Impacts of deer herbivory and visual grading on the early performance of high-quality oak planting stock in Tennessee, USA
Abstract
The growth of outplanted high-quality 1-0 northern red oak (Quercus rubra L.) seedlings, growth differences between two categories of visually graded seedlings and herbivory by white-tail deer (Odocoileus virginianus (Boddaert)) were examined after two growing seasons. Seedlings were planted in plots receiving three overstory treatments (high grade, commercial clearcut, and two age) and an uncut control on productive sites of the East Gulf Coastal Plain in Tennessee. Sixty seedlings were outplanted within each of 12 0.8 1-ha treatment units, resulting in three replicate blocks of the four treatments. Initial height, root-collar diameter and number of first-order lateral roots were recorded for each seedling prior to planting. Seedlings were visually graded into one of two categories (premium and good) based on morphological characteristics. Planted seedlings were measured at the end of the 2002 and 2003 growing seasons. Mean seedling survivorship after two growing seasons was 94, 92, 87 and 58% (P < 0.001) for the commercial clearcut, two-age, high grade and uncut control units, respectively. Differences in seedling height growth were found between the harvested units and uncut control units along with a significant interaction between overstory treatment and site (P = 0.03). Differences in seedling height were not significant among treatments involving harvest. After two growing seasons, seedlings graded as premium had produced 9 cm more height growth on average than seedlings graded as good (P = 0.002). In addition, seedlings browsed heavily during the 2002 and 2003 growing seasons were, on average, 36 cm shorter (P < 0.001) than unbrowsed seedlings. A significant level of mortality and diminished growth in the uncut control units suggests that pre-harvest enrichment planting without manipulating the overstory may not be a viable management option. Results from this study suggest a simple visual grading of seedlings prior to planting can result in significant growth gains early in the development of the seedlings. Further, the use of larger planting stock may have the added benefit of reducing the impacts of deer herbivory