Sweetgum Plantation Research Articles

Exploring the social acceptability of hybrid sweetgum plantations in the south-central United States

Hybrid sweetgum has potential as a dual-purpose plantation in the southern United States due to its rapid growth and suitability for planting on a wide range of sites. To understand its social acceptability, a survey instrument was administered among 3,000 private landowners in the states of Texas, Oklahoma, Louisiana, and Arkansas. The survey results showed that a considerable percentage of landowners (41 %) were uncertain and would probably benefit from more information available to them on the topic. A multinomial logit analysis found that landowners who had timber management objectives were more interested in growing hybrid sweetgum if it was profitable and practically feasible. Similarly, female landowners and those having higher education were found to be more interested in growing hybrid sweetgum. Study findings suggest a need for outreach on economic feasibility, management, start-up costs, and tax implications concerning hybrid sweetgum plantations.

Productivity of hybrid sweetgum (Liquidambar formosana x styraciflua) plantations compared to native sweetgum (L. Styraciflua) in the Western Gulf Region of south-central U.S.

Sweetgum (Liquidambar styraciflua) is an excellent short-rotation woody crop species for producing hardwood pulp and biofuel feedstock on marginal sites. A recent development which may improve growth is the production of hybrid sweetgum (L. formosana x styraciflua) clones. We compared the productivity and attributes, e.g., wood specific gravity and stand growth, of operational plantations of hybrid sweetgum clones to improved native sweetgum half-sib families in 36 stands in Oklahoma, Texas, and Louisiana, U.S. The least square means (LSMean) of wood specific gravity was significantly greater for hybrids clones than the half-sibs (0.49 vs. 0.46 g/cm3), and the hybrid clones had less taper which necessitated developing genotype-specific volume and biomass equations. Despite having less fertilizer inputs on average, the hybrids had greater standing green stem biomass than the half-sibs at an age of 8.5 years (LSMean of 73.3 vs. 51.9 Mg/ha). The hybrids as a group also exhibited greater green biomass growth during the 2022 growing season when compared to the half-sibs at 8.5 years (LSMean of 15.8 vs. 11.4 Mg/ha/y). Therefore, the hybrids provide growth and wood quality advantages that may provide an opportunity to increase productivity and profitability of hardwood SRWC plantings.

Perceived Obstacles in Land Use Change for Hybrid Sweetgum Plantations: Landowner Opinions from the South Central United States

Abstract Hybrid sweetgum (Liquidambar styraciflua × L. formosana) has received considerable attention as a potential feedstock for traditional and nontraditional forest-based enterprises due to its fast growth and large specific gravity. However, the perceptions of landowners are important to understand the degree of acceptance concerning land use change to consider this opportunity in the United States. We administered a survey instrument to three thousand landowners representing the states of Texas, Oklahoma, Louisiana, and Arkansas where hybrid sweetgum plantations would be feasible. A seemingly unrelated regression analysis was used to explore the attributes that may influence the environmental and economic obstacles in land use change for hybrid sweetgum plantations. Study results suggest that landowners who perceived higher importance of marketing aspects of hybrid sweetgum expressed greater economic concerns for land use change. In contrast, those having higher planted pine acres had higher environmental concerns about land use change. Female landowners were more concerned than their male counterparts. Landowners need access to accurate information from their trusted sources to make informed management decisions, especially when making decisions to adopt new opportunities such as hybrid sweetgum. Study Implications: Study results reveal the need for outreach to landowners in the south central United States, as many were not aware of fast-growing hardwood species such as hybrid sweetgum. Information on growth potential, economics, and management techniques can help facilitate the adoption of hybrid sweetgum. Field visits and peer-to-peer learning facilitated by early adopters can be effective strategies for outreach.

Expected Timber-Based Economic Impacts of a Wood-Boring Beetle (Acanthotomicus Sp.) That Kills American Sweetgum.

