A redbay at the NC Botanical Garden ©
Besides the near extermination of ashes and possibly other trees by the emerald ash borer, the subject of a previous post (April 16, 2016), there are a few other serious non-native threats to the integrity of North Carolina's environment, either established in nearby states or already found here (there is an overview at: ncforestservice.gov/forest_health/current_concerns.htm ). Another major threat to forest ecosystems is laurel wilt, a non-native fungal disease spread by the similarly exotic redbay ambrosia beetle, which kills trees in the laurel family, especially redbays, but also sassafras, avocados, and other species, and is already spreading in southeastern North Carolina.
In summer 2002 a USDA pilot project to detect newly arrived non-native insects, started only in 2001, caught redbay ambrosia beetles (Xyleborus glabratus) around Port Wentworth, Georgia, near Savannah. These tiny woodboring beetles, about 2 mm long, are native from eastern India and Bangladesh to Taiwan, southern Japan, and some Pacific islands, and are not a major pest there. Females were trapped in 2002, probably the first generation born in solid wooden packing material from Asia. It only takes one female to start an infestation and the beetles can complete their life cycle in as little as 40-60 days. There are multiple broods in a year and adults are around at any time of year and the winged females are most active late in the day, which is important when using some insecticides. By 2003 people realized that an unusual number of redbay trees were dying in Chatham County, Georgia (where Port Wentworth is located) and across the border in Beaufort and Jasper counties in South Carolina, and late in 2004 the cause was identified. Redbay ambrosia beetles tunnel into living trees, inoculating them with various fungi (what the beetles actually live off of), carried in pouches on the beetles' mandibles. Apparently the non-native fungus Raffaelea lauricola is what causes laurel wilt. R. lauricola spreads through a tree's xylem vessels, and the fungus itself and possibly the tree's over zealous response to the infection cuts off circulation, girdling and killing the aboveground parts of the tree over as little as 3-12 weeks. Redbay ambrosia beetles have been found carrying R. lauricola in Asia, but laurel family trees there must have co-evolved with the disease while it is a new epidemic in the Americas and can kill healthy trees. The beetles prefer large trees, mostly boring into the first 1.5 meters of the trunk, and sometimes it is possible to see tiny “sawdust toothpicks” marking the boreholes. Older trees are most at risk, but even saplings only 1 to 1.5 cm wide aren't safe. In one place in Florida redbays 1” wide or more were monitored and mortality rose from 10% to 92% in only 15 months and mortality was 98% between 2004 and 2009 on St Catherines Island, Georgia. The beetles prefer redbays (Persea borbonia) here, but have been found on non-laurels in Asia. R. lauricola has been found in live oaks, but only laurel family trees are thought to be at risk, and the fungus can be picked up and transmitted by other species of ambrosia beetle in the laboratory. There is some evidence that avocados might be getting laurel wilt from a different beetle.
