Date of sowing and emergence timing affect growth and development of loblolly pine seedlings

Loblolly pine (Pinus taeda L.) seeds were sown from February to June in Alabama, U.S.A. If sowing was conducted in May or June, seedling emergence was reduced and seedling mortality increased. Seedlings from earlier sowings grew to greater sizes, but seedlings from later sowings grew later into the fall. Within any given sowing date, the earliest seedlings to emerge grew largest. Seedlings from the February sowing formed buds in mid-summer, flushed, and in some instances flushed yet again. However, by early October, not all seedlings from May and June sowings had formed an initial bud.     

Long term growth responses of loblolly pine to optimal nutrient and water resource availability

A factorial combination of four treatments (control (CW), optimal growing season water availability (IW), optimum nutrient availability (FW), and combined optimum water and nutrient availability (FIW)) in four replications were initiated in an 8-year-old Pinus taeda stand growing on a droughty, nutrient-poor, sandy site in Scotland County, NC and maintained for 9 years. Results for the first 4 years after treatment initiation at this study were first reported by Albaugh et al. [For. Sci. 44 (1998) 317]. The site is primarily nutrient limited and all measured stand parameters (height, basal area, leaf area index, live crown length, stem mass accumulation, current annual stem mass increment) were increased with fertilization throughout the study period. Irrigation effects were also positive for these parameters but the increases were much smaller than those found with fertilization. For example, 9 years after treatment initiation, standing stem mass was increased 100 and 25% by fertilization and irrigation, respectively, while current annual increment of stem biomass production was increased 119 and 23% by fertilization and irrigation, respectively. Interestingly, stem density (stems ha⁻¹) was not significantly affected by treatment in any year of the study. Growth efficiency (stem mass increment per unit leaf area index) was 1.9 Mg ha⁻¹ per year per LAI for CW and influenced by treatment with IW, FW, and FIW achieving growth efficiencies of 2.4, 2.7 and 2.9 Mg ha⁻¹ per year per LAI, respectively. Growth efficiency appeared to be relatively stable in the last 4 years of the study. Ring specific gravity was measured in the third, fourth, and fifth years after treatment initiation. An average reduction in ring specific gravity of 7.5% was observed with fertilization while irrigation had little effect on specific gravity in any year measured. The continuation of high growth rates with no observable growth decline in the treated stands throughout the 9-year study may be a function of the age of the stands when treatments were initiated (8 years), the very poor initial nutrient and moisture availability, and/or the application of an ongoing optimum nutrient regime at the site. The fertilized plots are now at or near an age and a size when a commercial harvest would be feasible. For the stand conditions at this site, then, the optimum nutrient availability plots have achieved high productivity throughout the economic life of the stand without measurable declines in stand productivity.     

Aluminum sensitivity of loblolly pine and slash pine seedlings grown in solution culture

To probe variation in Al sensitivity of two co-occurring pine species, seedlings from six full-sib families of loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) were grown in solution culture containing 4.4 mM (high-Al) or 0.01 mM (low-Al) AlCl(3) at pH 4 for 58 days. On average, both pine species had 41% less total dry weight in the high-Al treatment than in the low-Al treatment. Stem volume growth of slash pine was more sensitive to the high-Al treatment than that of loblolly pine. In both species, the high-Al treatment inhibited root dry weight more than shoot dry weight. Within-species variation in Al sensitivity among families was greater in loblolly pine (24 to 52% inhibition of seedling dry weight) than in slash pine (35 to 47% inhibition of seedling dry weight). Foliar Al concentration was positively correlated with Al sensitivity in slash pine but not in loblolly pine; however, in both species, the concentration of Al in roots was 20-fold greater than in foliage.     

