Young Loblolly Pine Plantations Research Articles

Soil and Aggregate-Associated Carbon in a Young Loblolly Pine Plantation

In order to assess the carbon (C) footprint of forest-based bioenergy systems, it is necessary to quantify soil C storage. This study addressed effects of intercropping loblolly pine (Pinus taeda L.) with switchgrass (Panicum virgatum L.) for wood and bioenergy production on soil C storage in coastal North Carolina, USA. Spaces between rows of bedded pine were intercropped with switchgrass or contained native vegetative regrowth after site preparation. Two years after switchgrass establishment, soils were collected from beds and interbeds of each treatment, and C concentration and δ13C were measured in bulk soils and aggregate fractions. Soil C concentration, soil C density (Mg ha−1), and aggregate-associated C were lower in pine beds adjacent to switchgrass compared with pines adjacent to native regrowth. In the greater than 2,000-μm aggregate size class, 11% of C was derived from new pine inputs in beds of the pine-switchgrass treatment compared to the pine-native treatment. These results indicate that increased belowground C flow in pine beds adjacent to switchgrass may be driving breakdown soil C. In the pine-switchgrass intercropping treatment, a greater percentage of aggregates (by weight and C content) was found in the 2,000- to 250-μm size class of both beds and interbeds, suggesting that this aggregate size class is sensitive to management. This study provides a baseline analysis of C storage under different management scenarios in pine forests and for investigating long-term (10+ years) impacts. Although presence of switchgrass reduced soil C over the short term, bioenergy intercropping may still be pragmatic from an economical and land-use diversification view point.

Switchgrass intercropping reduces soil inorganic nitrogen in a young loblolly pine plantation located in coastal North Carolina

As biofuel production continues to increase, so will demand for forests to provide sources of biomass feedstocks. Intensively managed loblolly pine (Pinus taeda L.) plantations cover 15.8 million ha of the southeastern United States. Intercropping of switchgrass (Panicum virgatum L.) within loblolly pine stands offers an opportunity to use interbed space to produce an herbaceous biomass feedstock. Furthermore, removal of post-harvest woody residues could act as another forest-based biomass feedstock. Understanding how managing forests for biofuel production influences soil nitrogen (N) cycling and availability is crucial given the critical role N plays in terrestrial ecosystem productivity. Therefore, our objective was to study effects of harvest residue removal and pine-switchgrass intercropping on soil extractable NH4+ and NO3-. We used a randomized complete block design, consisting of four blocks of seven plots (0.8ha) established in the summer of 2008 on a recently harvested 34-year-old loblolly pine plantation in the Lower Coastal Plain of North Carolina, USA. Ion exchange membranes were deployed in the top 10cm of mineral soil starting in June 2009 and replaced continuously every 4–6weeks through December 2011. Presence of switchgrass significantly reduced soil extractable NH4+ and NO3-, amounting to a total reduction of 39% and 60%, respectively, over the course of the timeframe (30months) of this study. There was evidence that intercropping of switchgrass increased extractable NO3- in the adjacent pine bed, although this result was only found in the final 6months of the study. Presence or absence of harvest residues and/or interbed pines in the interbeds generally had no effect on soil inorganic N pools. These results indicate that switchgrass production effectively utilized inorganic N during a time when mineral N supply was greater than N demand by loblolly pines. Assessment of the long-term effects of switchgrass intercropping on soil nutrient cycling and availability and pine health and productivity will be essential to determine environmental and economic sustainability of intercropping.

Retained Woody Structure in 1- to 2-Year-Old Loblolly Pine (Pinus taeda L.) Plantations in Mississippi, Louisiana, and Arkansas: Implications for Wildlife Conservation

Information regarding how site preparation techniques affect residual woody structure is lacking for the southern United States in spite of the importance of such structure for many wildlife species. Therefore, we documented retained structure in young loblolly pine (Pinus taeda L.) plantations established using four common site preparation regimes: mechanical only, chemical only, chemical + mechanical, or chemical + prescribed burning. Herbicides reduced live tree density and increased snag density relative to mechanical methods. Prescribed burning reduced density of coarse woody debris (CWD) along with density and volume of piled CWD relative to chemical and mechanical methods. Our results provide a baseline for further studies of wildlife and retained structure in southern pine forests.

