Thinning in a 28-year-old Water Oak Plantation in North Louisniana: Seven-Year Results
A Pl-acre. 28-year-old water oak (Quercus nigra L.) plantation on in old-field loessial site near Winnsboro, LA. was subjected to three thinning treatments during the winter of 1987-88: (1) no thinning, (2) light thinning to 180 dominant and codominant trees per acre, and (3) heavy thinning to 90 dominant and codominant trees per acre. Prior to thinning, the plantation averaged 356 trees and 86 p of basal area per acre, with a quadratic meati diameter of 6.7 in. Thinning reduced stand basal areas to 52 and 34 f? per acre for the light and heavy thinning treatments, respectively. After 7 years, thinning did not significantly increase stand-level basal area growth, but both thinning treatments produced shifts in stand structure. Diameter distributions of thinned stands were skewed to the larger diameter classes and crown class distributions of thinned stands were skewed to the upper crown classes. Both thinning treatments increased diameter growth of residual trees, but there were no significant differences between the two levels of thinning. Diameter growth of residual trees in the lightly thinned stand averaged 1.63 in. after 7 years, whereas those in the heavily thinned stand averaged 2.02 in. on this relatively poor site. Trees in the unthinned stand grew an average of only 1.04 in. INTRODUCTION Information on growth and development of southern oak plantations greater than 20 years of age is lacking. Most past research on oak plantations emphasized the development of suitable techniques for successful plantation estab l ishment (A l len and Kennedy 1989, Kennedy 1993) . but subsequent growth was generally followed for only a few yea rs . Through the Conserva t ion Reserve Program and the Wetland Reserve Program, many thousands of acres of marginal cropland in the South have been reforested, primarily to various oak species (Kennedy 1990). As these oak plantations develop and mature, the demand for information on how to manage them will increase. Land managers will need practical guidelines on thinning and other intermediate silvicultural operations. However, information on growth and yield, pattern of stand development, and the response of older oak plantations to silvicultural operations is sparse. Consequently, few guidelines currently exist for successful management of these older plantations. For these reasons, a thinning study was established in the winter of 1987-88 in two 28-year-old water oak plantations in north Louisiana. The study was designed to determine the diameter growth and stand structure responses of water oak to three levels of thinning. Stand parameters of the plantations prior to thinning were previously described by Krinard and Johnson (1988). Meadows and Goelz (1993) reported fourth-year responses to thinning. METHODS Study Area The plantations were established in 1960 on old agricultural fields of loessial soil on the Macon Ridge landform in Franklin Parish east of Winnsboro, LA. The fields were under continuous cultivation for several decades prior to the establishment of the oak plantations. The two plantations encompass 21 acres (a 14.5acre tract and a nearby 6.5 acre tract). Both tracts are privately owned. Both fields were planted at the rate of aporoximatelv 950 water oak seedlings per acre. Initial spading was variable, but appears to have been about 5 x 9 ft. No cultivation or other means of weed control was conducted after planting at either site. The plantations are located on the Calhoun-Calloway-Loring soil association (Krinard and Johnson 1988) that developed from wind-blown silt, or loess. Within these terrace sites, Calhoun soils occur on the flats and depressional areas, Calloway soils are found on low ridges, and Loring soils occur on slightly higher ridges. Well over half of the study area consists of Calhoun soils, with lesser proportions of Loring and Calloway soils. The soils are generally poorly to somewhat poorly drained, but some of the higher ridges are moderately well-drained. Permeability is slow across most of the area. These soils have low-to-medium natural fertility that has been reduced through many years of use for crop production. Texture in the upper soil horizon at both sites is silt loam. Soil pH is very strongly to medium acid and ranges from 4.5 to 6.0 across both sites. Calloway and Loring soils both contain fragipans at depths of 20 to 30 in. that limit effective rooting depth and hinder tree growth. The loessial soils of the Macon Ridge are somewhat unproductive for the growth of hardwood species, when compared to well-drained alluvial soils or the loessial hills on the east side of the Mississippi River. Broadfoot (1976) reported an average site index of 83 ft at 50 years for water oak on Calloway soils, but did not provide similar information for Calhoun or Loring soils. Based on the method described by Baker and Broadfoot (1979) we estimated that site index for water oak averaged 86 ft at 50 years across the entire study area, but ranged as high as 90 ft on the higher ridges. Treatments In the fall of 1986, the plantations were divided into 12 treatment plots, nine on the larger tract and three on the smaller tract. Each treatment plot was 150 ft by about 400450 ft (45 rows) and covered an area of about 1.4 to 1.5 acres. Three O.l-acre square measurement subplots were systematically established within each of the 12 treatment ’ Paper presented at the Tenth Biennial Southerf Siivicultural Research Conference, Shreveport, LA, February 16-18, 1966. * Principal Silviculturist and Principal Forest Biometrician, USDA Forest Service, Soutbem Research Station, Stoneville, MS 38776, respectively.
