Plant communities,species richness and their environmental correlates in the sandy heaths of Little Desert National Park,Victoria

Plant community composition and its likely environmental controls were investigated for 200 sample plots (each 100 m²) from Mediterranean-type vegetation in the Little Desert National Park, Victoria. TWINSPAN classification revealed four readily identifiable vegetation types; mallee-broombush, heathland, stringybark open woodland, and an assemblage intermediate between mallee-broombush and heathland referred to here as broom-heath. Mallee-broombush was found on Parilla Sands characterized by high Ca levels relative to heathland and stringybark open woodlands on unconsolidated Lowan Sands. The first axis of a 2 dimensional non-metric MDS ordination also divided heathlands (high axis scores) from mallee-broombush (low scores), while the second separated these vegetation types from stringybark woodlands and broom-heath. Vector-fitting revealed significant correlations between the locations of samples in ordination space and exchangeable soil Ca, soil colour, aspect and Shannon–Weiner diversity. Highest species richness/diversity was associated with the ecotonal area between Parilla and Lowan Sands (i.e. broom-heath) where a number of species characteristic of different assemblages had overlapping ranges. The fire-sensitive conifer, Callitris rhomboidea, was preferentially located in stringybark woodland and broom-heath vegetation types. Its presence was positively associated with high species richness and aspects having a southerly component. Four Callitris stands sampled for population structure were all > 40 years old and showed evidence of interfire recruitment from seeds released by old, serotinous cones. Overall, results suggest that variations in plant community composition and structure in the eastern block of the Little Desert are primarily due to variations in soil properties associated with the distribution of the two dominant substrate types, Parilla Sand and Lowan Sand. However, the interplay of topography and fire behaviour has probably been more important than substrate type in determining the distribution and population structure of longer-lived, fire-sensitive species such as Callitris rhomboidea.