Development and applications of the relative spacing model for loblolly pine plantations

The development through time of relative spacing was modeled for loblolly pine ( Pinus taeda L.) plantations across the Lower Coastal Plain (LCP) and Piedmont and Upper Coastal Plain (PUCP) regions of the southern United States, using data from two culture/density studies. The lower asymptotic limit of relative spacing decreases exponentially with increasing planting density in both the LCP and PUCP regions. It is also correlated with site index in the LCP region, but not in the PUCP region. In the PUCP region, loblolly pine plantations with the intensive management regime approach a higher value of minimum relative spacing than those with the operational management regime. In the LCP region, however, for a given planting density and site index loblolly pine plantations approach the same limit of relative spacing, regardless of management regime. Site index, planting density, and management intensity also affected other model parameters. How the resulting relative spacing models are used to determine thinning schedules and indirectly derive the survival patterns over time for young loblolly pine plantations were explored and outlined.

Environmental and genetic effects on crown shape in young loblolly pine plantations

Tree crown shape is an important trait affecting the light environment in forest canopies. We examined genetic and environmental effects on outer crown shape of young single-family stands of loblolly pine ( Pinus taeda L.). Crown diameter profiles were measured after canopy closure at four experimental sites in the southeastern US. The two examined families of contrasting aboveground productivity differed in crown length but not in their outer crown shapes or crown shape ratios, defined as the ratio of crown diameter to crown length. Within each site, intensive silvicultural treatment, consisting of fertilization and control of competing vegetation, had little effect upon crown shape. A strongly significant effect of site on crown shape parameters was found in the family grown at all four experimental sites; however, density differences among the experimental series likely accounted for a part of the across-sites variation in crown shape. In contrast to other studies on crown shape in trees, and to findings at age 2 years in the same stands, we conclude that family effects on the outer crown shape were small compared with the environmental effects in these 5-year-old pine plantations, following canopy closure.

Nitrogen Accumulation and Use by a Young Loblolly Pine Plantation in Southeast Oklahoma: Effects of Fertilizer Formulation and Date of Application

Abstract Practices that enhance crop tree nitrogen (N) accumulation and use improve the efficiency of forest fertilization operations. This study was established to explore the N accumulation and use by a young loblolly pine plantation in response to (1) season of fertilizer application, (2) herbaceous vegetation suppression, and (3) fertilizer formulation. Water-soluble and slow-release urea formulations were applied to single-tree plots in January/February, April, June, August, and October of 2001 and 2002. Herbaceous vegetation was suppressed where appropriate with glyphosate. Foliage N accumulation was measured 1 and 2 months after fertilization; N use efficiency was measured 1 year after fertilization. Between 0.3 and 8.0% of applied N was recovered by the foliage within 1 month of application and 7–26% of applied N was used for stem growth within 1 year of application. In both years of this study, summer and fall applications produced the highest N accumulation and use. Suppressing herbaceous vegetation enhanced N accumulation and use when the plantation was 3 years of age (with an average tree height of 6 ft in January 2001). N accumulation and use of slow-release urea was similar to or lower than that of water soluble urea in both years of the study.

