Two factors that can degrade native plant community composition and structure, and hinder restoration efforts, are invasive species and chronic overbrowsing by ungulates such as white-tailed deer. Beginning in 2007, the effectiveness, costs, and impacts of Japanese barberry control treatments and herbivory on nonnative and native plant communities was examined at eight study areas over 4 to 5 yr. Prescribed burning and mechanical mowing by wood shredder or brush saw were utilized as initial treatments to reduce the aboveground portion of established barberry and were equally effective. Without a follow-up treatment, barberry had recovered to 56 to 81% of pretreatment levels 50 to 62 mo after initial treatment. Follow-up treatments in mid-summer to kill new sprouts included directed heating and foliar herbicide applications. Relative to untreated controls, follow-up treatments lowered barberry cover 50 to 62 mo after initial treatment by at least 72%. Although all follow-up treatments were equally effective, the labor cost of directed heating was four times higher than for herbicide applications. Follow-up treatment type (directed heating vs. herbicide) had minimal impact on species other than barberry. White-tailed deer herbivory had a larger impact on other species than did barberry control treatments. Native grass and fern cover was higher outside of exclosures. Areas inside exclosures had higher cover of Oriental bittersweet and multiflora rose, but not Japanese barberry. Thus, recovery of native communities will require more than simply removing the dominant invasive species where deer densities are high. Excellent reduction of Japanese barberry cover can be achieved using either directed heating or herbicides as follow-up treatments in a two-step process, but other invasive plants may become a problem when barberry is removed if deer populations are low.
Nomenclature: Glyphosate, triclopyr, 2,4-D, Japanese barberry, Berberis thunbergii DC. BEBTH, Oriental bittersweet Celastrus orbiculatus Thunb. CELOR, multiflora rose, Rosa multiflora Thunb. ex Murr. ROSMU.
Management Implications: Japanese barberry is an invasive shrub in the eastern United States and Canada that forms dense thickets that can inhibit forest regeneration and native herbaceous plant populations, and is associated with elevated populations of blacklegged ticks, which can be infected with the causal agent of Lyme disease, Borrelia burgdorferi. A reasonable objective of controlling an invasive species such as Japanese barberry, is not eradication of the invasive species per se, but the restoration of a community dominated by native herbaceous species and woody regeneration. This study found that a single treatment (e.g., mowing) is ineffective without a follow-up treatment. A variety of techniques using a two-step strategy can successfully control Japanese barberry for a period of at least 4 to 5 yr if there is an immediate follow-up treatment, albeit at a wide range of labor costs. Labor costs for follow-up treatments with a propane torch were at least four times higher than for herbicide applications, although both were equally effective at controlling barberry. However, invasive control by itself was insufficient to restore native communities in these areas with high white-tailed deer densities because deer herbivory had a larger impact on plant communities than control of Japanese barberry. Where deer densities are high, a successful restoration program must incorporate a program to reduce deer density to a level sufficient for native forbs to flower and set fruit and for tree seedlings to grow tall enough to be above browse heights—typically 2 m (6 ft). Successful restoration might also require introduction of locally extirpated species. A successful program should also include strategies to control those invasive species, such as Oriental bittersw
