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Lack of research into the complexity in urban land conversion, and paucity of observational data of soil organic carbon (SOC) beneath impervious surface area (ISA) limit our understanding of the urbanization effects on carbon (C) pools in dryland cities. Employing Landsat TM images acquired in 1990 and 2010, a hybrid classification method consisting of Linear Spectral Mixture Analysis and decision tree classification was applied to retrieve the land cover (water, ISA, greenspace, cropland, and remnant desert) of the largest dryland city in China—Urumqi. Based on vegetation carbon (VEGC) and SOC density data determined through field observations and literature reviews, we developed Urumqi’s C pool maps in 1990 and 2010, and assessed the urbanization impacts on ecosystem C. Our results showed that ISA tripled from 1990 to 2010 displacing remnant desert and cropland. The urban landscape, especially the greenspaces, became obviously fragmented. In 2010, more than 95% of the urban ecosystem C was SOC, 48% of which under the ISA. The city lost 19% of C stock from 1990 to 2010. About 82% of the ecosystem C loss was caused by the conversion of remnant desert and cropland into ISA, mainly in the northern city.

An analysis suggests that the time taken for ecosystems to recover from drought increased during the twentieth century. If the frequency of drought events rises, some ecosystems might never have the chance to fully recover. See Letter Droughts affect ecosystem carbon storage, but the factors influencing ecosystem recovery from droughts remain poorly understood. This study finds that gross primary productivity recovery times from droughts are strongly associated with climate and carbon cycle dynamics and to a much lesser extent with biodiversity and carbon dioxide fertilization. The authors find that recovery time is longest in the tropics and high northern latitudes. They also observe that the area of ecosystems under active recovery and the length of recovery time have increased globally over the twentieth century. If future droughts become more frequent this may lead to a chronic state of incomplete recovery with adverse consequences for the land carbon sink.

Inverse modeling techniques used to quantify surface carbon fluxes commonly assume that the uncertainty of fossil fuel CO2 (FFCO2) emissions is negligible and that intra-annual variations can be neglected. To investigate these assumptions, we analyzed the differences between four fossil fuel emission inventories with spatial and temporal differences over Europe and their impact on the model simulated CO2 concentration. Large temporal flux variations characterize the hourly fields (~40 % and ~80 % for the seasonal and diurnal cycles, peak-to-peak) and annual country totals differ by 10 % on average and up to 40 % for some countries (i.e., the Netherlands). These emissions have been prescribed to seven different transport models, resulting in 28 different FFCO2 concentrations fields. The modeled FFCO2 concentration time series at surface sites using time-varying emissions show larger seasonal cycles (+2 ppm at the Hungarian tall tower (HUN)) and smaller diurnal cycles in summer (−1 ppm at HUN) than when using constant emissions. The concentration range spanned by all simulations varies between stations, and is generally larger in winter (up to ~10 ppm peak-to-peak at HUN) than in summer (~5 ppm). The contribution of transport model differences to the simulated concentration std-dev is 2–3 times larger than the contribution of emission differences only, at typical European sites used in global inversions. These contributions to the hourly (monthly) std-dev's amount to ~1.2 (0.8) ppm and ~0.4 (0.3) ppm for transport and emissions, respectively. First comparisons of the modeled concentrations with 14C-based fossil fuel CO2 observations show that the large transport differences still hamper a quantitative evaluation/validation of the emission inventories. Changes in the estimated monthly biosphere flux (Fbio) over Europe, using two inverse modeling approaches, are relatively small (less that 5 %) while changes in annual Fbio (up to ~0.15 % GtC yr−1) are only slightly smaller than the differences in annual emission totals and around 30 % of the mean European ecosystem carbon sink. These results point to an urgent need to improve not only the transport models but also the assumed spatial and temporal distribution of fossil fuel emission inventories.

Woody encroachment of grasslands is a common phenomenon worldwide, but the consequences of this encroachment for ecosystem carbon storage, particularly belowground are not clear. We quantified total ecosystem carbon in the 3 major natural upland vegetation communities (grassland, shrubland, and forest) at the northern edge of the North American Great Plains. Total ecosystem carbon storage was significantly greater in forest (125.3 mg C·ha-1) than in shrubland (92.4 mg C·ha-1) or grassland (80.7 mg C·ha-1), and this difference was due mainly to greater aboveground biomass, coarse root biomass, and the presence of a humus layer in the forest. Fine and total root biomass were also greater in forest than shrubland or grassland. In contrast, soil carbon was significantly greater in shrubland (80.6 mg C·ha-1) and grassland (75.4 mg C·ha-1) than in forest (48.6 mg C·ha-1). We also investigated whether aboveground variables could be used to predict belowground carbon pools. Soil carbon increased signifi...

