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Given the large mole fractions of highly reactive species encountered in combustion, there is significant potential for chemically reactive collisions to occur on similar timescales as the energy-transferring collisions responsible for thermalization. Recent work has shown that this can result in “chemically termolecular” reactions of importance to combustion predictions. This type of reaction, where three reactants are involved in bond breaking and forming, has generally been neglected in previous phenomenological kinetic models. Combinatorially, there are hundreds to thousands of such reactions that are possible. Clearly, it is not feasible to perform detailed master equation analysis for all of these potential pathways, and yet, a priori, it is difficult to know which of these thousands of reactions are sufficiently likely to impact combustion predictions to warrant detailed master equation calculations. This paper presents a theoretical and computational framework that identifies and estimates rate constants for potential chemically termolecular reactions, for which information has been previously limited, based on information already available for known reactions in combustion mechanisms. Applications of this approach to flames, presented herein, reveal a few chemically termolecular reactions that impact flame emissions and flame speeds – including H + N2 + O = NH + NO, H + CO + H = H2 + CO, and H + C2H2 + O2/OH/H. These reactions, therefore, are worthwhile candidates for detailed master equation calculations for improved quantitative predictions.

Indonesia and Peru harbor some of the largest lowland tropical peatland areas. Indonesian peatlands are subject to much greater anthropogenic activity than Peru’s, including drainage, logging, agricultural conversion, and burning, resulting in high greenhouse gas and particulate emissions. To derive insights from the Indonesian experience, we explored patterns of impact in the two countries, and compared their predisposing factors. Impacts differ greatly among Indonesian regions and the Peruvian Amazon in the following order: Sumatra > Kalimantan > Papua > Peru. All impacts, except fire, are positively related to population density. Factors enhancing Indonesian peatlands’ susceptibility to disturbance include peat doming that facilitates drainage, coastal location, high local population, road access, government policies permitting peatland use, lack of enforcement of protections, and dry seasons that favor extensive burning. The main factors that could reduce peatland degradation in Peru compared with Indonesia are geographic isolation from coastal population centers, more compact peatland geomorphology, lower population and road density, more peatlands in protected areas, different land tenure policies, and different climatic drivers of fire; whereas factors that could enhance peatland degradation include oil and gas development, road expansion in peatland areas, and an absence of government policies explicitly protecting peatlands. We conclude that current peatland integrity in Peru arises from a confluence of factors that has slowed development, with no absolute barriers protecting Peruvian peatlands from a similar fate to Indonesia’s. If the goal is to maintain the integrity of Peruvian peatlands, government policies recognizing unique peatland functions and sensitivities will be necessary.

Peatlands play a critical role in terrestrial carbon (C) storage, containing an estimated 30% of global soil C, despite occupying only 3% of global land area. Historic management of peatlands has led to widespread degradation and loss of important ecosystem services, including C sequestration. Legacy drainage features in the peatlands of northern Minnesota, USA were studied to assess the volume of peat and the amount of C lost in the ~100 years since drainage. Using high-resolution Light Detection and Ranging (LiDAR) data, we measured elevation changes adjacent to legacy ditches to model pre-ditch surface elevations, which were used to calculate peat volume loss. We established relationships between volume loss and site characteristics from existing geographic information systems datasets and used those relationships to scale volume loss to all mapped peatland ditches in northern Minnesota (USA). We estimated that 0.165 ± 0.009 km3 of peat have been lost along almost 4000 km of peatland ditches. Peat loss upslope of ditches was significantly less than downslope (P < 0.001). Mean width of the entire ditch-effect zone was 333 ± 8.32 m. Using our volume loss estimates, literature estimates of oxidation, and mean bulk density and peat C% values from Minnesota peatlands, we calculate a total historic loss 3.847 ± 0.364 Tg C. Assuming a constant oxidation rate during the 100 years since drainage, euic and dysic peatlands within the ditch effect zone have lost 0.26 ± 0.08 and 0.40 ± 0.13 Mg C ha-1 yr-1, respectively, comparable to IPCC estimates. Our spatially-explicit peat loss estimates could be incorporated into decision support tools to inform management decisions regarding peatland C and other ecosystem services.

