A description of coastal heath at North Head, Sydney Harbour National Park: impact of recreation and other disturbance since 1951

Abstract

The current status of heath growing at North Head. Sydney Harbour National Park, and the way in which the vegetation has been altered by recreation and other factors since 195 1, were assessed by field survey and interpretation of aerial photographs. Pattern analysis showed that mature ( 10 years since last fire) heath could be divided into two areas based on the mutual exclusiveness of Leprosperrnum laevigatum on the one hand and Restio fastigiatus and Leucopogon microphyllus on the other. Leptospermum heath tended to be found on relatively deep sandy soil. whereas Restio-Leucopogon heath was found on shallow soil with subdued local relief. The delimitation of heath types could not be accounted for by differences in fire history. Leptospermum heath was floristically less rich than Restio-Leucopogon heath (13 cf. 26 species); and both types were less rich than heath that had been burnt 1.5 years previously (36 species). Regrowth in the recently burnt heath comprised species that regenerated from seed stored in persistent capsules (873, those that regenerated from soil-stored seed ( +67%), and those that had vegetative means of regeneration (28%). A large proportion (67%) of those species in the second category were rare or absent in mature heath, whereas all of those in the first were dominant in 10-year-old heath. Restio-Leucopogon heath has been burnt approximately every 10 years since 1951, and this interval between burns should be retained to maximize floristic diversity. Leptospermum heath has been burnt only once in the same period. This type of heath would need to be burnt every 10-20 years to increase floristic diversity of vegetative plants and to reduce canopy height, although species present as dormant viable seeds would not be eliminated by a less frequent burning program. Substantial areas of heath have been removed by earthworks, and heath and topsoil have been stripped from the lower parts of the Head by run-off from compacted and sealed surfaces. Pedestrian and vehicle traffic has not had a serious impact on the vegetation. In the absence of further disturbance, heath plants have colonized ground when topsoil material has been left in situ. Introduced grasses have become established at the junction of parking areas and paths with the heath. This has probably been assisted by nutrient enrichment via imported fill material.