The impact of rising temperature on insect populations and the environment is dramatically illustrated in the expanding ghost forests of North America .

Great swathes of white pines have been decimated by booming populations of mountain pine beetles. The beetle is cold sensitive and susceptible species of pine like white and jack pine have thrived at altitudes too cool for the beetle.

With consecutive warm seasons, the beetles moved into higher altitudes. They have over-wintered and turned vast areas of ancient pines into ghostly sentinels. Hundreds of years of embodied carbon are about to be released into the atmosphere.

Gardens are not immune to similar effects. The changes will be complex. There will be temporal changes to pests; warm season pests like aphids and cabbage moths will maintain populations over winter and attacks will start earlier.

Also, there will be spatial changes. The CSIRO predict that with warming in Australia, diseases and pests like the dreaded Queensland fruit fly will move southward.

The populations of existing species are also set to change. In southern Australia, some species of cockchafers and mites seem to be expanding. Remember that beneficial insects will also be affected. In areas where summer rainfall is set to increase fungal diseases will boom, so more black spot on the roses.

It need not be all doom and gloom - some pest populations are shrinking. Army worms and pea weevil populations are decreasing in Southern Australia and some snail and slug populations are declining with drier conditions.

As gardeners we will need to be more flexible in the timing of our planting and pest control measures and become more experimental in our approach.

From Complete Guide to the Flower Garden, by Clive Blazey

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