Management of forest carbon stocks on public lands is critical to maintaining or enhancing carbon dioxide removal from the atmosphere. Acknowledging this, an array of federal regulations and policies have emerged that requires US National Forests to report baseline carbon stocks and changes due to disturbance and management and assess how management activities and forest plans affect carbon stocks. To address these requirements with the best-available science, we compiled empirical and remotely sensed data covering the National Forests (one fifth of the area of US forest land) and analyzed this information using a carbon modeling framework. We demonstrate how integration of various data and models provides a comprehensive evaluation of key drivers of observed carbon trends, for individual National Forests. The models in this framework complement each other with different strengths: the Carbon Calculation Tool uses inventory data to report baseline carbon stocks; the Forest Carbon Management Framework integrates inventory data, disturbance histories, and growth and yield trajectories to report relative effects of disturbances on carbon stocks; and the Integrated Terrestrial Ecosystem Carbon Model incorporates disturbance, climate, and atmospheric data to determine their relative impacts on forest carbon accumulation and loss. We report results for several National Forests across the USA and compare their carbon dynamics. Results show that recent disturbances are causing some forests to transition from carbon sinks to sources, particularly in the West. Meanwhile, elevated atmospheric carbon dioxide and nitrogen deposition are consistently increasing carbon stocks, partially offsetting declines due to disturbances and aging. Climate variability introduces concomitant interannual variability in net carbon uptake or release. Targeting forest disturbance and post-disturbance regrowth is critical to management objectives that involve maintaining or enhancing future carbon sequestration.

Puntos clavesIndonesia y Peru albergan algunas de las areas de turberas tropicales de tierras bajas mas grandes. Las turberas en Indonesia estan sujetas a mucho mayor actividad antropogenica que en Peru, lo que resulta en grandes emisiones de particulas y GEI.Exploramos patrones de impacto en ambos paises y comparamos los factores que predisponen a su degradacion y conversion. Los impactos difieren enormemente entre las regiones de Indonesia y la Amazonia peruana, en el orden: Sumatra > Kalimantan > Papua > Peru.Todos los impactos, a excepcion de los incendios, estuvieron relacionados positivamente a la densidad poblacional.La integridad actual de las turberas en Peru es producto de una confluencia de factores que ha frenado el desarrollo, sin barreras absolutas que las protejan de un destino similar a las de Indonesia.Si el meta es mantener la integridad de las turberas peruanas, sera necesario que las politicas gubernamentales reconozcan sus funciones y sensibilidades unicas.

Background Forest biodiversity is the foundation of many ecosystem services, and the effect of biodiversity on ecosystem functioning and processes (BEF) has been a central issue in biodiversity studies. Although many hypotheses have been developed to interpret global gradients of biodiversity, there has not been complete agreement on mechanisms controlling biodiversity patterns and distributions. Differences may be due to limited observation data and inconsistencies of spatial scales in analysis. Methods In this study, we take advantage of USDA Forest Service forest inventory and analysis (FIA) data for exploring regional forest biodiversity and BEF in New England forests. The FIA data provide detailed information of sampled plots and trees for the region, including 6000 FIA plots and more than 33,000 individual trees. Biodiversity models were used to analyze the data. Results Tree species diversity increases from the north to the south at a rate about 2–3 species per latitudinal degree. Tree species diversity is better predicted by tree height than forest age or biomass. Very different distribution patterns of two common maple species, sugar maple (Acer saccharum) and red maple (Acer rubrum), highlight the vulnerability of sugar maple and its potential replacement by red maple on New England landscapes. Red maple generally already outperforms sugar maple, and will likely and continuously benefit from a changing climate in New England. Conclusions We conclude that forest structure (height) and resources (biomass) are more likely foundational characteristics supporting biodiversity rather than biodiversity determining forest productivity and/or biomass. The potential replacement of red maple for sugar maple in the New England areas could affect biodiversity and stability of forest ecosystem functioning because sugar maple plays important ecological roles distinct from red maple that are beneficial to other tree species in northern hardwood forests. Such a change may not affect forest resilience in terms of forest productivity and biomass as these are similar in red maple and sugar maple, however, it would almost certainly alter forest structure across the landscape.