An approach for using general soil physical condition–root growth relationships to predict seedling growth response to site preparation tillage in loblolly pine plantations

Tree seedling root growth rate can be limited by any one of three soil physical factors: mechanical resistance, water potential or soil aeration. All three factors vary with soil water content and, under field conditions, root growth rate will depend on the soil water content as a result of its relationship to each factor. For a specific site, the relationship between soil water content and each factor can be developed from periodic measurement in the field or estimated from intact soil core samples. A STELLA™ model of first-year pine seedling growth response to soil tillage was developed using previously established relationships between root growth and these growth-limiting factors. The model predicts reductions in root growth below optimal conditions from soil water content. Accumulated root length is then used to estimate aboveground size from an available allometric relationship. Model predictions were compared to results from a site preparation tillage study on an upland site for which soil water content had been measured bi-weekly. Treatments used for this comparison were: no tillage, bedded, subsoiled and bedded plus subsoiled. Seedling height predicted by the model differed from measured mean seedling height by −1 to +14% with absolute differences in height of 0.1 m or less. Predicted aboveground biomass was −12 to +41% of mean measured biomass. Our results suggest that this modeling approach is useful for integrating results from controlled greenhouse experiments with field results and may prove useful for predicting soil tillage response in young loblolly pine plantations.

Pitch Canker in Young Loblolly Pines: Influence of Precommercial Thinning and Fertilization on Disease Incidence and Severity

Abstract Pitch canker disease affects southern pines, causing shoot dieback, stem deformation, and reduced growth. Disease occurrence is influenced by genetic resistance, abiotic and biotic environmental factors, and cultural practices. In young loblolly pine plantations with significant disease occurrence, options for disease control must focus primarily on silvicultural practices such as precommercial thinning or fertilization. In this study, cumulative disease incidence levels of 90-98% in the control, fertilize-only, and fertilize + thin treatments were reduced to 64% by precommercial thinning. Similarly, cumulative disease severity was reduced by 43% in the thin-only treatment. The positive effects of precommercial thinning on disease occurrence and severity were most evident during conditions of severe disease outbreak. Fertilization with potassium plus micronutrients did not suppress disease occurrence or severity and when combined with thinning, potassium plus micronutrients increased disease incidence by 50% over the thin-only treatment. The mechanisms responsible for these effects are not clearly understood but may reflect silvicultural influences on physiologically active defense mechanisms. South. J. Appl. For. 23(3):139-143.

Hydrological components of a young loblolly pine plantation on a sandy soil with estimates of water use and loss

Fertilizer and irrigation treatments were applied in a 7‐ to 10‐year‐old loblolly pine (Pinus taeda L.) plantation on a sandy soil near Laurinburg, North Carolina. Rainfall, throughfall, stemflow, and soil water content were measured throughout the study period. Monthly interception losses ranged from 4 to 15% of rainfall. Stemflow ranged from 0.2 to 6.5% of rainfall. Rainfall, leaf area index (LAI), basal area (BA), and the interactions of rainfall with LAI or BA influenced prediction models of throughfall, but not stemflow, on a stand level. We found significant differences due to the effects of treatments in the soil water of the top 0.5‐ and 1‐m soil layers by the beginning of the second growing season and throughout the remainder of the study period. Average daily water use and loss from a 1‐m soil layer reflected the low water‐holding capacity of the sand. Soil water in a 1‐m layer was rapidly depleted to within 10% of available water during periods of little or no rainfall. Irrigation did not significantly affect productivity and created a greater potential for loss of water to drainage below 1 m. On the basis of Zahner's [1966] method of soil water depletion in a sandy soil under forest cover, total drainage to below l m was 55% of evapotranspiration in unirrigated plots and 150% of evapotranspiration in irrigated plots.

Establishment treatments affect the relationships among nutrition, productivity and competing vegetation of loblolly pine saplings on a Gulf Coastal Plain site