American sweetgum trees (Liquidambar styraciflua L. [Altingiaceae]) in China are being killed by a newly discovered wood-boring beetle "sweetgum inscriber" (Acanthotomicus sp.). It has not been detected in the United States yet, but given the extent of trade with Asian countries, eventual arrival of this beetle is a serious concern. The American sweetgum is one of the main hardwood species in the southern United States, and provides several economic and ecological benefits to society. We present the first economic analysis of the potential damage from sweetgum inscriber (SI) to timber-based land values in the southern United States. We modeled economic impacts for a range of feasible SI arrival rates that reflect policy interventions: 1) no efforts to prevent arrival (scenario A, once every 14 and 25 yr), 2) partial prevention by complying with ISPM 15 standards (scenario B, once every 33 and 100 yr), and 3) total prevention of arrival (scenario C, zero transmission of SI). Our results indicated much lower land values for sweetgum plantations without the prevention on SI establishment (scenario A, US$1,843-US$4,383 ha-1) compared with partial prevention (scenario B, US$5,426-US$8,050 ha-1) and total eradication of SI (scenario C, US$9,825). Across the region, upper bound timber-based economic losses to plantation owners is US$151.9 million (US$4.6 million annually)-an estimate that can help inform policy decisions.

Species characterization and responses of subcortical insects to trap-logs and ethanol in a hardwood biomass plantation

We characterized subcortical insect assemblages in economically important eastern cottonwood (Populus deltoides Bartr.), sycamore (Platanus occidentalis L.) and sweetgum (Liquidambar styraciflua L.) plantations in the southeastern U.S.A. Furthermore, we compared insect responses between freshly-cut plant material by placing traps directly over cut hardwood logs (trap-logs), traps baited with ethanol lures and unbaited (control) traps. We captured a total of 15 506 insects representing 127 species in four families in 2011 and 2013. Approximately 9% and 62% of total species and individuals, respectively, and 23% and 79% of total Scolytinae species and individuals, respectively, were non-native to North America. We captured more Scolytinae using cottonwood trap-logs compared with control traps in both years, although this was the case with sycamore and sweetgum only in 2013. More woodborers were captured using cottonwood and sweetgum trap-logs compared with control traps in both years, although only with sycamore in 2013. Ethanol was an effective lure for capturing non-native Scolytinae; however, not all non-native species were captured using ethanol lures. Ambrosiophilus atratus (Eichhoff) and Hypothenemus crudiae (Panzer) were captured with both trap-logs and control traps, whereas Coccotrypes distinctus (Motschulsky) and Xyleborus glabratus Eichhoff were only captured on trap-logs. Indicator species analysis revealed that certain scolytines [e.g. Cnestus mutilatus (Blandford) and Xylosandrus crassiusculus (Motschulsky)] showed significant associations with trap-logs or ethanol baits in poplar or sweetgum trap-logs. In general, the species composition of subcortical insects, especially woodboring insects, was distinct among the three tree species and between those associated with trap-logs and control traps.

Soil Accumulation of Nitrogen and Phosphorus Following Annual Fertilization of Loblolly Pine and Sweetgum on Sandy Sites

A key question that arises following fertilization of forest plantations in the southeastern United States is whether fertilization has a long‐term effect on nutrient availability and long‐term site quality. Site quality could improve if mineral soil N and P pools are increased but is less likely if only forest floor pools are increased. Rapid forest floor decomposition and nutrient release following harvest likely lead to only rotation‐length increases in nutrient availability. To examine the impact of repeated applications of N and P, forest floor and mineral soil N and P pools were measured at a 24‐yr‐old loblolly pine (Pinus taedaL.) plantation in North Carolina (Southeast Tree Research and Education Site [SETRES]) and 13‐yr‐old loblolly pine and sweetgum (Liquidambar styracifluaL.) plantations in Georgia (Mt. Pleasant) receiving annual incremental fertilizer applications totaling >1000 kg N ha−1and >160 kg P ha−1. Mineral soil N pools varied only slightly. In contrast, fertilization increased forest floor N pools by 300 kg N ha−1at SETRES. Long‐term impacts on site N availability and site quality following these large N applications are unlikely. The forest floor P pool at SETRES was increased by 19.8 kg P ha−1. Fertilization also increased the mineral soil extractable P pool at SETRES to a depth of 1.5 m by 56 kg P ha−1but not at Mt. Pleasant where P fertilization during the previous rotation may have already increased this pool. Observed increases in mineral soil P from fertilization indicated a potential for increased long‐term site quality in terms of higher P availability for future rotations.

