Browsing by Author "Palmroth, Sari"

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    AN ASSESSMENT OF ECOLOGICAL THINNING FOR STRUCTURAL DIVERSITY IN COASTAL FORESTS OF THE PACIFIC NORTHWEST, USA
    (2013-12-06) Bubel, Ansel
    Restoration for increased structural integrity is a relatively new strategy that is being applied to protected areas in the Pacific Northwest. Not enough data has been collected to determine how best to approach restoration, so the current projects have made educated guesses about what the best approach might be to increase structural diversity. My analysis seeks to determine the most effective thinning regime to increase structural diversity. The current stands which are undergoing restoration are young even aged plantations which have been acquired by conservation organizations and government agencies. Ecologically, these forests differ from the historical forests both in structure and species composition. Restoration seeks to remove a portion of the overstory trees to allow the recruitment of a new cohort of trees and increase the growth rate of the remaining overstory trees. This approach essentially involves tunneling through the classic development curve laid out by Odum (Odum, 1969). I used a version of FVS ported into the R language to model the background forest growth in the face of windthrow against 25 possible thinning types. I compared thinnings across a range of intensity of tree removal (10-50% of trees removed per cycle) and cycle length (10 to 50 years). I compared these results to a background scenario consisting of windthrow disturbance with a 1% probability of occurring each year and lognormally distributed impacts with low intensity damage more common than high intensity damage. My work has shown that removing 30 – 50 % of basal area every 30 to 50 years can help forests achieve structural complexity before it would develop on its own accord. Without restoration, natural forests achieve structure similar to old growth between 100 and 200 years of age depending on the frequency and intensity of windthrow. After 100 years of restoration, forests will achieve higher levels of structural complexity and tree growth.
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    Carbon Gain and Allocation in Five Shade Intolerant Pinus Species
    (2021-12-08) Wang, Yi
    Pinus virginiana (Virginia pine), Pinus echinata (shortleaf pine), Pinus taeda (loblolly pine), Pinus elliottii (slash pine), and Pinus palustris (longleaf pine) are five of the most dominant shade-intolerant pine species in the southeast region. These five species have overlapping geographic ranges, tolerate poor soil conditions and low water availability conditions, and have relatively high volume growth rate. Among the five species, P. virginiana and P. echinata have the shortest needles of around 5-7 cm. P. taeda and P. elliottii have the intermediate needle length of around 15-22 cm, while P. palustris has the longest needles of around 30 cm. To compare the among species differences in biomass growth rate based on their physiology, morphology, and hydraulics related leaf traits, shoot and crown structure, and biomass allocation, we collected the data from an experimental site in Duke Forest and compared the performance of these five species when trees of the same age were grown under the same climate and soil conditions. Our study revealed distinct differences in allometric relationships and biomass allocation patterns among the five species. Analysis of leaf functional traits and crown structure showed variation in the ability to support leaf area at a given leaf mass, branch mass, and sapwood area across species. Finally, the differences in total biomass and wood production among species reflected the combined effect of leaf area index and biomass allocation pattern. We found that, when growing in one environment, species with intermediate needle length (P. taeda and P. elliottii) were more efficient in biomass production and volume growth while balancing the investment in intercepting light and maintaining hydraulic system. The results of this study indicated that growth-related functional traits, combined with biomass allocation patterns that favor stem and aboveground production, make P. taeda and P. elliottii among the fastest growing conifers with high timber values, regionally and globally.
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    Changing the Paradigm: Inventory Review and Scenario Modeling for the Duke Forest
    (2017-04-28) Burrows, John; Burton, Harley; Hipp, Timothy
    Since it was founded in 1931, the Duke Forest has shown a commitment to sustainable timber management practices and forestry education. However, in recent years, a misalignment between revenue expectations and the timber management paradigm have resulted in an uneven age class distribution favoring younger age classes of pine. The purpose of this project is help the Duke Forest address this management challenge by reassessing its inventory and yield projections from its 2010 inventory to understand how the Forest might be able to improve its estimation of sustainable harvest by more accurately accounting for volume growth. Additional analyses were also conducted to model different harvest rotation lengths using the US Forest Service’s Forest Vegetation Simulator (FVS) to understand how more intensive management practices, such as shortening the pine rotation length and planting genetically improved stock, could help balance the Forest’s age class distribution in other divisions while keeping the forest profitable.
