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Moment of Nature - May 24, 2013

Alien invasion

Posted: May 22, 2013 2:47 p.m.
Updated: May 24, 2013 5:00 a.m.

In countries around the world, the oak tree is the symbol of strength, fortitude and endurance. In the U.S., the oak was designated in 2004 as our national tree. Despite this status as a stalwart of the forest and city alike, oaks in our native and urban ecosystems face tremendous challenges from diseases, insect pests and human-caused disorders.

No matter what area of the country they grow in, oak trees enjoy a special reverence from us people. They are not only significant trees for their diversity and use in our parks and along city streets, oaks are also highly valued by homeowners, and rightly so. Healthy and structurally-sound oaks give us great shade, filter dust and pollen from the air, provide habitat for birds and mammals, help increase/retain property values and create a sense of place. In South Carolina, more than 20 different species of oaks call our state home.

So, how does all of this relate to an alien invasion? Well, I’ve recently read about one more insect pest that is wreaking havoc on trees, specifically oaks in San Diego County, Calif. The culprit of tens of thousands of oak deaths occurring to West Coast trees is the goldspotted oak borer (Agrilus coxalis). This pretty looking beetle is yet another in a growing list of insect pests killing trees in our forests and communities. As with most boring beetles, the mode to mortality is: bore into tree wood just under the bark; lay eggs; eggs hatch; grow into larva (worm looking things); and tunnel through the nutrient-rich and water-conducting tissues of the tree, eating as they go. This girdles or strangles the tree from the inside and death may take anywhere from several months to several years depending on the extent of feeding. And, as with most boring beetles, the best control is preventing them from attacking trees in the first place.

Healthy trees are less susceptible to insect pest attacks in most cases, but environmental and human-caused stresses -- such as prolonged drought, tilling the roots to install turf, construction of pools, patios or driveways, installing raised flower beds under the tree canopy and over-watering, etc. -- are common causes of tree stress in community settings. One sure way to help keep our public and residential trees healthy is to provide them with organic mulch under the canopy area (spread it low and wide and not up against the bark) and regular watering. Supplemental fertilization may be needed at times, but it is best to get a soil analysis first from the Clemson University Cooperative Extension Service office located on DeKalb Street.  

The goldspotted oak borer joins those already classified as “alien invaders” such as the Asian longhorn beetle, the emerald ash borer and two-lined chestnut borer as well as a variety of diseases such as oak wilt, sudden oak death and thousand cankers disease to keep on the lookout for, as if we didn’t have anything else to worry about. The Asian long-horned beetle, is a large tree borer attacks maples, elms, birches and sycamores, and was first discovered in Brooklyn, N.Y., in 1996. It is now in two other states and Canada. The emerald ash borer, a metallic-looking tree borer, attacks mostly ash trees and was first discovered in 2002 in Michigan; it is now in 21 other states and Canada and has spread as far south as Virginia.

I once heard a saying that whatever is in California (fashion trends, laws, social movements, bugs, etc.) takes about 10 years to reach the East Coast. If that holds true, we better be moving fast to diversify our community forest. Thankfully, diversifying tree species composition within a community is a relatively easy pro-active and somewhat preventative fix to the growing alien invasion of insect pests and diseases that may likely be knocking at our back door in the years to come.  

Tree diversity is kind of like how I think of food… a well-balanced diet should be composed of meats, fruits, vegetables, breads and -- my personal favorite -- sweets. Too much of any one food category can contribute negatively to one’s health. Same goes for community trees; too much of any one tree species can make it much easier for insect pests and diseases to attack. Our public tree composition is already heavily skewed with oaks and as much as we love our oaks, we have got to expand the menu to include a variety of other trees.

With all of the stuff going on in the world, our state and community, you may be thinking…“Why is any of this even important? What relevance does it have for me?” It is important because history has taught us that entire populations of tree species (we’re talking millions of trees) can be wiped out in a matter of years. Case-in-point: Dutch elm disease and Chestnut blight. If you are not familiar with these tree diseases, I challenge you to “Google” or “Yahoo” them to find out what happened and why we no longer have any American elms and chestnut trees in our woodlands. It is relevant to you because more than 30 percent of our public trees here in town are oaks. You probably even have an oak tree in your yard. If we ever lost them due to an invasive disease or insect pest, we’d lose the charm and character that is Camden. Not to mention we’d be a hot city (and not in a good way) without all of that luscious green shade.

The bottom line is to take care of your trees, be observant of any changes in the way your trees look and consider diversity of species in your home landscape when you have a chance to plant a new tree.  The city has been purposely planting different trees throughout town to increase species diversity and potentially lessen the impact from marauding invaders in the future. More on this which I’ll share with you next month! In the meantime, if you have any questions regarding your trees, please feel free to call me at the Camden Dept. of Public Works at 432-6045, or send an email to lgilland@camdensc.org.

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