Clonal variation in crown structure, absorbed photosynthetically active radiation and growth of loblolly pine and slash pine

Crown structure, absorbed photosynthetically active radiation (APAR) and growth were analyzed in 300 replicated loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliotti) clones to: (1) quantify genetic variation in crown structural traits, growth and APAR at the species, family and clonal levels; and (2) estimate within-family genetic and environmental influences on measured variables. Species and family-within-species differences were found in some growth traits, crown size, leaf area, APAR and branch angle. Loblolly pine developed larger crowns, exposed more leaf area with an acute angle, and intercepted more radiation than slash pine. Significant differences among clones within-family were found for stem volume and crown architecture. Loblolly pine and slash pine within-family, individual-tree broad-sense heritabilities ranged from 0.00 to 0.41 for growth and crown structural traits and most were between 0.10 and 0.25 when estimated from a combined analysis across families. Genetic correlations of crown size, leaf area and APAR with volume increment generally ranged from 0.60 to 0.75. This knowledge of the genetic interactions among growth and crown structural traits improves our understanding of how crown morphology affects light interception and stand development, and ultimately how these attributes can be incorporated in the selection of families or clones for the development of new crop tree ideotypes.     

Integrating within-crown variation in net photosynthesis in loblolly and slash pine families

We examined photosynthetic characteristics of two fast- and two slow-growing half-sib families of both loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii var. elliottii Engelm.) on two sites in northern Florida to: (1) quantify variation in light-saturated net photosynthesis (Amax) associated with vertical crown position and foliage age; (2) quantify the amount and distribution of leaf area by foliage age class; and (3) determine whether photosynthetic indices, ranging from leaf-level through whole-crown Amax, were related to growth differences among species and families. In both species, leaf-level Amax was higher in more recently formed foliage both within the same year (where Amax in the third flush averaged 10 to 30% higher than Amax in the first flush) and between years (where Amax in current-year foliage averaged 20 to 40% higher than Amax in 1-year-old foliage). When expressed on a leaf area basis, Amax of current-year foliage was higher in slash pine than in loblolly pine, but Amax expressed on a mass basis did not differ between species. Loblolly pine had higher whole-tree leaf area than slash pine, whereas whole-tree Amax did not differ between species. When the mean values for fast-growing families were compared with the mean values for slow-growing families, there were no differences in leaf-level characteristics, whereas at the whole-tree level, fast-growing families had higher leaf area and whole-tree Amax than slow-growing families in both species. When comparisons were made among the individual fast- and slow-growing families, however, results were more variable. In both species, stem volume growth was strongly correlated with whole-tree Amax, with most of the strength of the correlation deriving from the relationship between volume growth and tree leaf area.     

Effects of nitrogen on leaf physiology and growth of different families of loblolly and slash pine

Leaf physiology and fractional dry weight allocation were examined in four open-pollinated families of loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Englm. var. elliottii) in response to growth under low and high N supply for six months. Nitrogen greatly influenced dry weight allocation, total mass, leaf net photosynthesis and leaf conductance in seedlings of both species. Family variation in fine root allocation was observed under low but not high N treatment, but for the majority of physiological and growth traits, family variation was stable under varying N treatment. Family rankings based on juvenile height, diameter and biomass accretion were similar to rankings based on field performance at 22 years in slash pine but not loblolly pine. Lower leaf maintenance respiration rates were associated with families exhibiting the most rapid juvenile growth.     

Aluminum fractions in root tips of slash pine and loblolly pine families differing in Al resistance

Aluminum (Al) distribution among several cellular fractions was investigated in root tips of seedlings of one Al-resistant and one Al-sensitive family of slash pine (Pinus elliottii Engelm.) and loblolly pine (Pinus taeda L.) grown in nutrient solution containing 100 microM AlCl3 (pH 4) for 167 h. Aluminum present in 5-mm-long root tips was fractionated into cell-wall-labile (desorbed in 0.5 mM citric acid), cell-wall-bound (retained after filtering disrupted cells through 20-microm mesh) and symplasmic (filtrate following cell disruption) fractions. When averaged across both species, 12% of Al absorbed by root tips appeared in the symplasmic fraction and 88% in the apoplasmic fraction (55% as cell-wall-labile, and 33% as cell-wall-bound). On a fresh mass basis, total Al in root tips was lower in loblolly pine than in slash pine, lower in the Al-resistant slash pine family than in the Al-sensitive slash pine family, and lower in the Al-resistant families than in the Al-sensitive families across species. Although the data support the hypothesis that Al-resistant plants limit Al uptake to root apices, they do not exclude other mechanisms of Al resistance. Differential Al resistance between the species and between slash pine families may also be associated with the size of the total non-labile and cell-wall-labile Al fractions, respectively. We were unable to identify the basis for differential Al resistance in loblolly pine.     