Soil carbon and nitrogen cycling and storage throughout the soil profile in a sweetgum plantation after 11 years of CO2‐enrichment

AbstractIncreased partitioning of carbon (C) to fine roots under elevated [CO2], especially deep in the soil profile, could alter soil C and nitrogen (N) cycling in forests. After more than 11 years of free‐air CO2 enrichment in a Liquidambar styraciflua L. (sweetgum) plantation in Oak Ridge, TN, USA, greater inputs of fine roots resulted in the incorporation of new C (i.e., C with a depleted δ13C) into root‐derived particulate organic matter (POM) pools to 90‐cm depth. Even though production in the sweetgum stand was limited by soil N availability, soil C and N contents were greater throughout the soil profile under elevated [CO2] at the conclusion of the experiment. Greater C inputs from fine‐root detritus under elevated [CO2] did not result in increased net N immobilization or C mineralization rates in long‐term laboratory incubations, possibly because microbial biomass was lower in the CO2‐enriched plots. Furthermore, the δ13CO2 of the C mineralized from the incubated soil closely tracked the δ13C of the labile POM pool in the elevated [CO2] treatment, especially in shallower soil, and did not indicate significant priming of the decomposition of pre‐experiment soil organic matter (SOM). Although potential C mineralization rates were positively and linearly related to total SOM C content in the top 30 cm of soil, this relationship did not hold in deeper soil. Taken together with an increased mean residence time of C in deeper soil pools, these findings indicate that C inputs from relatively deep roots under elevated [CO2] may increase the potential for long‐term soil C storage. However, C in deeper soil is likely to take many years to accrue to a significant fraction of total soil C given relatively smaller root inputs at depth. Expanded representation of biogeochemical cycling throughout the soil profile may improve model projections of future forest responses to rising atmospheric [CO2].

Net mineralization of N at deeper soil depths as a potential mechanism for sustained forest production under elevated [CO2

AbstractElevated atmospheric carbon dioxide concentrations [CO2] is projected to increase forest production, which could increase ecosystem carbon (C) storage. This study contributes to our broad goal of understanding the causes and consequences of increased fine‐root production and mortality under elevated [CO2] by examining potential gross nitrogen (N) cycling rates throughout the soil profile. Our study was conducted in a CO2‐enriched sweetgum (Liquidambar styraciflua L.) plantation in Oak Ridge, TN, USA. We used 15N isotope pool dilution methodology to measure potential gross N cycling rates in laboratory incubations of soil from four depth increments to 60 cm. Our objectives were twofold: (1) to determine whether N is available for root acquisition in deeper soil and (2) to determine whether elevated [CO2], which has increased inputs of labile C resulting from greater fine‐root mortality at depth, has altered N cycling rates. Although gross N fluxes declined with soil depth, we found that N is potentially available for roots to access, especially below 15 cm depth where rates of microbial consumption of mineral N were reduced relative to production. Overall, up to 60% of potential gross N mineralization and 100% of potential net N mineralization occurred below 15 cm depth at this site. This finding was supported by in situ measurements from ion‐exchange resins, where total inorganic N availability at 55 cm depth was equal to or greater than N availability at 15 cm depth. While it is likely that trees grown under elevated [CO2] are accessing a larger pool of inorganic N by mining deeper soil, we found no effect of elevated [CO2] on potential gross or net N cycling rates. Thus, increased root exploration of the soil volume under elevated [CO2] may be more important than changes in potential gross N cycling rates in sustaining forest responses to rising atmospheric CO2.

