Emerald ash borer – an unnecessary catastrophe for North Carolina

Little attention has been given to the arrival of the emerald ash borer in the Triangle, but this small, poorly studied beetle from East Asia is going to cause enormous ecological and economic damage and contribute to human mortality here in the near future. It was first discovered to have reached North America in 2002, near Detroit, but is thought to have actually arrived in the early 90's, hidden in solid wood packing materials, probably from China based on genetic analysis. Emerald ash borer grubs tunnel beneath the bark of ash and related trees for a year or two, before metamorphosing into adults that are metallic green and red (beneath their wing covers) and eat ash foliage. The problem is that the beetle has few natural controls here, so they reach such numbers that they girdle and kill almost every ash having a diameter of an inch or more. Borers usually stay within a few miles of their natal tree, and the majority only travel yards, and even in areas infested years ago they only spread about 20 kilometers a year, so they wouldn't be in North Carolina without human help, such as the transportation of infested firewood or ash saplings. The US imports firewood from China, Japan, Estonia, Indonesia, Argentina, Canada, and other countries, and we have to trust that it has been treated, and not all imported wood has to be treated. At a campground in New Hampshire, people were bringing in firewood from as far away as North Carolina and California.
     

Emerald ash borers quickly spread across much of the northeastern US and neighboring Canada, and in isolated patches south to Louisiana and west to Colorado. Much of eastern Tennessee is infested, as well as areas around Atlanta. Emerald ash borers reached northern Virginia and a few years later appeared in southern Virginia, without infesting the area in between. In June 2013 they were found in Granville County north of Durham, followed by Vance, Person, and Warren counties, and county quarantines on hardwood firewood, ash wood and trees, and the ash borer itself began. These quarantines, which most people probably haven't heard of, must have failed, because in fall 2015 it was announced that the beetle has been found in several counties throughout North Carolina and the entire state has been quarantined. This means that potentially infested material can be moved within the state, for example Durham's yard waste goes to Novozymes, located near Franklinton, and if an infested log falls off a truck, it could produce a new infestation, though in this case the beetle has already reached Franklin County. Beetles have been found in Eno River State Park just north of Chapel Hill and Durham and near Umstead State Park in Wake County.

White, green, pumpkin, and Carolina ash, trees in the genus Fraxinus, grow in North Carolina. White and green ash are sometimes used in landscaping, and green ash were often planted to replace elms killed after Dutch Elm Disease arrived in the 30's. White ash are common along small streams and on well-drained hillsides, while green ash is one of the main trees in low-lying areas. In general ash grow in young forests, especially in wet areas, and then persist as a forest matures. There could be some pumpkin and Carolina ash in the Triangle, but they are mainly found in wet areas in the Coastal Plain. There is a large ash beside Franklin Street at University Baptist Church in the heart of Chapel Hill, and several in the northern part of UNC's campus, around the Hanes Art Center, Morehead Planetarium, and in the Coker Arboretum. A huge white ash was one of the winners in Durham's Arbor Day contest in March. In my neighborhood not everyone lives next to an ash, but there are ash on most of the streets, and in some places ash are very common.
  

Ash are large trees, straight growing when young, and have opposite branches and leaves, each leaf composed of several oval leaflets with few or no serrations around the edge and arranged like a plume (a pinnate compound leaf), similar to walnut, pecan, and sumac leaves. Winged seeds called keys hang in clusters on female trees and are released in fall or winter and drift with the wind. 

Ash are common and important in local ecosystems, and provide food for many species, such as the big yellow, black, and blue Eastern tiger swallowtail butterflies that are common now, and ash could be the only food source for some species. The Encyclopedia of Life (eol.org) cites a study saying 43 arthropods entirely depend on ash and 30 others have only one or two choices besides ash.
 

Ash are economically important for their wood, especially white ash, which is the classic wood for baseball bats, combining strength, elasticity, and lightness. Green and pumpkin ash are also cut, and fortunately old trees are less valuable for wood than young trees. According to the USDA, just in the Eastern US almost 114 million board feet of ash, worth $25.1 billion dollars are cut. Ash have herbal uses and black ash, not found in NC, is culturally vital as a material for native basket weaving. The loss of trees to the ash borer has been shown to increase cardiovascular disease among women, so there will probably be an affect on human health.
  