Redbay is most at risk, but swamp bays (Persea palustris) and sassafras (Sassafras albidum) are also susceptible, as are two endangered small trees, pondberry (Lindera melissifolia) and pondspice (Litsea aestivalis). In experiments, Northern spicebush (Lindera benzoin), lancewood (Nectandra coriacea), and pepperleaf sweetwood/Gulf Licaria (Licaria triandra) can get laurel wilt to some degree and these small trees/bushes grow in areas already effected by the disease, but redbay ambrosia beetles prefer trees with thicker stems. Spicebush, which grows near waterways in the Triangle, apparently does not attract the beetles, so it may be at low risk, but the beetle likes Asian spicebush. Pepperleaf sweetwood is a Federal endangered species with fewer than 12 wild trees in Miami-Dade County, Florida, but it also grows on some Caribbean islands. By 2007 avocados (P. americana) were dying in yards in Jacksonville, Florida and in 2012 laurel wilt reached commercial groves in Miami-Dade County. The West Indian variety of avocado most common in Florida also happens to be the variety most susceptible to laurel wilt, and avocados are Florida's second biggest fruit industry. On the other hand, avocados on Merritt Island, Florida were surrounded by dying redbays for 3-4 years without major problems, and the beetles reproduce poorly in avocados. A fungus carried by a different ambrosia beetle is impacting avocados in California and affects over 200 plant species, but so far it is only a Western problem. In 2013 a bay laurel, an ornamental native to the Mediterranean, growing near an infected avocado in Gainesville, Florida was killed. Tests show that redbay ambrosia beetles are attracted to and can reproduce in California laurel (Umbellularia californica), and it is susceptible to laurel wilt if the disease gets to the West. Like redbay, California laurel is valued for woodworking, which makes human spread more likely. There is a Mexican redbay that is susceptible in the lab, and there are many related trees in Latin America, some important for timber. Bay laurel and viñátigo (P. indica), a common tree in Madeira and the Canary Islands, are susceptible. Ornamental camphortrees (Cinnamomum camphora) can be killed by laurel wilt, but they co-evolved with the redbay ambrosia beetle in Asia and aren't in much danger. In Asia the beetle is found in trees like Asian spicebush (Lindera latifolia), yellow Litsea (Litsea elongata), and sal (Shorea robusta), and is not known as a pest of avocados.
Sassafras grows throughout North Carolina, while redbay is found in the Coastal Plain, including Moore, Lee, Harnett, Johnston, and Wilson counties just south and east of the Triangle. There are some redbays growing behind the NC Botanical Garden's Totten Center, resembling more familiar broadleaved evergreen magnolias. Spicebush is also found throughout the state, but less so in the Coastal Plain. Pondspice grows in a few places in southeastern NC and pondberry grows in and around Bladen County, the epicenter of laurel wilt in southeast NC.
A single female beetle is all it takes to start an infestation, and they can travel about 15-34 miles (55 km) a year, and might also be carried in the wind, but they are spreading furthest through unwitting human transportation. In 2004 laurel wilt spread to a campground at Stephen C Foster State Park in Georgia, west of the Okefeenokee National Wildlife Refuge, probably with human help, and in 2007 it spread around a hardwood mulch producer close to Nahunta, Georgia. Earlier in 2006 an infestation started on a railroad line in Jesup, Georgia near a pulp plant and state prison, either on its own or with human help (see the Georgia Forestry Commission's Distribution and Spread of Laurel Wilt Disease in Georgia: 2006-08 Survey and Field Observations, 2008). In 2009 it spread to Richmond County, Georgia, 65 km from the nearest known infestation (Evaluation of Laurel Wilt Disease in Georgia: Progression in Redbay and Sassafras - 2008-2010). The NC Forest Service hasn't disseminated information this detailed about how laurel wilt is being spread, but might if asked. Logs brought in for woodturning took the beetle to Volusia County, Florida in 2008. It has been suggested that emerald ash borers are using vehicles to travel around Russia, and it seems possible that redbay ambrosia beetles could spread that way too. Human transportation seems to have carried the beetle and its fungus to the Gulf coast of Mississippi in 2009, the Florida Panhandle in 2010, central Alabama in 2011, northern Louisiana in 2014, and East Texas in 2015. There is some evidence that the redbay ambrosia beetle spread from Georgia and northern Florida separately, or got to Georgia in 2001, not 2002. The beetle and laurel wilt are now found in southeastern North Carolina, much of South Carolina, coastal Georgia, almost every county in Florida, coastal Alabama and Mississippi, along the Louisiana/Arkansas border (it was discovered in sassafras in Arkansas last February), and in extreme East Texas.