Plant and Soil Mediation of Elevated CO2 Impacts on Trace Metals

The cycling of trace metals through terrestrial ecosystems is modulated by plant and soil processes. Changes in plant growth and function and soil properties associated with increased atmospheric carbon dioxide (CO2) may therefore also affect the biological storage and stoichiometry of trace metals. We examined CO2 effects on a suite of metal micronutrients and contaminants in forest trees and soils at two free-air CO2 enrichment sites—a loblolly pine forest in North Carolina (Duke) and a sweetgum plantation in Tennessee [Oak Ridge National Laboratory (ORNL)]—and an open-top chamber experiment in a scrub-oak community in Florida [Smithsonian Environmental Research Center (SERC)]. We found that CO2 effects on soil metals were variable across sites; there were significantly higher surface soil metal concentrations with CO2 enrichment at Duke and ORNL (P < 0.05), but a trend of decreased soil metal concentrations at SERC (non-significant). These impacts on metals may be understood in the context of CO2 effects on soil organic matter (SOM); changes in percent SOM with CO2 enrichment were greatest at Duke (18% increase), followed by ORNL (7% increase), with limited effect at SERC (3% increase). There were significant effects of elevated CO2 on foliar metal concentrations at all sites, but the response of foliar metals to CO2 enrichment varied by metal, among sites, and within sites based on plant species, canopy height, and leaf age. Contrary to expectations, we did not find an overall decline in foliar metal concentrations with CO2 enrichment, and some essential plant metals were greater under elevated CO2 (for example, 28% increase in Mn across species and sites). Our results suggest that elevated CO2 impacts on trace metal biogeochemistry can be understood by accounting for both metal function (or lack thereof) in plants and the soil characteristics of the ecosystem.

Assessment of 10 years of CO 2 fumigation on soil microbial communities and function in a sweetgum plantation

Increased vegetative growth and soil carbon (C) storage under elevated carbon dioxide concentration ([CO 2]) has been demonstrated in a number of experiments. However, the ability of ecosystems, either above- or belowground, to maintain increased C storage relies on the response of soil processes, such as those that control nitrogen (N) mineralization, to climatic change. These soil processes are mediated by microbial communities whose activity and structure may also respond to increasing atmospheric [CO 2]. We took advantage of a long-term (ca 10 y) CO 2 enrichment experiment in a sweetgum plantation located in the southeastern United States to test the hypothesis that observed increases in root production in elevated relative to ambient CO 2 plots would alter microbial community structure, increase microbial activity, and increase soil nutrient cycling. We found that elevated [CO 2] had no detectable effect on microbial community structure using 16S rRNA gene clone libraries, on microbial activity measured with extracellular enzyme activity, or on potential soil N mineralization and nitrification rates. These results support findings at other forested Free Air [CO 2] Enrichment (FACE) sites.

Effects of elevated carbon dioxide and nitrogen fertilization on nitrate reductase activity in sweetgum and loblolly pine trees in two temperate forests

Nitrogen (N) availability is a major factor limiting plant production in many terrestrial ecosystems and is a key regulator of plant response to elevated CO2. Plant N status is a function of both soil N availability and plant N uptake and assimilation capacity. As a rate-limiting step in nitrate assimilation, the reduction of nitrate is an important component of plant physiological response to elevated CO2 and terrestrial carbon sequestration. We examine the effects of elevated CO2 and N availability on the activity of nitrate reductase, the enzyme catalyzing the reduction of nitrate to nitrite, in two temperate forests—a closed canopy sweetgum (Liquidambar styraciflua) plantation in Tennessee (Oak Ridge National Laboratory (ORNL)) and a loblolly pine (Pinus taeda) stand in North Carolina (Duke). Both CO2 and N enrichment had species specific impacts on nitrate reductase activity (NaR). Elevated CO2 and N fertilization decreased foliar NaR in P. taeda, but there were no treatment effects on L. styraciflua NaR at ORNL or Duke. NaR in 1-year P. taeda needles was significantly greater than in 0-year old needles across treatments. P. taeda NaR was negatively correlated with bio-available molybdenum concentrations in soils, suggesting that CO2 and N-mediated changes in soil nutrient status may be altering soil-plant N-dynamics. The variation in response among species may reflect different strategies for acquiring N and suggests that elevated CO2 may alter plant N dynamics through changes in NaR.