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    Conversion of natural forests to managed forest plantations decreases tree resistance to prolonged droughts
    (Forest Ecology and Management, 2015-01-01) Domec, Jean-Christophe; King, John S; Ward, Eric; Christopher Oishi, A; Palmroth, Sari; Radecki, Andrew; Bell, Dave M; Miao, Guofang; Gavazzi, Michael; Johnson, Daniel M; McNulty, Steve G; Sun, Ge; Noormets, Asko
    © 2015 Published by Elsevier B.V.Throughout the southern US, past forest management practices have replaced large areas of native forests with loblolly pine plantations and have resulted in changes in forest response to extreme weather conditions. However, uncertainty remains about the response of planted versus natural species to drought across the geographical range of these forests. Taking advantage of a cluster of unmanaged stands (85-130year-old hardwoods) and managed plantations (17-20year-old loblolly pine) in coastal and Piedmont areas of North Carolina, tree water use, cavitation resistance, whole-tree hydraulic (Ktree) and stomatal (Gs) conductances were measured in four sites covering representative forests growing in the region. We also used a hydraulic model to predict the resilience of those sites to extreme soil drying. Our objectives were to determine: (1) if Ktree and stomatal regulation in response to atmospheric and soil droughts differ between species and sites; (2) how ecosystem type, through tree water use, resistance to cavitation and rooting profiles, affects the water uptake limit that can be reached under drought; and (3) the influence of stand species composition on critical transpiration that sets a functional water uptake limit under drought conditions. The results show that across sites, water stress affected the coordination between Ktree and Gs. As soil water content dropped below 20% relative extractable water, Ktree declined faster and thus explained the decrease in Gs and in its sensitivity to vapor pressure deficit. Compared to branches, the capability of roots to resist high xylem tension has a great impact on tree-level water use and ultimately had important implications for pine plantations resistance to future summer droughts. Model simulations revealed that the decline in Ktree due to xylem cavitation aggravated the effects of soil drying on tree transpiration. The critical transpiration rate (Ecrit), which corresponds to the maximum rate at which transpiration begins to level off to prevent irreversible hydraulic failure, was higher in managed forest plantations than in their unmanaged counterparts. However, even with this higher Ecrit, the pine plantations operated very close to their critical leaf water potentials (i.e. to their permissible water potentials without total hydraulic failure), suggesting that intensively managed plantations are more drought-sensitive and can withstand less severe drought than natural forests.
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    Drone Use in Forestry 2021
    (2021-12-08) McElwee, Elisabeth
    In the last 20 years, advancements in technology, such as remote sensing, have facilitated improvements in forest management. The utilization of one remote sensing tool, in particular, an unmanned aerial vehicle (drone), has been gaining popularity in recent years. Drones provide an inexpensive alternative to aerial photos from a manned aircraft, providing quick access to high-resolution imagery, increased efficiency, reduced human risk, as well as a variety of other benefits. While there are many advantages to the use of drones in forestry and forest management, there are also limitations. These limitations are apparent when trying to apply methodologies across varying terrains, species compositions, and economic scales. Nevertheless, more people in forestry are beginning to explore the use of drones in forest management. In order to gain insight into the status and limitations of drone use in forest management in 2021, a nationwide survey targeted to those in forest management was developed and distributed. Ultimately the goal of this study is to provide a baseline for understanding how this technology is currently being used in forest management and to identify areas for improvement that may lead to greater utilization.
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    Evaluating the impact of managed wildfires as a restoration tool in southwestern ponderosa pine forests
    (2016-04-28) Tempest, Olivia
    Predating the 20th-century fires in the southwestern U.S., the ponderosa pine-dominated forests burned regularly and at low intensities. Yet these southwestern forests have become overgrown and dense as a result of fire exclusion and suppression policies. Only recently have managed wildfires been an active tool in an effort to return current forest stands within a historical range of natural variability. This study examines (1) the effects of recent wildfires managed for resource benefit use on stand structure in the Coconino National Forest, Arizona, (2) the prolonged impacts of simulated and repeated resource benefit fires of varying severity, and (3) what combination of management activities are necessary to return current stands to near historical reference conditions. Results show that managed wildfires may not be enough to return overstocked forests within historical conditions and mechanical treatments may be necessary to initiate a shift in composition and structure.