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.     

Seasonal shoot and needle growth of loblolly pine responds to thinning, fertilization, and crown position

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 (14.3 cm) and 65% of the final leaf area (15.0 cm²). Cumulative shoot length of first- and second-flush shoots achieved 95% of the annual length (30.3 cm), whereas total leaf area per shoot was 55% of the final value (75.3 dm²). 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.     

A summary of pine straw yields and economic benefits in loblolly, longleaf and slash pine stands

Forest landowners in the southeastern United States have the opportunity to manage their loblolly, longleaf and slash pine stands for pine straw (fresh undecomposed needles; the litter layer) for non-timber revenues. Pine straw is used primarily as mulch in landscaping and has grown in revenues paid to landowners in Georgia from $15.5 million in 1999 to $81 million in 2009. Pine straw is typically sold by the acre or by the bale. Selling pine straw by the acre may be advantageous to absentee landowners. Selling pine straw by the bale can generate more annual income, but bale counts need to be accurate and bale dimensions defined. For both methods, recent (2005–2010) pine straw multi-year revenues range from $50 to $150 per acre annually. Longleaf pine straw commands the highest price per bale, followed by slash pine, and lastly loblolly pine. Per rake yields from loblolly stands tend to be 15–30?% greater than slash and longleaf pine. Pine straw raking typically starts at canopy closure continuing to the first thinning, generating from $300 per acre to over $1000 per acre in new income. This paper summarizes pine straw yields and economics in loblolly, longleaf, and slash pine stands.     

Bud development and dormancy in slash and loblolly pine. II. Effects of ethephon applications

Ethephon application on four dates did not induce budset in slash and loblolly pine seedlings. Ethephon promoted slash pine budbreak by 11 days when applied in mid-November and delayed loblolly pine budbreak by 8 days when applied in late November. Mid-November and early February applications of ethephon promoted height growth of both species.     

Specific gravity responses of slash and loblolly pine following mid-rotation fertilization

Wood quality attributes were examined in six stands of slash pine (Pinus elliottii Engelm. var. elliottii) and loblolly pine (P. taeda L.) in the lower Coastal Plain of Georgia and Florida. Several plots comprised each stand, and each plot was divided so that it received three fertilizer treatments: a control treatment with herbaceous weed control at planting and brush control at mid-rotation only (control); 45 kg ha⁻¹ N + 56 kg ha⁻¹ P + herbaceous weed control at planting and 224 kg ha⁻¹ N + 45 kg ha⁻¹ P + brush control at mid-rotation (fertilizer with N at planting); and 56 kg ha⁻¹ P + herbaceous weed control at planting and 224 kg ha⁻¹ N + 45 kg ha⁻¹ P + brush control at mid-rotation (fertilizer without N at planting). Ring width, ring earlywood specific gravity (SG), ring latewood SG, whole ring SG, and ring percent latewood were measured on each of seven trees. Of these measurements, this study focused mainly on the properties related to SG. Examination of the rings showed that latewood SG was significantly lower in trees treated with fertilizers with and without N at planting in the two to three years following fertilization, but that latewood SG gradually returned to a level similar to the control. Fertilizer without N at planting may also have had a brief negative effect on earlywood SG following mid-rotation fertilization, but it was not as clear or lasting as the effect on latewood SG. Additionally, although slash and loblolly pine appear to differ in the developmental patterns of these SG properties, there were no significant differences in how these patterns interacted with treatment. This study demonstrated that fertilization treatments have similar short-term effects on the SG of slash and loblolly pines, particularly in latewood, but the trees will return to a SG pattern consistent with unfertilized trees within two or three years.     