CO2 enrichment increases carbon and nitrogen input from fine roots in a deciduous forest

* Greater fine-root production under elevated [CO2] may increase the input of carbon (C) and nitrogen (N) to the soil profile because fine root populations turn over quickly in forested ecosystems. * Here, the effect of elevated [CO)] was assessed on root biomass and N inputs at several soil depths by combining a long-term minirhizotron dataset with continuous, root-specific measurements of root mass and [N]. The experiment was conducted in a CO(2)-enriched sweetgum (Liquidambar styraciflua) plantation. * CO2) enrichment had no effect on root tissue density or [N] within a given diameter class. Root biomass production and standing crop were doubled under elevated [CO2]. Though fine-root turnover declined under elevated [CO2], fine-root mortality was also nearly doubled under CO2 enrichment. Over 9 yr, root mortality resulted in 681 g m(-2) of extra C and 9 g m(-2) of extra N input to the soil system under elevated [CO2]. At least half of these inputs were below 30 cm soil depth. * Increased C and N input to the soil under CO2 enrichment, especially below 30 cm depth, might alter soil C storage and N mineralization. Future research should focus on quantifying root decomposition dynamics and C and N mineralization deeper in the soil.

Nitrogen limitation in a sweetgum plantation: implications for carbon allocation and storage

The N status of temperate forests is closely linked to their C fluxes, and altered C or N availability may affect ecosystem C storage through changes in forest production and C allocation. We proposed that increased fine-root production previously observed in a sweetgum ( Liquidambar styraciflua L.) forest in response to elevated [CO2] was a physiological response to N limitation. To examine this premise, we fertilized plots in the sweetgum plantation adjacent to the Oak Ridge National Laboratory free-air CO2-enrichment (FACE) experiment. We hypothesized that N fertilization would increase sweetgum net primary production, leaf [N], and the relative flux of C to wood production. Annual additions of 200 kg·ha–1 of N as urea increased soil N availability, which increased stand net primary production, stand N uptake, and N requirement by about one-third. Increased leaf [N] and leaf area production in the fertilized plots increased stem production and shifted relative flux of C to wood production. We conclude that sweetgum production on this site is limited by soil N availability and a decreased fraction of net primary production in fine-root production with N addition is consistent with the premise that increased fine-root production in the adjacent FACE experiment is in response to N limitation.

Runoff, sediment, nitrogen, and phosphorus losses from agricultural land converted to sweetgum and switchgrass bioenergy feedstock production in north Alabama

Abstract Renewable energy sources such as bioenergy crops have significant potential as alternatives to fossil fuels. Potential environmental problems arising from soil sediment and nutrient losses in runoff water from bioenergy crops need to be evaluated in order to determine the sustainability and overall feasibility of implementing bioenergy development strategies. This paper discusses runoff, sediment, N, and total P losses from agricultural land (continuous cotton (Gossypium hirsutum L.)) converted to short-rotation sweetgum (Liquidamber styraciflua L.) plantations with and without fescue (Festuca elatior L.) and switchgrass (Panicum virgatum L.) bioenergy crops, compared to corn (Zea mays L.), on a Decatur silt loam soil in north Alabama, from 1995 to 1999. Runoff volume was significantly correlated to total rainfall and sediment yield in each year, but treatment differences were not significant. Sweetgum plots produced the highest mean sediment yield of up to 800 kg ha−1compared to corn and switchgrass plots, which averaged less than 200 kg ha−1. Runoff NH4+ N losses averaged over treatments and years for spring season (3.1 kg ha−1) were three to five times those for summer, fall, and winter seasons. Runoff NO3− N for no-till corn and switchgrass plots in spring and summer were five to ten times that for sweetgum plots. No-till corn and switchgrass treatments had 2.4 and 2.1 kg ha−1 average runoff total P, respectively, which were two to three times that for sweetgum treatments. Growing sweetgum with a fescue cover crop provides significantly lower risk of water pollution from sediment, runoff NH4+ N, and NO3− N.