Oak Regeneration: Serious Problems Practical Recommendations (Symposium Proceedings)
An Historical Perspective of Oak Regeneration F. Bryan Clark, USDA Foresf Service, Retired, Anmndale, VA 22003 Concerns about oak management in the middle ages led to forest ordinances in France designed to ensure oak establishment. Oak was an early export from the American colonies because it was scarce and expensive in England. Probably the first government sponsored forest research in the United States was attempts in Florida in the early 1800’s to establish live oak (Quercus virginiana) for shipbuilding. With the advent of technical forestry in this country there were references in early papers and textbooks to oak regeneration and the shelterwood method. This interest was primarily for academic study and followed European descriptions, but some of the earliest oak regeneration research related to concerns about areas without advance reproduction. In the late 1930’s understory oaks were described in relation to past treatment. In the 1950’s and 1960’s researchers and ecologists began to quantify oak reproduction under various stand conditions on different sites. Mostly they found lots of understory oaks, but there were exceptions. Researchers thought these exceptions might be important and started to look more carefully at the response of oaks to harvest cutting. Even-aged cuttings quickly showed that on good oak sites without substantial numbers of vigorous advance oak the stands of the future would be quite different. The new stands generally contained less oak. At the same time observers noted that oak types were changing in some areas. More recently, comparisons of repeat forest surveys show a decline of oak types in some states. Increased prices for oak timber suggest that accelerated harvesting is adding to the ecological changes taking place. We find ourselves with a growing knowledge about oak ecology and silviculture but without a convincing history of being able to prescribe with certainty ways to increase the amount of oak in new stands. Considering the tremendous value of oak forests there is an urgency to improve oak management and to give high priority to long-term research. INTRODUCTION Is oak regeneration really a problem? Experts believe that on many sites now occupied by oak, regeneration will become increasingly difficult. How can that be? Oaks are the most prevalent forest types in the United States and dominate much of the East’s landscape. Volume growth exceeds commercial removals. It is even more contusing to remember that the present stands were born out of very harsh efforts to either convert forest lands to agriculture through tire and grazing or to
Germination ecology of Central Asian Stipa spp: differences among species, seed provenances, and the importance of field studies
Stipa-species are wide-spread in Central Asia, but sexual reproduction in the dry steppes is rare. To facilitate conservation and restoration of these important rangelands, we studied germination characteristics of three common Mongolian Stipa-species under field- and lab conditions. Seeds of Stipa krylovii, Stipa gobica and Stipa glareosa were sown at the study site in Southern Mongolia over two consecutive years during which period tests were carried out to ascertain whether competition or herbivory are the main constraints of seedling establishment. In addition, we tested germination and seed viability in the laboratory under two different temperature regimes (20/10°C and 8/4°C), as well as the effect of cold-stratification. The lab experiments also included S. krylovii seeds originating from three climatically different provenances. None of the three Stipa-species seedlings emerged during the first 2 years of the field study. However, after an unusually intense rain event in the third year, 3% of S. krylovii, 0.6% of S. glareosa and 0.1% of S. gobica seeds germinated in the study plots. The factors ‘sowing-year’ and ‘vegetation’ significantly affected seedling emergence, whereas grazing had no effect at all. Under laboratory conditions a high percentage of viable seeds of S. gobica and S. glareosa germinated at both incubation temperatures, and cold-stratification had no effect on germination or viability. Germination of S. krylovii seeds required warmer temperatures and cold-stratification had a positive effect. Such evidence for dormancy was more pronounced in seeds from the moister, northern provenances. Germination of Stipa-species in the field is rare and only possible under exceptionally moist conditions. Conservation should thus concentrate on steppe conservation rather than on restoration. Where artificial reseeding is necessary, differences among species and also among different seed provenances should be taken into account.