You can’t see a forest without the trees
They took all the trees and put them in a tree museum,
And they charged all the people a dollar and a half to see ’em.
Don’t it always seem to go
That you don’t know what you’ve got ’till it’s gone?
They paved paradise and they put up a parking lot.
Joni Mitchell wrote those lines to her 1970 environmental anthem, “Big Yellow Taxi,” on her first visit to Hawaii. “I took a taxi to the hotel and when I woke up the next morning, I threw back the curtains and saw these beautiful green mountains in the distance. Then, I looked down and there was a parking lot as far as the eye could see, and it broke my heart. …”
The song’s “tree museum” refers to Honolulu’s 14-acre Foster Botanical Garden located in one of the busiest sections of the city. But it isn’t encroaching urbanization that’s the principle threat to America’s forests.
Most of us have some knowledge of the two great environmental catastrophes for North American forests during the first half of the 20th century. The chestnut blight is a fungus that was introduced to the U.S. on a shipment of Japanese chestnut nursery stock in 1904. By 1940, it had leveled almost every mature American chestnut in the nation – an estimated 4 billion trees – with enormous negative ecological and economic consequences.
In 1910, another fungus native to Asia, this one affecting elm trees, reached Europe. Eighteen years later, a shipment of infected elm timber from the Netherlands brought the malady, subsequently named Dutch elm disease, to America. Within 30 years, few of the many Elm Streets throughout the eastern half of the continent were graced by any of the majestic trees. Since then, increasing international trade – with the consequent movement of timber and wooden packaging materials from one part of the globe to another – has only exacerbated the problem.
Even well-intentioned human actions sometimes have led to unhappy results. The gypsy moth of Europe, whose hairy, blue and red-spotted larvae feed on the vegetation of more than 300 species of trees and shrubs, accidentally was released in Massachusetts in 1867 by a researcher studying silk production.
Unless controlled, a healthy tree can be completely defoliated by the larvae in two years. On a plus note, although the moth is now found in about three-quarters of Ohio’s 88 counties, Ohio Department of Natural Resources foresters have met with some success in “suppression projects” using hormone traps, biological controls and insecticides to keep populations below damaging levels.
It’s a different story with emerald ash borers. First discovered in southeastern Michigan in 2002, larvae of the half-inch long iridescent green beetles (native to Asia) feed on the inner bark of all American species of ash. As of 2017, it has devastated ash populations in 31 states – killing hundreds of millions of trees at an estimated cost to the timber industry of $2 billion and another $1 billion for removal of dead trees from public and private properties.
Among numerous newer threats to Ohio’s forests, I only have space to briefly discuss beech leaf disease (BLD), Asian long-horned beetles (ALB) and hemlock woolly adelgids (HWA). The scary thing about BLD is that no causal agent for the disease as yet been found. First seen in Lake County in 2012, it’s now spread through other northeastern Ohio counties and into Pennsylvania. In BLD-infected forests, it’s been killing nearly 100 percent of the beeches.
ALB first was discovered in the U.S. in Brooklyn in 1996. The 1 1/2-inch-long shiny black beetle with white spots on its back and extremely long, white-banded antennae is native to China and the Koreas. Its larvae feed on a variety of tree species, with maples, poplars, willows and elms among their favorites. Infected trees die within 10-15 years.
Only one population has so far been found in Ohio, in Clermont County (near Cincinnati) in 2011. The good news is that last month, ODNR announced the beetle has been eliminated in two of the county’s townships (Batavia and Stonelick).
HWA is a minute Asian aphid only 1/16-inch long that first was found in Richmond, Virginia, in the mid-1950s. The insects suck sap from the base of the conifer’s needles, killing them. Like many invasive species, it is kept under control in its native area by predators not found in the U.S. Though tiny, the aphids have short life cycles and reproduce asexually on hemlocks, so a single insect can create an enormous population in just one season.
Virtually all hemlocks of the once well-populated Smoky Mountains and neighboring areas have been destroyed by HWA. The aphid has been reported in about half of Ohio’s counties, primarily in the eastern and southeastern sections. Individual trees can be protected for 6-7 years with potent insecticides injected into the tree or sprayed on its base.
Let’s end with a couple of positive items. Researchers at Cornell University are working with a highly effective natural HWA predator, the Asian beetle Laricobius nigrinus, nicknamed “little Larry.” If the studies go well and little Larry can obtain governmental approval for release to the wild, we may be able to save our eastern and Carolina hemlocks – and perhaps even restore them to areas where they have been extirpated
At least as exciting, plant pathologists at Syracuse University have developed a genetically engineered blight-resistant American chestnut that so far has excelled in laboratory and field test exposures to the fungus. Just imagine if that magnificent tree were to one day find its way back to its former position as the dominant tree of the eastern deciduous forest. Just imagine.
Ken Baker is a scientist and a retired biology professor. If you have a natural history topic you’d like the author to consider for an upcoming column,
email your idea to rweaver