Phenological variation in height and diameter growth in provenances and families of loblolly pine

The phenology of 5- and 6-year old loblolly pine (Pinus taeda L.) trees was studied over two different growing seasons (1993 and 94) in southwest Georgia. These trees were from 7–9 open-pollinated families from each of four different provenances planted at two locations. The provenances were: Atlantic Coastal Plain (eastern SC), Gulf Hammock (north FL), Lower Gulf (south AL, MS) and Upper Gulf (north AL, MS). Provenances did not vary as to when height growth started in spring, but showed very significant differences for the date of growth cessation in fall. The Gulf Hammock source grew the most and also had the longest height growth period, while the Upper Gulf source was first to stop height growth and had the least annual height increment. Provenances were also significantly different for the date of cessation of diameter growth (a difference of 22 days between Gulf Hammock and Upper Gulf), and the order of cessation was the same as for height. Families within provenances were significantly different for date of cessation of height growth and diameter growth. When family means were considered across provenances, there was a correlation of 0.69 (p-value = 0.0001) between annual height increment and date of height growth cessation. There was a weaker association between faster growth and a longer growing season within provenances.     

Dry-matter partitioning in loblolly and slash pine: Effects of fertilization and irrigation

The effects of fertilization and irrigation, singly and in combination, on growth and dry-matter allocation in seedlings of Pinus taeda and P. elliottii were investigated under field conditions. Trickle irrigation was regulated to maintain soil water potential above −10 kPa and 111 g of fertilizer (N:P:K 10:10:10 plus micronutrients) were banded around each seedling on three occasions. Treatments were initiated at the beginning of the second growing-season in the field, the same year sampling was conducted. Sampling consisted of complete excavation of 15 seedlings per treatment per species beginning in early April and continued every 6 weeks through mid-November, 1986. Each seedling was measured for height, root-collar diameter, foliage, stem and root dry-matter, and total needle surface-area. Allometric growth-analysis was used to determine dry-matter partitioning among the various tree components.

The cultural treatments affected the two species differently. Loblolly pine responded to treatments by shifting dry-matter allocation from roots to shoots, with the greatest increase observed in the fertilization treatment. Slash pine showed a similar response to irrigation and to irrigation plus fertilization, but increased allocation to roots under the fertilization treatment. Allocation to stems was greater than to foliage in both species and treatments except the control loblolly pine.     

Measuring heights to crown base and crown median with LiDAR in a mature,even-aged loblolly pine stand

This study evaluated the possibility of measuring the height to the base of the live crown and the height to the median of canopy elements with airborne scanning LiDAR (Light Detection And Ranging) in a simple, even-aged stand of loblolly pine. The first step in determining these heights was fitting truncated Weibull functions to the vertical distribution of elevations where discrete laser pulses were reflected from the dominant canopy strata. The height to the canopy median was defined as height at the median of the distribution. The height to the base of the live crown was defined as the height where the upper tail the distribution asymptotes to zero returns. Ground-based and LiDAR-based estimates of the canopy median differed by 0.3 m and were not significantly different (P = 0.23). Ground- and LiDAR-based estimates of the base of the live crown differed by 0.6 m and were significantly different (P = 0.03). LiDAR-based estimates of the canopy median exhibited positive bias over most of the range of field-measured values. Analyses of the LiDAR data resulted in overestimating the height to the canopy base over most of the range in field-measured values; however, the difference between ground and LiDAR-based estimates were negatively correlated with ground-based measurements. Average tree diameter was calculated with LiDAR-generated heights to the canopy median and to the base of the live crown. The overall average diameter was not statistically different from the overall quadratic mean diameter measured on the ground, demonstrating the possible utility of these canopy variables to forest managers working with simple stands such as plantations.     

