Native trees do best when they are growing in healthy bushland. They rely on complex interactions with the soil and other plants and animals. When the balance is disturbed, by clearing for example, trees may not be able to function properly and may go into a slow decline as they struggle to cope with a changing environment. This can result in ill health and premature death.

Native tree decline is becoming alarmingly widespread across south-western Australia. It affects a variety of iconic species including tuart, flooded gum, marri, jarrah, wandoo, banksia, and peppermint. Consequences of native tree decline and death of native trees include loss of aesthetic values, reduced viability of ecosystems, and loss of environmental services.

What can landholders and community groups do about native tree decline?

If your trees are showing signs of stress or decline, you can increase their chances of survival. If your trees are healthy, it is important to understand how to keep them healthy. The best approach is to adopt a range of measures to prevent and manage tree decline.

Revegetation
Leave bushland around trees intact or restore native vegetation around trees. Bushland helps keep the soil intact and healthy, and buffers from human activities. Control weeds to assist natural regeneration and improve the survival of native seedlings, but be cautious with the use of herbicides.

Minimise soil compaction and root disturbance
Avoid digging around trees. Consider fencing off trees from livestock to prevent compaction and ringbarking, and promote natural regeneration. If soil is already compacted, a qualified arboriculturist can advise on mechanical methods of soil aeration.

Soil improvement
Mulching and composting can improve soil health. Seaweed products and fish emulsion encourage soil organisms for optimal root health.

Avoid poor pruning practices
Avoid lopping, which can cause structural weakness, tree stress, and allow disease to take hold. Seek the advice of a qualified arboriculturist who meets Australian Standards for tree pruning.

Control pests and diseases
Replant native vegetation to attract birds and insects that predate problem insects. Seek expert advice (e.g. Department of Agriculture and Food) to identify pests and how to control them.

Prevent and control dieback
Stem injection of phosphite every 3-4 years helps prevent and treat dieback caused by Phytophthora. Prevent the spread of dieback by buying certified dieback free mulch, plants, soil and compost.

Injections
Preliminary findings suggest nutrient and/or phosphite injection may help improve trees suffering from decline. The mode of action is not fully understood, but phosphite is thought to stimulate a tree’s natural defense system against pathogens, and nutrients are thought to act like a vitamin boost. Treatment guidelines and demonstration video are available. The results of a trial conducted in 2008/2009 by the Wandi Landcare Group and Green Skills will be available in September 2009.