There are a few native trees in the olive family that could be susceptible besides ashes. Near Dayton, Ohio in 2014 emerald ash borers were found in fringetrees and this has been seen elsewhere, though not yet in North Carolina, according to the NC Forest Service. It is possible that only fringetrees that are already sick are attacked, and at least around here, many fringetrees might be too small for the borers to use. Fringetrees have delicate white flowers in April and are sometimes planted as ornamentals, as are Chinese fringetrees.

The NC Forest Service estimates that there are 258 million ash trees growing in NC forests (as opposed to street trees), of which 60% are green ash, and the ash borer seems to prefer green ash most of the species growing in this state. According to the Federal agency APHIS, wild and planted ash in the US are worth over $282 billion dollars, and their worth is beyond accounting for organisms that need ash to survive. About 2 million saplings are grown in nurseries each year, worth $140 million dollars. In all, over 8 billion trees in the US are at risk, equally 2.6% of the country's “timber trees.” It is thought that about 100 million ash trees have been killed so far.
 
Ash are useful for wildlife even after they die, but hazards for people and property underneath, and there could be tree removal scams as the borers begin killing trees It is estimated that treatment, removal, and replacement costs for 37.9 million ash in developed areas in 25 states from 2009 to 2019 will reach $10.7 billion dollars, while cutting all of the ash would cost $25 billion. The City of Durham thinks it won't have a problem dealing with the coming increase in dead trees, and there have been some meetings about the borer, while UNC hasn't given any indication that it is prepared.
        

In Michigan the borer swiftly killed the monoculture of green ash planted along streets, and while genetically diverse wild trees might be a little better off, after several years almost every sizeable ash in an infested area will be dead, though they might be able to sprout from the roots and for a few years there will still be viable seeds in the soil. It is unknown if the few “lingering ash” left after most of the population has been wiped out have resistance or are just fortunate. American species of ash have been planted in Asia, and can grow there despite the borer, because it is not abundant in its native range.
 

An influx of woodpeckers is one of the first signs that the borer is around. Several native wasps feed on this exotic species, and observing Cerceris fumipennis wasps carrying borers into their burrows is a way to get early detection (see www.cerceris.info/index.html and info.ncagr.gov/blog/2014/02/12/a-wasp-biosurveillance-program-a-new-way-to-monitor-for-emerald-ash-borer-and-other-pests/ ). Tiny parasitoid wasps that parasitize a high percentage of emerald ash borer eggs (Oobius agrili) or grubs (Spathius agrili and Tetrastichus planipennsi) in China have been tested and approved for release here, including in Granville County, and surveys are finding more species in East Asia. This year the three wasps won't be released in Granville County, to see if they have become naturalized, but they will be released in Wayne County and possibly elsewhere. An Asian wasp (composed of only females in the US) that researchers hadn't realized was already here was found attacking the borer in western Pennsylvania. Some ash grow far enough north that winter cold will probably control or stop the beetle, but the rest of North America seems to have a congenial climate for it.

Ash can be kept alive with insecticides, such as controversial neonicotinoids injected into the soil or trunk, but this isn't a technique useful for saving an entire forest and treatment has to be repeated periodically. See the booklet Insecticide Options for Protecting Ash Trees from Emerald Ash Borer and the NCFS' Emerald Ash Borer Insecticide Guide, both of which are posted online. The NCFS recommends treating trees when the borer has been found within 10-15 miles. Ash seeds don't stay dormant in the soil very long, so the Federal government and a group at NCSU are preserving seeds. Possibly ash could be preserved as bonsai or espalier, as long as the stems are less than inch in diameter.

 

The borer is native from the Russian Far East and China to Taiwan and Japan, but there may be changes occurring there as well. In 2004 it was noticed that the beetle was killing American green ash in Vladivostok and investigations showed that white and green ash had been killed in Khabarovsk during the previous 5-10 years. In 2003 it was found attacking green and European ash near Moscow for the first time, and ash are 6^th most commonly planted tree there. A theory is that the borer is hitchhiking on vehicles, since Russians apparently don't transport firewood as extensively as Americans or burn ash for residential heating. It is thought to have gotten to Moscow in the 90's, without infesting cities in Siberia first, and it is unknown whether it got there from its native range or from North America. Emerald ash borer grubs are killed by chilling to -35.3°C and while Moscow isn't usually that cold, it has had record lows colder than that over three months of the year, according to Wikipedia. Apparently it hasn't gotten cold enough over 20 years, and the trend is for continued warming, though extreme temperature fluctuations might not benefit the borer. Ash further west in the EU are already threatened by a new fungal disease, ash dieback. It seems possible that there is a common cause for the borer's recent spread in both Russia and North America, and possibly also ash dieback, such as globalization and climate change. Where the borer is native, it attacks trees that are already stressed, for example by drought, which could be affected by climate change.
   