Water relations and growth of loblolly pine seedlings planted under a shelterwood and in a clear-cut

We investigated the influence of shelterwood conditions on water relations and growth of loblolly pine (Pinus taeda L.) seedlings on two harsh sites in eastern Texas. Site I was harvested to provide four overstory density treatments (0, 2.3, 4.6 and 9.2 m(2) of residual basal area per ha). To quantify the effects of overstory competition, trenched and nontrenched subplots, each containing 25 one-year-old seedlings, were established within each overstory treatment plot, and predawn and midday water potentials (Psi(w)), seedling growth and survival were measured during the growing season. Leaf area and seedling biomass partitioning were measured at the end of the growing season. Site II was harvested to provide two overstory density treatments (0 and 6.9 m(2) ha(-1)) and planted with one-year-old loblolly pine seedlings. Seedling Psi(w), stomatal conductance (g(wv)), transpiration flux density (E), leaf area, height and survival were determined. On Site I, seedling Psi(w) increased with increasing overstory basal area, whereas trenching only substantially affected Psi(w) of seedlings in the 9.2 m(2) ha(-1) overstory treatment. Growth was not affected by overstory treatment or trenching. On Site II, Psi(w) and g(wv) were highest during the morning hours and lowest in the afternoon, whereas E peaked in the afternoon. Vapor pressure deficits and photosynthetic photon flux density were major factors in determining g(wv) differences between treatments. On individual days, the presence of an overstory increased Psi(w) and reduced both g(wv) and E. On Site II, leaf area was affected by overstory treatment throughout most of the study. We conclude that the presence of an overstory can have ameliorative effects on harsh sites at the western fringe of the loblolly pine natural range.     

Water relations of loblolly pine seedlings from diverse geographic origins

Leaf conductance at three absolute humidity deficits (AHDs) (7, 14 and 21 g m(-3)), hydraulic conductance and components of tissue water potential were measured in one-year-old loblolly pine seedlings from six origins representing the geographic range of the species. Measurements were made on seedlings grown (a) with ample water (moist regime) and (b) with recurring severe drought (dry regime). However, all seedlings were well-watered prior to and during measurements. Seedlings grown in the moist regime had greater mean leaf conductances (0.30 versus 0.13 cm s(-1)) and greater responses to AHD than seedlings grown in the dry regime. They also exhibited greater hydraulic conductances (0.53 versus 0.35 microg cm(-2) s(-1) MPa(-1), less negative osmotic potentials (-1.45 versus -1.57 MPa) and higher relative water contents at turgor loss (0.72 versus 0.65). Seed source differences in water relations characteristics were detected only in seedlings grown in the moist regime. In these, trees from the three interior origins had greater mean leaf conductances than those from the three coastal sources (0.32 versus 0.28 cm s(-1)), but no differences in response to changing AHD were observed. Seedlings from North Carolina had lower osmotic potentials at turgor loss than those from Florida, Georgia or Texas. These differences in water relations characteristics are not clearly related to the observed greater survival ability of trees from interior origins compared with those from coastal origins.     

Prescribed burning increased nitrogen availability in a mature loblolly pine stand

Prescribed burning is a common management practice in loblolly pine (Pinus taeda L.) ecosystems. Several studies have examined the volatilization losses of nitrogen (N), but little information is available on subsequent availability of N. We examined the effects of a low-intensity prescribed fire in a mature stand of loblolly pine and found no significant reduction in the N content of the forest floor. However, the decomposition rate of the forest floor more than doubled for the first growing season after burning. This decomposition released 60 kg N ha⁻¹ more than measured for an unburned portion of the same stand. Increased N availability was also indicated by analysis of foliage and soil incubations. This pulse of available nitrogen may have a fertilization effect on pine growth and might substitute for late-rotation applications of N fertilizer.     

