Managing kangaroo grazing for the conservation of grassland and grassy woodland fauna
Date
2016
Authors
Howland, Brett William Allen
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Abstract
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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Keywords
kangaroo, grazing, reptile, bird, grazing, grass, grasslands, box-gum woodland, grassy woodland
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