Sycamore and sweetgum plantation productivity on former agricultural land in South Carolina☆

Former agricultural lands in the southern US comprise a significant land base to support short rotation woody crop (SRWC) plantations. This study presents the seven-year response of productivity and biomass allocation in operational-scale, first rotation sycamore ( Plantanus occidentalis L.) and sweetgum ( Liquidambar styraciflua L.) plantations that were established on drained Ultisols which were historically planted in cotton and soybeans. Three plantation systems, sycamore open drainage, sycamore plus water management, and sweetgum open drainage were established on replicate 3.5–5.5 ha catchments. Height, diameter, and mortality were measured annually. Allometric equations, based on three, five, and seven year-old trees, were used to estimate aboveground biomass. Below-ground biomass was measured in year-five. Water management did not affect sycamore productivity, probably a result of a 5 year drought. The sycamore plantations were more productive after seven growing seasons than the sweetgum. Sycamore were twice the height (11.6 vs. 5.5 m); fifty percent larger in diameter (10.9 vs. 7.0 cm); and accrued more than twice the biomass (38–42 vs. 17 Mg ha - 1 ) of the sweetgum. Sweetgum plantation productivity was constrained by localized areas of high mortality (up to 88%) and vegetative competition. Mean annual height increment has not culminated for either species. Diameter growth slowed in the sycamore during growing seasons five through seven, but was still increasing in the sweetgum. Both species had similar partitioning of above-ground (60% of total) and below-ground biomass (40% of total).

Rapid Indices of Potential Nitrogen Mineralization for Intensively Managed Hardwood Plantations

Short‐rotation hardwood plantations generally require repeated applications of nitrogen (N) fertilizer to maintain desired growth and are being installed on two previous land uses: agricultural fields and cutover forest lands. Because the soil organic matter chemistry is different between agricultural field and cutover soils, indices of N availability developed for one land use or the other may not work well across both land use types. The standard aerobic incubation index is time consuming and costly. Therefore, three rapid methods were tested for estimating it on six converted agricultural fields and seven cutover pine sites currently in intensively managed sweetgum plantations on the eastern coastal plain of the United States. Two procedures (anaerobic incubation and hot KCl extract) were not useful for estimating mineralizable N in either agricultural field soils or cutover pine soils. The third index, a 3‐day incubation of rewetted soils previously dried, was linearly correlated to mineralizable N (p<0.0001, R2=0.88). This method, which had not been tested in forest soils previously, worked best for the cutover soils (p<0.002, R2=0.82) and less so for the agricultural field soils (p<0.097, R2=0.66). However, none of the procedures estimated potentially mineralizable N better, across all sites, than total N (p<0.0001, R2=0.93). Total N was not effective, however, in estimating mineralizable N within the agricultural field sites (p<0.220, R2=0.44). Further work will be needed to assess if potentially mineralizable N, total N, or the drying‐rewetting index can be used to help predict fertilizer rates and timings in intensively managed hardwood plantations, especially on cutover forest lands.

05/00290 Growth and nutrition response of young sweetgum plantations to repeated nitrogen fertilization on two site types: Scott, A. D. A. D. et al. Biomass and Bioenergy, 2004, 27, (4), 313–325

05/00290 Growth and nutrition response of young sweetgum plantations to repeated nitrogen fertilization on two site types: Scott, A. D. A. D. et al. Biomass and Bioenergy, 2004, 27, (4), 313–325

