Loblolly Pine Stands Research Articles

Resin duct production of loblolly pine (Pinus taeda) in southeastern Oklahoma, USA is positively related to water availability, fertilization, and thinning

Resin duct production of loblolly pine (Pinus taeda) in southeastern Oklahoma, USA is positively related to water availability, fertilization, and thinning

Nitrous oxide and methane emissions from a Ferralsol as affected by loblolly pine cultivation time in subtropical Brazil

We hypothesized that the age of loblolly pine stands influences soil methane (CH4) and nitrous oxide (N2O) emissions. This is a relevant topic to be studied in subtropical Brazil, where the pine plantation area is increasing considerably. We evaluated N2O and CH4 emissions for two years in a Ferralsol under loblolly pine (Pinus taeda L.) stands of 1, 9 and 18year-olds and a native forest (NF). We calculated the net CO2eq emission by considering the N2O and CH4 emissions from soil and the carbon (C) accumulation as litter in the forest floor. The soil N2O emission reduced gradually over the loblolly pine cultivation years, whereas CH4 uptake rates showed no clear pattern. Soil N2O emission showed a positive relationship with soil temperature in NF, and with soil ammonium and nitrate intensities in the pine stands. Soil CH4 uptake was inversely related to water-filled pore space in the pine stands, but this relationship was not observed in NF. The soil CH4 uptake rate was 4.6 times higher (p <0.10) in NF than the average uptake in loblolly pine stands. On the other hand, soil N2O emissions in 9 and 18-year-old stands were similar (p>0.10) to those in NF (1.3kgNha-1yr-1). Our results suggest that cultivation with loblolly pine for 18years can reduce soil N2O emission, and the uptake of CH4 in this system offsets 17% of N2O emissions. Furthermore, the C accumulation as litter in the forest floor of the mature pine stands (9- and 18-year-old) generated a net emission of -1.6Mg CO2eq ha-1yr-1, showing to be an expressive offsetting mechanism. Therefore, we conclude that aged loblolly forests can reach N2O emissions levels comparable to those of NF, and the C sequestration in these forests floor can significantly contribute to offset N2O emissions and act as sink for net atmospheric CO2eq.

Gopher tortoise (Gopherus polyphemus) resource selection within a private working pine (Pinus spp.) forest landscape

• The strongest predictor of selection was distance to permanently open areas. • Selection was greatest proximate to permanently open areas. • Elevation and suitable soils were the second strongest predictors of selection. Private working forest landscapes provide wildlife habitat and understanding how species interact with these landscapes is critical to identifying conservation opportunities. The gopher tortoise ( Gopherus polyphemus ; hereafter, tortoise) is a species endemic to the Coastal Plain ecoregion of the southeastern United States, with private working pine ( Pinus spp.) forests encompassing a substantive portion of area within the species’ range. Although private working pine forests contain tortoises, uncertainty exists about how tortoises use these landscapes. Specifically, there is limited information regarding tortoise habitat associations within these landscapes relative to current forest management practices. Therefore, we used radio telemetry data from 55 adult tortoises collected over 3 years to estimate resource selection within a private working forest landscape dominated by planted loblolly pine ( Pinus taeda ) stands in the Upper Coastal Plain ecoregion of Georgia, USA. The strongest predictor of resource selection by tortoises was proximity to permanently open areas, specifically a utility right-of-way and areas adjacent to unpaved forest roads and, to a lesser extent, areas of higher elevation containing soils suitable for tortoises. On our study area, we identified permanently open areas as an important landscape component to adult tortoises. Although adult tortoises persist within these landscapes, more work is needed to understand tortoise recruitment in private working pine forest landscapes.

