Wednesday, March 23, 2016

More Skewed Logic on Invasive Species--Bradford Pear

Soon after writing a critique of the NY Times article that demonizes those of us who are concerned about invasive species, I received an email saying "They've done it again!" The email pointed to a NY Times oped by a science writer, Gabriel Popkin, about the Bradford Pear. Called The Ups and Downs of the Bradford Pear, most of the oped tells the standard story of how this tree, introduced by the nursery industry with great fanfare, became an ecological problem years later. Only at the end does the oped take a bizarre turn, using strange math and selective pessimism to conclude that, in a world full of bigger problems, we need not take any action.

The Bradford Pear turns our towns, and increasingly our countrysides as well, white with its intense, incandescent blooms in the early spring. It seems like a beacon after the long voyage of winter, telling us that the comforts of spring are close at hand.

But like many species introduced to our continent with great hopes,
the negative traits of Bradford Pear--one of the now many varieties of Callery pear--have come to outweigh the positive. Popkin describes these, completing the ups and downs of the oped's title. It's an oft-repeated story of a nonnative species turning invasive, despite all the promises to the contrary.

I can personally testify to how the Callery pear has begun to dominate along roadsides in central Jersey, invading edge habitat and fields. Some birds may get nourishment from the berries, but those are seasonal, and since wildlife don't eat the foliage, the landscape is becoming increasingly inedible. It would be like steadily displacing the food on grocery shelves with inedible merchandise, until there was no food left. That's the predicament for herbivores as we allow nonnative species to dominate the landscape.

The oped goes on to mention the trending popularity of native plants, link to an oped by entomologist Douglas Tallamy, and describe additional negative traits of the Bradford Pear.
Tastes have also changed. A manicured yard of foreign plants kept free of insects by chemicals is not necessarily the ideal anymore. Gardeners now choose native plants specifically to attract native insects. Common milkweed is not going to win any beauty contests, but thousands of people plant it anyway because it attracts butterflies. In newsletters and online, gardeners buzz about the insects pollinating and consuming their native plants. 
Science is now supporting this trend. The University of Delaware entomologist Douglas Tallamy recently compared the number of caterpillar species on a native white oak in his yard to those on a Bradford pear in his neighbor’s. The tally was 19 to one the first day, and 15 to one the next day. Birds, Dr. Tallamy notes, nourish themselves on these native caterpillars. To follow his logic, planting a Bradford pear would be tantamount to avicide. 
Municipal tree departments have turned squarely against the pear because of its tendency to shed branches onto sidewalks and power lines, especially when not pruned properly during its early years. Some cities, including Pittsburgh and Lexington, Ky., have banned new plantings of Bradford pear; others are removing the trees. Prince George’s County finally capitulated in 2009 and named the (native) willow oak its new official tree.
But then, out of the blue, there's a sudden pivot, and the writer leaps to the side of the Bradford Pear, as if pitying the tree species he's just spent considerable time criticizing.
I’m no Bradford pear fan, but I wonder if our need for villains in our environmental narratives has gotten the better of us on this one. Whatever the tree’s faults, it’s a living, respirating, photosynthesizing plant. It still makes shade on a hot day. It still sucks carbon dioxide out of the air. It still stops rainwater from pounding the soil and running off into sewers. The Bradford pear may not nourish 19 species of native caterpillars, but it seems to support one.
In one phrase, "our need for villains in our environmental narratives", all the evidence the author himself provides of the tree's negative qualities is recast as human bias, and that the Bradford Pear shares some positive traits with other trees is offered as somehow compensating for the negatives. 

Then there's some strange math, and a dismissing of Tallamy's patient research in ways reminiscent of the tactics used to minimize the dangers of climate change. Tallamy found 19 species of insect on a native oak, but only one species on the Bradford Pear. That big, big difference is now minimized by the armchair logic that one is greater than zero. In fact, over two days, Tallamy found 643 individual insects on the native oak, and only 2 insects on a Bradford Pear of similar size. That's a huge difference if you're a bird that needs insects to feed newborns. 

Immediately, one thinks of the oft-quoted "97% of climate scientists view climate change as human-caused". 97 to 3, 19 to 1--if those were sports scores, you'd call it a blowout, and yet when it comes to environmental issues, such numbers shift perceptions little if at all. Unless the score were 100 to nothing, there's still a smidgen of doubt to inhabit.

It's remarkable, too, how hard work is devalued here. Climate scientists brave the cold and danger of Greenland's ice sheets to study climate change; they spend months and years analyzing the data. Tallamy is out there watching, counting, studying how nature works. And yet, all of this patience and time and analysis is gleefully waved away by spectators who point to the crumbs of contrary evidence, in this case, the 2 insects out of 645 that were found on a Bradford Pear. 
In cities and suburbs, the Bradford may not be such a bad neighbor after all. Ecologically, it sure beats a road or a shopping center.
Better than concrete! This weak logic seems out of character for a thoughtful science writer.
At the same time, we’re losing more and more of our native tree options. American elms almost inevitably get Dutch elm disease if they live long enough, and can be maintained only through constant pruning and replacement, and at great expense. The seemingly unstoppable emerald ash borer is putting a quick end to the ash’s days as a street tree. Possible threats also loom over our oaks and maples, whose loss would be an urban ecological disaster.
All of this is true, though some American elm genotypes are proving sufficiently resistant to live long, productive lives. Many red and pin oaks are getting hit by bacterial leaf scorch, but many are not. If a pin oak can grow, feed and harbor birdlife, capture CO2, shade the sidewalk, and live a good life only partially shortened by bacterial leaf scorch, that's a plus, particularly given that very big trees growing near houses tend to make people nervous. The emerald ash borer does appear unstoppable, but there's been some success with stopping the asian longhorned beetle. Many native tree species not subject to imported diseases, such as hackberry, black gum, and basswood, are underutilized. So let's not use pessimism as an excuse not to take action against a very aggressive invasive like Callery pear.
All things considered, the pear’s crimes start to seem pretty minor. We certainly shouldn’t plant more Bradford pears. But if we’re going to spend time and money righting past environmental wrongs, there are far more important battles to fight than one against a lousy tree.
Here's the psychological payoff. A tree that's been called a "scourge" and a "monster" is then recast, thanks to some funny math and selective pessimism, as not so bad after all. Because there are other problems in the world--not clear which specifically are being referred to--we needn't deal with the problematic Callery pear. Action is left in the hypothetical. We get a good scare, and then are invited to sit back and relax. 

But, as with financial investment, isn't inaction a form of action? Every callery pear out there is spreading viable seed. Inaction insures the landscape will become steadily less edible to wildlife, as diverse native vegetation dwindles beneath the dense, expanding shade of callery pear. Unlike people, the tree has no capacity to rationalize inaction, and so continues to grow.

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