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Preliminary report on a survey of Utricularia (Lentibulariaceae) in the Howard River – Shoal Bay area



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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other species six species are aquatic. This diversity is nowhere better evident than on the extensive sand sheets of the so-called Koolpinyah land surface found in the Darwin Rural area. Here, on seasonal seepage zones along the margins of drainage floors, depressions and floodplains a layer of pure sand, of variable thickness, which has been leached by laterally flowing water overlies an impermeable clay layer close to the ground surface. Up to 14 species can be found on an area of no more than 0.1 ha, with 26 species found on a variety of seasonally waterlogged substrates and aquatic habitats within a few km. Unfortunately for Utricularia, this special hydrological situation also provides probably the most readily (and cheaply) extractable source of clean building sand in the Darwin area. Nine species of Utricularia in the NT had previously been identified as of some conservation significance (Leach et al., 1992) ranging from endangered to rare or poorly known (Table 1). For the most part these species are sand sheet specialists endemic to the Top End of the NT with some extending to the Kimberley region of WA. The other two species of significance are endemic to sand sheet habitats in western Arnhem Land. The aim of this study was to identify areas rich in Urticularia spp (especially those endemic or near endemic species favouring sand sheet habitats) in the Howard River catchment Shoal Bay area, so that options for conservation could be evaluated and to improve knowledge especially of the distribution, abundance and habitat preferences of rare or endemic species. Particular attention was paid to the Shoal Bay Reserve and East Howard borefields areas Methods Sampling was undertaken using standard 20 x 20 m floristic quadrats used by the NT Herbarium and was planned according to land units identified in various Land System/Land Unit mapping studies of the area (Wells & Harrison, 1978; Fogarty et al., 1979,1984; Lucas & Czachorowski, 1980; Van Cuylenberg & Czachorowski, 1984; and Lynch, 1985). Previous field experience and herbarium records indicated that land units mapped as upland depressions and floodways and broad lowland plains contained areas of Utricularia habitat. On geological maps of the area, these units corresponded to areas mapped as Quaternary colluvium (sand, silt, clay), deposited by unconcentrated sheetwash in broad drainage areas and on very gentle slopes marginal to estuarine and littoral areas (e.g. Pietsch, 1985). Land units were searched on foot, using a quad bike and by vehicle along existing tracks and roads. Quadrats were located in representative areas where Utricularia species were found, with a view to achieving good geographic coverage of the area and sampling all habitat types occupied. At each quadrat, location was recorded with a GPS, a range of environmental variables was assessed and the presence of all identifiable plant species recorded. Preliminary analysis of NT Herbarium records suggested that there can be some seasonal progression in flowering during the wet - early dry season period when Utricularias are most evident. Species such as Utricularia hamiltonii, U.kimberleyensis and U.lasiocaulis have been collected as early as February while U.triflora was quite late in the season with collections only from May to August. Also, there can be considerable variation in the onset, duration, and intensity of the wet season from year to year and the peak flowering time for highly moisture dependant annual herbs such as Urticularia could be expected to vary also (Taylor and Tulloch, 1985). Thus, field work was spread over 12 days from early March