Long-term growth and ecophysiological responses of a southeastern Oklahoma loblolly pine plantation to early rotation thinning

A thinning levels study was initiated in a 9-year-old loblolly pine (Pinus taeda L.) plantation containing 26.6 m² ha⁻¹ basal area during the spring of 1984 in southeastern Oklahoma. Thinning treatments consisted of (1) three control plots (BA100), (2) three plots thinned to approximately 50% of the original basal area (BA50) and (3) three plots that were thinned to 25% of the original basal area (BA25). In 1987 the BA50 and BA25 plots were both rethinned to a basal area of 12 m² ha⁻¹. No other thinnings were done through age 24.The control plots have attained a basal area of 45.3 m² ha⁻¹ and basal area is now starting to decline. The BA25 and BA50 plots have basal areas between 34 and 35 m² ha⁻¹. Mortality has averaged about 90 trees ha⁻¹ per year from age 10 to age 24 on the control plot, declining from 2078 trees ha⁻¹ at age 10 to 827 trees ha⁻¹ at age 24. Mortality losses in the BA25 and BA50 plots have been only 3.2–7.7 trees ha⁻¹ per year over the entire study period. Cumulative stem biomass lost to mortality was 10.5, 16.0 and 61 Mg ha⁻¹, respectively, for the BA25, BA50 and BA100 treatments. Cumulative standing live biomass at age 24 in the BA100 treatment is 132 Mg ha⁻¹. Cumulative standing live biomass in the BA25 and BA50 treatments at age 24 is 86 and 79%, respectively, of that observed in the BA100 treatment. These results suggest wide ranges of residual stand densities left after an early thinning will produce a high percentage of the potential total maximum standing stem biomass. Diameter distributions at age 24 show only 33% of the trees in the BA100 treatments have the dimensions to be sawtimber (≥30 cm) but 92 and 95% of the trees in the BA25 and BA50, respectively, are sawtimber dimension or larger. Mean annual stem biomass production (MAI) of the BA100 treatment is 7.5 Mg ha⁻¹ per year at age 24. MAI of the thinned treatments is about 5.1 Mg ha⁻¹ per year and is converging to that of the BA100 treatment. The basis for this convergence is not that the live trees in the BA100 treatment are producing live biomass less rapidly than the thinned plots, but that mortality losses in the BA100 plot are much higher. Current annual stemwood production in all treatments is often limited by the severe summer droughts that occur in this region. The wide variations in weather experienced at this site also result in variations in earlywood:latewood ratio and ring specific gravity.     

Seasonal changes in intensity of bud dormancy in loblolly pine seedlings

The terminal buds of six-month-old loblolly pine (Pinus taeda L.) seedlings remained closed for approximately six months, although bud dormancy, as measured by rate of bud break in a standard greenhouse environment, was only exhibited for about one month. The peak of bud dormancy was in December for seedlings grown near Auburn, Alabama. However, the timing and intensity varied with seed source and may have been affected by the warm fall temperatures. Seedlings from the more northern provenances entered dormancy first and reached a deeper state of dormancy than seedlings from southern provenances. The rate of shoot elongation was not consistently related to the rate of bud break.     

Post-fertilization physiology and growth performance of loblolly pine clones

The physiological processes leading to enhanced growth of loblolly pine (Pinus taeda L.) following fertilization are not clearly understood. Part of the debate revolves around the temporal response of net photosynthetic rate (A(n)) to fertilization and whether the A(n) response is always positive. We measured light-saturated photosynthetic rate (A(sat)), dark respiration rate, growth and crown silhouette area in eight clones of loblolly pine before and after nitrogen (N) fertilization (112 kg ha(-1)) to track the initial physiological changes prior to any changes in growth. Overall, there were positive photosynthetic and growth responses to fertilization; however, there were pronounced physiological and growth differences among clones, even among clones with the same parents. Clones 4, 6 and 7 showed large volume growth and A(sat) responses to fertilization. Clone 1 and Clone 8 (a full-sibling of Clone 7) mainly showed a volume growth response, whereas Clone 2 (full-sibling of Clone 1) showed an A(sat) response only. Clone 5 (full-sibling of Clone 6) showed little response to fertilization, whereas Clone 3 (full-sibling of Clone 4) showed a negative A(sat) response. Thus, within-family variation warrants further study to ensure that relatively expensive clonal material is used efficiently.     

