Growth Of Loblolly Pine Research Articles

Linking Growth and Yield and Process Models to Estimate Impact of Environmental Changes on Growth of Loblolly Pine

Abstract PTAEDA2 is a distance-dependent, individual tree model that simulates the growth and yield of a plantation of loblolly pine (Pinus taeda L.) on an annual basis. The MAESTRO model utilizes an array of trees in a stand to calculate and integrate the effects of biological and physical variables on the photosynthesis and respiration processes of a target tree on an hourly basis. PTAEDA2 sums the quantities for individual trees to obtain stand results; MAESTRO computes values for one tree at a time. These models were linked to provide a tool for further understanding stand, climatic, and edaphic effects on tree and forest productivity. PTAEDA2 predicts the characteristics of trees grown at a given stand density, on a given site, for a given length of time. These characteristics (outputs) are then used as direct inputs into MAESTRO which assesses the expected impact of environmental changes on tree function. The results from MAESTRO are fed back into PTAEDA2 to update future predictions by modifying the site index driver variable of the growth and yield model. An equation that predicts changes in site index as a function of net photosynthesis, age, and trees per unit area is the backbone of the dynamic linkage. The model changes required to link PTAEDA2 to MAESTRO were developed and reported earlier. This article reviews the earlier work and reports research results quantifying the relationships between net photosynthesis and the PTAEDA2 growth predictors, thus providing the basis for the MAESTRO to PTAEDA2 feedback process and integration of these two models. FOR. Sci. 47(1)77–82.

Fumigation with Chloropicrin, Metham Sodium, and EPTC as Replacements for Methyl Bromide in Southern Pine Nurseries

Abstract The effects of soil fumigation with chloropicrin alone or in combination with metham sodium and or with EPTC on the growth of loblolly pine (Pinus taeda L.) seedlings and on nutsedge (Cyperus spp.) control were investigated at three forest tree nurseries. Fumigation with chloropicrin plus metham sodium (CMS) significantly increased seedling numbers and growth compared to controls. Averaged among nurseries, mean root-collar-diameter increased from 0.14 to 0.17 in., and biomass from 0.14 to 0.20 lb/ft2. This produced seven more plantable seedlings and 6.5 more grade 1 seedlings/ft2 in CMS compared to not fumigated plots. Fumigation increased average potential sales $7,100/ac and increased present values, projected for the growth increases for additional grade 1 seedlings, by $25,900/ac. Fumigation increased biomass per unit area similarly at tested bed densities (10 to 29/ft2), but at low bed densities (≤20/ft2) the present values associated with grade 1 seedlings increased more than at higher densities. South. J. Appl. For. 24(3):135-139.

Species differences in early growth and rust incidence of loblolly and slash pine

Eleven field tests with two silvicultural treatments (intensive and less intensive) with three taxa (improved and unimproved Pinus elliottii and improved P. taeda) were established by the Cooperative Forest Genetics Research Program in the lower coastal plains of the southeast USA. Results from assessment at 3-years-old indicate that P. taeda is consistently taller with less rust incidence than P. elliottii in both intensive and less intensive cultures. The early superiority of P. taeda was only partially due to its lower rust incidence. The more intensive silvicultural treatment increased third-year height growth and also height differences among taxa on all sites. A slight increase of rust incidence was produced by increasing intensive management (29.2–33.6%). The increase in cultural management did not alter the ratios of infection percentages of any two taxa. The ratios of any two taxa, one to another, were essentially constant across all sites and in both silvicultural treatments. Significant genetic gain from breeding for rust resistance was detected at this age for P. elliottii. When 50% of unimproved P. elliottii trees were infected, 36.8% of improved P. elliottii trees were infected. For height growth, improved material was 4 and 8% taller than unimproved P. elliottii in less intensive and intensive treatment, respectively.