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    Evaluating the Relationship Between Timber and Forage Yields in a Loblolly Pine-Switchgrass Silvopastoral System
    (2020-04-22) Carroll, Colin
    As forest and agricultural landowners look to increase revenue streams and diversify risk, agroforestry systems could be viable land use options. Silvopasture is an agroforestry system that integrates the production of timber and livestock. Silvopasture is practiced globally and has great potential in the US South. Implementation of silvopastoral systems can vary, depending on landowner objectives. This investigation focuses on the relationship between timber (loblolly) and forage (switchgrass) yields for a non-industrial private landowner in Robeson County, NC. Managing for both silvopasture products presents establishment challenges and a nuanced understanding of how tree growth will affect forage yields over time. With careful planning, it appears that a silvopastoral system can be designed in which landowners can meet their objectives and balance yields from both products. In addition, the achievement of financial diversification through integration of both systems might be possible.
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    Impacts of Genetic Variation and Silvicultural Treatments on Loblolly Pine Water Use
    (2022-12-15) Liu, Azura
    Loblolly pine (Pinus taeda) is of high ecological and economical value in the U.S. for its abundance and rapid growth. P. taeda has adapted to a wide range of sites, exhibiting considerable plasticity in its physiology and morphology. In efforts of understanding such variation, transpiration has become a major study focus for its integral role in tree growth and survival. This master’s project examined sap flux data from an established experiment where four crown ideotypes were planted at two densities. The study explored the variation in P. taeda water use between planting densities, crown ideotypes, and environmental variables. By identifying genetic variation and treatment effects, this master’s project provides recommendations for further research and insights for forest management.
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    Influences of Windthrow in Forested Stream Buffers
    (2015-12-07) Blatt, Ethan; Caggiano, Thomas; Ulrich, Emily
    Forestry operations have long been understood to contribute to non-point source pollution. With the implementation of federal regulations to thwart such pollution and protect water quality, North Carolina adopted rules called Forest Practice Guidelines (FPGs). This research assesses the efficacy of a specific FPG called Streamside Management Zones (SMZs) for the North Carolina Forest Service (NCFS). Specifically, it examines whether SMZ characteristics influence tree windthrow and if such changes are related to differences in total suspended solids (TSS) levels in North Carolina Piedmont streams. Our results indicate that windthrow is more common in SMZs than in unharvested forest stands. We found that drivers of windthrow vary by location; slope, aspect, and distance to stream contribute to both increased and decreased probability of windthrow. Results also indicate differences in windprone species across sites, but similarities in windfirm species across sites. The majority of sites experienced greater windthrow of larger diameter trees. These results will help to inform the direction of future research conducted by the NCFS and to help develop guidance surrounding FPGs in North Carolina.
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    Inter-annual variability of precipitation constrains the production response of boreal Pinus sylvestris to nitrogen fertilization
    (Forest Ecology and Management, 2015-07-05) Lim, Hyungwoo; Oren, Ram; Palmroth, Sari; Tor-ngern, Pantana; Mörling, Tommy; Näsholm, Torgny; Lundmark, Tomas; Helmisaari, Heljä-Sisko; Leppälammi-Kujansuu, Jaana; Linder, Sune
    © 2015 Published by Elsevier B.V.Tree growth resources and the efficiency of resource-use for biomass production determine the productivity of forest ecosystems. In nutrient-limited forests, nitrogen (N)-fertilization increases foliage [N], which may increase photosynthetic rates, leaf area index (L), and thus light interception (IC). The product of such changes is a higher gross primary production and higher net primary production (NPP). However, fertilization may also alter carbohydrate partitioning from below- to aboveground, increasing aboveground NPP (ANPP). We analyzed effects of long-term N-fertilization on NPP, and that of long-term carbon storing organs (NPPS) in a Pinus sylvestris forest on sandy soil, a wide-ranging forest type in the boreal region. We based our analyses on a combination of destructive harvesting, consecutive mensuration, and optical measurements of canopy openness. After eight-year fertilization with a total of 70gNm-2, ANPP was 27±7% higher in the fertilized (F) relative to the reference (R) stand, but although L increased relative to its pre-fertilization values, IC was not greater than in R. On the seventh year after the treatment initiation, the increase of ANPP was matched by the decrease of belowground NPP (78 vs. 92gCm-2yr-1; ~17% of NPP) and, given the similarity of IC, suggests that the main effect of N-fertilization was changed carbon partitioning rather than increased canopy photosynthesis. Annual NPPS increased linearly with growing season temperature (T) in both treatments, with an upward shift of 70.2gCm-2yr-1 by fertilization, which also caused greater amount of unexplained variation (r2=0.53 in R, 0.21 in F). Residuals of the NPPS-T relationship of F were related to growing season precipitation (P, r2=0.48), indicating that T constrains productivity at this site regardless of fertility, while P is important in determining productivity where N-limitation is alleviated. We estimated that, in a growing season average T (11.5±1.0°C; 33-year-mean), NPPS response to N-fertilization will be nullified with P 31mm less than the mean (325±85mm), and would double with P 109mm greater than the mean. These results suggest that inter-annual variation in climate, particularly in P, may help explaining the reported large variability in growth responses to fertilization of pine stands on sandy soils. Furthermore, forest management of long-rotation systems, such as those of boreal and northern temperate forests, must consider the efficiency of fertilization in terms of wood production in the context of changes in climate predicted for the region.
