The majority of individual plants in the woodland at most times are adults. This is because most of the plant species are perennial, relatively long-lived and able to survive the hot summers and periodic droughts by regrowing from thickened rootstocks or tubers.
Adult plant growth is mostly in response to rain periods, and mostly during the cooler autumn and spring seasons. At other times plants may stay in a non-growing or dormant state, or in severe drought may lose all above-ground tissue. Most species will resprout from underground rootstocks when conditions improve.
Life spans
Populations are most vulnerable to change when adult plants die, particularly if a large number of individuals die at the same time. One of our particular interests has been to try to determine the potential lifespans of individual species. Our longevity estimates range from about 2 months for shortlived ephemeral species (e.g. Ranunculus sessiliflorus, Daucus glochidiatus, *Anagallis arvensis) to several hundred years for some long-lived trees and shrubs. General indications are that eucalypts may live up to 200 years, and judging by the size of some of our Narrow-leaved Ironbarks Eucalyptus crebra and Forest Red Gums Eucalyptus tereticornis, that some of these trees could pre-date European settlement.
There is also a group of species that have indeterminate life spans, that is they keep growing indefinitely, assuming that conditions remain favourable. These plants include species that reproduce by bulbs and tubers such as the lilies e.g. Tricoryne elatior or spread by rhizomes e.g. Scutellaria humilis and root suckers e.g. Clerodendrum tomentosum. There are also some woody plants, in particular Bursaria spinosa, where the leaves and stems may be killed by fire but resprout from the base again and again. In the absence of death from debilitating environmental conditions, such as severe drought or disease, these plants appear to have the ability to live indefinitely.
About half of the native species are relatively short-lived perennial species, that is living less than five years, though few of the native species (about 10%) are annuals with lifespans of less than one year. Indeed very few of these are true annuals in the sense that they come up reliably every year, annually. Rather they appear episodically from soil-stored seedbanks following specifically favourable conditions such as wet periods following drought, or in particular wet years, with gaps of perhaps 5-10 years when they are not evident.
In contrast to the native species most of the exotic weed species are short-lived perennial species, with nearly half as annuals. However it is the few long-term perennial species, particularly *Olea europaea subsp. cuspidata, and indefinite perennial species *Hypericum perforatum, *Heliotropium amplexicaule and *Nassella neesiana, that cause the main ongoing weed problems in the Australian Botanic Gardens woodlands.
Asterisk * indicates exotic species naturalised at the Australian Botanic Garden.