5BBlue Mountains Swamps

5B Blue Mountains Swamps

(5B) Blue Mountains Swamps

A range of swamps occurs within the Blue Mountains. Swamp vegetation develops on poorly drained sites where the soil is waterlogged for prolonged periods. Several variants are recognised and are described below.

In the Blue Mountains, swamps occur, not only in low-lying sites on valley floors (valley swamps), but also in the headwaters of creeks and on steep hillsides (hanging swamps). Some swamps represent a combination of valley swamp and hanging swamp. The upper boundary of the swamp is often clearly defined by the outcropping of a layer of claystone. Groundwater seeps along the top of the impermeable claystone layer, reaching the surface where the claystone protrudes, thus forming a swamp on the hillside below. Other swamps receive their water supply from feeder streams rather than groundwater, or from a combination of the two.

Blue Mountains Swamps vary greatly in their structure and plant species composition, ranging from closed-sedgeland or closed-fernland to open-heath or closed-heath, sometimes open-scrub or closed-scrub. The shrub-dominated swamps are similar in vegetation structure to some of the forms of Blue Mountains Heath/Scrub, but they differ in species composition and ecological function, and are more appropriately classified with the sedge and fern-dominated swamps. However, in many instances the botanical boundary between Blue Mountains Swamp and Blue Mountains Heath/Scrub communities is unclear or can only be defined at a small scale as the two vegetation types can intergrade extensively.

Common shrubs in the Blue Mountains Swamps that occur on the sandstone plateaux include Acacia ptychoclada, Baeckea linifolia, Banksia ericifolia, Callistemon citrinus, Epacris obtusifolia, Grevillea acanthifolia, Hakea teretifolia, Leptospermum grandifolium, L. juniperinum and L. polygalifolium. Common sedges include Empodisma minus, Gymnoschoenus sphaerocephalus, Lepidosperma limicola and Xyris ustulata. The main fern species is Gleichenia dicarpa. The swamps of the plateaux include communities described by Keith and Benson (1988) and Benson and Keith (1990) as Blue Mountains Sedge Swamps and Newnes Plateau Shrub Swamps.

The Kurrajong Fault Swamps are valley swamps that occur in the lower Blue Mountains on sandy alluvial deposits associated with the Kurrajong Fault. Common shrubs are Acacia rubida, Callicoma serratifolia, Callistemon citrinus, Leptospermum juniperinum and Melaleuca linariifolia. Common species in the understorey are Baumea rubiginosa, Gahnia clarkei, Gleichenia dicarpa and Schoenus melanostachys.

The Coxs River Swamps are another variant encompassed by this community. These swamps occur on the clayey organic sediments derived from the Illawarra Coal Measures where creeks drain at the base of the escarpment. They support a simple flora dominated by Leptospermum obovatum, L. juniperinum and Grevillea acanthifolia with a dense ground cover of Carex and Juncus.