Mowing and Herbicide of Scrub Oaks in Pine Barrens: Baseline Data (New York)

The Albany Pine Bush (APB) Preserve, located in densely populated east-central New York State, protects a globally rare inland pine barrens community dominated by pitch pine (Pinus rigida) and scrub oaks (Quercus ilicifolia, Q. prinoides). Despite its urban context and small area (1,255 ha), the APB supports many rare and declining shrubland fauna (Barnes 2003, Gifford et al. 2010), including the endangered Karner blue butterfly (Lycaeides melissa samuelis). Fire suppression has long been the primary threat to this pyrogenic community throughout the northeastern United States (Finton 1998). Without frequent fire, the unique shrubland ecosystem rapidly becomes tall dense thicket and eventually forest dominated by white pine (Pinus strobus), tree oaks, or invasive hardwoods (Finton 1998, Malcolm et al. 2008). Scrub oak density in major shrubland fragments of the APB is currently twice the desired amount, or about 60%–70%. A primary goal of APB ecological management is to reduce scrub oak density by about half to 30%–35%. Meeting this goal should facilitate the restoration of an open barrens where the grasses and forbs essential to the Karner blue and many other shrubland species are codominant with scrub oak and other native shrubs.

Scrub oak regenerates immediately after dormant-season prescribed fire or growing-season prescribed fire + mowing; the latter has been used since 2004 to restore APB shrubland. Posttreatment growth may decelerate within a few years, but open barrens may have already changed to thicket or begun the transition. An alternative restoration approach is needed that creates a less ephemeral open barrens. Combined mowing and herbicide was recommended in utility corridors to reduce thicket cover, promote wild blue lupine (Lupinus perennis), and thus increase suitable habitat for New York Karner blue populations (Forrester et al. 2005)—the same may be needed for APB scrub oak patches, as the Karner blue has rarely been observed in these areas.

In 2008, a growing-season mow + herbicide treatment was applied to four scrub oak patches (sites) totaling approximately 45 ha of APB preserve. Here we document first-year treatment effects on vegetation as a baseline for monitoring. No further management is scheduled in these areas for at least three years so as not to interfere with assessment of mow + herbicide effects on plant and animal communities.

Mowing and herbicide work was contracted to two private companies and supervised by APB staff. The four sites were mowed between 2 July and 6 August 2008. All vegetation was cut to 20–25 cm height using a Hydro-Ax, and debris was left on site. Between 2 and 23 September 2008, herbicide applicators equipped with backpack pump sprayers (ultra-low volume) walked five abreast along adjacent flagged routes, each spraying two scrub oak crowns (usually single stem of Q. ilicifolia or stem cluster of Q. prinoides) and then skipping one in a repeating pattern without regard to species. The herbicide mixture included Krenite “S” (active ingredient fosamine), which is selective for woody species and inhibits next year’s growth, and Arsenal (active ingredient imazapyr), which is nonselective and prevents amino acid synthesis.

Figure 1.

View of Kings Road Barrens in the Albany Pine Bush Preserve on 13 July 2009, approximately ten months after the herbicide treatment that followed mowing to open up the dense scrub oak canopy. Photo by Lee Demick

First-year treatment effects were assessed in July 2009, after surviving scrub oak leafed out. Using GIS software (ArcMap v. 9.2, ESRI, Redlands CA) to stratify the treatment areas into cells, we established permanent 30 m transects, representing 2.5% randomly selected cells, to measure live scrub oak density and height structure, live versus dead zones of nontarget vegetation, and nectar plant diversity.

Using the point-intercept method, at every meter along the transect live scrub oak was measured in height classes (0–0.5, > 0.5–1.0, > 1.0–2.0, and > 2.0 m). Densities were arcsine–square root transformed and compared among sites and before and after treatment using confidence intervals, ANOVA, and protected Tukey-Kramer comparisons...