Importance of weed control, fertilization, irrigation, and genetics in slash and loblolly pine early growth on poorly drained spodosols

Research reported here has evaluated interactions of factors limiting the biological potential of slash pine (Pinus elliottii var. elliottii Engelm.) and loblolly pine (P. Taeda L.). Water and nutrients were manipulated by irrigation, weed control, and intensive fertilization. Genetic factors were incorporated as (1) improved loblolly seedlings from a commercial clonal seed orchard and (2) slash seedlings from four fast-growing, open-pollinated seed-orchard clones. Three replications of a 2 × 2 × 2 factorial experiment were established on a Typic Haplaquod soil in northern Florida using four cultural treatments: no treatment (F0H0); weed control (F0H1); fertilizer (F1F0); and combination of weed control and fertilizer (F1H1) for each species. During the first year there were large, sustained responses to all cultural practices. Loblolly and slash pine showed similar growth responses and had a lengthened growing season (60–100 days). Slash pine growth was superior to that of loblolly. Growth responses observed during the first year continued. After 4 years, irrigation had no measurable effect on tree growth. Both pine species responded equally to F1H0 and F0H1, but slash retained a slight edge. Extra nutrients]available via fertilizer, reduced competition, or additional rooting space, increased slash-pine volume index from an average of 2.0 m³ ha⁻¹ (F0H0) to 11.90 and 13.59 m³ ha⁻¹ (F0H1 and F1H0, respectively). The F1H1 treatment produced the largest slash-pine response, diameter at breast height (D_bh) averaged 9.84 cm, height reached 5.02 m, and volume index rose to about 22.94 m³ ha⁻¹. With teh F1H1 treatment, average loblolly-pine height and volume exceeded that of the average slash pine. At age 4, the growth response due to increased nutrient supply was 13–29 times that of the best genetic response within F0H0 trees of the four slash-pine progenies. The best-growing slash-pine family (6–56) exceeded loblolly-pine growth under all four treatments and approximated the vigor shown by slash pine in the southern hemisphere.     

Thinning,fertilization, and crown position interact to control physiological responses of loblolly pine

To examine physiological responses to thinning, fertilization, and crown position, we measured net photosynthesis (P(n)), transpiration (E), vapor pressure difference (VPD), stomatal conductance (g(s)), and xylem pressure potential (Psi(1)) between 0930 and 1130 h under ambient conditions in the upper and lower crowns of a 13-year-old loblolly pine (Pinus taeda L.) plantation six years (1994) after the treatments were applied. Photosynthetic photon flux density (PPFD) and air temperature (T(a)) within the canopy were also recorded. Needle P(n) of thinned trees was significantly enhanced by 22-54% in the lower crown, because canopy PPFD increased by 28-52%. Lower crown foliage of thinned plots also had higher E and g(s) than foliage of unthinned plots, but thinning had no effect on needle Psi(1) and predawn xylem pressure potential (0430-0530 h; Psi(pd)). Tree water status did not limit P(n), E and g(s) during the late-morning measurements. Fertilization significantly decreased within-canopy PPFD and T(a). Needle Psi(1) was increased in fertilized stands, whereas P(n), E and g(s) were not significantly altered. Upper crown foliage had significantly greater PPFD, P(n), VPD, g(s), E, and more negative Psi(1) than lower crown foliage. In both crown positions, needle P(n) was closely related to g(s), PPFD and T(a) (R(2) = 0.77 for the upper crown and 0.82 for the lower crown). We conclude that (1) silvicultural manipulation causes microclimate changes within the crowns of large trees, and (2) needle physiology adjusts to the within-crown environmental conditions.     

Tissue culture method affects ex vitro growth and development of loblolly pine

Loblolly pine (Pinus taeda L.) propagules initiated adventitiously from cotyledons and via axillary-fascicular micropropagation from epicotyls were compared to seedlings grown from the same open-pollinated seedlot. Greenhouse and early field results indicate that unlike tissue culture propagules of cotyledon-origin, propagules originating via axillary-fascicular micropropagation from epicotyls do not display early reduced growth relative to seedlings. Further, axillary-fascicular micropropagules derived from cotyledon-origin adventitious shoots displayed early reduced growth. Early reduced growth and other differences between tissue culture propagules and seedlings previously observed in field plantings appear to be inherent to the cotyledon system of propagation and do not necessarily occur when other tissue culture procedures are used for propagation.     

