Stand Dynamics and Ecological Constraints on Growth in Young, Naturally Regenerated Hardwood Stands

Abstract

In the southern U.S., forests are generally managed as even-aged entities, and commonly regenerated using a clearcut reproduction method. Alternatives to clearcutting, namely low- and medium-density shelterwood methods, were assessed in North Carolina, South Carolina and West Virginia. Results suggested that the alternative methods afforded little to no advantage over traditional clearcut methods.

Weeding, fertilization and thinning treatments were employed post-harvest on rising 1-yr-old Hill Forest and rising 3-yr-old Duke Forest upland Piedmont sites. Stems at both sites responded to fertilization. Individual stem volumes increased 2 to 3-fold after three years. Weeding-alone increased growth on the Hill Forest. The response to weeding and fertilization treatments was usually additive. Thinning-alone had little effect on stem growth. However, thinning + weeding treatments simulated large increases in stem growth. For thinned stems, weeding generally had a greater affect on growth than fertilization at both sites.

Stems on the rising 1-yr-old Hill Forest site were tagged (>3000 stems) and monitored over three years. Stem survival was greatly affected by the weeding and fertilization treatments. Fertilization reduced survival for most species, especially for the lower initial height and diameter size classes. Weeding, by contrast, tended to increase survival in the small initial size classes. The survival data indicated that some of the growth response associated with fertilization might be due to mortality in the smaller sized stems.

Three-year growth and survival models based on initial stem size were generated for each species and treatment combination at the Hill Forest site. Comparisons were made between treatments for each species, and between Liriodendron tulipifera L. and Cornus florida L., Prunus serotina Ehrh., Pinus spp., Acer rubrum L. and Quercus alba L. for each treatment. Generally, most species responded favorably to weeding and fertilization treatments, although these responses were not always statistically significant. However, individual species differed in respect to their ability to increase growth and survival, although yellow-poplar ranked among the fastest growing species in every treatment after 3 years. These last data can be used to develop floristic models to predict species composition for other upland stands.