Limitations on regeneration potential after even-aged harvests in mixed-oak stands

Stochastic frontier analysis (SFA) was used to investigate the effects of preharvest levels of rhizomatous fern, mountain-laurel, and tall shrub cover on oak, red maple, and total tree regeneration in the decade after even-aged regeneration cuts in 18 mixed-oak stands. In nearly every case, interfering vegetation imposed an upper limit on the number and size of regeneration stems, a limit that significantly (P < 0.05) decreased as interference increased. Modeled responses to 30% cover of fern showed reductions in regeneration at age 10 of 42, 36, and 21% for oak, red maple, and total regeneration, respectively. For 30% cover of mountain-laurel, the respective values were 24, 23, and 31%, and for 30% cover of tall shrubs, oak and total regeneration were reduced by 47 and 30%, respectively. Fern cover was significantly more inhibiting to both oak and red maple regeneration than was mountain-laurel. Total regeneration (which included sweet birch, blackgum, and sassafras in the greatest numbers behind several oak species and red maple) responded similarly to all three cover categories. In their potential for regeneration development, oaks were no more disadvantaged by fern and mountain-laurel interference than was red maple. However, red maple was less sensitive than oaks to nonmodeled adverse conditions and, therefore, more often successful in reaching its regeneration potential. This study extends the successful application of SFA to a broad area of field research that must often rely on observational data for its best information.