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Agriculture & Natural Resources Updates for Fannin & Gilmer Counties

November has brought us some cooler weather, and with it the opportunity to enjoy time outdoors without the intense heat of summer. The fall color this season has been stunning and as more leaves senesce and dapple the forest floor, I’m reminded of another phase of fall. A short-lived time just after what most folks consider “peak leaf season”. Little to no green leaves remain, and the forest floor bears a striking resemblance to a blanket adorned in crimson and gold. Fallen leaves give rise to sprawling mountain views; squirrels hurriedly stock their larders. A few stubborn leaves hold fast but we know summer is at rest.

Seasonal needle loss is easy to spot on white pines, as they will shed up to one-half of their needles in early fall.

With all the emphasis we place on falling leaves, it is easy to overlook the fact that evergreen needles are falling now as well. Everyone seems to remember from their elementary school science classes that deciduous trees lose their leaves in the fall, but evergreen trees keep their needles all year. While that is essentially true, the concept is a little over simplified. While the needles of evergreen trees do persist on the tree longer than those of a maple or oak, the needles on an evergreen cannot last forever. Rather, the needles of evergreen tree species remain on the tree for 2-5 years, depending upon the tree species.

The process of evergreens shedding their needles is called seasonal needle drop. The process tends to be uniformly distributed throughout the inner part of an evergreen’s canopy, as the oldest needles are the ones that are shed. One of the most common evergreen trees in our area is the Eastern white pine (Pinus strobus). While the tree develops new growth each year on expanding branch tips, the needles on white pine generally last only two years. The next year these branches continue to grow and set new needles. By autumn of the second year, the original needles begin to change color. First, the needles become a straw-colored yellow, then they will turn brown and start dropping.

Seasonal needle loss is particularly easy to spot on white pines because this pine species is prone to shedding up to one-half of their needles in early fall. The change in color and sudden dropping of pine needles can be a shock to many mindful homeowners who may notice the change and fear their trees are either diseased or dying. If this sounds like what is happening in your yard this time of year, then seasonal needle drop is the likely cause.  When natural needle drop occurs, the branch tips remain healthy and green. Only the older needles located further back from the growing point should be dropping.

Pines are not the only evergreens to undergo seasonal needle drop. Though, the process tends to be less conspicuous on spruce and fir trees, as they then to drop less needles than other species. Having said that, just like the white pine, spruces and fir trees shed older, more interior needles. This can take up to five years or more depending upon the species. Arborvitae will also shed its older foliage.

The older needles on hemlock trees are usually shed during the third or fourth year after they were produced. Since many folks are watching their trees for signs of the dreaded hemlock woolly adelgid, natural needle drop can be alarming if you are not expecting it. American holly typically drops its thick prickly leaves during the spring of their second year. Southern Magnolia, another broadleaf evergreen, drops its oldest leaves in the spring as new growth begins.

To complicate matters, trees don’t shed the same amount of foliage each year. If we have very favorable growing conditions, rapid growth and heavy foliage development will occur. The following year if we experience a drought or other poor conditions little new growth may be formed. That means in the fall there will be relatively few healthy green needles to hide the mass of dropping two-year-old needles on your white pine.

Disease, transplant shock, “wet feet” and other conditions can cause evergreens to drop their foliage. Most of the time; however, the new foliage on branch tips will also be affected by these conditions. The bottom line is that if you are noticing the interior needles of your white pine turning yellow this fall, do not despair. Check the branch tips to see if they are green and healthy.  If the growing point looks healthy and only the older leaves are dropping, then you are witnessing a natural process called seasonal needle drop. After all, if pines did not drop their needles naturally, then we would have to cut down a tree just to get pine straw.

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