Process-based models are a powerful approach to test our understanding of biogeochemical processes, to extrapolate ground survey data from limited plots to the landscape scale, and to simulate the effects of climate change, nitrogen deposition, elevated atmospheric CO2, increasing natural disturbances, and land-use change on ecological processes. However, in most studies, the models are calibrated using ground measurements from only a few sites, though they may be extrapolated to much larger areas. Estimation accuracy can be improved if the models are parameterized using long-term carbon (C) stock data from multiple sites representative of the simulated region. In this study, forest biomass C stocks measured in 61 forested plots located in three research sites in the Delaware River Basin (DRB) were used to modify the PnET-CN model in three ways: (1) Field-measured mortality rates in each forest type were used to parameterize the wood turnover rate; (2) a numerical approach was used to calibrate the relationship between foliage N and maximum photosynthesis rate; and (3) stand age was incorporated into the model as an input variable, which determines the year of the last disturbance. The results showed that these model modifications improved model performance in capturing the spatial variation of forest C dynamics in the DRB forests. The spatial distribution of forest C pools and fluxes in the three sites was mapped using the modified model. The modified model was also used in experimental scenarios, which predicted that 39% of forest C sequestered over the past decade could be attributed to the combined effects of elevated CO2 and N deposition. This study demonstrated an effective method for using long-term biometric measurements of forest biomass C stocks to constrain and improve a process-based ecosystem model at a regional scale. Further research should target improving model parameters that are sensitive to the spatial variation of forest C dynamics.

Atmospheric inversions have become an important tool in quantifying carbon dioxide (CO2) sinks and sources at a variety of spatiotemporal scales, but associated large uncertainties restrain the inversion research community from reaching agreement on many important subjects. We enhanced an atmospheric inversion of the CO2 flux for North America by introducing spatially explicit information on forest stand age for US and Canada as an additional constraint, since forest carbon dynamics are closely related to time since disturbance. To use stand age information in the inversion, we converted stand age into an age factor, and included the covariances between subcontinental regions in the inversion based on the similarity of the age factors. Our inversion results show that, considering age factors, regions with recently disturbed or old forests are often nudged towards carbon sources, while regions with middle-aged productive forests are shifted towards sinks. This conforms to stand age effects observed in flux networks. At the subcontinental level, our inverted carbon fluxes agree well with continuous estimates of net ecosystem carbon exchange (NEE) upscaled from eddy covariance flux data based on MODIS data. Inverted fluxes with the age constraint exhibit stronger correlation to these upscaled NEE estimates than those inverted without the age constraint. While the carbon flux at the continental and subcontinental scales is predominantly determined by atmospheric CO2 observations, the age constraint is shown to have potential to improve the inversion of the carbon flux distribution among subcontinental regions, especially for regions lacking atmospheric CO2 observations.

Forest disturbances such as harvesting, wildfire and insect infestation are critical ecosystem processes affecting the carbon cycle. Because carbon dynamics are related to time since disturbance, forest stand age that can be used as a surrogate for major clear-cut/fire disturbance information has recently been recognized as an important input to forest carbon cycle models for improving prediction accuracy. In this study, forest disturbances in the USA for the period of ~1990-2000 were mapped using 400+ pairs of re-sampled Landsat TM/ETM scenes in 500m resolution, which were provided by the Landsat Ecosystem Disturbance Adaptive Processing System project. The detected disturbances were then separated into two five-year age groups, facilitated by Forest Inventory and Analysis (FIA) data, which was used to calculate the area of forest regeneration for each county in the USA. In this study, a disturbance index (DI) was defined as the ratio of the short wave infrared (SWIR, band 5) to near-infrared (NIR, band 4) reflectance. Forest disturbances were identified through the Normalized Difference of Disturbance Index (NDDI) between circa 2000 and 1990, where a positive NDDI means disturbance and a negative NDDI means regrowth. Axis rotation was performed on the plot between DIs of the two matched Landsat scenes in order to reduce any difference of DIs caused by non-disturbance factors. The threshold of NDDI for each TM/ETM pair was determined by analysis of FIA data. Minor disturbances affecting small areas may be omitted due to the coarse resolution of the aggregated Landsat data, but the major stand-clearing disturbances (clear-cut harvest, fire) are captured. The spatial distribution of the detected disturbed areas was validated by Monitoring Trends in Burn Severity fire data in four States of the western USA (Washington, Oregon, Idaho, and California). Results indicate omission errors of 66.9%. An important application of this remote sensing-based disturbance map is to associate with FIA forest age data for developing a US forest age map. The US forest age map was also combined with the Canadian forest age map to produce a continent-wide forest map, which becomes a remarkable data layer for North America carbon cycle modeling.