Until 2009 the beetle had only gotten as far north as the area around Charleston, SC, but then it jumped to the Myrtle Beach area (Horry County) bordering NC, and in March 2011 it was suddenly found near Colly, at the eastern end of Bladen County, NC and when the NCFS looked for it, it was found in three other counties within 15 miles of the first site. Laurel wilt was found in Brunswick County in 2012, New Hanover County in 2013, and now effects nine counties in NC. I wonder if laurel wilt could have spread more than the NC Forest Service realizes. One piece of good news is that a 2008 study predicted that by 2015 laurel wilt would have spread across most of NC, except for some of the northern Piedmont and mountains, but so far it is only found in Bladen, Brunswick, Columbus, Duplin, New Hanover, Onslow, Pender, Robeson, and Sampson counties, though it is still spreading within those counties and human transportation has greatly advanced the 'schedule' in other states. At the time sassafras was a wild card and studies have now shown that the beetle tolerates cold well enough to spread throughout the eastern US.
Symptoms of laurel wilt vary by the species affected. Evergreen redbays turn wilted and brown until the entire canopy is just dead leaves. There could be signs of boring, such as sawdust and dried sap. Peeling the bark back reveals dark lines in the sapwood beneath. Stricken trees attract additional redbay ambrosia beetles and other beetle species. The black twig borer is another Asian ambrosia beetle that attacks redbays and other trees, but it only kills isolated branches. Deciduous sassafras turn brown or display their bright fall color early and lose their leaves. The fungus seems to spread through interconnected roots in sassafras and avocado groves, and may be able to do so in pondberry as well.
Individual trees can be protected with fungicide for one to one and a half years at a time and insecticides and beetle-killing fungi can reduce the beetle population, but there is no way to protect an entire forest. So far there don't seem to be any parasites available in Asia to naturally control redbay ambrosia beetles, in contrast to emerald ash borer. In 2006 all infested trees on public and private lands on Jekyll Island, Georgia were removed in an attempt to get rid of the beetle, but the beetle remained in 2007. Transporting untreated wood and live plants long distances is very risky, but live plants and wood from trees in the laurel family especially should not be transported out of or through infested areas. Amazingly, while NC had county quarantines and now a state quarantine against emerald ash borer, there does not seem to be a quarantine against laurel wilt (see www.dontmovefirewood.org/the-problem/state-state-information/north-carolina.html ) and some infested states lack regulations. Maybe the rationale is that redbay wood is not often cut and transported.
The beetles and fungus can live in a dead tree for more than a year, and, ideally, infested wood should be chipped, burned, or buried on site. Leaving infested wood exposed in a dump allows redbay ambrosia beetles to reproduce and the fungus could be picked up by other beetle species. In a study, no beetles or fungus were found 2 days after chipping, but the wood still should not be considered clean. Covering a pile of chips with plastic kills the beetles, but the chips could attract new beetles and should not be transported. Advice to Florida avocado growers claims that high-speed mechanical pruning equipment does not spread laurel wilt, but hand saws can. Wounds such as pruned branches attract beetles. Cutting roots linking trees in infested groves using trenchers, etc. might help protect trees such as sassafras once an infection starts in a grove. Coppicing might allow homeowners to keep trees alive, but at a smaller size.
Redbays if not other trees can resprout from the ground after the tops are killed and there are seeds in the soil, so they probably don't face extinction, but this new growth can get re-infected as it gets larger. Strangely, redbays often re-sprout from the roots, while thicket-forming sassafras often re-sprout from the trunk. When people talk of trees being killed by disease, it is usually unclear if they mean the entire tree is dead or if the roots are still alive, so that regeneration is possible. Also according to the Georgia Forestry Commission, dead redbays rot faster than sassafras, but sassafras wood is also supposed to be rot-resistant. Researchers are testing resistant varieties and storing germplasm for future restoration, though it may be hard to store redbay seeds longterm.
Fear of laurel wilt or other new pests should not result in the killing of healthy trees. The situation may be the same as with emerald ash borer, where studies have shown that preemptively removing ash trees is more expensive than waiting and does not stop the borer. I might have seen this happen in Durham in December, and I am not advocating pointlessly hastening the downfall of these trees.
