Front yards in our Edmonton neighbourhood are fairly uniform – grass maintained at various degrees of perfection, a spruce or two, and perhaps a white birch, mountain ash, or low growing conifer. Plantings of annuals and herbaceous perennials tend to be near the foundation or in a narrow bed along the front walkway, so that whatever isn’t shaded out by the spruce is covered with grass. Weekend mornings groan with the sound of lawnmowers. In July 2002, we managed to garner one such yard with a mature specimen of cutleaf weeping birch (Betula pendula) in the midst of a ratty expanse of crabgrass and dandelions and flanked by towering spruce.
Weeping Birch are beautiful trees, especially in the winter, but they need a lot of water. For the five years or so previous to our arrival, Edmonton had experienced a prolonged drought. When water-stressed, birch are susceptible to attack by the infamous bronze birch borer (Agrilus anxius). The larvae of this small (~10 mm) blackish beetle bore through the cambium of the tree and kill it from the top down. The bronze birch borer was happily munching away on North American birch when European colonists arrived, but the weeping birch was introduced from Europe and appears to be especially susceptible to its attack. The top metre or so of each stem of the multi-stemmed birch that we acquired was already dead and infested with beetles eating their way towards the ground. Thus, we were immediately confronted with a serious aesthetic problem in the front yard and a bit of a moral dilemma.
In the posts that follow, I will be meandering between describing the evolution of the Home Bug Garden and more spontaneous posts about what is happening at the moment. Every now and then I will have a rant about something I think is important - after all, that is really what blogs are about.
We have some paper birches with similar symptoms as you describe. I have always assumed they are being slowly devoured by the bronze birch borer, but I have never actually seen them. Granted I had assumed they were very small and didn't try very hard, but now learning they are ~10mm I will have to try harder. It is interesting to know the bugs are pre-European contact. I am sure you have further posts on this topic, but in the meantime would be interested to hear your thoughts on the value of leaving a dying or dead birch standing as long as possible as a habitat for bugs, besides the issue of the neighbours' potential concern of the aesthetic implications. What other bugs other than the Bronze Birch Borer like to live in dying/dead birch trees?
ReplyDeleteHi Middle Earth:
ReplyDeleteThe adult birch borers are small, narrow beetles - and always look more black than bronze to me. You are only likely to see them when they are laying their eggs on a stressed birch or emerging from the dead bole (and leaving those small elliptical holes). The grubs that do the damage are under the bark and you'd have to debark the tree to find them.
I'm pretty happy with my more or less dead birch. It cost me about four hundred dollars to get it topped (twice - once trying to save the tree, a definite waste of money, and once to take it down to about 4 m to lessen the chance of a catastrophe during a wind storm). That averages out to 80 dollars a year over 5 years (aka 2 gardening books or 5 bottles of mid-price wine per year). As well as the wren/nuthatch house (cost of another book), the birch is always a good place to watch woodpeckers, winter redpolls, migrating warblers, and a host of other migrant birds. The white/black bark is great in the winter. Additionally, I've used the bolts and large branches cut from the dead wood to outline paths and buttress beds in the garden. Finally, the last meter or so at the base of the tree didn’t die – perhaps the parasites and predators of the birch borer caught up with them – and the tree has resprouted. The sprouts may not make it, but the illusion of a living tree is nice. The tree is surrounded by shrubs, herbaceous perennials, mulch – and flowering bulbs in the spring - so the dead bole fits the overall ambience quite well.
As for other insects living in the dead birch, we haven’t really tried to find out, mostly because it would mean ripping up the bole and bolts (and also because I am lazy). Heather did get a couple of good pictures of a pretty picture-winged fly (Ulidiidae) that breeds in birch logs, but that’s it. I think you’ve just suggested a good project for the winter.
Cheers,
Dave
Thanks for the post Dave. So far I haven't spent any money on the (three) trees. One is still 80% alive, one about 60% and one 0%.
ReplyDeleteI hacked some of the 60% tree back with a sawsall, which was more difficult than initially expected, but successful. The tree was already topped by a previous owner.
The completely dead tree is not very tall, so not too much of a hazard (yet). We have seen woodpeckers and other birds I haven't identified that love to stop by in the tree. In summer it seems they like the vantage they can get from a leafless tree. We will keep them as long as we can.
I have this topic on my "to blog about" list :-), nice to have some additional info.