Urban Heathlands

The Effects of Urbanisation on Leptospermum myrsinoides Heathland in the South-Eastern Suburbs of Melbourne (2000)

Heathland dominated by the Heath tea-tree (Leptospermum myrsinoides) was once widespread in the area now covered by the south-eastern suburbs of Melbourne. It is now highly fragmented and exists as a range of different sized remnants in urban and rural landscapes. Working with Mark McDonnell and Nick Williams, Gemma Phelan completed an Honours project investigating the effects of urbansiation on these heathlands. Her study addressed three questions:

1. What are the landscape and environmental differences between heathland patches in the south-eastern suburbs of Melbourne?
2. Do urban and rural heathland patches differ in terms of species composition and structure?
3. Are differences in the species composition and structure of heathland patches related to landscape and environmental difference?

Gemma assessed the vegetation composition and structure of sixteen heathland sites. Statistical analyses of the data revealed that patches of urban heathland differ from patches of heathland in rural landscapes in species composition and structure. Although environmental variables including climate and soil nutrient levels vary between sites, the differences in the vegetation could not be attributed to environmental variation between sites.

Among the findings of the study are:

In the absence of a recent fire, species diversity is much lower in urban heathland than rural heathland. However, when a fire has passed through the vegetation within 16 years, species diversity and quality does not differ markedly between urban and rural patches.

As a general trend, burnt rural patches consist of a diverse shrub layer with many co-dominant species, while burnt urban patches have a shrub layer that is dominated by a single species, Showy Bossiaea (Bossiaea cinerea ), with other shrubs present at much lower abundance levels. Rural patches that have not been burnt recently typically retain a diverse array of shrubs and herbs whereas unburnt urban patches lack a shrub layer, having instead, a dense canopy completely dominated by the Coastal tea-tree (Leptospermum laevigatum).

The findings of this study have important implications for the management of remnant urban heathlands. Current management practices, although ensuring a degree of vegetation quality, have not maintained urban heathland patches at the quality of those in rural landscapes. The greater effect of urbanisation on unburnt than recently burnt vegetation indicates the need for regular burning to be implemented, in part to remove the dense canopy of L. laevigatum that suppresses most other heathland species.

The Effects of Urbanisation on the soil seed bank of Leptospermum myrsinoides Heathland in the South-Eastern Suburbs of Melbourne

Tom Browning, a University of Melbourne honours student supervised by Dr Mark McDonnell, continued ARCUE's research into the effect of urbanisation on the heathlands of south-eastern Melbourne with a project investigating the effect of urbanisation on the soil seed bank of the heathland. Specifically, he aimed to determine the composition, the effect of fire exclusion and the effect of edges on the soil seed bank of the heathland remnants and whether the effects vary between urban and rural sites.

To do this, Tom collected soil samples from burnt and unburnt sections of six heathland sites in urban and rural areas south-east of Melbourne. The soil samples were treated with heat and smoke, which are known triggers of germination of the seeds of many heath species, and transferred to a glasshouse. The emergent seedlings were identified and counted.

In total, seeds of 97 species germinated. At urban sites, the composition of the soil seed bank displayed strong variation between burnt and unburnt sections of vegetation, with seeds of very few heath species germinating in the soil of unburnt areas. This is due to the fact that, in the absence of fire, urban heathlands become dominated by a dense canopy of L. laevigatum which excludes almost all other species. Leptospermum laevigatum had not invaded the rural sites, which displayed much less variation in the soil seed bank between burnt and unburnt sections of the vegetation. The edge effect on the soil seed bank heathland that has been burnt in the last 16 years was found to be less than ten metres wide. There was some evidence to suggest that edge effects are wider in unburnt areas or rural heathlands.

In terms of vegetation management, the results of this study suggest that L. myrsinoides heathland needs to be burned at least every 16 years in order to maintain a soil seed bank with abundant seed of heath species. It may also help to keep the vegetation dense at the edges, reducing invasion of non- indigenous species.