Redbay Ecology and Culture
Redbay and related trees are important members of forests in the coastal plain and barrier islands and are valuable for both wildlife and humans. Redbay grows naturally in the coastal plain from southern Delaware to East Texas and into southern Arkansas, as well as the Bahamas, so I don't have a lot of personal experience with it here in the Piedmont. It typically grows near water but also sometimes in drier sandy soil, often under longleaf pines. The Bald Head Woods Reserve conserves rare maritime forest on the coast of NC, where redbay is or was an understory tree making up about 11.4% of the vegetative cover, while in Florida's Everglades, redbays make up 30% of the canopy in forested areas, and possibly more in certain habitats. The loss of redbays could greatly change ecosystems, such as by opening gaps that non-native plants will fill. Redbays can grow up to 70' tall and 3' wide and are valued as ornamentals and were used to reclaim phosphate mines. Swamp bay is similar, possibly just a subspecies of redbay, and grows in swamps over about the same range. Silkbay is another subspecies or a separate species, found in oak-pine scrub habitat in Florida.
US animals very threatened by the laurel wilt epidemic are Palamedes swallowtails, large black butterflies with yellow markings whose caterpillars eat mainly redbay, three tiny leafmining moths in the Phyllocnistis genus, and the redbay psyllid (Trioza magnoliae), an insect that forms swollen galls on redbay leaves. Palamedes swallowtails feed only on redbay and possibly sassafras; in experiments their caterpillars can feed on exotic camphortrees, but females don't know to lay eggs on these Asian trees. A study in Mississippi found that the swallowtails were three times less common where laurel wilt had been around for three years or longer. Palamedes swallowtails are an important pollinator of the yellow-fringed orchid (Platanthera ciliaris), and possibly related orchids with deep flowers, though the orchid also grows where these swallowtails are absent, including in the Triangle and in western NC. Spicebush swallowtails are another pollinator, and also depend on trees in the laurel family. Few other animals seem to feed on redbay leaves, and they have alternatives. Avocado weevils eat plants in the laurel family, and despite their name, might prefer redbays. Deer and black bears eat the leaves and fruit. The fruit is bitter, but is eaten by turkeys and many other birds, while bobwhites and a seed beetle eat redbay seeds.
Fresh or dried leaves can be used like bay leaves in cooking. Redbay is a potential graft for avocados and a source of disease resistance through crossbreeding. According to Plants for a Future (pfaf.org), redbay had many uses in Seminole herbal medicine, such as treatment of constipation, rheumatism, fever, and to induce abortion. Bays in general are very important in Seminole and Miccosukee traditional medicine and ceremonies in Florida. Its red wood polishes well and is used in cabinetry and other interior uses and boats, but the wood is strong but brittle and straight trees are rare.
Sassafras Ecology and Culture
Sassafras is an important but probably overlooked tree that grows throughout much of the eastern US, from southern Maine and Michigan to East Texas and the Florida Panhandle. It can grow 90' tall, 6' across, and live 1000 years (longer than oaks or UNC's ancient Davie Poplar, a huge tuliptree), but around here they are usually 15' tall or shorter. The best and most public specimen I can think of is a pretty grove of saplings about 15' tall where Barbee Road crosses over I-40 in Durham. Sassafras have very distinctive soft and aromatic leaves, which can be oval, mitten-shaped, trident-shaped, and rarely five-lobed, probably depending on the amount of shade. Sassafras fills different niches across its large range, but around here they often grow along fencerows and as understory trees in somewhat moist and rich soil near streams and on hillsides. Sassafras is somewhat common in the Triangle, but might escape notice because it is usually small.
Many insects feeding on sassafras, including colorful and well-known spicebush swallowtails and Promethea, Cecropia, Io moths, and several less well-known moths, sassafras borers (a long-horned beetle), and other insects, but most or all of them have options if many sassafras succumb to laurel wilt. Deer, rabbits, and groundhogs also browse on sassafras. Black bears, fox squirrels, turkeys, bobwhites, robins, towhees, mockingbirds, catbirds, pileated woodpeckers, bluebirds, phoebes, and other birds eat the late summer or fall fruit.
