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Drought

Periods of drought are part of the natural environment of western Sydney, and most native plant species have strategies to survive.

The most common feature of many Cumberland Plain Woodland ground species is the possession of a thickened rootstock either as a taproot or cluster of roots or tuber or rhizome e.g. Brunoniella australis. During dry periods the leaves die and the plant retreats to the persistent rootstock to reshoot when moisture conditions improve. Many monocot species also have thickened roots or tubers. e.g. Arthropodium sp. B. While grasses do not have thickened roots many are also able to die back in dry periods and resprout when conditions improve. Most of these species are long-lived perennials.

Species that have developed the ability to resprout from rootstocks after dying back in response to drought, are also likely to be able to resprout when their top growth is removed by fire. In fact, 85% of our species have the ability to resprout, and use this as the predominant method of survival and persistence from year to year, through either drought or fire.

The 15% of non-resprouters, are not just 'annuals'. Their behaviour ranges from that of regular annual to very irregular ephemeral. Short-lived ephemeral species avoid drought conditions by having short-lived adult stages, and persist through drought as long-lived seed in the soil seedbank e.g. Ranunculus sessiliflorus, Daucus glochidiatus. These non-resprouters have an interesting variety of seed dormancy characteristics and germination cues, as germination opportunities will be episodic, perhaps ocurring only once in a decade e.g. for Daucus glochidiatusRanunculus sessiliflorus.

Tree death related to drought

An extended episode of selective tree death occurred over the 1988-95 period in our Australian Botanic Garden woodland.

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