[MAIPC] A theory of invasiveness and non-native control in forests

[Richard Gardner]

              About a week ago a woman Ihappened to meet on the Appalachian Trail (AT) and walk with for a few minutesasked about non-native plants spreading along trails. The day before I hadwalked a little used single-track trail I like and this past Saturday waswalking on the AT to the Allentown Shelter from a local road over the mountain.Then yesterday I walked another stretch of the AT below the Hawk MountainSanctuary which was a mix of trail and logging road. All these trails had the samepattern with some of their plants – they were transported along the trail thenspread outwards from the trails into the forest. This was very apparent withthe non-native Japanese barberry (Berberis thunbergii) on the way to the Allentown shelter and the native Eastern YellowStargrass (Hypoxis hirsuta) on the single-track trail.

              Over the years I have noticed thesame pattern beginning with grape hyacinth (Muscari armeniacum) and then with the AmericanChestnut tree (Castanea dentata). On the loop trail around a local lake,Blue Marsh, many years ago I saw that M. armeniacum was apparently being transported alonga trail from a homestead where it was originally planted along the trail in thedirection most commonly used by mountain bikers and hikers. Several years ago Irealized that C. dentata was seldom found more than 15 yards from atrail unless it was part of an old stand. This observation made me think aboutthe differences between open forest versus trails. The difference I saw was theresult of friction. Trails are low friction for birds and mammals whentravelling through a forest. Whereas friction is higher for animals travellingacross the forest. From experience “bushwhacking” from one trail to another ismuch harder than traveling on a trail. Basically, it appears that animals preferentiallymove on low friction trails as opposed to through high friction open forest.This preferential movement transports seeds and other propagules first alongtrails and then when established into the open forest.

              B. thunbergia is an unfortunately outstanding example of first spreading along a trailthen into the forest as I witnessed when walking the AT to the Allentownshelter. The plants were frequent along this stretch of trail and had not yetmoved into the forest unlike where this stretch of the AT near where it crossesHawk Mountain Road. Garlic mustard (Alliaria petiolate) is anotherexample of this pattern, both as early in this stage of spread and fullycovering a part of the forest as along the AT on Peter’s Mountain. Japanesestiltgrass (Microstegium viminium) is another excellent example of thispattern. Yesterday, it appeared that the native American Cancer-root (Conopholisamericana) is doing this on a stretch of the AT I was on below the HawkMountain Sanctuary.
              Mysuggestion is to monitor the trails and control the non-native invasives asthey migrate along trails before they enter the open forest. Costly remediationwill not be needed if an invasion is dealt with early alongside the trails beforeinvasive plants penetrate the open forest. This is especially true with aggressivelyinvasive plants such as B. thunbergii.
                                                                                                                                               Richard Gardner
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