Leaves can be eaten fresh and gumbo filé and soup thickener is made from dried and powdered shoots. Tea is made by boiling the washed roots and adding sugar or using the flowers. Twigs were boiled, mixed with molasses, and fermented for beer. Various parts of sassafras were used against many illnesses, and It had such a reputation that it was a principal export of Jamestown and other English colonies. It is probably more useful for its taste than as a cure, and has been used in soap, perfumes, and flavoring. Sassafras' popularity came to an end when the FDA classified its oil, safrole, as carcinogenic, though the risk might be overstated. Safrole is used to make the drug ecstasy, but the oil is usually harvested from related trees. Sassafras is also a source of dye. Sassafras wood is fragrant and was used in beds and chicken coops in an attempt to repel pests, as well as for posts, railroad ties, barrels, buckets, furniture, finishing, boats, and dugout canoes, as it resists rot and shrinkage.
A grove of miniature sassafras in January ©
Laurel Wilt and Imperialist Globalization
Laurel wilt is a disaster that could have been prevented and is only one of several invasive pests harming trees in the US in recent years, and non-natives species that run wild are a major problem worldwide, rarely highlighted by opponents of “free trade.” Changes in global trade patterns have caused trends in the organisms that reach the US and become established, despite the enactment of Federal regulations since 1912. A 2010 study (Historical Accumulation of Nonindigenous Forest Pests in the Continental United States, posted online) found that about 2.5 established non-native forest pests were detected per year from 1860 to 2006 (though studies of aquatic and other habitats have found accelerating colonization rates), but the most damaging pests (all 16 microbes and 62 insects, 14% of the insect total of 455 species) were discovered at a rate of one about every 2 to 2.5 years. The rate varied by how the pests live, so the highest rate of detection of leaf eating pests in the USA was around the 30's, while sap-feeding insects peaked in the early 1900s, but had a smaller secondary peak in the late 20th century that the study left unexplained. Discovery of high-impact pests and phloem vessel and woodboring insects has greatly increased since the 80's. 56% of the new insects detected between 1980 and 2006 were in this borer category. 56% of the high-impact pests with known detection dates came before 1930 and then fewer were detected per year until the trend greatly reversed around 1990, so that 24% of the total were detected after 1990. Since 1990 an average of 1.2 high-impact pests have been found per year, almost three times the rate from 1860 to 1990. 44% of the insects found between 1999 and 2006 were in the high-impact category. The study suggests that the rate has increased because of the use of wood in containerized shipping and heightened vigilance. In Canada detections peaked in the 40's-50's but only declined in the 80's, which a study attributed to new laws across the border in the US and a 1976 Canadian phytosanitary law, but I wonder if this could also relate to Canada's changing relations with US and British imperialism, effecting who Canada trades with and what laws are made.
Globalization seeks to 'flatten' the world, and in a sense that could mean our forests will be flattened, in exchange for greater business profits. Any long-distance trade and travel gives exotic organisms a chance to hitch a ride, but offshoring factories just to exploit workers and resources in other countries and importing labor rather than paying higher wages to attract workers who are already here increases the chance that something disastrous will become established. American species, from goldenrods to largemouth bass, likewise cause problems when transported to new places. In the Eastern US there has already been significant to catastrophic damage to American chestnuts, elms, Fraser fir, hemlocks, ashes, American beech, flowering dogwoods, butternut, black walnut, bays, sassafras, Western soapberry, and other trees, and serious threats to oaks and pines are waiting in the wings, in addition to damage caused by bad land management, the extinction of native animals that were beneficial for plants, competition with non-natives, air pollution, and climate change. Harm to trees in turn affects other plants and animals and the human inhabitants of this forested region.
National Invasive Species Awareness Week is February 27-March 3 ( www.nisaw.org/ )!
Some links about laurel wilt:
About ambrosia beetles:
About the Palamedes swallowtail:
General non-native issues: