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Soil disturbance by native mammals and the germination and establishment of plant species


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Pyrke, A 1994 , 'Soil disturbance by native mammals and the germination and establishment of plant species', PhD thesis, University of Tasmania.

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This thesis investigates disturbances created by the digging of small
native mammals and their role in the germination and establishment of native
plant species in eastern Tasmania, with a particular focus on species considered
to be rare or threatened. At least 15 rare and endangered plant species live in
habitats where digging appears to be common. Soil disturbances, which are
created by bettongs, bandicoots and echidnas, can be prolific, particularly on
soils of lower fertility. Turnover rates of up to 2.9% of the ground surface per
annum were recorded. Diggings by bettongs, and to a lesser degree by
bandicoots, are spatially associated with trees in dry sclerophyll and grassy
woodlands and forests. The understorey varies in species composition
depending on the degree of tree influence, so not all understorey species are
close (at the scale of several metres) to where digging disturbances are most
Digging creates small patches of bare ground which, on sandy soils,
can be a harsh environment with low nutrient and moisture availability.
However, diggings provide better conditions for the germination of many
species, particularly those with small seeds and perhaps also some species
which have hard-seeded dormancy. This latter effect may be a result of the
considerable soil heating imposed by direct solar radiation on bare soil. Several
species had higher densities of seedlings on animal diggings, although
mortality rates were generally very high on both digging disturbances and
undisturbed areas. Seedlings died faster, at the same rate, or slower on diggings
compared with undisturbed areas, depending on the species and the
circumstances. Simulated animal disturbances proved to be effective in
stimulating germination, and more substantial survival of seedlings was
recorded in these experiments than on natural diggings.
Many plant species in this study have seed stored in the soil at depth.
Digging probably brings buried seed to the surface which would otherwise
not germinate.
Rare or threatened species which were found to benefit from either
natural diggings or simulated disturbances included Lepidium hyssopifolium, L. peudotasman icum, L1siopetalum micranthum, Vittadinia muelleri and Velleia
paradoxa. No rare species appeared to be completely dependent on animal
digging for a regeneration niche, but the potential exists to use mechanical
disturbance as a management tool for some species.
The density of an exotic annual grass, Briza maxima, was considerably
less on larger digging mounds compared with undisturbed areas, even three
years after the creation of the mounds. There was evidence that native seedlings
were experiencing less competition from B. maxima on these mounds and
perhaps have a better opportunity for establishment.

Item Type: Thesis - PhD
Authors/Creators:Pyrke, A
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