It is thought that non-native species naturalize in the US at a rate of 2.5 species a year. A few of these new arrivals cause serious problems and emerald ash borer isn't the only new pest or disease to have reached North Carolina in recent years. Since 1957 the balsam woolly adelgid has killed 95% of mature Fraser firs high in the Appalachians and could eliminate the trees in the wild over the next 50 years. A similar insect, the hemlock woolly adelgid, got to Richmond, Virginia from Asia by the early 50's, and threatens to kill most of the Eastern and Carolina hemlock population. It reached Cary's Hemlock Bluffs Nature Preserve, where Eastern hemlocks have survived since glacial times, but the adelgid has been eliminated there. There are some planted hemlocks on the crest of the big hill behind the NC Botanical Garden. In the late 19^th century the European beech scale insect reached Nova Scotia, Canada, and in feeding the scale creates entrances for native and non-native fungi to infect beech, creating a new syndrome, beech bark disease, though many beech survive infection. Dogwood anthracnose is an introduced fungus first noticed in 1978 that kills dogwoods, but a warmer climate should decrease its impact. There are actually two fungi that cause Dutch elm disease; the less virulent species got here from Europe in the years before 1930, and an increasingly common, more virulent species that might have arrived in the 40's or 50's, and probably caused an outbreak of Dutch elm disease in the 70's. In 2003 laurel wilt disease was noticed near Port Wentworth, Georgia, and kills redbay and related trees, including avocados. It is caused by a non-native fungus, spread by non-native ambrosia beetles. Laurel wilt is a bigger problem in the Coastal Plain, where the disease is a serious threat to redbay, but it can also harm sassafras, which is relatively common in the Triangle, and bays are used in landscaping here, such as at UNC. It is currently in southeastern NC, though it was projected to have gotten to the Triangle by 2015. In contrast, the thousand canker disease fungus is spread by a beetle native to the US, in the Southwest, but in recent decades it suddenly appeared in the the East, where it threatens the valuable black walnut. Black walnuts seem to be rare in the Triangle unless planted, such as the large walnuts at West Point on the Eno, whether for natural reasons or because too many were cut for wood. Thousand canker disease has been found in Haywood County, on the border with Tennessee. These are only a few of the introduced organisms threatening trees native to NC, and there are more distant threats like sudden oak death from California and the Asian longhorn beetle, which is causing problems around New York and elsewhere, and arrived the same way as emerald ash borer. Eurasian gypsy moths, accidentally released in 1869, stress healthy trees rather than directly killing them, but the moth is poised to come across the border from Virginia or by transportation from another state (see the USDA's Southern Forest Futures Project, srs.fs.usda.gov/futures/ ).
 

It has been suggested that dinosaurs were already having problems before an object from space hit the Yucatán 65 million years ago, because at the time the continents were more connected, so there were fewer barriers to the spread of organisms across the world (see Robert Bakker's book The Dinosaur Heresies). Emerald ash borer and other non-natives threaten to drastically change American forests, and what we see today is already missing major pieces. For example, in parts of North Carolina American chestnuts were once a major canopy tree in oak-chestnut forests, but chestnut blight came from Europe prior to 1904 and left only a few precarious survivors, so now we have oak-hickory forests.  Chestnuts mostly grew in the western part of the state, but there were some in Orange County.         

Since the arrival of the ash borer, regulations have been changed to address the problem of wooden packing that could conceal dangerous pests, but the threat of globalized pests remains. Partly this is a problem of poor vigilance and lack of concern for the integrity of our native ecosystems, but imperialist globalization makes it more likely that there will be more catastrophic introductions. Offshoring factories to China or even Mexico saves money for capitalists by decreasing labor costs, etc., but the volume and variety of imports makes it more likely that exotic species will slip in and we have to trust countries to enforce existing biosecurity rules. The capitalists often don't have to pay for their damage, such as dumping carbon dioxide or heavy metals into the atmosphere, but society and our common environment is harmed. In addition, climate change could help some non-native species spread. For example, the woolly adelgids and emerald ash borers should benefit from milder winters.

[Note the Greener Durham forum on emerald ash borer at City Hall on April 28th, for details see a later post]