Floristic patterns in coastal rainforest of Shoalwater Bay, Central Queensland

Abstract

A study was undertaken of the floristic patterns in coastal rainforest (low closed forest) of Shoalwater Bay, central Queensland. The site encompasses 60 km of coastline, extending from latitude 22° 08' 30'' to 22° 30' 0'' and longitude 150° 02' 00'' to 150° 24'' 30''. The rainforest grows on coastal Holocene sand dunes, swales and sand flats, distributed as a series of 27 discrete patches greater than one hectare along 60 kilometres of coastline. Mean patch size was 10.7 hectares (maximum 150 hectares). The flora was predominantly woody, and lacked the complex growth forms of Webb (1968). Floristic links with central and north Queensland were strong, with some species distributions extending into Malesia and the Pacific. Three physical strata, emergent (composed of trees), canopy (composed of trees, vines and epiphytes) and sub-canopy (trees, vines and herbs) were recognised. The herb layer was very poorly developed. Eighty-one species were recorded, representing 42 families and 72 genera. Sixty three quadrats were sampled across the rainforest patches to measure abundance of all vascular taxa using frequency score. Five floristic groups were defined from agglomerative classification analysis, one representing mixed forest, two representing low microphyll vine forest (LMVF) and two representing microphyll vine thicket (MVT). The vegetation at the study site was predominantly MVT. Five species groups were defined, one correlated with the mixed forest, one with the LMVF and one with the MVT. The remaining species groups represented ubiquitous and widespread species. Floristic patterns were found to be strongly influenced by three environmental variables using canonical correspondence analysis. The strongest variable was drainage, which separated the mixed forest from the vine forest/thicket. The LMVF/MVT vegetation forms a continuum along an environmental gradient, influenced by exposure to onshore-winds and landform height. The mesic/protected extreme was represented by the tallest LMVF situated in swales, whilst at the exposure/ elevation extreme was represented by wind-sheared MVT located on foredunes.