Alter fire timing to recouple forage nutrients with herbivore nutrient demands

• Late summer nutritional stress period for white-tailed deer. • Growing season fire enhances nutrition during the late summer nutritional stress period. • Altering fire timing can be used to target nutritionally stressed periods and increase nutritional carrying capacity. • Diversity of prescribed fire can expand burn windows. • Maintain flammability in forest communities. Forests typically have limited high quality nutrition available to meet the seasonal needs of white-tailed deer ( Odocoileus virginianus ) during summer. Prescribed fire is used to enhance deer habitat in pyric-disclimax communities but is normally applied during the dormant season. Historically, lightning-ignited fires in pine systems occurred during summer in the southeastern US, but fire ignited by humans occurred at all times of the year and was most common in fall/winter. The different timing of prescribed fire may be important when trying to couple forage resources with nutritionally demanding periods for herbivores. We evaluated fire-timing effects (dormant season, March; growing season, June; and unburned control) on nutrient availability (crude protein, % phosphorus, and biomass) and nutritional carrying capacity (NCC) for moderate-high use forages of white-tailed deer during summer of 2018 and 2019 in nine mid-rotation loblolly pine stands. Fire increased nutrient content the year of the burn and the increase persisted into the second growing season following growing season fire. Dormant season fire increased protein- and phosphorus- based NCC for two growing seasons but growing season fire reduced biomass during the first year and delayed NCC improvement until the second year. Prescribed fire can be timed to manipulate forage quality, quantity, and improve NCC to recouple forage nutrient supply with herbivore seasonal nutrient demands. We recommend land managers consider diversifying fire timing across the landscape in pyric disclimax systems to support the changing nutrient requirements of large herbivores.

Estimating Marginal Costs of Additional Water Flow from a Loblolly Pine Stand in South Georgia, United States

AbstractCertain silvicultural operations enhance the flow of ecosystem services derived from forestlands. Monetary estimates of an increased flow of such services that can impact forest management decisions are generally lacking. Here we use a growth-and-yield model to estimate physical changes in water yield and assign monetary values to these changes under different regimes of forest thinning and planting density in a loblolly pine (Pinus taeda L.) stand located in South Georgia. The model is expanded to develop corresponding measures of water yield and net present value per each management scenario. Results show an expected inverse relationship between average annual water yield and economic rent. Further, the marginal costs associated with producing an extra liter of water (per unit area) decrease as thinning intensifies and planting density declines (US$1.35/kL to US$0.72/kL under a site index of 18.3 m and US$1.20/kL to US$0.66/kL, assuming a site index of 21.3 m) relative to our baseline scenario. We emphasize that a landowner’s profits may be negatively affected by the provision of improved water yield downstream as it competes with timber extraction. Monetary payments are needed to encourage the net production of water from existing loblolly pine stands in South Georgia, United States.

Does It Pay to Conduct Midrotation Competition Control and/or Fertilization? Results from Two Thinned Loblolly Pine Studies in the Coastal Plain of Georgia

AbstractThe effects of midrotation competition control and fertilization were studied in two loblolly pine stands in the Coastal Plain of Georgia. The use of fertilizer or herbicide alone did not enhance wood yields above the control, which negates the cost spent to conduct these practices. The combined treatment of fertilization and herbicide promoted higher average pine annual increment and greater proportion of sawtimber. Site limiting factors, most likely both competing woody vegetation and low nutrient status, largely determined the effectiveness and priority of midrotation treatments. The economic returns of the combined treatment varied considerably depending on stumpage prices, treatment costs, and magnitude and duration of the growth response. Sawtimber prices (absolute value and relative to pulpwood and chip-n-saw) play a critical role in the marginal returns of midrotation treatments. Continued depressed sawtimber prices will discourage private landowners from investing in midrotation vegetation control and fertilization.