After cultural treatments such as site preparation, release and fertilization, changes in the supply of mineral nutrients relative to each other and shifts in the composition of vegetation may have a delayed effect on the nutrition, carbon partitioning and growth of forest trees. This study was conducted to evaluate the influence of early management options that control vegetation and fertility on the nutrition and productivity of a young loblolly pine ( Pinus taeda L.) plantation on a phosphorus-deficient site in the Gulf Coastal Plain. Two levels each of herbicide application, fertilization and litter addition were applied in a factorial arrangement to three open-pollinated families of newly planted loblolly pine seedlings. Competing vegetation was evaluated after three growing seasons, loblolly pine nutrition and tannin synthesis were evaluated after four growing seasons and loblolly pine productivity was quantified after five growing seasons. Fertilization and herbicide application increased the growth and decreased the foliar tannin concentration of loblolly pine. Herbicide application also increased the potassium concentration of loblolly pine foliage. A negative correlation between foliar tannin and potassium concentrations was found on plots that were fertilized with nitrogen and phosphorus. On southern pine sites that are fertilized with phosphorus, the accelerated growth of planted pine and invading vegetation may create new nutrient limitations. Where phosphorus is limiting, however, nutrient utilization may not be great enough for new deficiencies to develop. Loblolly pine stand productivity and foliar nutrient concentrations were affected by genetic family and the foliar calcium and magnesium concentrations of loblolly pine families responded differently to the establishment treatments. We also found that the establishment treatments influenced the occurrence of herbaceous and woody competitors. We hypothesize that corresponding treatment effects on exchangeable cation concentrations and pH of the soil were caused by changes in vegetation.

Prediction models of Nantucket pine tip moth, Rhyacionia frustrana (Comstock) (Lep., Tortricidae) infestation using soil and tree factors

Abstract: Prediction models for estimating infestations by Nantucket pine tip moth (NPTM), Rhyacionia frustrana (Comstock) in young loblolly pine plantations in East Texas were developed using multivariate regression analysis based on selected soil and tree factors. Results of regression models show that foliage nutrients, tree water potential and tree height play important roles in NPTM infestation. Overall, these factors predict whole tree infestation better than top two whorls infestation. The importance and correlation of the factors differed for the prediction model of top two whorl and whole tree infestations.

Effects of temperature and tissue nitrogen on dormant season stem and branch maintenance respiration in a young loblolly pine (Pinus taeda) plantation.

We measured dormant season (November through February) maintenance respiration rates (R(m)) in stems and branches of 9-year-old loblolly pine (Pinus taeda L.) growing in plots under conditions of controlled nutrient and water supply in an effort to determine the relationships between R(m) and tissue size (surface area, sapwood volume, sapwood dry weight), tissue nitrogen content and temperature. Dormant season R(m) per unit size (i.e., surface area, &mgr;mol m(-2) s(-1); sapwood volume, &mgr;mol m(-3) s(-1); or sapwood dry weight, nmol g(-1) s(-1)) varied with tissue size, but was constant with respect to tissue nitrogen content (&mgr;mol mol(-1) N s(-1)). Cambium temperature accounted for 61 and 77% of the variation in stem and branch respiration, respectively. The basal respiration rate (respiration at 0 degrees C) increased with tissue nitrogen content, however, the Q(10) did not. Improved nutrition more than doubled stem basal respiration rate and increased branch basal respiration by 38%. Exponential equations were developed to model stem and branch respiration as a function of cambium temperature and tissue nitrogen content. We conclude that failure to account for tissue nitrogen effects on respiration rates will result in serious errors when estimating annual maintenance costs.

Modeling individual tree growth for juvenile loblolly pine plantations

Modeling juvenile growth of loblolly pine plantations is important for a better understanding of the whole process of stand development and helping to schedule appropriate silvicultural treatments for young stands. This paper evaluates spacing treatment effects on young loblolly pine trees and presents individual tree growth models for loblolly pine plantations. Using data from spacing trials (plot size ranging from 1.22 × 1.22 to 3.66 × 3.66 m 2) for loblolly pine plantations, a generalized randomized block design (GRBD) analysis was conducted to test spacing treatment and site quality effects on young tree growth. It is shown that planting density and site quality have significant influence, and spacing rectangularity is negligible. Based on the Bertalanffy differential equation and biologically reasonable assumptions regarding density and site quality effects on tree growth, a general projection model for individual tree diameter and height was developed. A stochastic model for generalizing tree height predictions within each diameter class was proposed. Models for crown ratio, and initial diameter distribution were also developed. The models were estimated with spacing trial data from young loblolly pine plantations. Validation results for these models showed that they are appropriate for predicting the juvenile growth of loblolly pine plantations where competing vegetation has been controlled in a similar manner to these spacing trials.