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    Nitrogen addition to a mixed pine-broadleaved forest under elevated atmospheric CO2 exacerbates phosphorus and potassium deficiencies
    (2022-04-22) Knier, Aubrey
    Forests are vital ecosystems because they capture and store carbon from our atmosphere; this is essential for maintaining the balance between carbon uptake and release in the global carbon cycle. However, human activities—mainly burning fossil fuels—are releasing carbon dioxide (CO2) into our atmosphere at a rate we are not confident forests can keep pace with. As we face climate change, it is critical to understand exactly how forests respond to elevated CO2 to inform best forest management practices. Since trees utilize CO2 to photosynthesize, it is generally thought that increased amounts of CO2 will increase biomass, which will create a positive feedback loop for carbon sequestration. However, there are likely limitations—namely of nutrients—to production that prevent this from being the case. This study aims to better understand such tree nutrient limitations and responses to climate change conditions through the most realistically simulated means possible. This project uses data from the Duke Forest Free-Air CO2 Enrichment (FACE) experiment to investigate the effect of CO2-fumigation and nitrogen (N)-fertilization on nutrient concentrations in trees in their natural ecosystems. The experiment began in 1993 in the Blackwood Division of the Duke Forest in Durham, North Carolina on a 90-ha loblolly pine plantation with relatively acidic soils of low fertility. The split-plot randomized block experimental design had two main levels: first, four of the eight 30mdiameter plots were fumigated with elevated CO2; next all eight plots were divided in half and only one half was fertilized with N. This created four distinct treatment groups: Ambient Control, Ambient Fertilized, Elevated Control, and Elevated Fertilized—each represented by four “half-plots.” Starting in 2010, loblolly pine and broadleaved foliage, wood, and roots were harvested and analyzed for the six main plant nutrients: carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). We hypothesized that low concentrations of any other main plant nutrients—not just N—would mute trees’ response to elevated CO2. That is, fertilizing with only N would not be sufficient to alleviate nutrient limitations. Data from the Duke FACE experiment were analyzed for a signature of any nutrient limitations under elevated CO2. Linear mixed models with random effects were created for each main plant element (C, N, P, K, Ca, and Mg) in each tree component. These components included foliage, branch wood, stem wood, and roots for loblolly pine, sweetgum, a collection of other broadleaved species, small understory specimens, and vines. The statistical models were used to assess whether nutrient concentrations were significantly affected by elevated CO2 and N-fertilization. Overall, elevated CO2 and N-fertilization did not significantly affect any nutrient concentrations across all species in all aboveground components. We then compared Duke FACE loblolly pine foliar nutrient ratios to reference values—or values that are considered adequate for normal tree growth—and found that the system was P- and K-limited (P:N and K:N were 24% and 26% below adequate). In fact, adding N not only failed to alleviate P- and K-limitations, but significantly exacerbated them. Interestingly, we found a strong response to elevated CO2 and N-fertilization in the roots, especially in loblolly pine. Under N-fertilization, [P] was almost 16% higher and [K] was 29% higher under elevated CO2 than under ambient CO2 in pine roots, suggesting increased root production and exploration for the elements that limited tree production. The additional C supplied by elevated CO2 and exacerbated nutrient limitation by N-fertilization created a high demand for P and K to support increased biomass production. In response, root biomass increased, and P and K were locked belowground and used locally. The Duke FACE experiment is special because it allows us to understand how trees will respond to future climate change conditions before they happen. With this vital information, we can implement preemptive forest management practices that support continued production and carbon sequestration under elevated CO2. The results of this study underscore that elevated CO2 will only increase tree production when all main plant nutrients are adequately available. Thus, balanced fertilizers, rather than only N-fertilizers, should be applied to forests to ensure that our global carbon cycle is maintained during a most imperative time.
