Friday, December 12, 2008

Christmas Tree

The lots full of Christmas trees felled on distant tree farms reminded us that 1) we hadn't yet purchased a tree and 2) aliens are killing our native forests. Didn't make the mental leap with us? Dark thoughts...that's what a few days of rain-forced confinement in the Audubon Center at Francis Beidler Forest will do to one's mind. Actually, continuing to read Dr. Douglas Tallamy's book Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens has reminded us of the dangers faced by our native trees and alerted us to a few new threats.

"Since the demise of the American chestnut, oaks have joined hickories, walnuts, and the American beech in supplying the bulk of nut forage so necessary for maintaining populations of vertebrate wildlife." (Tallamy, p. 128) In case you missed it, the "American chestnut (Castanea dentata) was the most common tree in the Piedmont and Appalachian regions of the East until the chestnut blight, brought to this country on resistant Japanese chestnuts, reduced our great chestnut forests to rare stump sprouts." (Tallamy p. 162) In addition to nut forage, the American chestnut was host to an unknown number of insects, which in turn became bird food.

"No other plant genus supports more species if Lepidoptera [517], thus providing more types of bird food, than the mighty oak." (Tallamy p. 128) Oaks provide vital nesting sites for birds and the acorns produced by some oak species can germinate days after they fall from the tree. "Restoring large stands of oaks to suburbia would go a long way toward shoring up the future of our nation's biodiversity." (Tallamy p. 130) "Well, good thing we've got plenty of oaks!" You might say that until you heard about Phytophthora ramorum, a fungus imported on ornamental rhododendrons from Germany, now called sudden oak death disease. This fungus has killed tens of thousands of oaks in California and Oregon before being shipped in nursery stock to Georgia where 49,000 plantings were sold before the fungus was detected. "It is not hard to find a plant pathologist who thinks our oaks will go the way of the chestnut, thanks to sudden oak death disease." (Tallamy, p. 66)

Come spring, the flowering dogwoods (Cronus florida) will add white to the myriad of colors produced by the non-native Asian azaleas now considered a natural part of the South. Snap you pictures now, because dogwood anthracnose (Discula destructive) [the species name says it all] arrived in the 1970s aboard imported and resistant kousa dogwoods (Cornus kousa) from Asia. While you're taking pictures, head to the Upstate and take some of the remaining hemlocks before they succumb to the imported hemlock woolly adelgid (Adelges tsugae).

We have several species of ash (genus Fraxinus) in the old-growth Francis Beidler Forest, but ash trees too are under attack from the emerald ash borer, which was accidentally imported from Asia. According to the U. S. Forest Service, the ash borer has killed millions of ash trees in the Upper Midwest and is rapidly moving east. If the borer doesn't get the white and green ashes throughout the Northeast, the non-native ash yellows disease certainly will.

Finally, the American beech (Fagus grandifolia) is on a per-species basis, more productive in its support of wildlife than even the number-one-ranked oaks. (Tallamy p. 160) Unfortunately, the only beech species in North America is under attack from a native fungus spread by the non-native scale insect (Cryptococcus fagisuga), which was brought to our shores on European beech nursery stock. This fungus-insect partnership causes the fatal beech bark disease.

Again, you may ask, "What this has to do with me?" Not a big tree fan...or insect fan...or bird fan? Do you like food at a reasonable cost? The soybean aphid (Aphis glycines) caught a ride to North America on ornamental Chinese buckthorn (Rhamnus utilis). The aphid has done millions of dollars in damage to soybean crops. Soybeans show up in plenty of foods. Guess who ultimately bears the additional cost of crop production? Enjoy your orange juice, because Candidatus liberibacter, "a bacterium that causes greening disease in citrus, a deadly disease that makes fruit inedible before it kills the tree altogether" is threatening to wipe out the $9 billion Florida citrus industry. (Tallamy, p. 68) It is unlikely to be contained because it is spread by the Asian citrus psyllid (Diaphorina citri), which arrived on orange jasmine sold as an ornamental plant throughout Florida.

Oh, now we remember why we made the connection between the Christmas trees for sale and death in the forest. The balsam woolly adelgid (Adelges piceae) was imported from Europe to New England and then to North Carolina on nursery stock and "has all but eliminated the Fraser fir (Abies fraseri) from the high altitudes of the Great Smoky Mountains National Park." (Tallamy, p. 68) Guess from where those Christmas tree firs arrived?

Give nature a wonderful Christmas present this year! Eliminate non-native plant species (especially as gifts) and plant or protect native flora! Merry, Christmas! See, we can be upbeat!!

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