Botanic Gardens Trust, Sydney, Australia

Key ecological features of the woodland vegetation

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.

Issues covered are:

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 plants, Aging death and decay, Rootstock 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

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.

Go to Impacting events - Fire for more information.

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.

For further information see Grassland remnants and recolonisation in Community Ecology.

Exotic species

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 plants 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.

Ecology of Cumberland Plain Woodland

Woodland at Mount Annan Botanic Garden
Cumberland Plain Woodland at Mount Annan with flowering Bursaria spinosa shrubs.

Arthropodium sp B tubers
Persistent tuberous roots of Arthropodium sp. B allows tolerance of drought conditions.

Localised patch of Vittadinnia sulcata
Localised patch of Vittadinia sulcata plants.

Geranium homeanum seedling
Geranium homeanum seedlings appear commonly after winter rainfall.

Woodland fire
Ecological burn at Mount Annan, September 2002.

Remnant grassland
Grassland rehabilitation area along woodland margin.

Hypericum perforatum flower
*Hypericum perforatum, St John's Wort, was originally introduced as an ornamental plant.

Woodland conservation
Grassland rehabilitation is part of ongoing conservation management.