Selecting a sampling method to aid in vegetation management decisions in loblolly pine plantations

Objective methods to evaluate hardwood competition in young loblolly pine (Pinustaeda L.) plantations are not widely used in the southeastern United States. Ability of common sampling rules to accurately estimate hardwood rootstock attributes at low sampling intensities and across varying rootstock spatial distributions is unknown. Fixed area plot, polyareal plot, and Batcheler's triple-point distance sampling estimators of hardwood rootstock density, total height, and crown area were evaluated using computer simulation. Rootstock age, density, and spatial pattern combinations defined 24 artificial populations representative of hardwood rootstocks found in young loblolly pine plantations. Relative bias, relative precision, and within-and between-sample variance of the estimators were used as evaluation criteria. Eighteen sampling estimators with sampling intensities of approximately 1% were evaluated. Mean relative bias ranged from 1.2 to 7.0%, −1.5 to 1.0%, and −3.8 to 3.4% for fixed area, polyareal, and distance estimators, respectively. Spatial pattern affected evaluation criteria. Relative precision was highest in uniform populations and lowest in clumped populations. Variance was lowest in uniform populations and highest in clumped populations. Batcheler's distance estimator performed poorly. The 0.01-acre (1 acre = 0.405 ha) circular plot, vertical line, and horizontal point estimators were deemed "best" for density, total height, and crown area estimation, respectively. Vertical line sampling estimated all three attributes well and is recommended for field testing in young conifer plantations.

Predicting the impact of interspecific competition in young loblolly pine plantations with diameter distribution models

A system of prediction equations was developed to examine the effects of interspecific competition on diameter distributions for young loblolly pine ( Pinus taeda L.) plantations in the piedmont of Georgia, USA. Very little difference was detected among three types of models to predict the effects of hardwoods and total vegetation control on quadratic mean diameter (15 cm agove ground level). The percentile-based parameter recovery system for a three-parameter Weibull distribution function included direct and indirect effects of competition. Diameter distributions were compared among specific site preparation treatments and by systematically varying the amount of one hardwood species. The effects of increasing interspecific competition included skewing the distributions toward smaller diameters, decreasing the variation in diameters, and increasing the coefficient of variation in diameters. The system was sensitive to differences in interspecific competition at early ages, and could be adapted to young plantations of other commercial species.

Estimating diameter increment by DBH class with horizontal point sampling data

The estimation of diameter increment by diameter classes using methods suggested for ‘per-tree’ estimates in horizontal point sampling is discussed. The estimator usually recommended for this situation can be viewed as a ratio estimate, where the numerator is an estimate of the sum of the per-tree characteristics per hectare, and the denominator is an estimate of the number of trees per hectare having the desired characteristic. The ratio estimate is compared to the estimation of diameter increment in a DBH class by a simple arithmetic average of trees sampled. Simulation studies in a young loblolly pine plantation are used to make the comparisons. A maximum bias of about 7% occurred from using a simple arithmetic average of individual tree diameter increments. The ratio-estimate bias was always smaller than the arithmetic-average bias and was usually negligible. Variance estimators for the estimates of diameter increment were also evaluated.

Effects of harvest intensity, site preparation, and herbicide use on soil nitrogen transformations in a young loblolly pine plantation

The interactive effects of harvest intensity (whole-tree vs. stem-only), site preparation (chop and burn vs. shear-pile-disk), and silvicultural treatment (herbicide-pesticide vs. none) on N pools and transformations were determined in a young loblolly pine plantation on the North Carolina Piedmont. Harvest intensity had little effect on N transformations in years 3–5 post establishment, but shear-pile-disk site preparation and especially herbicide treatment caused increased net N mineralization and nitrification in the treated plots. Laboratory experiments with 15N label yielded reduced rates of N immobilization in the herbicide treated plots, demonstrating long-term consequences of treatment for soil N transformations.

