Warren bioregion

Warren, also known as Karri Forest Region and the Jarrah-Karri forest and shrublands ecoregion, is a biogeographic region in southern Western Australia. Located in the southwest corner of Western Australia between Cape Naturaliste and Albany, it is bordered to the north and east by the Jarrah Forest region. Its defining characteristic is an extensive tall forest of Eucalyptus diversicolor (karri). This occurs on dissected, hilly ground, with a moderately wet climate. Karri is a valuable timber and much of the karri forest has been logged over, but less than a third has been cleared for agriculture. Recognised as a region under the Interim Biogeographic Regionalisation for Australia (IBRA), and as a terrestrial ecoregion by the World Wide Fund for Nature, it was first defined by Ludwig Diels in 1906.

The Warren region is defined as the coastal sandplain between Cape Naturaliste and Albany. Extending from the ocean to the edge of the Yilgarn craton plateau, for most of its extent it may be adequately approximated as the land within ten kilometres (6.2 miles) of the coast. North of Point D'Entrecasteaux, however, it extends inland almost as far as Nannup and Manjimup. It has an area of about 8,300 square kilometres (3,200 sq mi), making it about 2.7% of the South West Province, 0.3% of the state, and 0.1% of Australia. It is bounded to the north and east by the Jarrah Forest region. Much of the region is unpopulated, but there are a number of towns with substantial populations, most notably Margaret River, Augusta, Pemberton, Walpole, Denmark and Albany.^{[citation needed]}

Warren has a hilly topography, caused by two factors: the underlying geology, which consists of infolded metamorphic rock of the Leeuwin Complex and Archaean granite of the Albany-Fraser Orogen; and the dissection of rivers such as the Blackwood, Warren, Shannon and Frankland. The western extent of the region takes in the Leeuwin-Naturaliste Ridge, an 80 kilometres (50 miles) long strip of coastal limestone on top of a ridge of granite, with an extensive cave system. There are a number of soil types, including hard setting loamy soil, lateritic soil, leached sandy soil and Holocene marine dunes.

Warren has a moderate Mediterranean climate. It has the highest rainfall in the state, with annual falls of from 650 to 1,500 millimetres (26 to 59 inches), and a short dry season of only three to four months.

The characteristic vegetation of the Warren region is the karri (Eucalyptus diversicolor), at 90m the tallest trees in Australia, in association with the three tingle trees, which are endemic to this coast: rates tingle (E. brevistylis), red tingle (E. jacksonii) and yellow tingle (E. guilfoylei). Karri has a thick undergrowth of flowers and shrubs such as coral vine (Kennedia coccinea). The most important plant families are Fabaceae (including the colourful wisteria, Hardenbergia comptoniana), Orchidaceae, Mimosaceae, Myrtaceae and Proteaceae.

The karri forest occurs in deep loam, and covers nearly half of the region. Although very moist in winter, it is not considered to be a rainforest because the dry season precludes the establishment of a characteristic rainforest understory of epiphytes, liverworts, ferns and mosses. Some rainforest relict species do occur, however, such as Anthocercis sylvicola, Albany pitcher plant (Cephalotus follicularis) and wild plum (Podocarpus drouynianus).

The poorer, lateritic soils, about a quarter of the region, are vegetated by medium forest of jarrah (Eucalyptus marginata), which can grow up to 40m tall, and marri (Corymbia calophylla) (up to 60m). Other significant vegetation forms include low woodland of E. marginata and Banksia species (8%); Agonis flexuosa woodlands or scrub on Holocene marine dunes (5%); and swamps supporting sedges (5%) or low woodlands of Melaleuca (4%).

As of 2007^[update], the Warren is known to contain 1865 indigenous vascular plant species, and a further 419 naturalised alien species. The endangered flora of the Warren region consists of 28 species, with a further 160 species having been declared Priority Flora under the Department of Environment and Conservation's Declared Rare and Priority Flora List.