We measured soil CO2 efflux (Fs) in four loblolly pine plantations in the coastal plain of South Carolina in an effort to understand how site preparation, drainage, and microclimate affect Fs, root biomass, and soil carbon pools during early stand development. All plantations were site prepared: sheared, raked, and bedded. Soil CO2 efflux, temperature (Ts), moisture (θ), root biomass (Rb), coarse (COF) and fine (FOF) organic fragments, and mineral soil carbon (Cs) were measured quarterly during the first two years of stand growth. Mean daily Fs were similar between sites and ranged from 0.5 to 12 mmol m-2 s-1 during the winter and summer, respectively. Soil CO2 efflux, COF, FOF, and Cs were significantly greater in the beds than inter-rows on wet sites, but not on the dry site. Soil temperature accounted for 26-55 percent of the variation in Fs across all sites. Soil θ and Cs explained a significant, but small amount (6-22 percent) of variance in Fs. Annual soil carbon efflux ranged from 12 to19 Mg C ha-1 yr-1. We conclude that bedding during site preparation can have significant effects on the spatial variation in Fs and associated drivers, with some site-specific caveats.

Soil incorporation of postharvest forest floor or logging residues during site preparation increased mineral soil carbon (C) and nitrogen (N) concentration and had a differential effect on early stand growth in a clonal loblolly pine (Pinus taeda L.) plantation. Incorporating 25 Mg ha−1 of forest floor (FF) (C/N ratio ≈ 112:1) or 25 (1LR) or 50 (2LR) Mg ha−1 masticated logging residues (C/N ratio ≈ 856:1) increased soil C concentration by 24–49

The effects of two treatments, irrigation and fertilization, were examined on specific gravity (SG)-related wood properties of loblolly pine trees (Pin us taeda L.) grown in Scotland County, North Carolina. The effects on the core as a whole, on the juvenile core, on the mature core, and from year to year were all analyzed. The results indicate that fertilization significantly lowered latewood SG, overall SG, and percent latewood and did so consistently throughout the period of study. Irrigation significantly lowered earlywood SG during the phase of juvenile wood production but significantly raised latewood SG during the period of mature wood production. Significant interaction between fertilization and irrigation indicated that irrigation helped overall SG and percent latewood of fertilized trees to increase to the level of untreated trees. Therefore, this study provides evidence that although fertilization significantly affects several SG;related properties, water availability is beneficial to the fertilization process; over time, an adequate water supply may help fertilized trees to maintain SG levels similar to those of unfertilized trees. FOR. SCI. 56(5):484-493.

Achieving maximum stand leaf area early in the rotation can have large positive effects on plantation productivity. Two silvicultural management strategies that can enhance leaf area development are increasing planting density and improving nutrition. A trial was established to determine how these two silvicultural management strategies affect the growth of Pinus taeda L. in the Virginia Piedmont. The study was designed as a factorial with two planting densities (363 and 726 trees ac(-1)) and three levels of nutrient additions. The three nutrient levels were aimed at maintaining the current site index (SI(25)) of the stand (55 ft) or improving the SI(25) to 70 and 80 ft. None of the treatments affected survival or height during the first 9 years. At age 9, the lower stand density treatment had a greater average diameter (6.03 in.) compared with the high stand density treatment (5.10 in.) averaged across all nutrient levels. The intermediate and high nutrient treatments increased diameter by 0.21 and 0.35 in., respectively, compared with the low nutrient treatment (5.38 in.), when averaged across both stand densities. Intraspecific competition affected diameter growth from age 5, whereas nutrient additions increased growth from age 4.

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 area in both years of the study.

