Barbarea Australis (Native Wintercress) Barbarea Australis
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Listing Statement for Barbarea australis (native wintercress) Barbarea australis native wintercress T A S M A N I A N T H R E A T E N E D S P E C I E S L I S T I N G S T A T E M E N T Image by Mick Ilowski Scientific name: Barbarea australis Hook.f., Fl. Nov.-Zel. 1: 14 (1852) Common name: native wintercress (Wapstra et al. 2005) Group: vascular plant, dicotyledon, family Brassicaceae Status: Threatened Species Protection Act 1995: endangered Environment Protection and Biodiversity Conservation Act 1999: Endangered Distribution: Endemic status: Endemic to Tasmania Tasmanian NRM Region: Cradle Coast, North, South Figure 1. Distribution of Barbarea australis Plate 1. Barbarea australis growing amongst river (unconfirmed Parramatta Creek location not shown) rocks (image by Mick Ilowski) 1 Threatened Species Section – Department of Primary Industries, Parks, Water and Environment Listing Statement for Barbarea australis (native wintercress) IDENTIFICATION AND ECOLOGY Confusing species Barbarea australis is an annual or short-lived Three species of Barbarea occur in Tasmania, (perhaps biennial) perennial herb in the two of them, Barbarea intermedia and Barbarea Brassicaceae family, occurring along flood- verna, being introductions from the northern prone rocky river systems. Being a short-lived hemisphere. The introduced Barbarea species species, it is largely reliant on germination of can be distinguished from Barbarea australis by seed for recruitment and population their deeply-divided upper stem leaves and by persistence. It is a prolific seed producer and seeds that lack a defined edge and that are after disturbance such as flooding, hundreds of relatively rounded. seedlings can emerge in resultant gaps in winter and early spring. However, few generally DISTRIBUTION AND HABITAT survive to maturity due to browsing (mainly by native species) and disturbance by natural flood Barbarea australis is endemic to Tasmania, events. In the wild, bare ground is required for known from about 10 river systems extending recruitment. Seed is set in the first year of from northern Tasmania to rivers flowing growth. The plant can also reproduce south from the Central Highlands (Figure 1, vegetatively with a new plant growing from the Table 1). Based on extant subpopulations, the base of an existing plant (TSU 2005). Barbarea linear range of the species is about 170 km, 2 australis appears to be a poor competitor. extent of occurrence 13,045 km (Table 1), and area of occupancy 0.2 km2. Survey techniques Barbarea australis is a riparian plant species Surveys should be conducted during the found near river margins, creek beds and along species’ peak flowering period, which is flood channels adjacent to the river. It has not November to February (Kirkpatrick & been found on steeper sections of rivers, and Gilfedder 1998). Any survey effort should be tends to favour slower reaches. It occurs in focused on potential habitat (i.e. flood-prone shallow alluvial silt deposited on rock slabs or riparian habitats). Due to the wide variation in rocky ledges, or between large cobbles on sites numbers in any one year, it is advisable that a frequently disturbed by fluvial processes. Some relatively extensive survey is undertaken at any of the sites are a considerable distance from the site because the species can be spread over river in flood channels scoured by previous several kilometres of river system, and may flood action, exposing river pebbles. One site shift from site to site between years, dependent observed was on bare soil at the base of a cliff on disturbance conditions. approximately 40 m from the river and 3 to 4 m above a secondary stream. There was little Description apparent influence of water at the site but active soil movement kept the site bare and Barbarea australis is an erect plant up to 50 to 100 cm high. The lower stem leaves are 8 to 10 moisture seeping from the base of the cliff kept cm long and form a rosette or radiating cluster. it moist. The sites range in altitude from 260 to The leaves are stalked, broader at the ends and 700 m on alluvial silt overlying a number of develop 2 to 3 small lateral lobes on the leaf rock types including dolerite, basalt and granite. stalk below the main part of the leaf. The leaves A number of the localities are associated with on the upper stem are simple with wavy watercourses along contact zones between margins. The flowers are yellow, the petals 2 to Permian mudstone and either dolerite or basalt. 