Early Field Growth of Loblolly Pine Rooted Cuttings and Seedlings

Abstract Early growth and fusiform rust resistance of loblolly pine (Pinus taeda L.) rooted cuttings and seedlings from the same nine full-sib families established on two sites (Nassau Co., FL and Monroe Co., AL) were compared. Although site effects on growth were large, height, diameter and volume growth of the rooted cuttings and seedlings did not differ through the first six growing seasons in the field (with the exception of first year height growth at the Florida site). Fusiform rust (caused by Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme [Cumm.] Burds. et Snow) incidence at age 6 yr was significantly lower in the rooted cuttings than the seedlings at both the Florida site (15.6 versus 22.3 %, respectively) and the Alabama site (46. 0 versus 51.0%, respectively). In addition, correlations of full-sib family performance between (1) rooted cuttings and seedlings and (2) rooted cuttings and seedling progeny test data were positive, statistically significant and moderate to high for both growth traits and fusiform rust incidence. Thus, families or individual trees selected from seedling genetic tests in existing tree improvement programs should also perform well as rooted cuttings. These results and those from similar studies indicate that field performance of loblolly pine rooted cuttings derived from seedling hedges should not be a concern. Large-scale propagation using rooted cuttings will deliver predicted gains from the selection and deployment of elite full-sib families and clones. In addition, the use of rooted cutting planting stock may offer a further reduction in fusiform rust incidence. South. J. Appl. For. 24(2):98-105.

Computer modeling of dynamically changing distributions of random variables

Physiological characteristics of populations are often described with two types of data and with analyses that coexist in mutual independence. One type targets global measures like mean and standard deviation, prevalence, incidence, or distributions of weights, sizes, or some physiological markers, while the other type describes physiological or metabolic processes in individuals, such as growth or the accumulation of a metabolite. The paper describes a methodological framework for bridging the gap between the two aspects. It shows how a dynamic model that characterizes the accumulation process in individuals and is represented by a set of ordinary differential equations can be reformulated as a transformation function that changes the statistical distribution of the physiological marker over time. The method and its limitations are illustrated with data describing growth and size distributions of loblolly pine ( Pinus taeda).

Growth and development of loblolly pine in a spacing trial planted in Hawaii

Loblolly pine ( Pinus taeda L) was planted at four square spacings (1.8, 2.4, 3.0, and 3.7 m) on the Island of Maui in 1961, and measured periodically for 34 years. Patterns of stand growth and development were examined and compared with yield model estimates of stand characteristics of plantations of the same initial spacings, ages, and site index in the southeastern United States. The Hawaiian plantings had much higher survival at all spacings and sustained high diameter growth in the face of intense competition. At Age 34, the 1.8 m spacing had 1585 stems/ha averaging 24.1 m tall and 28.8 cm DBH; the widest spacing (3.7 m) had 725 stems/ha, 26.1 m tall and 38.2 cm DBH. The highest basal areas (∼100 m 2/ha) were double maxima attained in the southeastern United States and were reflected in similar differences in volume yields. The Hawaiian plantings demonstrate that growth potential of loblolly pine is far greater than is apparent from observations on plantations in its native habitat. To capture this potential in other situations, research must identify the tree, stand, and environmental characteristics associated with low mortality rates and high diameter growth in Hawaii, and, conversely, the factors that limit loblolly's potential in the southeastern United States.

Previous Tip Moth Infestation Predispose Trees to Heavier Attacks in Subsequent Generations

