The impacts of edge effects and other disturbances on Tasmanian coastal heathlands

Widespread clearing of Tasmanian heathland for pasture and crops has resulted in small remnants within the agricultural landscape. The conventional wisdom has been that such small remnants are susceptible to adverse edge effects, particularly those related to nutrient accession, and thus are not worth conserving. Previous research into the addition of nutrients in heathlands has involved large amounts of fertiliser. In this thesis realistic experimental manipulation in the field and widespread observation of boundaries are used to determine whether there could be a future for small heath remnants. The effects of irrigating a coastal heathy woodland with sewage water were monitored. The addition of small amounts of nutrients in the wastewater caused a small increase in live plant cover but no major plant death or changes in species composition. In a manipulative field experiment, small amounts of fertilisers were added to simulate nutrient drift from pasture topdressing, and were combined with fire and weed seed treatments. There were no effects on cover, species richness and species composition. In a second manipulative field experiment, fire-fighting foam was applied in combination with burning. Foam effects included increases and decreases in canopy growth of different species, a reduction in species richness, reduced flowering and leaf damage. In all three experiments, exotic species either did not invade over the period of the study or, when weed seeds were sown, failed to establish. In a survey, the observations of heath‚ÄövÑvÆpasture boundaries showed that different management regimes affected the condition of coastal heath remnants. The major disturbance that encouraged weed invasion in heathlands was an increase in soil fertility. Stock grazing, native herbivore grazing and physical disturbance also adversely affected heath condition. However, edge effects in the form of increased nutrients and the presence of exotic species did not penetrate more than a few metres into heathland. In summary, with careful management, small heathland remnants can be quite resistant to weed invasion and are worth conserving.