VEGETATION MANAGEMENT PLAN for Bidjigal Reserve - Land

Vegetation Management Plan - Bidjigal Reserve7.5 Potential for Regeneration – Ecosystem ResilienceEcosystem resilience is defined as “the degree, manner and pace of restoration of the structure andfunction of the original ecosystem after disturbance” (Westman 1978), or put more simply, as theability of an ecosystem to recover from disturbance.When assessing site resilience, key indicators are the standing biomass of remaining native plants(particularly naturally regenerating seedlings), and the potential reservoir of propagative material(seeds, spores, rhizomes) in the soil seed bank, although the latter is difficult to assess accuratelywithout extensive trials.Resilience in some parts of the Reserve is expected to be ‘low’ or possibly ‘absent’ because of theimpact of past land uses, including stripping of native topsoil, excavation and/or deposition of fill,enrichment of the parent soils through the incorporation of compost and garden topsoil,replacement of native understorey with horticultural specimens and introduced turf grasses,changes to local drainage patterns, long-term weed invasion, and of particular importance, thesuppression of the ‘natural’ fire regime, with a consequent reduction of vigour in older plants andloss of viability in the soil seed bank. Such areas occur below sporting fields such as Eric MobbsReserve where fill soils have spilled over into the Reserve, along the sewer line emplacements whichwere similarly filled with imported soils, where previous lands uses and activities have impacted onbushland soils (e.g. old quarry site near Excelsior Avenue, M2 bushland)m around the stormwaterdetention basin).However, for those areas where past disturbance events have been arrested, and where parent soilshave not been overly disturbed, site resilience is expected to be ‘moderate’, with some sites ofincreased resilience in more open areas where native understorey plants have managed to reestablishin the absence of dense weed thickets or planted shrubs.Where site resilience is ‘low’ or ‘absent’, reconstruction of the native vegetation community throughthe clearing of weeds and other unwanted vegetation, followed by broad-scale replacement plantingwill be required.In areas with more potential for natural regeneration (i.e. where some site resilience is anticipated),if after a period of (say) 12 months, natural regeneration is sparse (or absent), enrichment plantingmay be necessary to stabilise soils and to provide a native understorey to serve as habitat for nativeflora and fauna.Note: It must be stressed that the natural regeneration of a few shrubs or native ground covers in adegraded site does not indicate that the site is capable of regenerating naturally (i.e. withoutplanting) to a floristically and structurally intact bushland habitat. The presence of disturbancetolerant,commonly-occurring species (e.g. Acacia spp, Pittosporum undulatum or Commelinacyanea) is at times used to support an oversimplified approach to bushland rehabilitation, whichsuggests that all degraded sites retain some resilience, and can, if given enough time and resources,be regenerated to a diverse and fully functioning ecosystem.UBM Ecological Consultants Pty Ltd 135