The Nantucket pine tip moth, Rhyacionia frustrana (Comstock) (Lepidoptera: Tortricidae), is a common regeneration pest of pine plantations in the southeastern U.S.A. The insect has two to five generations annually depending on climate (Fettig et al. 1999a, USDA For. Serv. Res. Pap., In press). Following oviposition and eclosion, first-instar larvae bore into needles and begin mining between the epidermal layers. Resin from this boring is the first visible sign of tip moth infestation but is often difficult to detect. Second-instar larvae feed at needle and bud axils and produce a web which becomes covered with resin and is the first readily visible sign of attack. Third through fifth instars enter the buds and shoots where their feeding severs the vascular tissue and kills the apical meristem. Pupation occurs in the buds or shoots killed by larval feeding (Berisford 1988, In A. A. Berryman, ed. Dynamics of Forest Insect Populations, Plenum Pub. Corp.). Tip moth infestations have been shown to reduce tree growth in young loblolly pine (Pinus taeda L.) stands (Nowak 1997, M.S. Thesis, Univ. of GA, Athens; Cade and Hedden 1987, South. J. Appl. For 11: 128-133; Stephen et al. 1982, Ark. Farm Res. 31 : 10). Chemical control of R. frustrana infestations usually consists of three insecticide applications per year in the Piedmont region of Georgia (Gargiullo et al. 1983, Ga. For. Comm. Res. Pap. No. 44). However, it has recently been shown that repeated insecticide applications within a single year may be unnecessary to protect trees from volume losses attributed to tip moth damage (Fettig et al. 1999b, South. J. Appl. For. In press). Fettig et al. (199913) found a 74.5% increase in volume yield when insecticide applications were limited to the first generation of the first two years following planting. They also observed that previous tip moth attacks appeared to predispose trees to heavier attacks in subsequent generations, and listed this observation as a potential cause or contributor to their findings To test this possibility we selected two sites in Oglethorpe Co., GA where three tip moth generations occur annually (Fettig et al. 1999a). As part of a larger study, 80

Projecting the Growth of Loblolly Pine in a Changing Atmosphere

Abstract Recent findings regarding the magnitude of the influence of carbon dioxide concentration on the rate of photosynthesis in loblolly pine have been incorporated into Pipestem, a model of carbon allocation and growth. Pipestem translates photosynthetic rates into rates of change in stand basal area, quadratic mean diameter, tree density, average tree height, average crown length, dominant tree height, and woody dry matter. Projections of loblolly pine growth were run under the assumption that the atmospheric concentration of CO2 will continue to increase by 1.6 ppm/yr, the average rate of increase in the last 10 yr. Standing crops of woody dry matter in 20-yr-old loblolly pine stands in Buckingham County, Virginia, are projected to increase, on the average, by 9.8% in 20 yr. It is concluded that the CO2 effect should be accounted for in long-term projections of loblolly pine growth. South. J. Appl. For. 23(4):212-216.

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 cm 2). 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 dm 2). 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.

Identification of quantitative trait loci influencing annual height- and diameter-increment growth in loblolly pine (Pinus taeda L.)

Quantitative trait loci (QTLs) for annual height- and diameter-increment growth were estimated in each of two three-generation loblolly pine pedigrees. Annual height-increment was measured in three consecutive years in the BASE pedigree and in four consecutive years in the QTL pedigree. Annual diameter-increment was measured only in the QTL pedigree for two consecutive years. An interval mapping-approach was used to estimate the number of QTLs, the magnitude of QTL effects, and their position on genetic linkage maps. Thirteen different height-increment and eight different diameter-increment QTLs were detected, suggesting that the these traits are, at least in part, controlled by a few genes of large effect. Little evidence was found for the expression of individual QTLs in multiple years or in multiple genetic backgrounds. These results were discussed in terms of the power of the experiment and their consequences for marker-assisted breeding.

Bedding and Fertilization Ameliorate Effects of Designated Wet-Weather Skid Trails after Four Years for Loblolly Pine (Pinus taeda) Plantations

