Warren (biogeographic region)

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. 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.

Geography and geology

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 mi) 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 (3200 mi²), 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.cite paper | author = Beard, J. S. and B. S. Sprenger | year = 1984 | title = Geographical Data from the Vegetation Survey of Western Australia | version = Occasional Paper No. 2] 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.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 kilometre (50 mi) long strip of coastal limestone on top of a ridge of granite, with an extensive cave system.cite web | author = Mockrin, Miranda | year = 2001 | title = Jarrah-Karri forest and shrublands | url = http://www.worldwildlife.org/wildworld/profiles/terrestrial/aa/aa1204_full.html | accessdate = 2007-02-15 | publisher = World Wide Fund for Nature] There are a number of soil types, including hard setting loamy soil, lateritic soil, leached sandy soil and Holocene marine dunes.cite paper | author = Environment Australia | title = Revision of the Interim Biogeographic Regionalisation for Australia (IBRA) and Development of Version 5.1 - Summary Report | publisher = Department of the Environment and Water Resources, Australian Government | url = http://www.deh.gov.au/parks/nrs/ibra/version5-1/summary-report/index.html | accessdate = 2007-01-31] cite journal | author = Beard, J. S. | year = 1980 | title = A new phytogeographic map of Western Australia | journal = Western Australian Herbarium Research Notes | issue = 3 | pages = 37–58]

Climate

Warren has a moderate Mediterranean climate. It has the highest rainfall in the state, with annual falls of from 650 to 1500 millimetres (25.6–59.1 in), and a short dry season of only three to four months.

Vegetation

The characteristic vegetation of the Warren region is the Karri forest, a tall forest of "Eucalyptus diversicolor" (Karri) in association with "E. brevistylis" (Rates Tingle), "E. jacksonii" (Red Tingle) and "E. guilfoylei" (Yellow Tingle). The most important plant families are Fabaceae, 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", "Cephalotus follicularis" (Albany Pitcher Plant) and "Podocarpus drouynianus" (Wild Plum).

About a quarter of the region is vegetated by medium forest of "E. marginata" (Jarrah) and "Corymbia calophylla" (Marri); this occurs on the poorer, lateritic soils. 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, 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.cite web | title = Florabase | url = http://florabase.calm.wa.gov.au | accessdate = 2007-01-31]

The region is considered one of the most important centres of plant endemism in the South West. The three Tingle species are endemic to the region, as is "Eucalyptus ficifolia" (Red Flowering Gum) and "Cephalotus follicularis". The area around Albany is especially rich in endemics.

Fauna

The Warren region supports a rich diversity of fauna, much of which is apparently Gondwanan in origin. Mammal species include Western Ringtail Possum ("Pseudocheirus occidentalis"), Chuditch ("Dasyurus geoffroii"), Brush-tailed Phascogale ("Phascogale tapoatafa"), Quokka ("Setonix brachyurus"), Yellow-footed Antechinus ("Antechinus flavipes leucogaster"), Southern Brown Bandicoot ("Isoodon obesulus") and Woylie ("Bettongia penicillata ogilbyi"). The first four of these are endangered species.

As with the rest of the South West, there is a fairly low diversity of bird species. Endemism is similarly low, as most South West bird species are habitat generalists with wide distributions. Exceptions include the Red-eared Firetail ("Stagonopleura oculata") and the White-breasted Robin ("Eopsaltria geogiana"), both of which occur only in the Karri forest; the Western Bristlebird ("Dasyornis longirostris"), Western Whipbird ("Psophodes nigrogularis nigrogularis") and Western Ground Parrot ("Pezoporus wallicus flaviventris"), all of which inhabit the region's heath vegetation; and the Noisy Scrub-bird ("Atrichornis clamosus"), which inhabits densely vegetated gullies.

The freshwater streams of the Warren region support only a low diversity of fauna, but much of it is highly endemic. A number of frog species are endemic or nearly so, including the Orange-bellied Frog ("Geocrinia vitellina"), the White-bellied Frog ("Geocrinia alba"), and the Sunset Frog ("Spicospina flammocaerulea"). Endemic freshwater invertebrates include worms of the family Phreodrilidea, and crayfish of the genera "Cherax" and "Engaewa".

