass structure (Paper I) ; 2) high intensity kangaroo grazing had a negative effect on the reptile community (Paper I) ; 3) birds with similar traits favoured similar grazing intensities, with different grazing intensities favoured by different trait groups (Paper II) ; 4) the occurrence of a threatened grassland reptile, the striped legless lizard (Delma impar) was positively related to fine scale grass complexity, and negatively related to kangaroo density at the broad scale (Paper III) ; 5) kangaroos selected forage habitat away from roads, in areas with a high cover of short grass (Paper IV) ; and 6) line transect sampling undertaken from vehicles driven along tracks can provide an accurate method to survey the kangaroo population provided knowledge of kangaroo distribution relative to tracks is known and accounted for (Paper V). My investigation into the relationships between kangaroos, grass structure and fauna indicated that grass structure has a strong effect on many reptiles and birds, and that intervention may be needed to change kangaroo habitat selection in a way that mimics natural foraging patterns in order to promote optimal vegetation structures for the conservation of native biodiversity. Therefore, to preserve a full-complement of species in these grassy habitats, I recommend that : 1) management of grazing is based on direct measures of grass structure, not herbivore abundance, 2) the extent and duration of intense grazing is limited ; and 3) grazing pressure is rotated to create mosaics of different levels of grass structure in space and time. In making these recommendations, I emphasise that management of grazing by kangaroos will be necessary for ongoing conservation of biodiversity in grasslands and grassy woodland and that further research is needed on how to manage kangaroo grazing patterns for the conservation of biodiversity in grasslands and grassy woodlands in south-eastern Australia

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