Abstract Wet-weather harvesting operations on wet pine fiats can cause soil disturbances that may reduce long-term site productivity. Site preparation and fertilization are often recommended as ameliorative practices for such disturbances, but few studies have actually quantified their effects on restoration. The purposes of this study were to quantify the effects of wet-weather harvest traffic in designated skid trails on soil properties and loblolly pine (Pinus taeda) growth, and to evaluate the ameliorative effects of site preparation. Study sites were established on wet pine flats of the lower Coastal Plain within the Francis Marion National Forest (Berkeley County, SC). Treatments were arranged in a split-split plot within a randomized complete block design. Treatments were two levels of traffic (nontrafficked, trafficked), four levels of mechanical site preparation (none, disking, bedding, disking + bedding), and two levels of fertilization (none, 337 kg /ha of 10-10-10 fertilizer). initially, the trafficking increased soil bulk densities and reduced soil water movement and subsequent growth of loblolly pine (years 1 and 2). Bedding combined with fertilization restored site productivity to non trafficked levels within 4 yr, but disking or fertilization treatments alone were not effective at ameliorating the traffic effects. The effectiveness of the bedding and fertilization treatments for amelioration of traffic effects was probably facilitated by the relatively small area of disturbed skid trails (<10%) found on these sites. Areas having more severe disturbance or higher percentages of disturbance might not be ameliorated as rapidly. South. J. Appl. For. 22(4):222-226.

Assessing potential climate change effects on loblolly pine growth: A probabilistic regional modeling approach

Most models of the potential effects of climate change on forest growth have produced deterministic predictions. However, there are large uncertainties in data on regional forest condition, estimates of future climate, and quantitative relationships between environmental conditions and forest growth rate. We constructed a new model to analyze these uncertainties along with available experimental results to make probabilistic estimates of climate change effects on the growth of loblolly pine ( Pinus taeda L.) throughout its range in the USA. Complete regional data sets were created by means of spatial interpolation, and uncertainties in these data were estimated. A geographic information system (GIS) was created to integrate current and predicted climate data with regional data including forest distribution, growth rate, and stand characteristics derived from USDA Forest Service data. A probabilistic climate change scenario was derived from the results of four different general circulation models (GCM). Probabilistic estimates of forest growth were produced by linking the GIS to a Latin Hypercube carbon (C) budget model of forest growth. The model estimated a greater than 50% chance of a decrease in loblolly pine growth throughout most of its range. The model also estimated a 10% chance that the total regional basal area growth will decrease by more than 24×10 6 m 2 yr −1 (a 92% decrease), and a 10% chance that basal area growth will increase by more than 62×10 6 m 2 yr −1 (a 142% increase above current rates). The most influential factor at all locations was the relative change in C assimilation. Of climatic factors, CO 2 concentration was found to be the most influential factor at all locations. Substantial regional variation in estimated growth was observed, and probably was due primarily to variation in historical growth rates and to the importance of historical growth in the model structure.

Influence of Plant Density and Soil Organic Matter on the First-Year Growth of Loblolly Pine and Sweetgum

Abstract Loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.) seedlings were planted at a range of densities on a formerly cultivated field which varied in soil organic matter (soil OM) in the upper 15 cm of the soil. Mean aboveground biomass per plant at the end of one growing season was examined to see how it varied as a function of plant density and soil OM. Biomass per plant as a function of density, holding soil OM constant, was described well by a reparameterized form of a standard yield density equation. A simple linear equation suitably described per plant biomass as a function of soil OM, holding density constant. Effects of soil OM on biomass were positive for both species, with sweetgum exhibiting a stronger response than loblolly pine. Based on the results of fitting equations to single factors, an equation considering both density and soil OM was developed and fitted using all data for each species. The equations explained 85% of the variation in response for both species. The inclusion of soil OM was more important in describing response of sweetgum than for loblolly pine. Inclusion of both density and soil OM in a single equation to describe mean response of plants in a monoculture might be extended to a mixture of species and used to examine intraspecific and interspecific competitive effects of competition and their relationship with productivity. For. Sci. 44(3):397-404.