Assessing imidacloprid for Nantucket pine tip moth (Rhyacionia frustrana) suppression through regional collaborative research and focus group evaluation

Nantucket pine tip moth (NPTM) [Rhyacionia frustrana (Lepidoptera: Tortricidae)] is a pest of young pine trees. The goal of this research project was two-fold: 1) to evaluate imidacloprid for NPTM suppression in South Georgia and 2) to incorporate county agents into a research project to facilitate knowledge transfer and extension training. Research sites in one-year planted loblolly pine stands were established by an extension specialist and county agents in five counties in South Georgia. Loblolly pines were assigned one of three treatments: untreated control, soil drench, and foliar spray. Trees were treated at a rate that would treat 500 trees per acre. Pines were assessed for NPTM infestation five times during the year, set to coincide with each NPTM generation. Tree height was measured at the end of the growing season. Qualitative data was collected on the agents' experience during a Zoom focus group and with emailed questionnaires. Imidacloprid drench and spray treatments resulted in lower NPTM infestation rates compared to untreated controls. However, while infestations rates were significantly lower, benefits were not conveyed to increased tree height. Imidacloprid treated trees were no taller than control trees. Collaborating with county agents enhanced this research project and benefitted both agents and the extension specialist. County agent involvement enhanced their job performance, allowed them to positively influence county stakeholders, contributed to core job competencies, and increased knowledge in forest health. Incorporating extension with research throughout the course of this study has been beneficial for both research outcomes and knowledge transfer.

Rethinking maximum stand basal area and maximum SDI from the aspect of stand dynamics

Abstract The maximum stand basal area (BA) and maximum stand density index (SDI) are often used to express stand carrying capacity in forestry. But their definitions are inconsistent in the literature. The maximum stand BA in most previous studies is associated with an upper boundary for a population of stands and is commonly derived from maximum size-density relationships (MSDRs). The maximum stand BA implied by MSDRs, under the assumption that stands attain maximum BA while attaining maximum SDI, is non-decreasing and divergent. We defined the maximum stand BA and maximum SDI for individual stands based on their BA and SDI development behaviors. Based on the mathematical relationships among stand BA, SDI, thinning, and quadratic mean diameter trajectories and their observed full trajectories in 551 unthinned plots selected from six long-term loblolly pine experimental studies, we theoretically and empirically proved that stands would achieve their maximum BA only after reaching their maximum SDI. The general mean maximum stand BA and maximum SDI for loblolly pine in the southern US were 46.2 m2 ha−1 and 1002 trees ha−1, respectively, and both showed significant variation (30.2–61.7 m2 ha−1 and 600–1410 trees ha−1, respectively). With the information of site quality, initial density and silvicultural treatments, our developed models could estimate the magnitude and timing of maximum stand BA for loblolly pine stands. Insights into individual stand BA and SDI trajectories provide more information for developing site specific silvicultural prescriptions.

Age and site index evaluations for loblolly pine in urban environments

Abstract Conventional site index (tree height at base age) may not be suitable for urban trees, therefore it is important to assess its applicability in urban environments. In addition, rapid and non-destructive tree age evaluation methods need to be developed. The objectives of this study were to: (1) develop a rapid and non-destructive method to determine tree age in urban environments, (2) examine the relationship between tree height, age, location, and soil type, and (3) compare the measured site indices with traditional site indices reported in Soil Survey Geographic Database (SSURGO). The study was conducted at the Clemson Experimental Forest (CEF) using conventionally-managed loblolly pine (Pinus taeda) stands, and loblolly pines in the urban environment of the Clemson University campus (CUC). Tree age obtained with a recording resistance drilling method and stump tree ring counting were comparable (R2 = 0.98, n = 14). Tree age estimates from recording resistance drilling and from increment boring were also similar (R2 = 0.93, n = 25). Replicate drilling samples had a low standard deviation, which indicated the high precision of the methodology. An additional benefit of the recording resistance drilling method is the ability to enable rapid evaluation of tree age across an urban forest. There was no discernible relationship between tree height and recording resistance drill age estimate for loblolly pines on the CUC (n = 25). In contrast, there was a relationship between measured diameter at breast height (DBH, cm) and recording resistance drill age estimates. A portion of the loblolly pine trees in the urban environment on the CUC appeared to have reduced productivity, as measured by the height/age relationship when predominantly surrounded by pavement or grass areas.