Terrestrial carbon dynamics have been vastly modified because of changes in atmospheric composition, climate, and land-use. However, few studies provide a complete analysis of the factors and interactions that affect carbon dynamics over a large landscape. This study examines how changes in atmospheric composition (CO2 ,O 3 and N deposition), climate and land-use affected carbon dynamics and sequestration in Mid-Atlantic temperate forests during the 20th century. We modified and applied the PnET-CN model, a well established process-based ecosystem model with a strong foundation of ecosystem knowledge from experimental studies. We validated the model results using the U.S. Forest Inventory and Analysis (FIA) data. Our results suggest that chronic changes in atmospheric chemistry over the past century markedly affected carbon dynamics and sequestration in Mid-Atlantic temperate forests, while climate change only had a minor impact although inter-annual climatic variability had a far more substantial effect. The NPP response to a century of chronic change in atmospheric composition at the regional scale was an increase of 29%, of which, 14% was from elevated CO2, 17% from N deposition, 6% from the interaction between CO2 and N deposition, and minus 8% from tropospheric ozone. Climate change increased NPP by only 4%. Disturbed forests had 6% lower NPP than undisturbed forests after seven decades. Regrowing forests after harvesting and natural disturbances had much greater capacity for sequestering carbon than undisturbed old-growth forests even though the newer forests had slightly lower net primary production (NPP). The modeling results indicated that N deposition was a stronger force than elevated CO2 for increasing NPP and fast turnover tissues, while elevated CO2 favored more sustainable carbon storage and sequestration. The model results are consistent with various experiments and observations and demonstrate a powerful approach to integrate and expand our knowledge of complex interactive effects of multiple environmental changes on forest carbon dynamics.

This report assesses past and prospective carbon stocks for 4.5 million ha of forest land in northern Wisconsin, including a baseline assessment and analysis of the impacts of disturbance and management on carbon stocks. Carbon density (amount of carbon stock per unit area) averages 237 megagrams (Mg) per ha, with the National Forest lands having slightly higher carbon density than other ownership classes. Over the last decade, carbon stocks of northern Wisconsin forests have been increasing by about one teragram (Tg) per year or 0.22 megagrams per ha per year, with most of the increase in live biomass. Harvest, wind, and fire have been principal drivers of forest carbon dynamics over the last century. For all forest types in northern Wisconsin, there is potential to increase stocking on the land by allowing more of the forested area to reach older age classes or by increasing productivity. Opportunities to increase afforestation and reduce deforestation are limited, but the potential exists for utilizing biomass energy as a substitute for fossil fuels. There are several options for private landowners to participate in carbon markets or greenhouse gas registries and receive some credit for additional actions to reduce emissions or increase sequestration of carbon. The methods used here can be adapted for use by other regions or forests to assess carbon stocks and effects of management on future carbon stocks.

We studied the effect of 15N labelling duration on the mineralisation and immobilisation of native and applied (residual) N in the humus layer of a Humo-Ferric Podzol. Ammonium sulphate, labelled with 15N, was applied to 1 m2 plots at a rate of 200 kg N ha−1. Fertiliser application was timed so that when samples were collected they had been labelled with 15N for 24 hours, 7 months and 31 months. In a 42-day aerobic incubation of the samples, net mineralisation of total and applied N was greatest in the 24-hr treatment followed by those from the 31-month treatment (p 24-hr > 31-month treatment. Net mineralisation of C and N was poorly correlated with each other (r=-0.02, p=0.89). Anaerobic incubation showed net mineralisation for the 7- and 31-month treatments but net immobilisation for the 24-hr treatment for both total and applied N, suggesting that immobilisation of inorganic N was encouraged when there was a large pool of mineral N in the soil. Both total and applied N in the extractable organic N fraction and in the N flushed after fumigation with chloroform had the following order: 24-hr > 7-month > 31-month treatment. The results confirmed that N fertiliser was being immobilised within hours after application by the humus material through the microbial population and that the immobilised N had a low mineralisation potential after one growing season.

