The scourge of tree decline

As climate change begins to grip, one of the first great casualties of this environmental onslaught may well be the health and survival of our beautiful and iconic trees.

It is disturbing that we are seeing increasingly more trees lose their vigour, decline and, in the worst cases, die.

No species seem to be immune and what used to be just a problem for jarrah and banksia now threatens all major tree species, including the mighty tuarts, marri, flooded gum, wandoo, peppermints and a host of eastern states gum trees.

In Busselton, you can see the devastation to the tuarts, or head east through the jarrah forest and the Wheatbelt and you will see signs of tree decline.

The causes are varied, complex and poorly understood, but clearing and fragmentation, climate change, rising or falling water tables, changing ground water quality, disease, insects, loss of biodiversity — the same old nasty bunch — are implicated.

In many cases, some trees are well over 100 years old. They have grown beyond a point where they can quickly adapt to the change in climate.

The decline in the health of these trees has important implications for the animals, plants, fungi, insects and soil micro-organisms that rely on them, while the dwindling seed production in their canopy means fewer seedlings to kick-start the next generation.

This should be a wake-up call to garner support for large-scale environmental restoration programs.

It should be of immense comfort to know that while the problem has expanded in scope and intensity, so too has the research, understanding and strategies for dealing with this arboreal crisis.

The Dieback Working Group and Murdoch University are leading an impressive counter-offensive to better understand the scourge of tree decline.

Stem injection and implant strategies

Research has found that for some plants, stem injection with phosphite (potassium phosphonate — a low-toxicity, biodegradable fungal suppressant) or implanting with specially formulated slow-release nutrients can make a big difference.

In the best cases, the effect is dramatic and sick trees respond with vigorous regrowth. For more information, visit www.treehealth.murdoch.edu.au.

Spraying foliage

If injection sounds too fiddly or your plants are too small and numerous to individually inject, then spraying might be the answer. Shrubs and seedlings can be sprayed with a weak (0.3 per cent phosphite) solution, bolstered with a wetting agent or penetrant to improve the spray’s ‘stickability’. Huge areas of the Fitzgerald National Park have been aerial sprayed in a bid to stop the spread of phytophthora dieback.

Soil improvement

Healthy soil will foster healthy plants. Conversely, when soil is out of balance and degraded by years of neglect, it is hardly surprising that plants will be sick and diseased. It is advisable to add:

•Compost as a solid, liquid or even pellet form

•Rock dust

•Fish and seaweed solutions

•Dolomite, lime and gypsum

•Biodynamic preparations

•Specially blended fertilisers like ‘Shades of Green’ that have microbial inoculants

•Mycorrhizal fungi inoculant applications Use quality mulch

To give your plants a helping hand, you may find that tree pruning mulch can be a big hit. At its best, it can mimic the life-giving mulch layer of healthy forests and it will cool the overheated landscape, nurture the soil’s biological life and improve moisture retention.

When mulch is spread 75mm to 100mm thick and as far as the drip line or beyond, it has been shown to do remarkable things to turn trees’ fortunes around.

Unprotected trees are doomed

Maintaining healthy trees is next to impossible if your stock have unfettered access. Stock gravitate to paddock trees and what starts out as a quest for shade and shelter quickly turns into vandalism.

Plant understorey

A long-term strategy will not get very far without a concerted effort to reinstate the understorey that has been lost. Only this biodiversity can bring back the birds, reptiles and insects that will rein in pests and re-establish soil health.

The most appropriate species to use will depend on your region, but they should be drawn from a local endemic shrub list, available from your local landcare officer or from groups like Men of the Trees, Greening Australia and the Department of Environment and Conservation.

Useful websites

•Murdoch Uni —www.treehealth.murdoch.edu.au

•DEC —www.dec.wa.gov.au

•Greening Australia —www.greeningaustralia.org.au

•Men of the Trees —www.menofthetrees.com.au

•Dieback Working Group —www.dwg.org.au