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    Optimizing Nutrient and Timber Management for the Town of Butner, NC
    (2011-04-29) Cass, David; Levo, Brian; Lott, Elizabeth
    The following report documents the findings of a client-focused group Master’s Project completed at the Nicholas School of the Environment at Duke University. The project’s purpose is to support the client’s goal to optimize nutrient and timber management in a 750-acre forested tract owned by the Town of Butner in Granville County, North Carolina. Excess nitrogen and phosphorus delivery to drinking water reservoirs has become a concern in the North Carolina piedmont as development pressure increases in surrounding watersheds. The Falls Lake Nutrient Strategy is among several new regulations aimed at reducing nitrogen and phosphorus delivery to an increasingly eutrophic public water supply. While the regulation pressures upstream communities to reduce their impact, mitigation strategies are diverse and can be costly to local governments. Even though a market-driven nutrient trading credit system is included in the Falls Lake Nutrient Strategy, there is currently no opportunity to earn credits through avoided deforestation or land conservation, commonly called “conservation credits”. The Town of Butner is interested in novel approaches to managing its nutrient loading and the possibility of earning conservation credits while managing its forestland for timber. There were four objectives to this project, 1) to estimate the value of timber on the property, 2) to determine the range of impacts that different timber management scenarios will have on nitrogen and phosphorus loading from the property, 3) to develop a simple tool that land managers can use to predict optimal outcomes for different timber and nutrient management scenarios, and 4) to inform state policy on the value of conservation credits and the effects of forest management on nutrient loading. A range of forest management scenarios with different harvest practices and maintaining 50-ft to 200-ft streamside management zones were modeled over a 30- year timeline. The USDA Forest Service’s Forest Vegetation Simulator (FVS) and Timber-Mart South were used to project harvested and standing timber values under each scenario. GIS-based models were employed to predict nitrogen and phosphorus delivery to perennial and intermittent streams under each scenario. The future value of conservation credits was assumed to be the sum of the value of nitrogen and phosphorus credits in the existing NC Department of Environment and Natural Resources, Nutrient Offset Program. The findings of this project suggest that the monetary value of timber within the 50-ft to 200-ft buffer zone far exceeds any reasonable economic value of conservation credits earned by not harvesting within the buffer zone during a 30-year time horizon. Timber harvesting, and in particular changing the buffer zone width from 50-ft to 200-ft, had a relatively small impact on nitrogen and phosphorus loading when compared to other land uses. The implication is that nutrient management and productive forest management are not mutually exclusive. The minimum buffering requirement of 50-ft was effective at removing nutrients, while still permitting the maximization of timber revenue.
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    Piedmont Longleaf Pine Restoration: A Management Plan for the Private Landowner
    (2016-04-27) Worthington, Cakey
    Once abundant across the southeastern United States, longleaf pine communities now cover only 3-5% of their native range. Much of this land has been converted to fire-excluded loblolly pine plantations to supply the South's burgeoning timber market. Ecosystems dominant in longleaf pine provide valuable habitat to many unique and threatened southern species as well as financial gain from timber and alternative uses such as leasing for pine straw or hunting. Restoration efforts are currently being implemented on a variety of public and private lands, bringing a heightened awareness and scrutiny of the management practices necessary to bring back this important species. This study examines the potential for restoration of longleaf pine habitat on 3300 acres of private land in the central Piedmont of North Carolina. The intent of this management plan is to provide: a historical background on management of the property, current ecological and site conditions, a projection of future forest growth and value, and recommendations for restoration and future management in accordance with the landowner’s vision for the property. The study included collection and compilation of data on site qualities, an assessment of the current remaining timber stock, a forecast of the potential longleaf pine growth including the impact from fire management, and the potential economic value of the forest conservation investment. Major findings of the study include that fire is beneficial for competition control and that the potential for ecological and economic gain from this effort is dependent on selection of appropriate management techniques and alternative uses.
