Forestry in Fairfax, not an oxymoron

In honor of Arbor Day, coming up this Friday, and the Virginia Invasive Plant Removal Day, coming up this Saturday, we have a guest article written by Jim McGlone, Urban Forest Conservationist with the Virginia Department of Forestry, and Chapter Advisor of the Fairfax Master Naturalist chapter. It is reprinted with permission from the TREE Cookies Etc. newsletter, volume 5(1), published by Adam Downing, Forestry and Natural Resources Extension Agent for the Northern VA region. To read the whole newsletter, or to subscribe yourself, visit http://offices.ext.vt.edu/madison/programs/anr/tree_cookies_newsletter/treecookies-7.pdf.

I work in Fairfax County. For most people in the forestry trade that means concrete and congestion. There is plenty of that, but there is also 40,000 acres of forest. There are also plenty of deer and invasive plant species. The deer and invasives are threats to the forest and to good forest management.

The Virginia Department of Game and Inland Fisheries has estimated deer densities in Fairfax county range between 100 per square mile in more developed areas to 400 per square mile in less developed areas. In a fall 2006 three day public hunt on 3,000 acres of Mason Neck State Park and the adjoining Fish and Wildlife Refuge 172 deer were taken. The county reports 4,000 to 5,000 deer vehicle collisions in 1998. Impressive statistics, but what do they mean?
Some time ago I visited an 80 acre property in the Potomac Palisades region of the county. Except for the home site the entire property was forested with beautiful stands of oak and poplar, some measuring over 30 inches. There is a nice riparian stand of mixed hardwoods including black walnut and ash. The forest floor was carpeted with new sprouts showing 2 or 3 leaves and identifying them as oaks or maple. But there were no shrubs other than paw-paw. Aside from the sprouts, there were no trees less than 10 inches DBH. The laurel and holly were completely browsed up to 4 feet and the only herbaceous plants were garlic mustard and stiltgrass. After 3 years, there was literally nothing growing in a wind throw gap from hurricane Isabel. I told the land owner she had a regeneration problem; she said “send me men with guns.”
This is the norm for Fairfax forests: beautiful healthy mature trees with nothing growing underneath, forests that look like they have been mowed, unexploited gaps in the canopy, failing stands of Virginia pine and eastern red cedar with no hardwoods succeeding them. Where there are shrubs and herbs in the forest they are usually invasive plants that deer won’t eat. Park managers have told me that paw-paw and spicebush (apparently two truly deer resistant species) are expanding within the parks where invasive plants have yet to become a significant problem.

Invasive plants have moved into the deer browsed forests and occupied the space they have left behind. While the invasive shrubs and herbs seem to out-compete native tress and other vegetation, the vines – kudzu, bittersweet and porcelain berry – attack and kill the mature trees. It is difficult to separate the effects of these two pressures. Do the invasives suppress native flora or do the deer eat the native flora and leave behind the invasives?
Ironically, the deer browse and invasives have awakened land managers in Fairfax to the need to actively manage the forest rather than let nature take its course. I have used this awakening to guide their thinking about forest management by explaining about succession and the silvics of tree species and how to use these concepts to achieve desired outcomes. I have also explained about tree time; if your management goal is a mature oak stand and you don’t have an oak component, then it will take you 50 years to get there. When these discussions get to the need to cut trees as part of some management practices, I run into the problem of deer browse and invasive plants.

Many traditional forestry practices do not achieve the desired results under the deer browse and invasive species pressures here in Fairfax county. Opening up the canopy to allow more sunlight on the forest floor just produces more food for deer or encourages the growth of invasive species.

--By Jim McGlone, Urban Forest Conservationist with the Virginia Department of Forestry, and Chapter Advisor of the Fairfax Master Naturalist chapter.