Arboriculture & Urban Forestry 42(4): July 2016 because grapevines are shade-intolerant. While wild grapes are shade-intolerant throughout their lives, and oriental bittersweet is considered shade toler- ant (though argued in the current study as possibly being less shade-tolerant) as a seedling and shade- intolerant as a climbing vine, control recommen- dations for grape and large bittersweet vines are intriguingly similar. Smith (1984) well captured the recommendation for grapes that has bearing for ori- ental bittersweet, paraphrased as follows. Vines can be controlled in shaded areas of forest stands by sev- ering or cutting the large vines that grow in trees. Vines can be severed near groundline using blades, hatchets, or chain saws depending on vine size. The cut vine will likely resprout, but those sprouts will die within a few years and not become a problem in the future, barring any drastic increase in sun- light with overstory removal or natural disaster,. Research on use of herbicides to control orien- tal bittersweet should continue to confirm (or not) and extend the results of the current study. At the least, the current study could be duplicated to deter- mine if the high two-year mortality by cutting vines alone without herbicides can be reproduced. Future cut-stump studies with glyphosate could follow the same designs in the current study, but should add the following independent variables: size of vines that are smaller (<1.3 cm) and younger than in the current study; cut stumps of treated vines exposed to varying amounts of sunlight aſter treatment; and measured levels of herbivory (fence off some of the treated stumps to control herbivore access). Clearly, the mechanisms to explain why there was such high mortality in the cut-only plots aſter two years across treatments needs to be investigated with both observational and manipulative experiments. Results of the current study do not address the prob- lems of oriental bittersweet growing in open fields with shrub-like form. The high density and small stem diameter does not match well with cut-stump methods, but other herbicide application techniques could be tested, including cut stubble and foliar. Like cut-stump treatments of oriental bittersweet, there is a paucity of published research on foliar applica- tion of herbicides to control oriental bittersweet. 263 Management Implications for Utility Foresters and Other Arborists Managing Hazard Trees Hazard tree management revolves around evaluating individual tree risk and actively removing high-risk trees. Highly hazardous trees are those with struc- tural problems that may cause near-term failure— the trees could fall over due to excessive crown weight and loading (snow, wind), as well as stem de- fects (decay, lean, deformity). Vines, including but not exclusive to oriental bittersweet, can cause both these problems. A hazard tree management pro- gram should include a vine management program. When large oriental bittersweet vines (where “large” is defined as those vines growing into tree canopies with a stem diameter of 2 cm or more) are observed growing in danger trees, they should be killed before they cause damage to the tree and increase hazard. Today, this is a low cost treat- ment by just cutting vines in danger trees as they are encountered; a management program of this type could save hundreds or thousands of dollars of treatment later on to remove a tree that is too hazardous or recover from the damage of a fallen tree. It is important to emphasize, and based on the current research reported in this paper, that cutting vines alone can work to kill or otherwise control the vine problem, particularly vines growing in forest where the stem is in the shade. Herbicide treatment of large oriental bittersweet vines—and likely other vines, such as grapes, Virginia creeper, and poison ivy—is not necessary in shaded situations, which can save time, money, and associated environmen- tal effects that come with cut-stump treatment. It is important to reflect on the fact that exist- ing management guidelines for oriental bitter- sweet include cut-stump treatment with herbicide to kill tree-climbing vines. It seems these guides are in error, and in fact are based on no empirical research. Vegetation managers—utility foresters, arborists, and all practitioners for this matter— should be critical of vegetation management guide- lines that are not based on empirical field research. ©2016 International Society of Arboriculture
July 2016
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