WEST KIMBERLEY PLACE REPORT - Department of Sustainability ...

Kimberley has three plant families not present in Cape York, whereas 65 Cape York
families are not found in the Kimberley region (Mackey et al. 2001). The generally
higher rainfall in the tropical east is matched by a greater diversity of closed or
swamp forest communities which support many of the Cape York families that are
missing from the Kimberley. Orchidaceae and Sapindaceae, which favour closed
forest communities, appear in the top ten families for Cape York while
Amaranthaceae (Amaranth herbs) and Malvaceae (including Hibiscus), which have
better adapted to drier environments, replace them in the Kimberley. The Kimberley
is more significant for the families Asclepiadaceae, Chenopodiaceae and
Scrophulariaceae, and Acacia species numbers are double those found in Cape York
Peninsula (Clarkson and Kenneally 1988; Mackey et al. 2001).
Meaningful assessments of the richness and endemism of large areas, such as the
Kimberley, must relate to defined, comparable areas. Increasingly, geographical
definition in Western Australia has come to rely on ecological regionalisations. Based
on the development of phytogeographic regions in earlier work, Beard and co-workers
were able to undertake a Western Australian state-level comparison of the Southwest
Province (Perth and wheatbelt country), the Eremaean Province (west coast and
central arid country) and the Northern Province, which included the Kimberley (Beard
1980; Beard et al. 2000). Beard et al. (2000) noted that in terms of plant richness the
Northern Province had more families, fewer genera and less than half the species
found in the Southwest. A recent inventory of WA plant taxa numbers (DEC 2010)
provides a useful comparison for the three provinces: Northern (2,904), Eremaean
(5,759) and Southwest (9,481). While there no doubt are many undiscovered and
undescribed plant taxa across WA, this state of knowledge differs between the
provinces and is considered by the Western Australian Herbarium as being
particularly poor in the Kimberley. However, asymptotic modelling undertaken by the
herbarium to help track the rate of plant discovery has predicted that the Northern
Province will fall further behind the other two provinces in species richness.
West and others (2002), using the IBRA regionalisation, undertook a national analysis
that showed the greatest richness for Acacia (222 species) and eucalypts (160 species)
are in a single subregion of semiarid southwest Western Australia. Moderately species
rich bioregions were found to be in the Kimberley, Arnhem Land, Barkley Tableland,
the subtropical humid and the subtropical and temperate coastal areas of eastern
Australia. Using more recent ecological regionalisation data (DEC 2010), the
Southwest Province is richer for both Acacia and eucalypts (566 and 425) than both
the Eremaean Province (430 and 290) or the Northern (Kimberley) Province (149 and
82).
ANHAT analysis displays the Kimberley as having close to the highest national
species richness score for Combretaceae (plums, bullwaddies, mangroves and
bushwillow) along the Kimberley north coast. This observed richness is supported by
Wheeler et al. (1992) who notes that all 12 of the Kimberley Terminalia species are
found in this area. However higher scores for Combretaceae richness were found in
the east Kimberley and the Darwin regions. Apart from these regionally high values,
no other groups on current analysis were shown to have species richness scores of
significance when compared nationally.
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