Pine Tip Moth (Lepidoptera: Tortricidae) Infestation Rates as Influenced by Site and Stand Characteristics in Loblolly Pine Plantations in East Texas

Three young loblolly pine plantations grown on contrasting soil types produced quantitatively and qualitatively different host material for pine tip moths during 1985 and 1986. Amounts, periodicity, and availability of soil moisture regulated internal moisture conditions within host trees. Host xylem moisture potential in conjunction with soil nutrient status governed tree growth and influenced pine tip moth infestation rates. Pines on a sandy site exhibited the poorest growth with lowest infestation rates, indicative of low-quality hosts with little if any tolerance to damage. A clayey site produced vigorous plant growth with moderate infestation rates. The less apparent hosts appeared capable of withstanding pine tip moth attack and overcoming damage. Pines on a loamy site grew at moderate rates and received the highest infestation rates. This moderate growth indicated susceptible stand conditions.

Response of a young loblolly pine ( Pinus taeda) plantation to herbicide release treatments using hexazinone

In March 1980, a study was initiated on a site in the Piedmont of Alabama to examine the effect of hexazinone rate and formulation in releasing newly planted and 1-year-old loblolly pine in a dense stand of hardwoods (4.6 m 2 ha −1 groundline basal area, 17 100 rootstocks ha −1). Treatments included a factorial combination of three hexazinone formulations (1 cc 10% a.i. pellet, 1 2 cc 10% a.i. pellet, 20% a.i. granules) at three rates (1.12, 1.68, and 2.24 kg a.i. ha −1), plus an untreated control (10 treatments). Hardwood density following treatment decreased with increasing herbicide rate. Reduction in hardwood density was similar for the two pelleted formulations and lower for the granules. High rainfall amounts soon after application (13.2 cm within 10 days) appeared to have washed some herbicide from the granule-treated plots prior to uptake by hardwoods, possibly causing lower reduction of hardwoods relative to the pellets. Effects of treatment on pine mortality differed between newly-planted (interplants) and 1-year-old (original) pines. This is likely due to differences in root system development and overall size between the two classes of pines at the time of treatment, and associated differences in both the ability to compete with hardwoods for site resources and the likelihood of uptake of a fatal dose of hexazinone. Five growing seasons after treatment, mean pine size (height, groundline diameter, and dbh) differed among treatments for both interplanted and original pines, with size increasing with increasing hexazinone rate. Mean tree volume of pines was more strongly correlated with hardwood groundline basal area than with any other measure of hardwood density ( r = −0.61 for interplanted pines ( P < 0.001), r = −0.51 for original pines ( P < 0.001)) five growing seasons after treatment.

A simulation study of hardwood rootstock populations in young loblolly pine plantations

A computer program to simulate spatial distribution of hard wood rootstock populations is presented. Nineteen 3 to 6 year- old loblolly pine (Pinus taeda L.) plantations in Alabama and Georgia were measured to provide information for the simula tor. Spatial pattern, expressed as Pielou's nonrandomness index (PNI), ranged from 0.47 to 2.45. Scatterplots illustrated no rela tionship between pattern, species relative density, site prepara tion, or stand age. Newnham's point pattern generator was modified to reduce execution time. Equations to predict program inputs as a func tion of PNI and desired number of points were developed for uniform, random, and randomly clumped populations. Total rootstock height distribution was fitted using a two-parameter, left- and right-truncated Weibull function. Crown area was de termined conditionally by total rootstock height. The simulator may be used to generate populations for evaluating different sampling methods for hardwood rootstock attributes or in in dividual tree growth and yield models.