Long-term impact of prescribed burning on the nutrient status and fuel loads of rehabilitated bauxite mines in Western Australia

Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah (Eucalyptus marginata) forest of Western Australia for more than 35 years. It is a requirement of Alcoa’s completion criteria that rehabilitated areas can be incorporated into the prescribed burning program implemented in the surrounding forest. Rehabilitated areas may be more susceptible to nutrient losses following burning because of their relatively young age and reliance on N fixation from a legume understorey. The objective of this study was to assess the impact that prescribed burning has on the nutrient pools within rehabilitated ecosystems 5 and 8 years after fire, and compare these responses to unburnt rehabilitated areas and the unmined forest. The nutrient status of sites established in previous studies were assessed five (burnt and unburnt forest, 1989 and 1992 rehabilitation) and 8 (spring, autumn and unburnt 1981/1982 rehabilitation) years after burning. Soil, litter and understorey samples were collected and analysed for nutrient content. Burning 1981/1982 rehabilitation in either season 8 years earlier had no long-term negative effect on the nutrient status of the rehabilitation compared to the unburnt controls. Spring burning increased the nitrogen status of the rehabilitated areas by 52 kg ha⁻¹ compared with the unburnt control. Sites rehabilitated in 1989 and burnt 5 years ago showed similar post-fire recovery of nitrogen status to that of the burnt native forest sites (77–85%), while 1992 rehabilitation sites had only recovered 52% of the of the nitrogen of the unburnt sites. Therefore, the impact of burning on nitrogen status was greatest in the 5-year-old rehabilitation and least in the 12–13-year-old sites. Phosphorus was less affected by burning than nitrogen largely because the majority of P is bound in the soil in the jarrah forest. It is recommended that rehabilitated sites are burnt under low intensity in spring when they are 12–15-year-old to ensure rapid post-fire recovery of nutrients.     

Durability of selected mulches,their ability to control weeds,and influence growth of loblolly pine seedlings

Several mulches of natural, synthetic, or blends of natural and synthetic fibers were tested around newly planted loblolly pine (Pinus taeda L.) seedlings on a sheared and windrowed site in central Louisiana, USA. The vegetation was primarily winter annuals, some residual grasses and forbs, and sparse woody regrowth. Study 1 was rotary mowed just prior to planting in March 1992, and 35 mulches and an untreated check were established. In Study 2, 15 mulches and an untreated check were established in a 1-year-old rough in March 1993. In both studies, a single loblolly pine seedling formed each plot established in a randomized complete block design, with 10 blocks as replicates. Each block was planted with a separate open-pollinated loblolly pine family.Nearly all mulches had deteriorated to some extent after three growing seasons. Synthetic mulches were generally more durable than the natural or natural/synthetic mulches. Mulching eliminated the established vegetation and germinants, and vegetation did not readily reestablish following the deterioration of a mulch. The soil seed bank apparently was not sufficient to regenerate areas that were once covered with mulch and many of the natural materials deteriorated into a fibrous cover that acted like a natural litter layer. Both of these residual weed control effects -- insufficient soil seed bank and formation of a fibrous cover -- were important in stopping vegetation from reestablishing after a mulch had deteriorated. After three growing seasons, the loblolly pine seedlings generally grew better if mulches were used.     

