Sunday, February 17, 2008

Braford Pear

What’s still green: Conifers, rose stems, yuccas, coral bell, sea pink, Saint John’s wort, yellow evening primrose, Mount Atlas daisy, some grasses

What’s gray or gray-green: Salt bush, winterfat, snow-in-summer, some pinks.

What’s red: Cholla, some pinks, small-leaved soapwort, coral and purple beardtongues, purple aster.

What’s blooming inside: Aptenia, zonal geranium, kalanchoë; Christmas cactus in bud.

Animal sightings: Sharp-clawed, four-toed paw prints in driveway mud.

Weather: First part of the week I drove out when it was 20 degrees and returned home after temperatures had risen to 50; the ground continued to harden at night, and soften during the day. Night temperatures warmed late in week when a predicted storm didn’t materialize. Some ice remains above bulbs in the garage drip line. Last snow 2/4/08; 10:59 hours of daylight.

Weekly update: In the past few weeks I’ve noticed greater color differences between the small twigs at the tops of trees and their trunks. The variations are most obvious with the Bradford pears growing at the post office, where smooth cinnamon limbs arise from vases of furrowed, gray bark.

Part of the difference is simply age. The outer edge of woody stems accumulates dead cells as the inner tissues continue to produce new layers. Younger brown stems simply haven’t acquired the patina of age.

Weather, like that of the past few weeks, introduces more changes when moisture gathers in crevices between branches, then freezes to pressure brittle limbs until one splits away. The trees build scar tissue necklaces around the breaks, which expands the gray bark up into the more golden branches.

The freeze-thaw cycle also affects the outer water-bearing cells of the woody stems. After enough expansion cycles, the inelastic bark shucks off, exposing the smoother layer behind the outer cork. On some trees at the post office, those exposed cells have whitened, while other tree trunks still have red inlays.

The damage is invisible in April when the trees are covered with five-petaled white flowers, and remains hidden under shiny-topped green leaves in summer. However, trees rarely reach their ultimate age of thirty because the constant splintering kills them.

The problems weren’t foreseen when the USDA released the sterile, fast-growing, pollution-tolerant, narrow, upright trees to nurseries in 1960. It no doubt spread as a replacement for elms that were being devastated in city and city. Some nurserymen later developed new cultivars with more open branches, but some of these went to seed and produced thornier problems.

The agriculture department originally imported Pyrus calleryana seed from China for Frank Reimer, who had discovered it was resistant to the fireblight bacteria that was then destroying Oregon orchards. It eventually became a popular rootstock for the edible fruit tree, Pyrus communis.

It wasn’t until the expansion of suburbs around Washington in the 1950's that department growers saw the callery pear’s potential for beautifying raw, barren streets. According to Theresa Culley and Nicole Hardiman, they selected one tree growing in Glenn Dale, Maryland, from seed collected by Reimer in 1919 near Neijing for cuttings to graft onto other callery pear stock.

When it was released, the USDA recommended that home buyers look for trees that nurseries had pruned and trained into open forms. However, some nurseries may have saved costs by avoiding that pruning, and others may have deliberately trained saplings to a tighter upright form. Still others may have done poor grafts which sprouted scion pears that could pollinate the Bradfords.

Meantime, landscape designers are abandoning the Bradford pear, because it becomes unsightly before it self-destructs and leaves clients unhappy with maintenance problems that lead to replacement costs. I have no idea if the post office will replace these trees when they die. My guess is one has already died and its space been left empty.

However, it is striking that someone here in the valley made a decision to plant white flowering trees on government-controlled land in the first place. The April-blooming Bradford pears are on the north side of the parking lot, while northern catalpas flower in June on the east end. A large bittersweet holds forth in May by the front door. The trees aren’t tall enough to provide summer shade, but right now the just opened sun burnishing red wood at 9am justifies the weekly trek into town to empty junk mail from my PO box.

Culley, Theresa M. and Nicole A. Hardiman. "The Beginning of a New Invasive Plant: A History of the Ornamental Callery Pear in the United States," BioScience 57:956–964:2007.

USDA, Plant Science Research Division. Growing the Bradford Ornamental Pear, Home and Garden Bulletin 154, 1968, revised 1971.

Photograph: Bradford pear at post office, 16 February 2007.

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