Modulus of elasticity declines with decreasing planting density for loblolly pine (Pinus taeda) plantations

Context

Loblolly pine is often grown in intensively managed plantations for wood production. In order to fully evaluate the effects of management practices on wood quality and ultimately value, it is necessary to relate mechanical properties to management practices.

Aims

The aim of this study was to evaluate the effect of planting density on mechanical properties of lumber recovered from loblolly pine trees from a 27-year-old spacing trial and develop prediction equations for modulus of elasticity and modulus of rupture from stand, tree, and board characteristics.

Methods

Regression methods were applied to sample trees from three planting densities (2,989, 1,682, and 746 trees ha^?1) and used to relate mechanical properties of lumber extracted from the trees to stand, tree, and board characteristics.

Results

Initial planting density was found to be correlated with modulus of elasticity and, to a lesser extent, with modulus of rupture. Including board characteristics and utilizing the visual grade and board position as regressors produced improved prediction equations.

Conclusions

The mean modulus of elasticity declines with decreasing planting density while the variability increases, suggesting that planting density is a surrogate for frequency and size of knots. Thus, lower planting densities, while producing more lumber, may produce proportionally fewer boards of greater modulus of elasticity than higher planting densities.     

Growth responses to planting density and management intensity in loblolly pine plantations in the southeastern USA Lower Coastal Plain

? Background

A culture/density study was established in 1995 in the Lower Coastal Plain of the southeastern USA to evaluate the effects of intensive silviculture and current operational practices on the growth and yield of loblolly pine plantations across a wide range of planting densities (741–4,448 trees/ha). The operational regime consisted of bedding and herbicide application in site preparation and fertilizer applications at planting and in the eighth and 12th growing seasons. The intensive management regime had additional complete competition control, tip moths control, and more repeated fertilization treatments.

? Methods

The data from 14 locations from this split-plot experiment design with repeated measurements were analyzed with a mixed-effects model approach in terms of average DBH, average height, average dominant height, survival, stand basal area, and stand volume.

? Results

In the first few years after planting, there were no significant effects of management intensity and planting density. In later years, both management intensity and planting density significantly impacted response variables, and their interaction was only significant for average diameter at breast height (DBH). Responses to intensive management in DBH were greatest at the lowest planting densities. Intensive management resulted in larger average DBH, average height, dominant height, stand basal area, and volume. Intensively managed plots had more mortality at age 12. There were negative average DBH, average height, dominant height, and survival responses but positive stand basal area and volume responses to increasing planting density. However, there were no significant differences for planting densities above 2,224 trees/ha.

? Conclusions

The results demonstrate that both management intensity and planting density significantly affect loblolly pine productivity in the Lower Coastal Plain, and their effects are additive in nature due to the general lack of interactions.     

火炬松人工林间伐效应的研究

在8、12、16年生火炬松人工林中设置了不同间伐强度试验林，通过对林分树因子和间伐作业经济效益的分析表明，间伐对火炬松林分保留木个体生长具有一定的促进作用，对幼龄林的促进作用明显大于中大龄林分，随着间伐强度增大，较大径阶立木株数比例增大，但期末总收获量减少。火炬松人工林第1次间伐宜在12年生之前进行，保留1000－1100株／hm^2。在造纸材有销路的地区，初植密度较大的林分第1次间伐可在8年生时进行，保留1100－1300株／hm^2；第2次间伐的间隔期为6年，以培育大中径材为目标的大龄林分，应以弱度至中度调整为主，保留1000株／hm^2。另外，间伐有利于提高保留木材性的均质性。     