Land use

The Warren region falls entirely within what the Department of Agriculture and Food calls the "Intensive Land-use Zone" (ILZ), the area of Western Australia that has been largely cleared and developed for intensive agriculture such as cropping and livestock production. Despite this, only a small amount of the region's natural vegetation has been cleared and given over to agriculture. The proportion of cleared land was calculated as 13.2% in 2002,cite paper | author = Shepherd, D. P., G. R. Beeston and A. J. M. Hopkins | title = Native vegetation in Western Australia: Extent, Type and Status | version = Resource Management Technical Report No. 249 | publisher = Department of Agriculture and Food, Government of Western Australia | url = http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/LWE/VEGT/TR249_INDEX.HTM | accessdate = 2007-02-15] although Beard gave a much larger figure of 31% in 1984. The remaining land is considered to be native vegetation, but this need not be pristine; a substantial proportion of the remaining native vegetation has been degraded by selective logging and other human activities.

Historically, logging was the primary land use in the region, and this remains a significant industry. There has been substantial selective logging in the region, and some clearfelling. There has also previously been some bauxite mining in the area, but this has now ceased, and the mining areas are at least partially reforested. Dams have also been constructed in high-rainfall forest areas.Fact|date=July 2008

The most important land uses for the region are now biodiversity conservation and tourism. More than half of the remaining vegetation is now in protected areas, including Shannon National Park, D'Entrecasteaux National Park, Mount Frankland National Park, Leeuwin-Naturaliste National Park and Walpole-Nornalup National Park. These contain numerous tourist attractions, most notably the Walpole-Nornalup National Park's Valley of the Giants, which includes a "Tree Top Walk".

Conservation

The main threat to the biodiversity of the Warren region is the South West's epidemic of dieback, a disease caused by the introduced plant pathogen "Phytophthora cinnamomi". Introduced animals such as feral cats, foxes and rats prey on native wildlife and occupy ecological niches to the detriment of native species. Populations are controlled through 1080 baiting as part of the highly successful Western Shield program. Other threats include human activities related to infrastructure and silviculture, such as roads changing surface runoff patterns, and changes to the fire regime.

Because so much of the Warren region is already protected, it has low priority under Australia's National Reserve System.cite web | title = Priority Bioregions for Developing National Reserve System | url = http://www.environment.gov.au/parks/nrs/ibra/priority.html | accessdate = 2007-02-08 | publisher = Department of Environment and Water Resources, Australian Government]

Biogeography

The Warren region first appeared in Ludwig Diels' 1906 biogeographical regionalisation of Western Australia. Diels' concept of Warren region was effectively all the land south of a line from Albany to Busselton; thus it included a substantial area east of Margaret River that is now part of the Jarrah Forest region. The region was not recognised as one of Edward de Courcy Clarke's "natural regions" in 1926, but was resurrected in Charles Gardner's regionalisations of the 1940s and 1950s.

In 1980, John Stanley Beard published a phytogeographical regionalisation of the state based on data from the Vegetation Survey of Western Australia. This new regionalisation included a "Warren Botanical District" that is essentially identical with the present-day Warren. By 1984, Beard's phytogeographic regions were being presented more generally as "natural regions", and as such were given more widely recognisable names. Thus the "Warren Botanical District" became the "Karri Forest Region".

When the IBRA was published in the 1990s, Beard's regionalisation was used as the baseline for Western Australia. The Warren region was accepted as defined by Beard, but reverted to the name "Warren". It has since survived a number of revisions. When the IBRA subregions were introduced in IBRA Version 6.1, the whole of Warren was defined as a single subregion.

Under the World Wildlife Fund's biogeographic regionalisation of the world's terrestrial surface into "ecoregions", the Warren region is equivalent to the Jarrah-Karri forest and shrublands ecoregion of the Mediterranean forests, woodlands, and shrub biome.

References

Further reading

*cite paper | author = Berry, Christopher | year = 1987 | title = The history, landscape and heritage of the Warren district | publisher = Shire of Manjimup
*cite paper | author = Hopper, S. D., Keighery, G. J. and Wardell-Johnson, G. | year = 1992 | title = Flora of the karri forest and other communities in the Warren Botanical Subdistrict of Western Australia | publisher = Department of Conservation and Land Management | version = Occasional Paper 2/92 | pages = 1-32
* Thackway, R and I D Cresswell (1995) "An interim biogeographic regionalisation for Australia : a framework for setting priorities in the National Reserves System Cooperative Program" Version 4.0 Canberra : Australian Nature Conservation Agency, Reserve Systems Unit, 1995. ISBN 0642213712

*cite journal | author = Wardell-Johnson, G. and P. Horwitz | year = 1996 | title = Conserving biodiversity and the recognition of heterogeneity in ancient landscapes: a case study from south-western Australia | journal = Forest Ecology and Management | volume = 85 | pages = 219–238 | doi = 10.1016/S0378-1127(96)03760-7