Eleventh-Year Response of Loblolly Pine and Competing Vegetation to Woody and Herbaceous Plant Control on a Georgia Flatwoods Site

Abstract Through 11 growing seasons, growth of loblolly pine (Pinus taeda L.) increased after control of herbaceous, woody, or both herbaceous and woody vegetation (total control)for the first 3 yr after planting on a bedded site in the Georgia coastal flatwoods. Gains in stand volume index from controlling either herbaceous or woody vegetation alone were approximately two-thirds that from controlling both types of vegetation. Pine response through age 11 was approximately equal for herbaceous control alone and woody control alone, whereas, response through age 5 was greater with control of only herbaceous vegetation. The impact of woody vegetation should continue to have a strong effect on pine growth through midrotation because of its continued development. This is in contrast to herbaceous weeds that have greatly decreased in abundance since age 6. South. J. Appl. For. 22(2):88-95.

Loblolly Pine Root Growth and Distribution under Water Stress

AbstractA rhizotron study was conducted to assess the relationship between soil water availability and shoot and root growth of loblolly pine (Pinus taeda L.) under conditions where O2 availability and mechanical resistance were considered not limiting. Relationships between soil water availability and (i) root growth rate, (ii) root distribution, (iii) growth periodicity, and (iv) above‐ and belowground allocation were evaluated under four watering regimes ranging from maintaining profile near field capacity (WK 1) to withholding moisture for 4 wk (WK 4). The final distribution of cumulative root growth was similar among watering treatments, even though root growth shifted downward with depth during the growing period due to water depletion in surface soils. Relative root elongation rates were found to be linearly related to soil water potential. The strength of this relationship was improved by considering only periods of active root growth. Reductions in above‐ and belowground growth were proportional among water‐restricting treatments. Stem volume and root growth in the driest treatments were reduced 46 and 41%, respectively, compared with the WK 1 cells, indicating that patterns of biomass allocation above and below ground were similar among treatments. In the absence of other limiting soil factors, flushes of root growth in this study were a function of relatively short‐term changes in soil water potential. Our results indicate that when maximum tree biomass is desired, management efforts in establishing pine should be aimed at reducing any restrictions to root growth during establishment.

Immature Loblolly Pine Growth and Biomass Accumulation: Correlations with Seedlings Initial First-Order Lateral Roots

Abstract Five to seven years after being graded by first-order lateral root (FOLR) numbers and outplanted, loblolly pine (Pinus taeda L.) seedlings were excavated using a commercial tree spade and root systems re-evaluated. Current competitive position of trees was related to initial FOLR numbers of 1-0 seedlings. Current FOLR numbers were comparable among tree size classes, but root diameters where the spade severed the root were different. The dominant and codominant individuals had much larger FOLR cross sectional area at the severed point. The larger diameter laterals allow exploration of larger soil volume since they extended greater distances from the tree. Root biomass allometric equations were developed from excavating 175 individuals in 3 separate plantations. Root biomass was readily predicted based on either stem diameter breast height squared (D²H), or total aboveground biomass. Approximately 75% of standing tree biomass was aboveground and 25% belowground for all initial root grades, current crown classes, and sites. Subsoil compaction layers appeared to have a major impact on tree development at any specific location within a plantation. Compaction layers affected heights and diameters but not root/top ratios or the relative competition position based on initial FOLR numbers. These compaction layers resulted in plate-like taproots that suggested further root penetration was unlikely. South. J. Appl. For. 22(2):117-123.

Effects of Carbon Dioxide and Nitrogen on Growth and Nitrogen Uptake in Ponderosa and Loblolly Pine