Soil respiration and organic matter decomposition dynamics respond to legacy fertilizer and weed control treatments in loblolly pine stands

Abstract Most studies examining how forest soil carbon (C) cycling responds to silvicultural treatments are restricted to a single rotation, with the legacy effects of past management practices being relatively unstudied. Here, we examined soil respiration and organic matter decomposition dynamics (important proxies for C dynamics), climate, and nutrient cycling in a second rotation, 2-year-old loblolly pine (Pinus taeda L.) plantation in north Florida. Carryover (C-) effects of the previous rotation's control (CC), fertilizer (CF), weed control (CW), and combined fertilizer and weed control (CFW) treatments were examined for residual effects on soil respiration (Rs), heterotrophic respiration (Rh), and substrate decomposition potential. Repeated measurements were made over 13 months. The mean Rs for both the CF (4.56 μmol CO2 m−2 s−1) and CFW (4.49 μmol CO2 m−2 s−1) treatments were increased by 29% and 27%, respectively, compared to the CC (3.53 μmol CO2 m−2 s−1) treatment. The Rh in the CW (2.97 μmol CO2 m−2 s−1) was significantly lower compared to the CF (4.02 μmol CO2 m−2 s−1) and CFW (3.66 μmol CO2 m−2 s−1) treatments, despite having warmer soil temperatures than the CF treatment, and no differences in soil moisture contents. Soil temperature and Mehlich III soil extractable manganese (Mn) concentrations (0–10 cm) were the only variables that explained variation in Rh. Decomposition rates for a common substrate were also lower in the CW compared to the CF, treatment (p = 0.027), potentially because the removal of understory plants in the CW treatment affected both microclimate and Mn cycling compared to the CF treatment where understory plants were retained and micronutrients were added as fertilizers. Overall, forest management affected organic matter cycling after replanting and 12 years after the last treatment in the previous rotation, suggesting that long-term studies are needed to understand the effects of silvicultural practices on ecosystem C cycling.

Comparison of plot- and stand-level projections of simulated loblolly pine (Pinus taeda) stands

Estimating current stand conditions and value is often required for making management decisions. However, costs and logistical constraints make yearly inventory impractical in most settings, necess...

Landsat 8 Based Leaf Area Index Estimation in Loblolly Pine Plantations

Leaf area index (LAI) is an important biophysical parameter used to monitor, model, and manage loblolly pine plantations across the southeastern United States. Landsat provides forest scientists and managers the ability to obtain accurate and timely LAI estimates. The objective of this study was to investigate the relationship between loblolly pine LAI measured in situ (at both leaf area minimum and maximum through two growing seasons at two geographically disparate study areas) and vegetation indices calculated using data from Landsat 7 (ETM+) and Landsat 8 (OLI). Sub-objectives included examination of the impact of georegistration accuracy, comparison of top-of-atmosphere and surface reflectance, development of a new empirical model for the species and region, and comparison of the new empirical model with the current operational standard. Permanent plots for the collection of ground LAI measurements were established at two locations near Appomattox, Virginia and Tuscaloosa, Alabama in 2013 and 2014, respectively. Each plot is thirty by thirty meters in size and is located at least thirty meters from a stand boundary. Plot LAI measurements were collected twice a year using the LI-COR LAI-2200 Plant Canopy Analyzer. Ground measurements were used as dependent variables in ordinary least squares regressions with ETM+ and OLI-derived vegetation indices. We conclude that accurately-located ground LAI estimates at minimum and maximum LAI in loblolly pine stands can be combined and modeled with Landsat-derived vegetation indices using surface reflectance, particularly simple ratio (SR) and normalized difference moisture index (NDMI), across sites and sensors. The best resulting model (LAI = −0.00212 + 0.3329SR) appears not to saturate through an LAI of 5 and is an improvement over the current operational standard for loblolly pine monitoring, modeling, and management in this ecologically and economically important region.