乔木柳无性系木材基本朱内变异的研究

利用乔木柳12年生无性系对比试验林的材料，研究了13个柳树无性系木材基本密度株内径向和纵向的变异模式，并对密度选择的时期和取样位置进行了探讨。结果表明：（1）在1.3m高度，乔木柳无性系各年轮组木材戏向变异多数为“M”型曲线，即从木芯向外第、至第3年轮组（1－6a）的木材密度逐渐增加，第4年轮组（7－8a）略有下降，第5年轮组（9－10a）又有明显增加，至最外侧年轮（11－12a）木材密度则显著下降，根据各无性系的变异特点，分成3种类型，其中无性系221的变异较为独特，为典型的“N”型；（2）乔木柳无性系生长期密度变化的规律为：1－2年生时木材基本密度相对较低，3－4a以后密度相对稳定并接近无性系加权平均密度，3－4年生时木材基本密度与5－12年生时的测定值相关系数为0.789－0.985，均达到极显著相关水平（α＝0.01），5－12年生乔木柳无性系木材基本密度的变异为62.2％－97.0％与3－4年生时木材基本密度的值有关，3－4a作为5百木柳木材基本密度的选择年龄最为合适；（3）供试群体木材密度株内纵向变异模式大多也可用“M”型曲线加以描述，具典型的苴孔材绷向密度变异特征，根据各无性系的变异特点，分成4种变异类型；树干高1.3，3.6和7.2m处的木材基本密度与无性系平均密度的相关系数达到显著和极显著水平，可以在树干1.3m处取样以推测无性系平均值；（4）在供试群体中，有的无性系木材基本密度纵向和径向变异的幅度均很小，木材较为均一，如苏柳791，表明在乔木柳杂种后代中选择木材均一的柳树新品种是可能的。     

Modeling survival in juvenile and mature loblolly pine plantations

Data from a large, region-wide set of permanent plots were used to develop equations for predicting stand-level survival in thinned and unthinned loblolly pine plantations growing in the southeastern United States. A pre-competitive model predicts survival at young ages based on age and total number of trees surviving. A post-crown closure model predicts survival after the onset of intraspecific competition based on age, site index, thinning intensity, percent hardwood basal area and number of trees surviving. Analyses of the pre-competitive data indicated that survival trends differed by drainage class and site preparation method. Thus, separate sets of coefficients were estimated for two drainage class/site preparation groups. Analyses of the post-competitive data indicated that survival trends differed for thinned and unthinned stands and were affected by the amount of hardwood competition. Therefore, the post-crown closure model was developed and parameterized to reflect the changes in survival as a result of hardwood competition and thinning from below.     

造林初植密度的合理确定

植树造林是林业的基础工作 ,是培育森林资源、实现森林资源可持续利用的有效措施之一。在植树造林工作中 ,造林的初植密度的确定将直接影响着林木的生长效果 ,对林木的速生、丰产、优质起着巨大作用。1现阶段造林初植密度的基本情况从抚松县林业现阶段造林密度情况看 ,总体偏大     

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.     

Modeling production and decay of coarse woody debris in loblolly pine plantations

Forest management can have large impacts on the production and yield of coarse woody debris (CWD) in terrestrial ecosystems, yet few modeling tools exist to inform such efforts. The goal here was to develop a set of prediction equations for use in conjunction with loblolly pine (Pinus taeda L.) modeling and inventory systems to estimate CWD yields at scales ranging from individual trees to whole plantations. Permanent field plots from a 21-year study of thinning effects on plantation growth and yield across the commercial range of the species in the southern United States were surveyed to obtain sample data on CWD volume, density, and mass. Measured CWD properties were combined with inventory records of tree mortality over the study duration to characterize CWD production, decay and yield in a series of prediction equations. The resulting equations predict CWD attributes of dead trees including dry weight (kg) and fraction of standing versus downed woody material based on the time since death (years), tree diameter at breast height (cm) and height (m) at time of death and geographic coordinates of latitude and longitude. A stand-level equation predicts total CWD yield (Mg ha⁻¹) for thinned or unthinned stands based on plantation age, stem density (trees ha⁻¹), and the average height of dominant and codominant trees (m). Piece-level equations predict dry density (kg m⁻³) or nitrogen concentration (%) of CWD pieces based on their position (standing or down), ordinal decay classes, and latitude. The tree and stand-level prediction equations are designed for use in GIS or growth and yield modeling systems. The piece-level equations are designed to be used in inventory applications that survey CWD. The equations should facilitate the accurate and facile determination of mass, carbon, and nitrogen contents of CWD in planted loblolly pine forests of the southern United States.     

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.Alabama Experiment Station Journal Series No. 9-85802.     

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.     