8 mm long. The many seed capsules or pods Barbarea australis is found at the margins of are 20 to 40 mm long and 2 to 2.5 mm wide. riverine scrub with Leptospermum lanigerum, The seeds are broad and oval, 1.5 mm long and Dodonaea viscosa and Pomaderris species in forest have irregular edges or narrow wings. communities dominated by Eucalyptus [description from Hooker 1859, Curtis 1956, delegatensis, E. dalrympleana, E. pauciflora and Hewson 1982] E. ovata. Adjacent sites often consist of tussock grassland or grassy woodland dominated by Poa 2 Threatened Species Section – Department of Primary Industries, Parks, Water and Environment Listing Statement for Barbarea australis (native wintercress) labillardierei or Themeda triandra. At most sites it RESERVATION STATUS grows in open rocky situations with little Barbarea australis is reserved within Mole Creek competition from other plant species, although Karst National Park, Mersey River Forest at some localities it grows amongst large Poa Reserve, Hellyer Gorge State Reserve and tussocks in relatively dense vegetation. North Esk Forest Reserve. Protection to some subpopulations is also afforded by their POPULATION ESTIMATE occurrence in Crown river reserves (e.g. parts Total population size is estimated to be about of the St Patricks River subpopulations) or in 900 mature individuals (Table 1; TSU 2005). As informal reserves under Forestry Tasmania’s the species is short lived and recruitment is Management Decision Classification mapping largely by seed, particularly following system (Orr & Gerrand 1998). disturbance, numbers of individuals in subpopulations can fluctuate widely from year CONSERVATION STATUS to year though subpopulation sizes are typically Barbarea australis was listed in 1995 as no more than 50 mature individuals and often a endangered on the Tasmanian Threatened Species lot smaller. Estimates in Table 1 are counts of Protection Act 1995, meeting criterion C: total mature individuals from subpopulations when population estimated to number fewer than last seen. The largest subpopulation yet 2,500 mature individuals, specifically criterion recorded had 135 mature individuals C2. a continuing decline, observed, projected, (St Patricks River), while other subpopulations or inferred, in numbers of mature individuals with over 100 mature individuals are known and population structure in the form of either: from the River Ouse near Waddamana, the a.(i). severely fragmented (i.e. no subpopulation River Clyde and the Nive River (Table 1). The estimated to contain more than 250 mature number of subpopulations is also likely to individuals); and b. extreme fluctuations in the fluctuate as local extinctions occur due to number of mature individuals. It also meets increased risks associated with small criterion D: total population very small or area populations (TSU 2005). of occupancy restricted, specifically D1. total population estimated to number fewer than It is likely that Barbarea australis has always been 1,000 mature individuals. relatively locally uncommon. Barbarea australis was presumed extinct until rediscovered in the THREATS, LIMITING FACTORS AND 1980s, having not been collected since the MANAGEMENT ISSUES 1830s from northwest Tasmania. However, the Barbarea australis is at risk because most close similarity of Barbarea australis with subpopulations are on private land and are at introduced Barbarea species may have caused risk from habitat loss and modification, the species to be overlooked by collectors. increased grazing pressure and stochastic events Since 2000, only two additional subpopulations as follows. have been located. Of these, the Hellyer River site is a significant extension of the extant range Habitat loss and modification: Barbarea into the State’s far northwest. While there is australis has suffered significant loss of potential considerable potential habitat within the habitat since European settlement (TSU 2005). species’ current known range, formal and This was largely due to land clearance through informal surveys have failed to locate further early exploitation of accessible and relatively subpopulations. fertile areas including riparian ecosystems for agricultural purposes. It should be noted that It is unlikely that the recording of additional much of the habitat of the species is ‘Riparian subpopulations will alter the estimates of total scrub’, a threatened vegetation community population numbers by orders of magnitude listed under Nature Conservation Act 2002. because all known subpopulations tend to be of relatively low numbers (usually less than 100). 3 Threatened Species Section – Department of Primary Industries, Parks, Water and Environment Listing Statement for Barbarea australis (native wintercress) Table 1. Population summary for Barbarea australis Subpopulation Tenure NRM 1:25 000 Year last Area of Number of region mapsheet (first) seen occupancy plants (ha) 1 River Clyde private land South Dennistoun 1999 0.0003 3 (seedlings) (north of Bothwell) 2 River Clyde private land South Cawood