Deer Forage in a Loblolly Pine Plantation

Browse yields in a 30-year-old plantation thinned at ages 20 and 25 years were directly related to the amount of pine removed and varied from 154 lb (oven-dry) per acre under light thinning to 199 lb/acre under heavy thinning. At plantation age 35, five growing seasons after a third thinning, browse yields were inversely related to pine-thinning intensity, ranging from 255 lb/acre in lightly thinned stands to 195 lb/acre in those heavily thinned. Many of the young hardwoods and shrubs had grown beyond the reach of deer and formed a multilayered midstory that inhibited plant growth beneath. Midstory density increased with intensity of pine thinning. In recent years more than 12 million acres of uplands in the South have been planted to pines. Even though the primary objective is to grow merchantable timber on these lands, the plantations offer food and cover for deer and other wildlife. Limited cattle grazing is also afforded, though herbage is often scarce. A study was initiated in 1957 to find how yields of understory vegetation, especially deer browse, were influenced by different intensities of intermediate thinning in a loblolly pine (Pinus taeda) plantation. The study was in central Louisiana on the Alexander State Forest, an area supervised by the Louisiana Forestry Commission. Pines were then 30 years old and plots within the plantation had been thinned twice-at plantation ages 20 and 25-to specified basal areas. 1 Contribution from the Wildlife Habitat and Silviculture Laboratory, maintained at Nacogdoches, Texas, by the Southern Forest Experiment Station in cooperation with Stephen F. Austin State College. This content downloaded from 157.55.39.176 on Sat, 09 Apr 2016 05:57:33 UTC All use subject to http://about.jstor.org/terms DEER FORAGE IN A PINE PLANTATION * Blair 433 Combined yields of herbage and browse in 1957 were greatest where thinning had been heaviest, but a midstory of invading hardwoods was developing and it, like the understory vegetation, was densest where thinnings had been heaviest (Blair 1960). This paper describes the timber and understory vegetation in 1962, five growing seasons after a third pine thinning in the winter of 1957-58. THE STUDY PLANTATION The plantation is on a relatively flat area of fine sandy loam soil with moderately good surface and internal drainage. Pine seedlings were planted in 1928 at a spacing of 8 x 8 ft. The site is about average for loblolly pine, and expectable heights of the trees at 50 years of age are 77-87 ft. In early 1948, when pines were 20 years old, randomized 0.4-acre plots were thinned to residual basal areas of 100, 85, and 70 square feet per acre, representing light, medium, and heavy cuts. The plots were rethinned to the same levels in 1953 and 1958. Except in 1948, when an occasional hardwood was cut for pulpwood, only pines were removed. Each thinning intensity was replicated four times. The plantation is managed for high-quality sawtimber on a long rotation. Fire has been excluded. The timber stands and yields of understory vegetation were sampled in October of 1957 and 1962, immediately before pine thinnings. Pines and hardwoods 1.6 inches diameter at breast height (dbh) and larger were inventoried by 1-inch diameter classes on the central 0.1 acre of each 0.4-acre plot. To evaluate changes in forage, the current season's growth of leaves and stems on understory vegetation was clipped from the ground to a height of 5 ft on nine 1-milacre quadrats within each 0.1-acre plot. Herbaceous growth was sampled separately by major vegetal classes. Browse, consisting of twigs and leaves of shrubs, hardwood reproduction, and woody vines, was sampled by species or species groups. Clipped plant material was dried to a constant weight at 65 C and then weighed. For an estimate of the total browse available in winter, dried twigs, less leaves, of deciduous and semi-evergreen browse species were combined with the leaves and twigs of evergreen species. The determination of palatable and nonpalatable browse species was based on local observations and on studies by Goodrum and Reid (1959) in the southern longleaf pine belt and by Lay (1956b) in the loblolly pine-hardwood type of east Texas. TIMBER STOCKING AND COMPOSITION In 1957 pine basal area ranged from 118 square feet per acre in lightly thinned stands to 92 square feet with heavy thinning (Table 1). Hardwoods and large shrubs formed a multilayered and scattered midstory beneath the dominant pines. Both the stocking and basal area of midstory hardwoods were directly proportional to the intensity of pine removal. Below the midstory was an understory of woody and herbaceous plants. The hardwood component increased after pines were again thinned early in 1958. By the fall of 1962 stocking increases were 44 percent for light thinning, 8 percent for moderate thinning, and 11 percent for heavy thinning. As in 1957, the midstory hardwoods were most numerous in heavily thinned stands. The basal area of hardwoods had increased and was greater in relation to pine in 1962 than in 1957 (Table 1). Under light thinning, for example, about 5 percent of the total overstory basal area was hardwood in 1957, whereas by 1962 the proportion was nearly 8 percent. In heavily thinned stands, where competition from dominant pines This content downloaded from 157.55.39.176 on Sat, 09 Apr 2016 05:57:33 UTC All use subject to http://about.jstor.org/terms 434 Journal of Wildlife Management, Vol. 31, No. 3, July 1967 Table 1. Timber stand characteristics of trees 1.6 inches dbh and larger in the fall of 1957 and 1962 (means of four 0.1acre plots per thinning intensity).