AbstractThe purpose of this paper is to summarize the results of a series of greenhouse and open‐ top chamber studies on the effects of N and elevated atmospheric CO2 on ponderosa and loblolly pine (Pinus ponderosa Laws, and P. taeda L.) to evaluate common patterns of response. Growth response to elevated CO2 ranged from zero to more than 1000%, depending largely upon N status. In both species, growth response to CO2 was greater under moderate N deficiency than under extreme N deficiency or N sufficiency/excess. Elevated CO2 generally caused lowered tissue N concentrations in many (but not all) cases, which in turn resulted in smaller increases in N uptake than in biomass. Growth response to N ranged from −50 (in ponderosa pine) to more than 1000%, depending upon the N status of the control medium. Growth response to N was enhanced by elevated CO2 when N was in the extreme deficiency range but not when N was in the moderate deficiency range. In two separate studies, ponderosa pine responded negatively to high N inputs, and in each case this response was mitigated by elevated CO2. Collectively, these results show that (i) N deficiency is a continuum rather than a step function, (ii) responses to elevated CO2 vary across this continuum of N deficiency, and (iii) elevated CO2 greatly enhances growth response to N additions when N is initially in the extremely deficient range.

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.

Growth and Physiological Responses of Young Loblolly Pine Stands to Thinning

Abstract Although yield responses to thinning in loblolly pine have been well documented, short- and long-term morphological and physiological changes are largely unknown. To investigate these responses, three 8-yr-old, 0.2024 ha replicate stands of loblolly pine were thinned by 50% in May 1988, and bole growth and morphological changes in the crown were measured annually for the next 6 yr. In situ gas exchange measurements were monitored in the upper and lower third of the crowns monthly during the third through sixth growing seasons following thinning. First- and second-year physiological responses to thinning have been reported earlier (Ginn et al. 1991). Thinning slowed live crown recession and increased crown diameters resulting in increased photosynthetic surface area per tree. Over the 6 yr study period, the crown diameters of thinned trees increased 82% while the crown diameters of control trees increased only 20%. Larger bole diameters were observed for thinned trees four growing seasons after thinning. Photosynthetic rate and needle conductance did not increase overall, but were increased in the lower crown foliage of thinned trees. Needle dark respiration was higher in thinned stands in both the upper and lower crowns. Increased bole diameter growth is likely the result of the large increases in foliar biomass as well as initially higher physiological activity in the lower crowns of thinned stands. For. Sci. 43(4):529-534.

Atmospheric CO2 enrichment increases growth and photosynthesis of Pinus taeda: a 4 year experiment in the field

ABSTRACTForest trees are major components of the terrestrial biome and their response to rising atmospheric CO2 plays a prominent role in the global carbon cycle. In this study, loblolly pine seedlings were planted in the field in recently disturbed soil of high fertility, and CO2 partial pressures were maintained at ambient CO2 (Amb) and elevated CO2 (Amb + 30 Pa) for 4 years. The objective of the study was to measure seasonal and long‐term responses in growth and photosynthesis of loblolly pine exposed to elevated CO2 under ambient field conditions of precipitation, light, temperature and nutrient availability. Loblolly pine trees grown in elevated CO2 produced 90% more biomass after four growing seasons than did trees grown in ambient CO2. This large increase in final biomass was primarily due to a 217% increase in leaf area in the first growing season which resulted in much higher relative growth rates for trees grown in elevated CO2. Although there was not a sustained effect of elevated CO2 on relative growth rate after the first growing season, absolute production of biomass continued to increase each year in trees grown in elevated CO2 as a consequence of the compound interest effect of increased leaf area on the production of more new leaf area and more biomass. Allometric analyses of biomass allocation patterns demonstrated size‐dependent shifts in allocation, but no direct effects of elevated CO2 on partitioning of biomass. Leaf photosynthetic rates were always higher in trees grown in elevated CO2, but these differences were greater in the summer (60–130% increase) than in the winter (14–44% increase), reflecting strong seasonal effects of temperature on photosynthesis. Our results suggest that seasonal variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non‐structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy‐level adjustments in carbon assimilation, enhanced levels of leaf photosynthesis coupled with increased total leaf area indicate that net carbon assimilation for the whole tree was greater for trees grown under elevated CO2 compared with ambient CO2. If the large growth enhancement observed in loblolly pine were maintained after canopy closure, then these trees could be a large sink for fossil carbon emitted to the atmosphere and produce a negative feedback on atmospheric CO2.