In designing the gardens and landscaping at the BMLL, one of our tenets is to use and emphasize that which is intrinsic* to the site. We are framing views of some of the more substantial red oaks that occupy the property; and we have begun to select, and feature, some young white pines, which will eventually become matriarchs like the red oaks. After each visit or work session, the site’s tree inventory grows a little richer.
Last Friday’s mixed weather and scant volunteer turnout gave Cathy a chance to notice a couple of tree-related items. First, among the seedling birches dug into on of the nursery areas, it is now clear that only three of the small trees are paper birches; the rest are gray birches. These youngsters were transplanted before the leaves appeared, and we took their donor’s identification for granted.
The distinctions among very young, dormant, birches can be subtle, requiring a hand lens and Campbell’s Winter Keys to Woody Plants of Maine for accurate identification. Differences in twig bark and the arrangement of male (staminate) catkins distinguish paper from gray birch if one is looking to identify different species. (Winter tree and shrub identification is rewarding, and potentially one of the workshops NGBH will be able to offer at the site.)
Cathy also noticed and photographed a trio of gray, paper and yellow birch, right by the driveway. These three trees looked fetching with their young, bright green leaves and characteristic barks. The yellow birches found so far on the property delight us. Gray birch was expected; in any of the disturbed areas we would have been surprised not to find the species. Gray birch is a pioneer eventually replaced by trees with fussier nutritive requirements. Yellow birch has the greatest longevity of any of Maine’s birches. Its beauty is at least equal to the iconic paper birches, though the comparison is pointless since the duo species occupy different ecological niches. That said, how nice to have these three trees growing together.
We have been wrestling with the introduction of paper birches, in two prominent areas of the garden design, because paper birches have become afflicted by bronze birch borers, a beetle native to North America. Wild seedlings and imported nursery plants will have different susceptibilities to the borer.
There are plenty of insects who dine on birches without damaging their hosts. Birches rank fourth (after oaks, willows, and the cherry/plum family) in Douglas Tallamy’s tabulation of trees that support Lepidopteran (butterfly and moth) caterpillars. There are eight birches native to Maine, including three that are alpine specialists. The family Betulaceae includes alders, birches, hornbeams, hazelnut, and hop-hornbeam.
An insect we may experience in the garden is an aphid that alternates between birches and witch-hazels to complete its life cycle. The aphids are barely noticeable on the birch leaves, but they create peculiar galls on the witch-hazels - soft–spined, almost ornamental growths on the twigs. We plan to have groups of witch-hazels throughout the gardens.
*BMLL’s property was most likely cleared for pasture or marginal farmland, and kept “open” well into the 20th century when it became a house lot. Investigating the site’s history could add to the narrative we are creating for the garden. Any volunteers?
List of flora mentioned in the article:
red oak (Quercus rubra)
white pine (Pinus strobus)
paper birch (Betula papyrifera)
gray birch (Betula populoifolia)
yellow birch (Betula alleghaniensis)
alder (Alnus species)
hornbeams (Carpinus caroliniana ssp. virginiana)
hazelnut (Corylus species)
hop-hornbeam (Ostrya virginiana)
witch-hazel (Hamamelis virginiana)
List of fauna mentioned in article:
bronze birch borer (Agrilus anxius)
aphid (Hamamelistes spinosus)