Acclimation of loblolly pine (Pinus taeda) seedlings to high temperatures

To determine the extent to which loblolly pine seedlings (Pinus taeda L.) acclimate to high temperatures, seedlings from three provenances-southeastern Texas (mean annual temperature 20.3 degrees C), southwestern Arkansas (mean annual temperature 16.2 degrees C) and Chesapeake, Maryland (mean annual temperature 12.8 degrees C)-were grown at constant temperatures of 25, 30, 35 or 40 degrees C in growth chambers. After two months, only 14% of the seedlings in the 40 degrees C treatment survived, so the treatment was dropped from the experiment. Provenance and family differences were not significant for most measured variables. Total biomass was similar in the 25 and 30 degrees C treatments, and less in the 35 degrees C treatment. Foliage biomass was higher, and root biomass lower, in the 30 degrees C treatment compared with the 25 degrees C treatment. Net photosynthesis and dark respiration of all seedlings were measured at 25, 30 and 35 degrees C. Both net photosynthesis and dark respiration exhibited acclimation to the temperature at which the seedlings were grown. For each temperature treatment, the highest rate of net photosynthesis was measured at the growth temperature. Dark respiration rates increased with increasing measurement temperature, but the basal rate of respiration, measured at 25 degrees C, decreased from 0.617 &mgr;mol m(-2) s(-1) in the 25 degrees C treatment to 0.348 &mgr;mol m(-2) s(-1) in the 35 degrees C treatment, resulting in less carbon loss in the higher temperature treatments than if the seedlings had not acclimated to the growth conditions. Temperature acclimation, particularly of dark respiration, may explain why total biomass of seedlings grown at 30 degrees C was similar to that of seedlings grown at 25 degrees C.     

The influence of nutrient and water availability on carbohydrate storage in loblolly pine

We quantified the effects of nutrient and water availability on monthly whole-tree carbohydrate budgets and determined allocation patterns of storage carbohydrates in loblolly pine (Pinus taeda) to test site resource impacts on internal carbon (C) storage. A factorial combination of two nutrient and two irrigation treatments were imposed on a 7-year-old loblolly pine stand in the Sandhills of North Carolina. Monthly collections of foliage, branch, stem, bark, and root tissues were made and total non-structural carbohydrate analyses were performed on samples collected in years 3 and 4 after treatment initiation. Seasonal fluxes of carbohydrates reflected the hypothesized use and storage patterns. Starch concentrations peaked in the spring in all tissues measured; however, minimum concentrations in aboveground tissue occurred in late winter while minimum concentrations in below ground tissue occurred in late fall. Increased nutrient availability generally decreased starch concentrations in current year tissue, while increasing starch in 1-year-old woody tissue. Irrigation treatments did not significantly impact carbohydrate flux. The greatest capacity for starch storage was in below ground tissue, accounting for as much as 400 kg C/ha per year, and more than 65% of the total stored starch C pool. The absolute amount of C stored as starch was significantly increased with increased nutrient availability, however, its relative contribution to the total annual C budget was not changed.     

Predicted leaf area growth and foliage efficiency of loblolly pine plantations

Foliage dynamics research is helpful for better understanding the process of forest production and improving silvicultural practice. However, the difficulty of measuring foliage amount has slowed down the research progress. Since leaf area of an individual tree can be reliably predicted from its diameter, growth and yield models that provide detailed information for each diameter class can be used to benefit foliage dynamics research. Simulation results from a growth and yield system for unthinned loblolly pine plantations indicated that foliage area increased with stand age, peaked between ages 36 and 51, and decreased after that. Volume growth increased with leaf area for young stands and decreased for older stands, whereas foliage efficiency consistently decreased with age. Better sites supported higher levels of leaf area index, volume growth, and foliage efficiency. Higher planting densities led to higher maximum leaf area indices and shorter time to reach that level. Initial density had no effect on foliage efficiency through time.     

Early gains from planting large-diameter seedlings and intensive management are additive for loblolly pine

A seedling size/intensive management study with Pinustaeda L. was established in 1993 on two sites in the CoastalPlain of Georgia and South Carolina. Each site contained a 2 × 2split-plot study involving two seedling sizes and two levels ofestablishment intensity. Ideotype ``B' seedlings averaged 5.0 mmin diameter (at the root collar) and were 43 cm tall. Ideotype``A' seedlings averaged 8.5 mm in diameter and were 50 cm tall. ``Standard' establishment practices included herbicides(hexazinone and sulfometuron) and fertilizer (DAP) appliedduring the first year. The ``intensive' management involved twoherbicide applications during the first year and two during thesecond year, fertilizer during the first and third years, andinsecticide applications during the first two years (for controlof tip moth, Rhyacionia frustrana Comstock).Intensive management did not affect survival but planting largerseedlings increased survival slightly on one site. However,treatments affected early growth at both sites. On both sites,fourth-year plot-volumes were increased with greaterestablishment intensity and larger seedlings but there was nointeraction between stock size and establishment intensity. Early growth gains were greatest when both intensive managementand larger seedlings were combined. Depending on site, thiscombination resulted in 21% to 51% more volume (at age 4) thanthe next best treatment (standard seedlings with intensivemanagement).     

