Management and restoration of native grassy woodland in the Midlands of Tasmania

This thesis examines the effects of agricultural and conservation management practices on grassy communities in the sub-humid, low altitude Midlands of Tasmania. The results of an extensive survey were examined to assess the effects of grazing by sheep and cattle, fertilisation and the introduction of exotic pasture species on the grassy communities. Sites were classified according to the degree of pasture conversion and the level of the main limiting nutrient phosphorus, by annual rainfall and by geological substrate. Exotic species replaced native species with increasing degrees of pasture conversion and levels of phosphorus. Effects of management varied rainfall and different geological substrates. Raunkiaer life-form groups were a useful aid in the identification of patterns of species' responses. Exotic therophytes and flat/versatile rosette hemicryptophytes were the most invasive exotic life-forms in native communities. The native species in the flat/versatile rosette and caespitose hemicryptophyte life-form groups were the most tolerant of disturbance. The effects of fertilisation alone on native communities were increased agricultural productivity but a reduction in the diversity of native species and the conservation values of the communities. At the Township Lagoon Nature Reserve, three levels of grazing pressure, light in the reserve and moderate and higher levels in adjacent paddocks, were compared. The moderate level of grazing altered species composition but native species diversity declined only under the high grazing regime. A replicated experiment, with a gas flame used to provide heat energy, compared the responses of vegetation to burning. Treatments were single bums at four different times of the year, bums at those times in two consecutive years and a no burning treatment. Phenology varied considerably between species. Burning promoted most species when it occurred a short time before main growing season of that species. In addition, most species were suppressed by burning which occurred during their main growing season or before seed dispersal. Burning in two consecutive years tended to increase the seasonal effects. The effects of weeding techniques on species and life-forms in grassland dominated by exotic species were examined over a 10 month period from spring 1991. The weeding techniques were removal of topsoil, herbiciding and burning. The effects varied between species, and depended on the protection of buds from disturbance, the presence of seed for recruitment and the conditions for growth of the species. The levels of dissimilarity between the responses of all pairs of species to disturbance in this study were calculated using the Gower metric index of dissimilarity. The degree of dissimilarity within the life-form groups was less than that between the life-form groups for only a small proportion of comparisons. Species were classified using TWINSPAN into response or functional groups based on their responses to disturbance. Groups were classified mainly by responses to agricultural management, and the responses to grazing level, burning and weed-control techniques were highly variable. The response groups were not associated with the Raunkiaer life-form group to which the species belonged. The responses of species classified into Raunkiaer life-form groups were highly variable. The life-form group was an aid to describing overall responses of species, but would be a poor predictor of the likely response of any one species to management. Active management of grasslands could be used to manipulate their species composition as many species are highly sensitive to the types and levels of disturbance. Conservation management of native grassy communities must be based on the site-specific responses of individual species to disturbance.