We examined the effects of atmospheric vapor pressure deficit (VPD) and soil moisture stress (SMS) on leafand stand-level CO2 exchange in model 3-year-old coppiced cottonwood (Populus deltoides Bartr.) plantations using the large-scale, controlled environments of the Biosphere 2 Laboratory. A short-term experiment was imposed on top of continuing, long-term CO2 treatments (43 and 120 Pa), at the end of the growing season. For the experiment, the plantations were exposed for 6–14 days to low and high VPD (0.6 and 2.5 kPa) at low and high volumetric soil moisture contents (25–39%). When system gross CO2 assimilation was corrected for leaf area, system net CO2 exchange (SNCE), integrated daily SNCE, and system respiration increased in response to elevated CO2. The increases were mainly as a result of the larger leaf area developed during growth at high CO2, before the short-term experiment; the observed decline in responses to SMS and high VPD treatments was partly because of leaf area reduction. Elevated CO2 ameliorated the gas exchange consequences of water stress at the stand level, in all treatments. The initial slope of light response curves of stand photosynthesis (efficiency of light use by the stand) increased in response to elevated CO2 under all treatments. Leaf-level net CO2 assimilation rate and apparent quantum efficiency were consistently higher, and stomatal conductance and transpiration were significantly lower, under high CO2 in all soil moisture and VPD combinations (except for conductance and transpiration in high soil moisture, low VPD). Comparisons of leafand stand-level gross CO2 exchange indicated that the limitation of assimilation because of canopy light environment (in well-irrigated stands; ratio of leaf : stand 5 3.2–3.5) switched to a predominantly individual leaf limitation (because of stomatal closure) in response to water stress (leaf : stand 5 0.8–1.3). These observations enabled a good prediction of whole stand assimilation from leaf-level data under water-stressed conditions; the predictive ability was less under well-watered conditions. The data also demonstrated the need for a better understanding of the relationship between leaf water potential, leaf abscission, and stand LAI.

We used estimates of autotrophic respiration (RA), net primary productivity (NPP) and soil CO2 evolution (Sff), to develop component carbon budgets for 12‐year‐old loblolly pine plantations during the fifth year of a fertilization and irrigation experiment. Annual carbon use in RA was 7.5, 9.0, 15.0, and 15.1 Mg C ha−1 in control (C), irrigated (I), fertilized (F) and irrigated and fertilized (IF) treatments, respectively. Foliage, fine root and perennial woody tissue (stem, branch, coarse and taproot) respiration accounted for, respectively, 37%, 24%, and 39% of RA in C and I treatments and 38%, 12% and 50% of RA in F and IF treatments. Annual gross primary production (GPP=NPP+RA) ranged from 13.1 to 26.6 Mg C ha−1. The I, F, and IF treatments resulted in a 21, 94, and 103% increase in GPP, respectively, compared to the C treatment. Despite large treatment differences in NPP, RA, and carbon allocation, carbon use efficiency (CUE=NPP/GPP) averaged 0.42 and was unaffected by manipulating site resources.

The effects of different silvicultural practices on site, especially soil, carbon (C) pools are still poorly known. We studied changes in site C pools during the first 5 years following harvesting and conversion of two extensively managed pine-hardwood stands to intensively managed loblolly pine plantations. One study site was located on the lower Atlantic Coastal Plain in North Carolina (NC) and another on the Gulf Coastal Plain in Louisiana (La). Four different harvesting-disturbance regimes were applied: stem only harvest (SO), whole tree harvest (WT), whole tree harvest with forest floor removal (WTFF), and full amelioration, i.e. whole tree harvest, disking, bedding and fertilization (EA; only in NC). Each harvesting-disturbance regime plot was split and one-half received annual herbicide treatments while the other half received no herbicide treatments.In NC, soil C decreased slightly with WT, and increased with EA, otherwise no significant changes were detected. In La, there was a consistent decrease in soil C content from the pre-harvest value in all cases where herbicides were applied. All treatments caused a reduction in the forest floor C pool in NC. In La, the most intensive treatments also resulted in a decrease in the forest floor C, but to a smaller extent. In contrast, there was no net change in forest floor C with the SO and WT treatments, even though significant amounts of logging slash were added to the forest floor at harvest in the SO plots and not in the WT.Herbicide treatment clearly decreased the C pool of hardwoods and understory, and more than doubled that of planted pines. Carbon accumulation in the planted pines was similar for trees growing in the SO, WT, and WTFF treatments on both the LA and NC sites. The full amelioration treatment (only applied at the NC site) led to a significant increase in C sequestration by the planted pine component. Due to a large amount of voluntary pines, total 5-year pine C pool was highest on the non-herbicided intensive management plots on the NC site, however.The differing response patterns of soil and forest floor C pools between the two sites may be due to their differing drainage-summer rainfall regimes. Our results suggest that while poor drainage-wet summer conditions may be impeding carbon loss from the soil component it may be accelerating the rate of decomposition of the forest floor and slash on the soil surface. (C) 2002 Elsevier Science B.V. All rights reserved.