Atmospheric inversions have become an important tool in quantifying carbon dioxide (CO2) sinks and sources at a variety of spatiotemporal scales, but associated large uncertainties restrain the inversion research community from reaching agreements on many important subjects. We enhanced an atmospheric inversion of the CO2 flux for North America by introducing spatially-explicit information on forest stand age for US and Canada as an additional constraint, since forest carbon dynamics are closely related to time since disturbance. To use stand age information in the inversion, we converted stand age into an age factor, and included the covariances between sub-continental regions in the inversion based on the similarity of the age factors. Our inversion results show that, considering age factors, regions with recently-disturbed or old forests are often nudged towards carbon sources, while regions with middle-aged productive forests are shifted towards sinks. This conforms to stand age effects observed in flux networks. At the sub-continental level, our inverted carbon fluxes agree well with continuous estimates of net ecosystem carbon exchange (NEE) upscaled from eddy covariance flux data (EC) based on MODIS data. Inverted fluxes with the age constraint exhibit stronger correlation to these upscaled NEE estimates than those inverted without the age constraint. While the carbon flux at the continental and sub-continental scales is predominantly determined by atmospheric CO2 observations, the age constraint is shown to have potential to improve the inversion of the carbon flux distribution among sub-continental regions, especially for regions lacking atmospheric CO2 observations.

This report describes the database used to compile, store, and manage intensive ground-based biometric data collected at research sites in Colorado, Minnesota, New Hampshire, New Jersey, North Carolina, and Wyoming, supporting research activities of the U.S. North American Carbon Program (NACP). This report also provides details of each site, the sampling design and collection standards for biometric measurements, the database design, data summary examples, and the uses of intensive ground-based biometric data. Additional information on location descriptions, data, databases, and documentation may be accessed at http://www.nrs.fs.fed.us/data/lcms.

Fertilizer labeled with 15N was used to study the fate of N in forest soil–plant systems with (control) and without competition (treated) from an ericaceous evergreen shrub, salal (Gaultheriashallon Pursh), on a western red cedar (Thujaplicata Donn ex D. Don)–western hemlock (Tsugaheterophylla (Raf.) Sarg.) clear-cut site on northern Vancouver Island. Fertilizer was applied in April 1991 at 200 kg N•ha−1 as (NH4)2SO4 (3.38044% 15N enrichment) to single-tree plots of 1 m radius. Four-year-old western red cedar, western hemlock, and Sitka spruce (Piceasitchensis (Bong.) Carrière) were used and the plots were destructively sampled after two growing seasons (October 1992). The distribution of 15N within trees was virtually unaffected by the treatment but displayed differences among species. The majority of the 15N in a tree was found in the current-year needles. Because of the dilution effect, 15N abundances in the above ground tree components were not different between treatments but 15N contents were significantly increased by salal removal. The pattern of and treatment effect on total N distribution were similar to those of 15N. Total recovery by trees of applied 15N was 7.7, 17.8, and 10.3% in the treated plots planted with cedar, hemlock, and spruce, respectively. The corresponding values for the control plots were 4.1, 2.0, and 4.9%. Understory in the control plots immobilized 14.8, 24.6, and 13.5% of the applied N for plots planted with the respective species. Total recoveries in soil and vegetation ranged from 57 to 87%, of which 59 to 82% was recovered in the soil compartments. Results clearly showed that trees competed poorly with the understory vegetation for the applied fertilizer N.

Most forests of the world are recovering from a past disturbance. It is well known that forest disturbances profoundly affect carbon stock and fluxes in forest ecosystems, yet it has been a great challenge to assess disturbance impacts in estimates of forest carbon budgets. Net sequestration or loss of CO2 by forests after disturbance follows a predictable pattern with forest recovery. Forest age, which is related to time since disturbance, is the most available surrogate variable for various forest carbon analyses that concern the impact of disturbance. In this study, we compiled the first continental forest age map of North America by combining forest inventory data, historical fire data, optical satellite data and the dataset from NASA's LEDAPS project. Mexico and interior Alaska are excluded from this initial map due to unavailability of all required data sets, but work is underway to develop some different methodology for these areas. We discuss the significance of disturbance legacy from the past, as represented by current forest age structure in different regions of the US and Canada, tracking back disturbances caused by human and nature over centuries and at various scales. We also show how such information can be used with inventory data for analyzing carbon management opportunities, and other modeling applications. By combining geographic information about forest age with estimated C dynamics by forest type, it is possible to conduct a simple but powerful analysis of the net CO2 uptake by forests, and the potential for increasing (or decreasing) this rate as a result of direct human intervention in the disturbance/age status. The forest age map may also help address the recent concern that the terrestrial C sink from forest regrowth in North America may saturate in the next few decades. Finally, we describe how the forest age data can be used in large-scale carbon modeling, both for land-based biogeochemistry models and atmosphere-based inversion models, in order to improve the spatial accuracy of carbon cycle simulations.

