Stump sprout dynamics in response to reductions in stand density for nine upland hardwood species in the southern Appalachian Mountains
Much about stump sprout dynamics of upland hardwood trees species has been obtained in clearcuts. Information on the response of stump sprouts to alternative silvicultural treatments, including treatments that manipulate stand density and stand structure is lacking. In this study we examined the influence of harvest season and levels of basal area reduction on the probability of sprouting and subsequent sprout growth in the southern Appalachian Mountains. In 2009, 24 - 0.1 ha plots were established in fully-stocked mixed-hardwood forests near Asheville, North Carolina, USA. Basal area was mechanically reduced from below by 10%, 20%, 30%, or 40% between January and February, 2009 (dormant season) and again between July and August, 2010 (growing season), with each harvest season and level of basal area reduction combination randomly applied to three plots. For each stump, we recorded: (1) presence of live sprouts (yes/no); (2) height (m) of the dominant (i.e., tallest) sprout, and (3) area (m2) occupied by individual sprout clumps. All measurements were conducted one, two, and three years post-harvest. We used logistic regression and ANOVA to analyze the probability that a stump sprouts one year post-harvest and annual stump survival (i.e., the presence of at least one live sprout), sprout height, and area. Probability of sprouting was independent of dbh for red maple, dogwood, sourwood, hickory spp., chestnut oak, yellow-poplar, and sweet birch. For sweet birch the probability of sprouting was affected by harvest season, with 54% and 93% of stumps producing sprouts one year following growing and dormant season harvests, respectively. For blackgum and white oak, dbh was negatively correlated with the probability of sprouting. Stump survival varied by species and year. Third year stump survival was 38% lower for oak and hickory than sourwood and 32% lower than red maple. Dominant sprout height was significantly greater for red maple and sourwood than for oak and hickory, with the greatest height achieved under the 40% reduction in basal area treatment. By year three, dominant sprout height for both red maple and sourwood was 40% greater than for oak and hickory and 58% greater than other shade-tolerant midstory species. Our results suggest planning harvests to occur during a particular point in the year with the idea it will limit sprouting and subsequent sprout growth is ineffective and should not be considered a viable means of reducing the production or growth of stump sprouts.