Dieback of loblolly pine (Pinus taeda L.) has been observed in certain inten- sively managed plantations throughout the South. There are two distinct types of dieback; winter dieback usually appears in February and March while summer dieback appears in July (or later) and increases during the fall. Both types have very high levels of K in terminal shoots. Winter dieback progresses in a "top-down" pattern while summer dieback progresses in a "bottom-up" pattern. Winter-dieback appears to be related to freezes and growth rate as slower-growing wildlings in the plantation almost never exhibit dieback. Freeze injury (brown cambium) is sometimes observed in the stem (at breast-height) and in the terminal shoot. Often the terminal pith turns brown. One fast-growing family, 7-56 from the Coastal Plain in South Carolina, is sensitive to freezes and is prone to tip-dieback. Although winter dieback is most noticeable in plantations, it also occurs on open-grown trees that are growing in weedy, non-fertilized areas. Land managers have grown accustomed to this dieback in rapidly growing plantations that are 2 to 5 years old. On some soils, summer dieback appears to be exacerbated after fertilization with macronutrients. There is currently no consensus as to the cause of this phenomenon but we believe that growth rate, freezes, K, and B may be involved. This paper reviews some of the literature on dieback on pines and proposes some hypotheses to test.

Dieback of loblolly pine (Pinus taeda L.) has been observed in certain inten- sively managed plantations throughout the South. There are two distinct types of dieback; winter dieback usually appears in February and March while summer dieback appears in July (or later) and increases during the fall. Both types have very high levels of K in terminal shoots. Winter dieback progresses in a top-down pattern while summer dieback progresses in a bottom-up pattern. Winter-dieback appears to be related to freezes and growth rate as slower-growing wildlings in the plantation almost never exhibit dieback. Freeze injury (brown cambium) is sometimes observed in the stem (at breast-height) and in the terminal shoot. Often the terminal pith turns brown. One fast-growing family, 7-56 from the Coastal Plain in South Carolina, is sensitive to freezes and is prone to tip-dieback. Although winter dieback is most noticeable in plantations, it also occurs on open-grown trees that are growing in weedy, non-fertilized areas. Land managers have grown accustomed to this dieback in rapidly growing plantations that are 2 to 5 years old. On some soils, summer dieback appears to be exacerbated after fertilization with macronutrients. There is currently no consensus as to the cause of this phenomenon but we believe that growth rate, freezes, K, and B may be involved. This paper reviews some of the literature on dieback on pines and proposes some hypotheses to test.

•  Availability of growth limiting resources may alter root dynamics in forest ecosystems, possibly affecting the land-atmosphere exchange of carbon. This was evaluated for a commercially important southern timber species by installing a factorial experiment of fertilization and irrigation treatments in an 8-yr-old loblolly pine (Pinus taeda) plantation. •  After 3 yr of growth, production and turnover of fine, coarse and mycorrhizal root length was observed using minirhizotrons, and compared with stem growth and foliage development. •  Fertilization increased net production of fine roots and mycorrhizal roots, but did not affect coarse roots. Fine roots had average lifespans of 166 d, coarse roots 294 d and mycorrhizal roots 507 d. Foliage growth rate peaked in late spring and declined over the remainder of the growing season, whereas fine roots experienced multiple growth flushes in the spring, summer and fall. •  We conclude that increased nutrient availability might increase carbon input to soils through enhanced fine root turnover. However, this will depend on the extent to which mycorrhizal root formation is affected, as these mycorrhizal roots have much longer average lifespans than fine and coarse roots.

