Sapling white pine (Pinus strobus L.) exhibits growth response following selective release from competition with glossy buckthorn (Frangula alnus P. Mill) and associated vegetation

Abstract

Invasive glossy buckthorn (Frangula alnus) hampers management of white pine (Pinus strobus) in the northeastern USA, especially when these species co-establish following harvest activities. Our objective was to test the effects on pine sapling growth of a simple, quick, and novel silvicultural procedure involving local buckthorn stem removal. We identified 75 five-year-old pine saplings in a Durham, NH, forest regeneration area that was clear-cut in 2009 and which was heavily invaded by buckthorn. All selected pine saplings were surrounded primarily by glossy buckthorn. Around each of 50 of these pine saplings, a 1mradius was cleared (‘cut only’ treatment) and for half of these there was a follow-up herbicide application (‘cut+herbicide’ treatment). Remaining saplings were untreated controls. After one growing season, pines responded to treatment with increased terminal leader biomass (+75%), basal stem diameter (+12%) and bark starch (+140%). Treated pines displayed even greater diameter increase (+29%) after two growing seasons. None of these variables differed across the two treatments. Height of treated pines did not differ from controls, even after the second growing season. When herbicide was used, there were 86% fewer buckthorn sprouts in treated areas, but pine mortality was five times greater (n=5) than in the cut only treatment (n=1). Our results show that, regardless of herbicide use, those pines cleared of surrounding vegetation and not subject to post-treatment mortality exhibited increased vigor and growth, suggesting a greater potential to eventually outgrow competing buckthorn and thus more rapidly reach commercial size.