A New Method for Evaluating the Visual Quality of Loblolly Pine (Pinus Taeda L.) Forest

&lt;p&gt;Most of the forested lands in the south-eastern United States were largely the result of the frequent, low intensity, non-lethal fires that swept through the pre-settlement forests. In the absence of fire, forested stands develop a thick undergrowth of broad-leaved species and herbaceous vegetation. In this study, we compared the influence of prescribed fire on the understory vegetative cover of loblolly pine stands in relation to visual quality assessment. To examine the visual quality of prescribed fire management, a box-counting method was used to analyze photographs of prescribed fire management. The photographs were taken from: a) one-year fire return interval, b) two-year fire return interval, c) three-year fire return interval, and d) no-burn. The objectives of this study were: 1) develop a comparison of aesthetic value of the different fire return intervals of fire management with areas not experiencing prescribed fire; and 2) provide an estimate of enhancing visual quality of forest stands with prescribed fire management. The results showed that one-year interval prescribed fire application stands had more abundant grass cover (Andropogon sp.) than two- and three-year interval treatments. There was a significant decrease in grass cover between one-year and two-year prescribed burning. A positive relationship was also found between frequency of fire treatment and abundance of grass. No burn areas were covered by woody vegetation which may have a negative impact on scenic beauty and visual quality.&lt;/p&gt;

Relationships among growth, δ13C, foliar nitrogen concentration, foliar nitrogen content and intercepted radiation at different cultural intensities, planting densities and site indices reveal the importance of water use efficiency in mid-rotation loblolly pine stands

Abstract Carbon isotope composition (δ13C), intercepted photosynthetically active radiation (IPAR), foliar nitrogen (N) content and foliar N concentration are all factors related to stand growth and productivity. The relationships between these attributes and growth were studied in 15 and 16-year-old loblolly pine (Pinus teada L.) stands at planting densities ranging from 1483 to 4448 tree ha−1 grown under two silvicultural management intensities, both having different fertilization inputs. Measurements were conducted on six sites in the lower and upper coastal plains of Florida, Georgia and Alabama at site indices (SI) (base age 25 years) ranging from 18.6 to 29.6 m. The effects of planting density, cultural intensity and SI on the aforementioned attributes were studied. Correlations between δ13C, foliar N concentration, foliar N content, IPAR and current annual increment (CAI) of stem volume, stem wood biomass, branch biomass, foliage biomass and total above-ground biomass were also studied. We hypothesized that foliar N would be a better predictor of growth than either δ13C or IPAR, and that IPAR would be the same across planting densities due to canopy closure. The results indicated that CAI of stem volume, stem wood biomass and total above-ground biomass were affected by SI or the interaction between SI and management intensity. The significant relationships between SI and CAI growth indices were all positive indicating greater growth at greater site indices. A negative correlation was found between δ13C, a surrogate for water use efficiency, and SI, meaning stands had lower water use efficiencies at sites with higher SI values. Foliar N concentration and content were both affected by silvicultural intensity, while IPAR was only affected by planting density. Among the physiological parameters, δ13C was the only parameter significantly correlated with the CAI indices. Significant negative correlations were found between CAI of stem volume, stem wood biomass, total above-ground biomass and δ13C. These results indicated that moisture availability affected growth of the highly fertilized mature stands in this study. The findings reported here, when compared to similar studies in younger stands, suggest that growth limitations shifted from light availability to soil moisture availability in older stands when nitrogen was not limiting.

Trapping for Sirex Woodwasp in Brazilian Pine Plantations: Lure, Trap Type and Height of Deployment

The Sirex woodwasp, Sirex noctilio (Hymenoptera: Siricidae) is considered a secondary pest of pine in its native range but has caused considerable economic losses in pine plantation forests in the southern hemisphere. In Brazil, trap trees are the primary tool used for early detection purposes but these are costly, labor-intensive to install and require stressing trees by herbicide application. Flight intercept traps baited with synthetic blends of host volatiles are an attractive alternative but have performed poorly in some settings. This study was carried out to look for alternatives to trap trees for use in Brazilian pine plantations for early detection of S. noctilio. Four field experiments were conducted in two consecutive flight seasons (2015–16 and 2016–17), in planted loblolly pine (Pinus taeda) stands, to compare captures among flight intercept traps baited with different lures, deployed at different heights and among different intercept trap designs. Two experiments compared different host volatile lures and a significant treatment effect was observed in one. No effect of trap design or height was observed.

