James P. Barnett

A repellent to reduce mouse damage to longleaf pine seed

Direct seeding is a potential method for reforestation of pines on many southern sites. The success of direct seeding, however, depends, at least in part, in reducing seed predation by birds and rodents. We conducted a series of tests to assess the efficacy of capsicum and thiram in reducing mouse damage to longleaf pine (Pinus palustris) seeds. House mice (Mus musculus) predation was reduced (P<0.05) by treating seeds with either capsicum or thiram or a mixture of the two ingredients. Deer mice (Peromyscus maniculatus) avoided seeds treated with a mixture of capsicum and thiram. We conclude that the capsicum and thiram mixture should be pursued as a potential repellent to protect longleaf pine seeds from animal predation when these seeds are used in direct seeding efforts to establish southern pine forests.

Seasonal photosynthesis and water relations of juvenile loblolly pine relative to stand density and canopy position

To assess the effects of stand density and canopy environment on tree physiology, we measured gas exchange responses of the same needle age class of 16-year-old loblolly pines (Pinus taeda L.) in thinned (512 trees ha−1) and non-thinned treatment plots (2,863 trees ha−1) in central Louisiana. Physiological data were collected in the upper and lower canopy positions on 26 sunny days between July 1996 and June 1997 (one-half of the leaf life span). Mean net photosynthesis was highest (4.3xa0µmol m−2 s−1) in the spring and closely corresponded with light intensity in the canopy. Photosynthesis in the winter was nearly 3.0xa0µmol m−2 s−1, indicating that loblolly pine enables substantial carbon fixation all year around in the Gulf Coastal Plain region. Mean transpiration and stomatal conductance were highest in the summer and lowest in the winter. With increased light availability after thinning, needle photosynthesis, transpiration and stomatal conductance rose 84, 40 and 23%, respectively, in the lower canopy of the thinned-treatment trees. Light-saturated photosynthetic capacity of the lower canopy needles was 5.2xa0µmol m−2 s−1 for the thinned treatment and 4.2xa0µmol m−2 s−1 for the non-thinned treatment. It is concluded that thinning-induced light penetration through the canopy enhances physiological activities in the lower canopy foliage of residual trees, and that light availability is the only significant variable for predicting needle-level photosynthesis rates.

Temporal and spatial patterns of net photosynthesis in 12-year-old loblolly pine five growing seasons after thinning

Physiological parameters were measured under natural light conditions and needle orientation from towers and walkways erected in the canopy of a loblolly pine (Pinus taeda L.) plantation. Four silvicultural treatments were randomly assigned to the twelve plots in the fall of 1988. Plots were thinned to a density of 731 trees per hectare or left unthinned, at a density of 2990 trees per hectare. The plots were left unfertilized or fertilized with 744 kg/ha of diammonium triple superphosphate was applied. During the fifth growing season (1993) following thinning and fertilization, needle level physiology was not different with respect to the thinning treatment for fertilized or unfertilized plots. In contrast, upper crown levels within the fertilized and unfertilized plots had significantly higher light levels and photosynthetic rates than lower crown foliage. Light levels were greater in the thinned, fertilized plots than in the unthinned, fertilized plots. In contrast, no effect of thinning on canopy light levels was found in the unfertilized plots. Within crown variation in photosynthesis was strongly dependent on canopy light levels. A strong interaction of canopy level with thinning was apparent for net photosynthesis. Loblolly pine, being a shade intolerant species, showed only small physiological differences between needles from different parts of the crown. Because of the variability found in this study, more extensive sampling is needed to correctly describe the physiology of a forest canopy with adequate precision.

Herbicides and planting date affect early performance of container-grown and bare-root loblolly pine seedlings in Alabama

The survival of bare-root and container-grown loblolly pine (Pinus taeda L.) seedlings exceeded 90% when outplanted in March at two sites in Lee County, Alabama. At both sites, soil moisture and seedling survival were greater in March than in May. A March herbicide application reduced weed biomass by 75–80% at both sites. At the moist site, herbicide application did not affect survival. However, at the drier site, a reduction in weed biomass increased both the percent soil moisture and the survival of May-planted bare-root seedlings. When soil moisture at planting time was less than 13% on a dry weight basis container-grown seedlings survived better than bare-root seedlings. At both sites, reduced weed competition resulted in greater seedling heights and diameters.