Response of Carbon Dioxide Efflux from a 550m Soil Bed to a Range of Soil Temperatures R. Murthy, K. L . Griffin, S. J. Zarnoch, P.M. Dougherty, B. Watson, J. van Haren, R. L. Patterson, and T. Mahato 1 Columbia Earth Institute, Lamont-Doherty Earth Observatory, Biosphere 2 Center, Columbia University, Oracle, AZ 85623(Email: rmurthy@bio2.edu, Tel: 520-896-6422, fax: 520-896-5034); 2 Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964; 3 USDA Forest Service, Southern Research Station, Asheville, NC 28802; 4 Westvaco Corp., Forest Research, P.O. Box 1950, Summerville, SC 29484; 5 Biosphere 2 Center, Columbia University, Oracle, AZ 85623

This chapter is a synthesis of the findings of those projects in the Southern Global Change Program (SGCP) that measured the effects of environment on physiological and growth processes. This synthesis will not attempt to be exhaustive or encyclopedic, instead it will focus on key findings from the program, building conclusions from these results whenever possible. In addition to these conclusions, we will discuss the similarities and differences in results among the projects in the program, as well as with the general body of knowledge of global change effects on trees.

Linking models of different scales (e.g., process, tree-stand-ecosystem) is essential for furthering our understanding of stand, climatic, and edaphic effects on tree growth and forest productivity. Moreover, linking existing models that differ in scale and levels of resolution quickly identifies knowledge gaps in information required to scale from one level to another, indentifies future research needs to fill these information gaps, and provides a test of the present state of modeling sciences for creating model systems for predicting responses to natural and human-based disturbances.

The decomposition of plant-derived organic matter exerts strong control over the cycling of carbon and nutrients in terrestrial ecosystems and may be significantly altered by increased precipitation and nitrogen deposition associated with global change. It was the goal of this study to quantify the rate of belowground decomposition in an intact loblolly pine forest, and determine how this was affected by increased availability of water and nitrogen. A randomized complete-block factorial of irrigation and fertilization treatments was installed in an 8 yr old loblolly pine plantation in Scotland county, North Carolina. Fresh root samples of three size classes were buried in fiberglass mesh bags in January, 1994 and recovered at two-month intervals for two years. Samples were analyzed for percent mass remaining and contents of macro-nutrients. Roots decomposed in a two stage process: early in the incubation mass loss was correlated to size class and nutrient concentrations, but this correlation disappeared later in the incubation when rates of mass loss converged for all size classes. Decomposition was seldom affected by the irrigation and fertilization treatments, due to the buffering capacity of soil moisture and complex ecosystem-level responses to fertilization. Net mineralization of N, P, K, Ca, and Mg occurred in the smaller size classes of roots providing a source of these nutrients to the aggrading plantation for an estimated 2 to 15 years. The largest size class of roots was a sink for N, Ca, and Mg for the duration of this study, and was a source of P and K for an estimated 20 and 4 years, respectively. It is concluded that in moist temperate ecosystems belowground decomposition will be less affected by the projected increases in moisture and nutrient availability than will decomposition of the forest floor due to the buffering capacity of the soil. Further, small roots provide important sources of macro-nutrients for several decades to aggrading forests after large-scale disturbances such as harvesting of aboveground biomass.

Equations to predict foliage weight and surface area, and their vertical and horizontal distributions, within the crowns of unthinned lablolly pine (Pinus taeda L.) trees are presented. A right-truncated Weibull function was used for describing vertical foliage distributions. This function ensures that all of the foliage located between the tree tip and the foliage base is included. Foliage distribution prediction is based on actual two-dimensional foliage location. It is shown that the average time of full foliage, and hence average foliage weight or surface area prediction, is highly variable for loblolly pine and subject to considerable error. To help account for the old and new foliage differences during the approximate time of ''full leaf,'' the prediction equations for new and old foliage weight and surface area include a day-of-year term. New equations to predict branch weight, surface area, and the vertical distributions of branch biomass and surface area were also developed, The vertical distributions of branch biomass and surface area are described with logarithmic equations constrained to equal zero when relative crown depth is equal to zero, and to equal one when relative crown depth is one.