Bud development and dormancy in slash and loblolly pine. I. Speed of budbreak and second year height as related to lifting date

Slash and loblolly pine 1-0 seedlings were lifted from the nurserybed in late November, mid-December, late December, and mid-February. The buds of the seedlings were classified as set or growing two weeks prior to lifting and were re-examined upon lifting. For both species, buds that had set remained set whereas those that were classified as growing showed an decreasing trend of setting from November through December. A subset of seedlings was potted and maintained in a greenhouse to determine rate of budbreak; the remainder were field planted. In the greenhouse, loblolly pine broke bud fastest and slowest when lifted in mid-February and mid-December, respectively. The rate of slash pine budbreak increased over successive lifting dates. In the field, loblolly pine lifted in mid-December exhibited the highest percentage of growing seedlings; these seedlings were also tallest after one year in the field. Field-planted slash pine had the highest percentage of growing seedlings when lifted in late November. However, seedlings lifted in mid-December were tallest after one year.     

Impact of intraspecific competition on growth and financial development of loblolly pine plantations

Five stocking levels of 2,471, 1,483, 741, 494, and 247 trees/ha (TPH) were established to study competition among young loblolly pine (Pinus taeda). Growth comparisons were made between pairs of adjacent densities, which had measurement trees of similar characteristics but had differing stocking densities. Measurable competition, inferred by reduction in diameter increment, began shortly after age 6 at 2,471 TPH, at approximately age 7 at 1,483 TPH, age 8 at 741 TPH, and age 9 at 494 TPH. By age 21, total merchantable volume was the same for all density levels, (209 m³/ha) but sawtimber volume was inversely related to density level. Competitive growth pressures exerted by the higher stand densities through age 21 affected crop tree growth between ages 21 and 31. Although densities were thinned at ages 21 and 26, crop tree growth on the 2,471, 1,483, and 741 TPH densities was less than the 494 and 247 TPH densities.     

国外松混交林的生长及对土壤肥力的影响

对国外松生态混交林的林分生长及其对土壤肥力的影响进行研究。结果表明，针阔混交林不仅可提高林分生产力，而且对土壤质地、通气性、土壤肥力都比纯林有明显的改善；通过逐步间伐国外松，把达到数量成熟年龄的国外松针阔混交林更替为生产大径材的阔叶林，是国外松生态栽培的一种有效途径；在国外松人工林早期间伐后的林分中引进速生阔叶树种和在灌木林下开天窗营造国外松的试验林，综合效益高。     

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.     

Vascular cambial sucrose metabolism and growth in loblolly pine (Pinus taeda L.) in relation to transplanting stress

Sucrose synthase (SS) was the dominant enzyme of sucrose metabolism in both stem and root vascular cambial zone tissues of nursery-grown loblolly pine (Pinus taeda L.) seedlings. Acid invertase (AI) and neutral invertase (NT) activities were generally less than 10% of the SS activity in both tissues. In both cambial tissues, seasonal patterns of enzyme activity were observed for SS but not for AI or NI. The seasonal patterns of SS activity in stem and root cambia paralleled the periodic growth of stems and roots. Stems had high SS activity and growth during summer and early fall. Roots had substantial SS activity and growth during summer and fall, but SS activity and growth were even higher in winter. When seedlings were transplanted, about eight months elapsed before stem and root cambia resumed rates of growth and sucrose metabolism similar to those in control nontransplanted seedlings. Two months after transplanting, root SS was at its lowest, whereas AI activity in transplants was 50% higher than in control nontransplanted seedlings. In stems, SS activity decreased in response to transplanting, whereas AI and NI activities did not change appreciably. In loblolly pine tissues, SS was specific for uridylates, whereas the nucleotide triphosphate-dependent phosphofructokinase (NTP-PFK) had similar activity with either UTP or ATP. Except in winter, the NTP-PFK was less active than the pyrophosphate-dependent phosphofructokinase (PPi-PFK) during all seasons. The PPi-dependent PFK activity in nontransplanted seedlings followed similar seasonal and spatial patterns to those of SS activity. In actively growing tissues, such as stem cambial tissues in summer and root cambial tissues in winter, the measured total PFK to SS ratio ranged between 1.5/1 and 3/1. In contrast, in less actively growing tissues or transplanted seedlings, a greater decrease occurred in SS than in PFK activity, hence the ratio rose to as high as 12/1. It was concluded that: (1) SS was the dominant enzyme for sucrose metabolism in root and stem cambial tissues of loblolly pine seedlings; (2) both SS and PPi-PFK in the cambial tissues can be used as biochemical indicators of growth sink strength in stems and roots; and (3) both enzymes can be used as indicators of seedling stress caused by events such as transplanting and winter freezing.