Mound springs in the Dawson River Valley, Queensland. Vegetation-environment relations and consequences of a proposed impoundment on botanical values

Boggomosses are perennial mound springs in the Dawson River Valley, Queensland, an area subject to seasonal and often more prolonged drought. The results of a vegetation survey of the boggomosses are presented and assessed in relation to an impoundment proposed for the area. A classification of site-species data defined four boggomoss communities having distinct associations with soil texture and fertility, landscape position and possibly the age of springs. A measure of biogeographic significance was assigned to the plant species on the basis of rarity, isolation, affinity with the coastal flora and latitudinal limits. An impoundment at the maximum proposed height of 185 m would: a) inundate about 58% of the total number of springs; b) inundate 62% of significant community 1 springs that have high conservation significance; c) inundate all boggomoss populations of 26% of native plant species; d) inundate 30% of the boggomoss populations of the species that currently have two or more boggomoss populations to a level of one or less boggomoss populations; e) inundate all boggomoss populations of two out of 25 biogeographically significant species; f) inundate six out of 12 boggomoss populations of the vulnerable species Arthraxon hispidus; g) not inundate the single population of the vulnerable species Thelypteris confluens although the population would be within 1 m altitude of the maximum water height; h) not inundate the two populations of the endangered species Eriocaulon carsonii and Myriophyllum sp. (Aramac B. Wilson 110). Substantial lessening of impact on community 1 sites are achieved at dam water levels down to 177 m altitude and this trend is reftected in a progessive increase in the security of individual species. For example at the latter level, 88% of species would remain intact in more than one population and all known populations of Arthraxonwould remain intact.