ALM Note: Drought and Plant Survival

There is absolute certainty that at the end of next week Melbourne will move into Stage 2 Water Restrictions. Unlike Stage 1 which has been virtually business as usual for anyone with an automatic irrigation system, Stage 2 will place severe restrictions on the application of irrigation water.

Initially the effect will be minimal as daily evaporation at this time of the year is low and even below average rainfall will enable survival of most species.

As we move into spring and summer, daily evaporation may increase fourfold and the effects will be significant particularly on turf areas that cannot be irrigated at all.

In response to this and in providing sustainable water management we should be increasing our awareness of the drought strategies used by plants and how we can use this knowledge to provide landscape amenity with reduced irrigation water application.

Plants that are able to survive in dry regions or withstand drought are called xerophytes.

Drought damages plants through dessication.

Xerophytes can be divided into two groups in terms of their basic strategies for withstanding drought:

• drought sensitive
• drought resistant

Drought sensitive species avoid drought or avoid drought during sensitive phases of their lifecycle.

Drought resistant species either avoid dessication or are dessication tolerant.

In the broad public landscape perhaps we should be focussing on the drought resistant group and perhaps even more so on the dessication tolerant sub-group. In order to do this we need to increase our knowledge of the nature of these strategies and identify species which demonstrate these strategies.

Dessication tolerant species clearly can be managed without irrigation. Dessication avoiders provide opportunities to 'stress manage' plants and maximise the use of rainfall as a substitute for irrigation.