Thursday, April 23, 2009

Crabgrass, Dandelions, and a Dying Birch II

When last we visited the early evolutionary stage of the Home Bug Garden, I ended with a serious aesthetic problem in the front yard (a birch dying from drought and beetles) and a bit of a moral dilemma (I’m not against pesticides properly used, but poison in my own yard? and pay for it?). Moreover, the birch was surrounded by alien invasive plants – plants officially listed as ‘nuisance weeds’ in Alberta: quackgrass (aka crabgrass) Agropyron repens and dandelion, listed as Taraxicum officinale, but actually a complex of mostly asexual ‘species’. Although a weed, I’ve always found dandelions fascinating – edible leaves, flowers with which you can make wine, and a nagging question - why does an apomictic plant place such a large investment in flowers and nectar that gain it no obvious benefit at all?

‘Nuisance’ is the lowest rank under the Weed Control Act, ‘Noxious’ is worse, and ‘Restricted’ a real problem. However, it didn’t take much poking around to find that our new yard was infested with quite a few other nuisance weeds that we were supposed to ‘prevent the spread of’ (e.g. Creeping bellflower, Wild buckwheat, Common chickweed, Rough cinquefoil, Hemp nettle, Annual sow thistle, Shepherd's-purse, and probably several other weedy mustards that I was too lazy to key out) and two ‘noxious’ weeds that we were obligated to ‘control’: lots of Canada Thistle (Cirsium arvense) and one Oxeye daisy (Chrysanthemum leucanthemum). To add to the complexity of the problem, these weeds were providing the only real sources of nectar and pollen in our yard.

To top this off, I hate mowing the lawn, hate the sound of lawn mowers, and generally think weekends should be for relaxing in the garden with a couple of bottles of wine, a good book, and some good food. My wife found a non-solution to the second complaint – she bought me a push mower - but that did nothing to quiet the neighbours, and in general I would have to say that push mowing, while inducing a certain sense of moral superiority, is not conducive to relaxing weekends. Push mowing weeds interspersed with spruce cones and birch branches is especially lacking in satisfaction.

Thus came the idea of a ‘home bug garden’ – why not get rid of all these weeds and plant lots of good plants, especially ‘natives’, and make our home a nice place for people and bugs (and other animals)? Why not do nothing about the birch (only the top 2m were dead and at least that gave our garden one species of beetle), but almost completely replace the grass and weeds with a diversity of herbaceous perennials, shrubs, trees, and potager beds of vegetables, herbs, and annual flowers? I’ll deal with the extermination of the enemy weeds, the rediversification of the flora, and the exploding diversity of arthropods and lesser animals in later posts – it took a long time. The birch also took a long time, but is simpler to explain.

If you have a tree infested with a destructive beetle pest such as the bronze birch borer, you may have a moral (and possibly a lawful) obligation to your neighbours. As the new generations of beetles emerge, they won’t just eat more of your tree, but disperse to your neighbours’ yards to continue the outbreak. Chemical control of insects under bark is difficult, expensive, and limited by legislation. When thousands of trees are already dead and dying around you, and producing large crops of beetles, then you have no hope of protecting your tree. Probably the most logical and practical approach would be to drop the tree, bark it, and burn it. We didn’t adopt this simple solution, nor did most people in our neighbourhood: the dead birch are gradually being removed, but it has taken years. We, instead, tried to keep the tree healthy and limit the infestation by aggressive watering – made easier than expected by the end of the drought.

This ‘water and pray’ approach was completely ineffectual and ultimately more costly than the logical solution, but did have the advantage of keeping the birch limping along until at least last Fall (only the aspen have yet to burst bud this year, so no prediction). Birch are pretty trees, and the birds certainly like foraging in ours each spring, fall, and winter. In 2008 we installed a bird house on one of the dead boles, and a house wren (Troglodytes aedon) soon chased off the rather bird-brained house sparrows (Passer domesticus) that spent much of that Spring trying to force themselves into the too small hole. But each year the beetles spread further and further down the bole.

During a storm in the winter of 2004-5, the top 2m of one bole came crashing down. Fortunately, no person or plant was hurt, but it was obvious we had to do something, so we forked out $200 to have the beetle infested tops of the tree cut out – and baked the logs in the sun to kill the beetle larvae. The next year another few metres of tree were dead, and so on. The birch has tried to come back and sprouted from the base, but all but the last metre and a half of the bole is dead. This Spring we spent another $200 to prune it to about 4m height, just above the level of the bird house.

So did we obtain any benefits from ‘water and pray’? Well, yes, I think it has been just about worth it. Birch branches make excellent poles in the garden and segments of trunk make very attractive stands for bird-feeders and nice backdrops for informal beds. A dead tree may look unsightly, but when every other yard in the neighbourhood has a dead birch, there doesn’t seem to be much social pressure to remove it, and a dead tree is heaven to a bird or a bug. Did we save any money? Well, no – we could have had the tree removed for little more than the initial topping and the extra water we put on cost dearly. But how do you estimate the benefit of five years of migrating warblers foraging in the tree, of wrens, chickadees, and nuthatches checking out the bird box, or of strange spittlebugs drowning even stranger wasps? In the Home Bug Garden, the last trumps all.

1 comment:

  1. Dead birch? What dead birch? I've never seen and dead birch...;)

    Nice photo's by HP!