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Key ecological features

This is a summary of the key ecological features that we have identified in the woodland at the Australian Botanic Garden, Mount Annan. Many of the features are relevant to a wide range of grassy woodland communities.

Plant species persistence

  • In Cumberland Plain Woodland, most of the native plant biodiversity, with over 80% of the plant species, is in the ground layer (see Plant community structure).
  • Most species are long-lived and persist in dry conditions, regeneration from rootstocks is predominant (see Adult plantsAging death and decayRootstock Gallery).
  • Shortlived species may have longlived soil seedbanks (see Seed).
  • There are no species with plant-stored seedbanks (see Seed).
  • In the recent drying years 2000-2005 some species have increased, other decreased (see Notes from the 2002 drought).

Species distribution patterns

  • Species distribution patterns appear to relate mainly to soil and topographic microhabitats, and past soil disturbance (See The importance of soil).
  • Common species are widespread and have remained common for nearly 20 years - these species are widespread and similarly common in other Cumberland Plain remnants.
  • Many species persist as small populations of <10-20 plants with little change evident over at least 10-20 years e.g. Sorghum leiocladumLomandra multiflora, Vittadinia sulcata.
  • Some species are limited by available physiographic habitat e.g. the ferns Pellaea falcata, Asplenium flabellifolium in the dry creek (see Competition for light and moisture).
  • Some species may be part of a larger, widely dispersed population e.g., perhaps the wind-dispersed vines Parsonsia straminea, Marsdenia viridiflora, Clematis glycinoides, and bird-dispersed shrubs Exocarpus cupressiformis and Myoporum montanum (see Localised habitats).
  • Some species may need particular episodic climatic conditions for recruitment, which we are not, or no longer, experiencing e.g. perhaps Sorgum leiocladum.
  • Some species may be limited by biotic interactions e.g. predation, lack of pollinators etc, mostly yet unidentified e.g. Calotis lappulacea restricted by rabbit grazing.
  • Canopy tree species influence groundcover composition by an increase in bird-dispersed species, the impact of shading/moisture composition/animal camps may be involved.
  • A group of species are restricted to open/mown/bare areas often associated with human activities, roadsides, paths e.g. Chloris truncata, many exotic species.

Recruitment

  • Existing occupant plants are strongly persistent (See Rootstock gallery).
  • Growth and flowering of many species tends to be opportunistic in relation to rain, rather than fixed in response to day length or time of year. (see flowering).
  • Seed set is variable and influenced by weather and biotic interactions e.g. pollination (see Pollination and seed set).
  • Seedling recruitment is episodic and relatively rare, maybe 1 major event per 3-5 years.
  • Sustained rainfall events are necessary to initiate recruitment and establishment. The force driving processes in the woodland appears to be rainfall rather than temperature (see The importance of rainfall).
  • Recruitment events for some species may also depend on drought, fire and/or animal digging.
  • Many of the species have very limited locally dispersed seed, and are not capable of long-distance dispersal, especially between today’s fragmented woodland areas.
  • Some may be distance dispersed by ingestion or adhesion (See Seed dispersal).

Fire

Most species survive fire as adults - ~90%. For most species persistence is via rootstocks, evolved in response to periodic dryness, but enabling survival after fire. ( See Resprouting gallery, Rootstock gallery).
  • Fire may create suitable open space and reduced canopy cover. It is not a major driver of seedling recruitment, but may promote vigorous flowering and seeding of pre-existing plants, thus contributing to subsequent soil seedbanks.
  • There has been a decrease in above-ground native species richness in the absence of fire, but it is likely these species remain in the soil seedbank.
  • Periodic fire may help control some perennial exotic species particularly African Olive, *Olea europea subsp. cuspidata.
  • Periodic drought, rather than fire, appears to have been a driving evolutionary force for individual species.

Grassland remnants and recolonisation

  • The species composition of grassland sites may or may not differ from woodland sites depending on past management history.
  • Remnant sites where there has been no past soil disturbance/cultivation/complete removal of native vegetation may be recognised by a group of persistent, but poorly dispersed ‘survivor’ species including Brunoniella australis.
  • Where there has been significant past soil disturbance/cultivation/complete removal of native vegetation, recolonisation by native species is limited to a small set of mainly grass species, which are presumably easily dispersed and recruit into open conditions.
  • Such sites do not however develop species rich groundcovers similar to the remnant sites, at least not in a 20 year timeframe, due to absence of seed propagules of most species.

Exotic species

  • Threatening exotic species are large perennials that outcompete natives by shading or vigorous growth e.g. *Olea europaea subsp. cuspidata, *Nasella neesiana, *Heliotropium amplexicaule, *Hypericum perforatum. Like natives these can survive fire and drought (see Interactions between native and exotic plants).

Conservation

  • Cumberland Plain Woodland is listed as an Endangered Ecological Community under the NSW Threatened Species Conservation Act (see Western Sydney Woodland).
  • Cumberland Plain Woodland has been severely depleted and now exists as very small remnants; our experience suggests that individual remnants may have a locally high floristic richness or species not occurring or uncommon in other remnants.
  • Today’s remnants need to be managed to conserve all species at each site.
  • Patchy plant distributions mean remnants vary in their species composition, and conservation of all today’s remnants, not just the large ones, are likely to be needed to conserve the biodiversity.
  • However, many species will be restricted to a few remnants.
  • Given the natural tendency for long term persistence in situ of many of these plant species, we believe that populations of these plant species in remnants will continue to survive into the foreseeable future despite the fragmented nature of the habitat.
  • The episodic recruitment and opportunistic behaviour of most species mean a variety of treatments in management processes such as fire, removal of competing weeds, control of predators, may be needed, particularly in the context of changing climate.
  • The number of species visible at any site fluctuates in response to seasonal variables, particularly rainfall; multiple surveys over several seasons may be needed to record all species present.
Asterisk * indicates exotic species naturalised at the Australian Botanic Garden.
 
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