Effects of elevated CO2on nutrient cycling in a sweetgum plantation

The effects of elevated CO2 on nutrient cycling and selected belowground processes in the closed-canopy sweetgum plantation were assessed as part of a free-air CO2 enrichment (FACE) ex- periment at Oak Ridge, Tennessee. We hypothesized that nitrogen (N) constraints to growth response to elevated CO2 would be mitigated primarily by reduced tissue concentrations (resulting in increased biomass production per unit uptake) rather than increased uptake. Conversely, we hypothesized that the constraints of other nutrients to growth response to elevated CO2 would be mitigated primarily by increased uptake because of adequate soil supplies. The first hypothesis was not supported: although elevated CO2 caused reduced foliar N concentrations, it also resulted in increased uptake and require- ment of N, primarily because of greater root turnover. The additional N uptake with elevated CO2 constituted between 10 and 40% of the estimated soil mineralizeable N pool. The second hypothesis was largely supported: elevated CO2 had no significant effects on tissue concentrations of P, K, Ca, or Mg and caused significantly increased uptake and requirement of K, Ca, and Mg. Soil exchangeable pools of these nutrients are large and should pose no constraint to continued growth responses. Elevated CO2 also caused increased microbial biomass, reduced N leaching and increased P leaching from O horizons (measured by resin lysimeters), reduced soil solution NH þ ,S O 2� 4 , and Ca 2þ concentrations, and in- creased soil solution pH. There were no statistically significant treatment effects on soil nutrient availability as measured by resin capsules, resin stakes, or in situ incubations. Despite significantly lower litterfall N concentrations in the elevated CO2 treatment, there were no significant treatment effects on translocation or forest floor biomass or nutrient contents. There were also no significant treatment effects on the rate of decomposition of fine roots. In general, the effects of elevated CO2 on nutrient cycling in this study were not large; future constraints on growth responses imposed by N limitations will depend on changes in N demand, atmospheric N deposition, and soil mineralization rates.

Growth and nutrition response of young sweetgum plantations to repeated nitrogen fertilization on two site types

Short-rotation intensive tree culture is being investigated in the southern United States as a method of producing hardwood fiber, but little is known about the early productivity and nutritional needs of these systems, especially on different site types. We studied the growth and foliar nutrition response of two sweetgum ( Liquidambar styraciflua L.) plantations on a converted agricultural field and a pine cutover site to biannual applications of three nitrogen (N) fertilizer rates: 0, 56, and 112 kg N ha −1 . The trees did not respond to treatment at any age on the agricultural field site, but the fertilized trees on the cutover site had about 60% greater biomass at ages 5 and 6. Fertilization doubled foliar biomass on the cutover site in the years fertilizer was applied. Stem biomass was directly related to foliar biomass, but the relationship was age-specific at both sites. Stem biomass was also related to the foliar N concentration. Foliar critical values of N were about 18 g N kg −1 . Foliage phosphorus (P) and potassium (K) contents were diluted by the N fertilization-induced growth responses at both sites. Fertilization of young intensive-culture sweetgum plantations is necessary for optimum foliar N concentrations and foliar and stem biomass production, but is site-specific.

Nitrogen supply and demand in short-rotation sweetgum plantations

Intensive management is crucial for optimizing hardwood plantation success, and nitrogen (N) nutrition management is one of the most important practices in intensive management. Because management of short-rotation woody crop plantations is a mixture of row-crop agriculture and plantation forestry, we tested the usefulness of an agronomic budget modified for deciduous perennial trees for estimating N fertilizer recommendations. We studied the foliar N demand, resorption, and uptake response of two sweetgum ( Liquidambar styraciflua L.) plantations on a converted agricultural field and a pine cutover site to biannual applications of three nitrogen (N) fertilizer rates: 0, 56 and 112 kg N ha −1. We also estimated soil N supply, foliar N uptake efficiency, and apparent fertilizer N uptake efficiency. Fertilization increased foliar demand (defined as total foliar N content), resorption, and uptake at both sites, but to a greater degree on the cutover site, which had lower soil N supply. Resorption efficiency did not increase with fertilization, but resorption proficiency, the N concentration of senesced leaves, was reduced (N concentrations higher) at the drier agricultural field site and in the fertilized trees. Based on our budget analysis, we recommend fertilizing sweetgum plantations with 50 kg N ha −1 for each 2000 kg ha −1 of foliage biomass, assuming they have 45–65 kg ha −1 of soil N supply.