Fertilizer was applied on snow in January 1981 at 100 kg N•ha−1 as [15N]urea, 15NH4NO3, and NH415NO3 to 11-year-old lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) at Spillimacheen in the British Columbia interior and as [15N]urea (200 kg N•ha−1) to 13-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) at Green Mountain, a coastal site in British Columbia. Recovery of labelled N after one growing season was determined in soil and biomass at both sites, and it was also monitored during the growing season in snow and soil at Spillimacheen. At Green Mountain, 5.5% of urea N was recovered in tree biomass, 10.8% in understory, and 33.4% in soil organic N (total recovery 49.7%). Leaching may have contributed to N losses at Green Mountain, but was probably not a direct consequence of the application on snow. At Spillimacheen, total recovery of [15N]urea was 93.3%, with 10.1% in tree biomass, 2.4% in understory, and 80.8% in soil. For 15NH4NO3, recoveries were 5.3% in tree biomass, 2.9% in understory, and 87.0% in soil, for a total of 95.2%. For NH415NO3, recoveries were 1.9% in tree biomass, 3.4% in understory, and 39.1% in soil, for a total of 44.4%. At Spillimacheen, the performance of 15NH4NO3 was comparable to that of urea in tree uptake and soil retention. There were large losses with the NH415NO3 source, however, most likely due to leaching and denitrification during snowmelt. For this reason, fertilization with nitrate on snow is not recommended because of nitrate's susceptibility to leaching, but urea and ammonium sources may be applied under these conditions.

We compared estimates of net primary production (NPP) from the MODIS satellite with estimates from a forest ecosystem process model (PnET-CN) and forest inventory and analysis (FIA) data for forest types of the mid-Atlantic region of the United States. The regional means were similar for the three methods and for the dominant oak-hickory forests in the region. However, MODIS underestimated NPP for less-dominant northern hardwood forests and overestimated NPP for coniferous forests. Causes of inaccurate estimates of NPP by MODIS were (1) an aggregated classification and parameterization of diverse deciduous forests in different climatic environments into a single class that averages different radiation conversion efficiencies; and (2) lack of soil water constraints on NPP for forests or areas that occur on thin or sandy, coarse-grained soil. We developed the "available soil water index" for adjusting the MODIS NPP estimates, which significantly improved NPP estimates for coniferous forests. The MODIS NPP estimates have many advantages such as globally continuous monitoring and remarkable accuracy for large scales. However, at regional or local scales, our study indicates that it is necessary to adjust estimates to specific vegetation types and soil water conditions.

In this study, we applied a process-based forest ecosystem model, PnET-CN, to estimate inorganic N (nitrate) loading and retention under chronic increases of atmospheric N deposition in the Chesapeake Bay (CPB) watershed. The results indicated that the average N leaching loss from forested lands in the CPB watershed is 1.23 kg N ha−1 y−1 at current N deposition levels, suggesting approximately 88% of N is retained by forest ecosystems. Total dissolved inorganic N exported from the forested watersheds was 11,617 Mg N yr−1. The predicted rates of the nitrate losses are well validated by the United States Geological Survey–National Water-Quality Assessment data measured from the gauged stations for forested drainages within the CPB watershed, and are also compatible with the field data of N loads associated with forests in the CPB watershed. If N deposition were twice current levels, the retention by forests would drop to 81%. Total N leaching loss to surface waters would then increase more than threefold. A nonlinear increase in N loads from forests under the extreme scenario of atmospheric N deposition shows the symptom of N saturation and an accelerated decline of forest functioning to retain atmospheric N deposition in the CPB watershed with rising levels of nitrogen deposition.