Variation in the diversity-productivity relationship in young forests of the eastern United States.

The diversity–productivity relationship has not been studied as extensively in forests as in other ecosystems. We address this gap in our knowledge by examining the relationship of productivity (primarily the periodic annual increment in aboveground biomass, but also the mean annual increment) with five species diversity indices, stand, and environmental factors. We used 967 naturally regenerated Forest Inventory and Analysis plots with stand age ≤30 years, located in the conterminous thirty-one eastern states, and satisfying strict selection requirements. Generally, mixed-species (heterospecific) stands were as productive as or even somewhat more productive than pure (monospecific) stands. The periodic and mean annual increments were both positively correlated with species richness (R2 = 0.04 and 0.20, p<0.001). Similarly, the zero-order and partial correlations with productivity were positive for four of the diversity indices (species richness, functional diversity, phylogenetic diversity, and phylogenetic species richness) and not significant for the fifth (functional dispersion). Greater diversity was more important on low-productivity sites and in stands with low stocking. As forests generally get more diverse and productive away from the poles, we tested if the nature of the productivity-diversity relationship changed latitudinally. Productivity was weakly positively correlated with four of the diversity indices north of 40° latitude, but weakly negatively with three of the indices to the south. Our examination of the productivity–diversity relationship in stands containing either of the two most dominant species, quaking aspen or loblolly pine, revealed that pure loblolly pine stands were somewhat more productive than only three of the eight mixtures with loblolly in the composition, while pure aspen stands were no more productive than any of the aspen mixtures. Overall, monospecific stands did not seem to have a clear productivity advantage over mixtures. The findings of this study have implications for woody biomass production, carbon sequestration by forests, and biodiversity conservation.

Rotation-Length Effects of Diverse Levels of Early Competition Suppression and Precommercial Thinning on Loblolly Pine Stand Development

Rotation-Length Effects of Diverse Levels of Early Competition Suppression and Precommercial Thinning on Loblolly Pine Stand Development

Inter-Rotational Effects of Fertilizer and Herbicide Treatments on the Understory Vegetation Community in Juvenile Loblolly Pine (Pinus taeda L.) Stands

Two randomized, complete block design experiments were established in north Florida to examine the inter-rotational effects of fertilization and herbicide applications on understory community responses in 2-year-old Pinus taeda L. stands. One experiment was left untreated (carryover [C]; CC, CF, CW, and CFW) and the second received the same first-rotation treatments—control (C), fertilizer (F), herbicide (W), and fertilizer and weed control (FW)—in the second rotation. In both experiments, herbicide applications alone and when combined with fertilization suppressed woody species such as Ilex glabra (L.) A. Gray and Serenoa repens (W. Bartram) Small (CFW: 0.26; FW: 0.01 Mg ha−1 biomass) but favored graminoids such as Andropogon virginicus L. var. glaucus Hack. and Dichanthelium acuminatum (Sw.) Gould & C.A. Clark (CFW: 3.1; FW: 1.1 Mg ha−1 biomass). Although the CW (0.99) and W (0.99) treatments did not affect understory diversity (H′), the CFW (0.45) and FW (0.5) treatments exhibited reductions compared with the CF (1.24) and F (1.33) treatments, respectively. In both experiments, fertilizer alone did not affect understory composition and diversity compared with the control. These results suggest that intensive additions of either herbicide alone or in combination with fertilization affected understory composition and diversity in the subsequent rotation. Management and Policy Implications The maintenance of long-term site productivity and associated ecological functions are central tenets for developing sustainable forest management systems. In addition to the overstory, the composition and diversity of understory vegetation represents an important component of forest ecosystems. Understanding how forest practices affect the inter-rotational development of understory vegetation is critical for advancing future management systems used in southern pine plantation ecosystems because of possible impacts, for example, on species diversity and nutrient cycling processes. This study examined how fertilizer additions and herbicide treatments affected understory redevelopment in second-rotation juvenile loblolly pine stands growing in north Florida. One experiment remained untreated to examine carryover effects of previous treatments whereas the second was actively managed using the same treatments as the prior rotation. The results for both experiments showed that intensive weed control treatments applied alone or in combination with fertilizer additions suppressed woody understory species development and favored graminoid vegetation (grasslike morphology) early in the next rotation. However, fertilizer additions alone did not affect understory composition and diversity when compared with the untreated control. When making forest management decisions in loblolly pine plantations, land managers should recognize that historical and intensive weed control treatments can have inter-rotational effects on understory species richness, diversity, and composition.