马尾松纸浆林造林密度对木材性质的影响

本文研究了龙里林场5种造林密度，15年生马尾松纸浆林木材基干密度和管胞形态。结果表明：造林密度对木材基本密度影响不大，但具明显的趋势，即一定造林密度条件下，木材基本密度随造林密度增加而增加，造林密度对管胞形态的影响，表现出因年龄而异，不同造林密度马尾松管胞形态总平均值变化不大，但管胞长度随树龄的增大而增加的趋势，受到造林密度影响，较低的造林密度各生长轮管胞形态差异不显著。管胞长度频率分布具一定的规律，中等长度（2501－3500um)管胞长度频率分布最大，占总频率的45％－74．19％，随着造林密度加大，中等长度的管胞增加，较短管胞长度（≤2500um)减少。     

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.     

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。     

Spatial variation in tree seedling density after the site preparation for planting in a cleared coniferous plantation in Hokkaido,northern Japan

To study spatial variation in natural tree seedling density and the relationship between variation in seedling density and seed dispersal mode at a cleared site, we surveyed natural tree seedlings after the site preparation for planting in a coniferous plantation cleared by a typhoon disturbance in 2004. The site was located near Sikotsuko Lake, Hokkaido, northern Japan. Twenty-five tree seedling species were found and the mean seedling density was 9.8 seedlings/m². Seedlings of non-animal-dispersed species (7.2 seedlings/m²) were approximately five times more abundant than those of animal-dispersed species (1.4 seedlings/m²), and 87% of all seedlings were current. The seedling density of non-animal-dispersed species (almost all wind-dispersed) decreased with distance from a natural forest; however, this trend did not hold for animal-dispersed species (almost all bird-dispersed). The spatial variation in seedling density was lower in animal-dispersed species than in non-animal-dispersed species. Seed dispersal patterns and the viability duration of buried seeds likely affected the variation in seedling density by seed dispersal mode.     

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.     

Preliminary studies on establishment of genetic transformation system in loblolly pine

A transformation system was established for loblolly pine (Pinus taeda L.) mature zygotic embryos usingAgrobacterium tumefaciens. The gene coding for the β-glucuronidase (GUS) gene was introduced into loblolly pine tissues and its transient expression was detected with histochemical staining. The influences of different genotypes.Agrobacterum concentrations. and cocultivation time on GUS expression and kanamycin resistant callus and shoot regeneration were investigated. The results showed that the highest GUS expression frequency (16.3%) and shoot regeneration frequency (78%) were obtained from genotype 9–1003 withAgrobacterium concentration decreased 9 times and cocultivation time of 56 hours respectively. GUS expression was obtained in all genotypes tested. The successful expression of the GUS gene in different genotypes suggested that it will be a useful transformation system for loblolly pine. (Responsible Editor: Chai Ruihai)     

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.     

The effect of tree planting density on the relative development of weeds and hybrid poplars on revegetated mine slopes vulnerable to erosion

New Forests - In reclaimed waste rocks slopes, the soil cover spread for revegetation is prone to erosion. This soil needs to be immediately protected from soil erosion by above and belowground...     

Genetic variation in rooting ability of loblolly pine cuttings: effects of auxin and family on rooting by hypocotyl cuttings

After about 20 days, hypocotyl cuttings from 20-day-old loblolly pine (Pinus taeda L.) seedlings rooted easily in the presence of the auxin indole-3-butyric acid (IBA), with roots forming directly from xylem parenchyma. In contrast, woody cuttings from 1-2-year-old hedged seedlings formed roots indirectly from callus tissue in 60-90 days, but IBA had little effect on rooting. Variation in rooting among hypocotyls from both half- and full-sib families was highly significant in response to IBA, and rooting did not occur within 20 days unless IBA was applied. Hypocotyls from poor rooting families tended to produce fewer roots per cutting than hypocotyls from good rooting families. Rooting by woody cuttings and hypocotyl cuttings from the same nine full-sib families was weakly correlated, raising the possibility that at least some common genetically controlled processes were affecting rooting by both types of cutting. The phytotropin N-1-naphthylphthalamic acid (NPA), supplied at 1 micro M with 10 micro M IBA, significantly inhibited rooting by hypocotyl cuttings from both good and poor rooting families, but there was no significant family x treatment interaction. Family variation in rooting ability may be a function of the frequency of occurrence of auxin-responsive cells in the hypocotyls.