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    PRODUCING GROWTH ESTIMATES OF DUKE FOREST PINE STANDS USING USDA’S FOREST VEGETATION SIMULATOR
    (2021-04-28) Bowman, Hunter
    Duke Forest manages its loblolly pine stands for timber revenues. Duke Forest seeks construct a management plan informed by an optimized harvest schedule. This project aims to produce a reliable growth and yield model in order to produce the volume yield estimates necessary to compute the optimized harvest schedule. This was accomplished by testing and calibrating USDA’s Forest Vegetation Simulator (FVS) using Duke Forest Continuous Forest Inventory data. FVS was tested by using different site index inputs, and the diameter growth modifiers of FVS were then applied to reproduce current loblolly pine stand characteristics. It was found that the observed site index of a Duke Forest loblolly pine stand produces a better estimate of Duke Forest basal areas than do the Natural Resource Conservation Service’s Web Soil Survey site indices. Despite the use of the more accurate site index numbers, FVS needed further calibration in order to produce statistically significant estimates of Duke Forest basal areas. Diameter growth modifiers of 1.25, 2.6, and 2.6 were applied to stands with low, average, and high site indices respectively, which calibrated the model. FVS, when calibrated, can provide Duke Forest with a workable growth and yield model. In the future, even more precise calibrations will be possible as the continuous Forest Inventory process continues, and plots sampled for this project are re-sampled. This will inform the diameter and height growth increments FVS uses to grow the inputted trees into the future.
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    Remote Sensing Tree Physiology
    (2021-08-17) Frear, Joshua
    Transpiration, or plant water loss, is a critical component of water balance and flux for terrestrial systems worldwide, yet uncertainty in large-scale estimates create significant challenges for water resource forecasting (Jasechko 2013, Coenders-Gerrits 2014). Effectively measuring changes in transpiration over time can provide insight into water availability issues facing a tree, a stand, or a landscape. As temperature and precipitation patterns change in the next century and cause shifts in water availability, forest health around the world is likely to change, too, and should be monitored. Currently, transpiration is often monitored at research sites with specialized eddy covariance flux towers, or sap-flux sensors installed in trees that measure the transpiration of individual trees or stands. To measure transpiration frequently across the Earth, a different approach is required. One possible tool for this is ECOSTRESS (Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station). ECOSTRESS is an experiment run by NASA’s Jet Propulsion Laboratory that measures elements of plant transpiration worldwide (Fischer 2020). Attached to the International Space Station, the ECOSTRESS radiometer measures latent heat flux and estimates plant water loss occurring around the world every day. The objective of this project is to investigate and compare ECOSTRESS to more traditional methods of measuring transpiration at three temperate forest research sites in the US and France. Comparing transpiration and evapotranspiration data at each site since the inception of ECOSTRESS in 2018 reveal significant but weak correlations between the two measurements (all r2 < 0.4). ECOSTRESS generally measured much higher transpiration for the days of overpass compared to sap-flux measurements. Time of day of overpass had a significant relationship with the difference between the two measurements, but sub-setting the data to exclude times of day with low transpiration or winter months generally did not improve the correlations, except for excluding morning observations. Based on these observations, ECOSTRESS should be used with caution for non-spatial time-series-type studies. Additionally, there remains a significant spatial difference between the two approaches, as one ECOSTRESS pixel covers about half a hectare.
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    The carbon bonus of organic nitrogen enhances nitrogen use efficiency of plants.
    (Plant, cell & environment, 2017-01) Franklin, Oskar; Cambui, Camila Aguetoni; Gruffman, Linda; Palmroth, Sari; Oren, Ram; Näsholm, Torgny
    The importance of organic nitrogen (N) for plant nutrition and productivity is increasingly being recognized. Here we show that it is not only the availability in the soil that matters, but also the effects on plant growth. The chemical form of N taken up, whether inorganic (such as nitrate) or organic (such as amino acids), may significantly influence plant shoot and root growth, and nitrogen use efficiency (NUE). We analysed these effects by synthesizing results from multiple laboratory experiments on small seedlings (Arabidopsis, poplar, pine and spruce) based on a tractable plant growth model. A key point is that the carbon cost of assimilating organic N into proteins is lower than that of inorganic N, mainly because of its carbon content. This carbon bonus makes it more beneficial for plants to take up organic than inorganic N, even when its availability to the roots is much lower - up to 70% lower for Arabidopsis seedlings. At equal growth rate, root:shoot ratio was up to three times higher and nitrogen productivity up to 20% higher for organic than inorganic N, which both are factors that may contribute to higher NUE in crop production.