Within-crown acclimation of leaf-level physiological and morphological parameters in young loblolly pine stands

Light plays a minor role in the within-crown acclimation of physiological and morphological parameters in small loblolly pine trees. Whether the plasticity of foliage within the crown is driven by light or height is still not well known, especially for small trees. The present study was conducted in two loblolly pine (Pinus taeda L.) stands growing on two sites, during the third year after planting. The following traits were investigated in the lower and upper crowns of the same individuals twice per season (spring, summer, and autumn): photosynthesis (A sat), stomatal conductance (g s), intrinsic water use efficiency (WUEint), nitrogen concentration ***(N), specific leaf area (SLA), photosynthetic nitrogen use efficiency (PNUE), fascicle diameter, and needles per fascicle. The trees were open-grown at the beginning of the study; thus, any vertical gradient of the traits was not assumed to be driven by light. Overall, A sat, g s, PNUE, and SLA tended to be higher in the lower than in the upper crown, whereas N, fascicle diameter, and needles per fascicle were higher in the upper than in the lower crown. However, although all traits were affected by crown position, the magnitude of this effect differed by season. The fact that crown position affected most of the traits in spring and summer, but not in autumn, suggest that height might be the main driver of foliage acclimation. However, considering that crown position affected SLA in autumn but not the photosynthetic rate or N concentration, it is possible that foliar acclimation of these traits was mainly driven by light in this season.

Pinus taeda forest growth predictions in the 21st century vary with site mean annual temperature and site quality.

Climate projections from 20 downscaled global climate models (GCMs) were used with the 3-PG model to predict the future productivity and water use of planted loblolly pine (Pinus taeda) growing across the southeastern United States. Predictions were made using Representative Concentration Pathways (RCP) 4.5 and 8.5. These represent scenarios in which total radiative forcing stabilizes before 2100 (RCP 4.5) or continues increasing throughout the century (RCP 8.5). Thirty-six sites evenly distributed across the native range of the species were used in the analysis. These sites represent a range in current mean annual temperature (14.9-21.6°C) and precipitation (1,120-1,680mm/year). The site index of each site, which is a measure of growth potential, was varied to represent different levels of management. The 3-PG model predicted that aboveground biomass growth and net primary productivity will increase by 10%-40% in many parts of the region in the future. At cooler sites, the relative growth increase was greater than at warmer sites. By running the model with the baseline [CO2 ] or the anticipated elevated [CO2 ], the effect of CO2 on growth was separated from that of other climate factors. The growth increase at warmer sites was due almost entirely to elevated [CO2 ]. The growth increase at cooler sites was due to a combination of elevated [CO2 ] and increased air temperature. Low site index stands had a greater relative increase in growth under the climate change scenarios than those with a high site index. Water use increased in proportion to increases in leaf area and productivity but precipitation was still adequate, based on the downscaled GCM climate projections. We conclude that an increase in productivity can be expected for a large majority of the planted loblolly pine stands in the southeastern United States during this century.