Preliminary report on a survey of Utricularia (Lentibulariaceae) in the Howard River – Shoal Bay area
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Plant conservation; Revegetation
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through to the end of April, 2001 to try to sample as many species as possible, and minimise the risk that all field work would fall too late in the season for significant populations of Utricularias to still be present. Data collection in the 2001 season was designed to extend geographically that data collected using an identical methodology in the Shoal Bay reserve at the end of the wet season the previous year. To gain a broader perspective on the distribution and habitat preferences of Utricularia species outside the survey area, additional plots were located on colluvial drainage floors during a number of other surveys conducted during the wet - early dry season of 2001. Thus, Utricularia habitat was sampled to a greater or lesser extent during floristic and vegetation surveys of Bathurst Island, Nitmiluk NP, Sturt Plateau wetlands and part of Arafura Swamp catchment. Results and Discussion Many areas of high richness in sand sheet Utricularia species were located. These were generally along the mid to upper parts of the Howard River floodplain (Whitewood Rd to Goode Rd) and along the western margin of the Adelaide River floodplain (Fig. **). Conversely, sites on much of the mid to lower Howard River floodplain (north of Whitewood Rd) and drainage lines to the north of the Gunn Point Road (e.g. the East Howard system) were lower in Utricularia species, and suitable habitat was more sparsely distributed. However, some species (U.triflora, U.involvens and U.circumvoluta) were only recorded in these more northerly areas during the survey. Many sites on the west side of the Howard River floodplain including the formerly rich McMinns Lagoon area were likewise depauperate in Urticularias, probably because of habitat modification linked to surface mining and rural residental subdivision. Shallow surface mining has affected extensive areas of formerly suitable habitat in the study area as well as adjacent colluvial lower slopes formerly dominated by Eucalyptus woodland. The East Howard system to the south of the Gunn Pt Rd has been extensively mined with more limited areas mined to the north. Much of this system to the north has probably been less suitable for sand sheet Utricularias, as it consists of extensive area of shallowly flooded drainage floor with limited areas of pure sand along the margins. Relative abundance of species of conservation significance Of those species recorded during the survey and regarded as of conservation significance (Leach et al., 1992), Utricularia dunstaniae remains by far the rarest, despite intensive searching. It was located at only three sites, all with other sand sheet species, including U.holtzei and U.hamiltonii. Two of these sites were in the middle parts of the Howard River floodplain (between Girraween Rd and Gunn Pt Rd) and the third was on the western margin of the Adelaide River floodplain north of Black Jungle. Taylor (1989) gives three other records for the species - from McMinns lagoon (although it was not relocated there during the survey), from near Jabiru and from northern Kimberley. The type collection is from the Howard River although the exact location is not known. U.holtzei and U.hamiltonii were found to be widespread, and locally abundant in the mid to upper Howard River area (Whitewood Rd south to Goode Rd) and along the western margin of the Adelaide River floodplain (north of Black Jungle). More localised populations
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