Crown characteristics of juvenile loblolly pine 6 years after application of thinning and fertilization

Abstract Total foliage dry mass and leaf area at the canopy hierarchical level of needle, shoot, branch and crown were measured in 48 trees harvested from a 14-year-old loblolly pine ( Pinus taeda L.) plantation, six growing seasons after thinning and fertilization treatments. In the unthinned treatment, upper crown needles were heavier and had more leaf area than lower crown needles. Branch- and crown-level leaf area of the thinned trees increased 91 and 109%, respectively, and whole-crown foliage biomass doubled. The increased crown leaf area was a result of more live branches and foliated shoots and larger branch sizes in the thinned treatment. Branch leaf area increased with increasing crown depth from the top to the mid-crown and decreased towards the base of the crown. Thinning stimulated foliage growth chiefly in the lower crown. At the same crown depth in the lower crown, branch leaf area was greater in the thinned treatment than in the unthinned treatment. Maximum leaf area per branch was located nearly 3–4xa0m below the top of the crown in the unthinned treatment and 4–5xa0m in the thinned treatment. Leaf area of the thinned-treatment trees increased 70% in the upper crown and 130% in the lower crown. Fertilization enhanced needle size and leaf area in the upper crown, but had no effect on leaf area and other variables at the shoot, branch and crown level. We conclude that the thinning-induced increase in light penetration within the canopy leads to increased branch size and crown leaf area. However, the branch and crown attributes have little response to fertilization and its interaction with thinning.

Seasonal Shoot and Needle Growth of Loblolly Pine Responds to Thinning, Fertilization, and Crown Position

Abstract The impacts of thinning, fertilization and crown position on seasonal growth of current-year shoots and foliage were studied in a 13-year-old loblolly pine ( Pinus taeda L.) plantation in the sixth post-treatment year (1994). Length of new flushes, and their needle length, leaf area, and oven-dry weight were measured in the upper and lower crown from March through November. Total shoot length was the cumulative length of all flushes on a given shoot and total leaf area per shoot was the sum of leaf areas of the flushes. By the end of June, first-flush foliage reached 70% of the November needle length (14.3xa0cm) and 65% of the final leaf area (15.0xa0cm 2 ). Cumulative shoot length of first- and second-flush shoots achieved 95% of the annual length (30.3xa0cm), whereas total leaf area per shoot was 55% of the final value (75.3xa0dm 2 ). Fertilization consistently stimulated fascicle needle length, dry weight, and leaf area in the upper crown. Mean leaf area of upper-crown shoots was increased by 64% six years after fertilization. A significant thinning effect was found to decrease mean leaf area per shoot in the crown. For most of the growing season, the thinned-fertilized trees produced substantially more leaf area per shoot throughout the crown than the thinned-nonfertilized trees. These thinned-fertilized trees also had greater needle length and dry weight, longer first flush shoots, and more leaf area per flush than trees in the thinned-nonfertilized plots. Needle length and leaf area of first flush shoots between April and July were linearly related to previous-month canopy air temperature ( T a ). Total shoot length strongly depended on vertical light gradient (PPFD) within the canopy, whereas shoot leaf area was a function of both PPFD and T a . Thus, trees produced larger and heavier fascicles, more and longer flush shoots, and more leaf area per shoot in the upper crown than the lower crown. We conclude that thinning, fertilization, and crown position regulate annual leaf area production of current-year shoots largely by affecting the expansion of first flush shoots and their foliage during the first half of the growing season.

Ecophysiological Response of Managed Loblolly Pine to Changes in Stand Environment

Anticipated shifts in our global climate may expose southern pine ecosystems to such environmental stimuli as elevated carbon dioxide and water and nutrient deficiencies (Hansen et al., 1988; Kirschbaum et al., 1990; Peters, 1990). Global climate change may also increase the degree of stress to which trees are presently exposed (Kirschbaum et al., 1990; Peters, 1990). For example, the western extent of loblolly pine (Pinus taeda L.), now dictated by moisture availability for seedling establishment, is predicted to shift eastward with temperature and precipitation changes that may occur with global climate change (Miller et al., 1987).

Five-year field comparison of naturally regenerated Pinus taeda L. to genetically improved container stock, with and without release

A field study compared genetically improved, container-grown loblolly pine (Pinus taeda L.) seedlings to naturally established loblolly seedlings on a cutover pine site in southern Arkansas, USA. Pines on 50% of all plots were released from woody and herbaceous competition within a 61 cm radius of each tree stem. Woody competition was controlled by hand cutting for 5 consecutive years and herbaceous competition was controlled with herbicides (sulfometuron methyl and glyphosate) for 4 consecutive years. Competition control increased 5-year survival by 21–23% for natural and planted seedlings, respectively, with no statistically significant difference between the two regeneration techniques. Five years after field establishment, planted pines averaged 85% more volume than naturally established pines. Nevertheless, greater volume gains (551–688%) were achieved within regeneration techniques, as a result of competition control, than were achieved between the two regeneration techniques.