Black polyethylene mulch improves growth of plantation-grown loblolly pine and yellow-poplar

The effects of mulching with perforated black plastic, in combination with fertilization and induced mycorrhizal symbioses, on the growth of loblolly pine (Pinus taeda L.) and yellow-poplar (Liriodendron tulipifera L.) were studied in a plantation under intensive, short rotation management. Mulching effects on soil temperature were also examined in order to assess the potential influence of this treatment on temperature-dependent processes in soils affecting tree growth. Mulching significantly increased height and stem diameter growth of both species, attributable largely to improved water relations resulting from diminished soil surface evaporation and elimination of transpirational losses from competing vegetation. Mulching effects on soil temperature were insufficient to contribute substantially to the growth response exhibited by mulched trees. Multiple applications of urea-N promoted enhanced growth in both loblolly pine and yellow-poplar, an effect accentuated by mulching, but the field performance of trees inoculated in the nursery with selected mycorrhizal fungi was poor relative to that of the other treatments investigated.     

Responses of loblolly pine seedlings to elevated CO(2) and fluctuating water supply

Osmotic adjustment of loblolly pine (Pinus taeda L.) seedlings to fluctuating water supply in elevated CO(2) was investigated. Seedlings were grown in controlled-environment chambers in either 350 or 700 micro l l(-1) CO(2) with weekly watering for four months, after which they were either watered weekly (well-watered treatment) or every two weeks (water-stress treatment) for 59 days. Osmotic adjustment was assessed by pressure-volume analysis of shoots and by analysis of soluble carbohydrates and free amino acids in roots during the last drying cycle. In well-watered seedlings, elevated CO(2) increased the concentration of soluble sugars in roots by 68%. Water stress reduced the soluble sugar concentration in roots of seedling growing in ambient CO(2) to 26% of that in roots of well-watered seedlings. Elevated CO(2) mitigated the water stress-induced decrease in the concentration of soluble sugars in roots. However, this was probably due, in part, to carbohydrate loading during the first four months when all seedlings were grown in the presence of a high water supply, rather than to osmotic adjustment to water stress. Water stress caused a doubling in the concentration of free primary amino acids in roots, whereas elevated CO(2) reduced primary amino acid and nitrogen concentrations to 32 and 74%, respectively, of those in roots of seedlings grown in ambient CO(2). There was no indication of large-scale osmotic adjustment to water stress or that elevated CO(2) enhanced osmotic adjustment in loblolly pine.     

The effects of sulfometuron on the root growth of loblolly pine

The effect of sulfometuron (Oust) on the root growth of loblolly pine (Pinus taeda L.) seedlings was studied in the field and in two soil types in the greenhouse. In the greenhouse study sulfometuron was applied to the foliage only, the soil only, and to both foliage and soil at the rates of 0.10, 0.21, and 0.42 kg ai/ha. Twenty-eight days after application root growth significantly decreased for all methods of application and with increasing rates e.g., 0.10, 0.21, and 0.42 kg ai/ha sulfometuron reduced new root length by 42%, 53%, and 64%, respectively. Application in the field at the rate of 0.30 kg ai/ha resulted in a 68% reduction in root growth. However, by the end of the growing season treated seedling root and shoot biomass were 115% and 64% greater, respectively. To ensure earlier season survival the rate of sulfometuron applied should be kept at a minimum level that will allow both weed control and adequate root growth. Low rates would be particularly important during a dry planting season.