VEGETATION MANAGEMENT PLAN for Bidjigal Reserve - Land

Vegetation Management Plan - Bidjigal Reserve4.4 Bushland Condition and Priority Ranking4.4.1 Bushland Condition Weed MappingTen (10) Management Zones were established for the Bidjigal Reserve bushland. In each of theseZones four (4) types of Management Units were designated: Riparian Corridor, Track/Trail, Urban-Bushland Interface, and Core Bushland.Riparian CorridorsThe riparian corridors in the Reserve are in most cases a major reservoir of weeds. Small ephemeralcreeks and stormwater outlets feed into the larger creeks; the latter being located at the end ofmost suburban streets, bringing weed propagules into the bushland. Weeds are well establishedwhere sediments washed down from higher in the catchment settle and provide a rich substrate forweeds to colonise. Privet is particularly adapted to growing in such silt ‘slugs’, which eventuallycreate islands or lateral benches in the creekbed; thus accelerating soil erosion as the water divertstowards the creek banks in an attempt to bypass these obstructions.On steeper, rockier land; and in areas where the creek is broader (and where silt slugs are absent)and intensity of water flow decreases there are fewer riparian weeds present. However, wheremajor disturbance has taken place (e.g. as a result of earlier drainage works – sewer and watermains) weed densities remain high – possibly as the result of weedy fill soil important at the time ofconstruction, and it must be acknowledged, because of periodic overflows from sewer mains afterheavy rain.Note that the construction for the installation of the sewer line through the Reserve in the 1970sutilised a great deal of clay fill, and no site rehabilitation was undertaken at the time, so that thepipeline corridors which were located on ‘benches’ on the lower sideslopes eventually becamenuclei of weeds which eventually spread into adjacent bushland.Weeds in the riparian corridors were targeted in the early 1990s by Sydney Water through its SpecialEnvironmental Levy Program. This Program, which continued for four (4) years, was successful inachieving its objectives, but a general lack of follow-up and regular maintenance by Council insubsequent years has allowed weeds to again establish in these areas of on-going disturbance.A list of the weed species associated with this Management Unit is presented in Section 5 of theVMP.Tracks & TrailsThere are two (2) types of tracks in the Reserve: narrow foot tracks/trails, and wider vehicle tracks.In general, weeds are more extensive and occur in higher densities on the vehicle tracks (e.g. trackdown to Excelsior Creek from Candowie Crescent). This is because most tracks are subject to regulardisturbance events (most of which cannot be avoided), and it is also likely that service vehiclesentering the reserve for routine maintenance will transport soil and weed propagules fromcontaminated sites elsewhere into the bushland. On the other hand, the bushland along the narrowwalking trails generally display fewer weeds except in those places where they cross highly disturbedareas (e.g. power lines corridors, stormwater outlets). A list of the weed species associated with thisManagement Unit is presented in Section 5 of the VMP.UBM Ecological Consultants Pty Ltd 68