Forests contain the world's largest terrestrial carbonstocks, but in seasonally dry environments stock stability can be compromised if burned by wildfire, emitting carbon back to the atmosphere. Treatments to reduce wildfireseverity can reduce emissions, but with an immediate cost of reducing carbonstocks. In this study we examine the tradeoffs in carbonstock reduction and wildfireemissions in 19 fuels-treated and -untreatedforests burned in twelve wildfires. The fuels treatment, a commonly used thinning ‘from below’ and removal of activity fuels, removed an average of 50.3 Mg C ha-1 or 34% of live tree carbonstocks. Wildfireemissions averaged 29.7 and 67.8 Mg C ha-1 in fuelstreated and untreatedforests, respectively. The total carbon (fuels treatment plus wildfireemission) removed from treated sites was 119% of the carbon emitted from the untreated/burned sites. However, with only 3% tree survival following wildfire, untreatedforests averaged only 7.8 Mg C ha-1 in live trees with an average quadratic mean tree diameter of 21 cm. In contrast, treatedforest averaged 100.5 Mg C ha-1 with a live tree quadratic mean diameter of 44 cm. In untreatedforests 70% of the remaining total ecosystem carbon shifted to decomposing stocks after the wildfire, compared to 19% in the fuels-treatedforest. In wildfire burned forest, fuels treatments have a higher immediate carbon ‘cost’, but in the long-term may benefit from lower decomposition emissions and highercarbon storage.

Forest ecosystems are an integral component of the global carbon cycle as they take up and release large amounts of C over short time periods (C flux) or accumulate it over longer time periods (C stock). However, there remains uncertainty about whether and in which direction C fluxes and in particular C stocks may differ between forests of high versus low species richness. Based on a comprehensive dataset derived from field-based measurements, we tested the effect of species richness (3-20 tree species) and stand age (22-116 years) on six compartments of above- and below-ground C stocks and four components of C fluxes in subtropical forests in southeast China. Across forest stands, total C stock was 149 ± 12 Mg ha

We evaluated modified Soil-Plant-Atmosphere model`s performance to simulate the seasonal variation of net ecosystem exchange (NEE) of carbon and examined the critical controlling mechanism on carbon exchange using the model over a deciduous forest at Gwangnung in 2006. The modified Soil-Plant-Atmosphere (mSPA) model was calibrated to capture the mean NEE during the daytime (1000-1400 LST) and used to simulate gross primary productivity (GPP). Ecosystem respiration () has been estimated using an empirical formula developed at this site. The simulation results indicated that the daytime mean stomatal conductance was highly correlated with daily insolation in the summer. Low stomatal conductance in high insolation occurred on the days with low temperature rather than with high vapor pressure deficit. It suggests that the forest rarely experienced water stress in the summer of 2006. The model captured the observed bimodal seasonal variation with a mid-season depression of carbon uptake. The model estimates of annual GPP, and NEE were , , and , respectively. Compared to the observed annual NEE, the modeled estimates showed more carbon uptake by about . The uncertainty of the estimate of annual NEE in a complex terrain is discussed.

A study was conducted to determine if consideration of ecological site classification in combination with stand age would describe total ecosystem carbon (C) better than consideration of just stand age alone. The research was conducted in the 9250 ha University of Northern British Columbia/The University of British Columbia Aleza Lake Research Forest in central British Columbia. Over three field seasons (2003–2005), 38, 72, and 27 plots were established in mesic, subhygric, and hygric stands, respectively, with stand ages ranging from 5 to 350+ years. Mineral soil C stocks were significantly influenced by moisture regime, where hygric > subhygric > mesic (93, 77, and 65 t C·ha–1, respectively). Mineral soil and forest floor C stocks were not related to stand age, indicating their resilience to partial-cut and clear-cut forest harvesting systems historically implemented throughout the study area. Subhygric stands had the highest total ecosystem C stocks in the Aleza Lake Research Forest, having approximately 18% more C than mesic and hygric stands, principally due to higher mineral soil C stocks (than mesic stands) and improved C sequestration in large trees (over hygric stands). Consideration of ecological site classification in addition to stand age information improved total ecosystem C stock estimates over the use of stand age alone.

Alpine ecosystems are extremely vulnerable to climate change. To address the potential variability of the responses of alpine ecosystems to climate change, we examined daily CO2 exchange in relation to major environmental variables. A dataset was obtained from an alpine meadow on the Qinghai-Tibetan Plateau from eddy covariance measurements taken over 3 years (2002–2004). Path analysis showed that soil temperature at 5 cm depth (Ts5) had the greatest effect on daily variation in ecosystem CO2 exchange all year around, whereas photosynthetic photon flux density (PPFD) had a high direct effect on daily variation in CO2 flux during the growing season. The combined effects of temperature and light regimes on net ecosystem CO2 exchange (NEE) could be clearly categorized into three areas depending on the change in Ts5: (1) almost no NEE change irrespective of variations in light and temperature when Ts5 was below 0 °C; (2) an NEE increase (i.e. CO2 released from the ecosystem) with increasing Ts5, but little response to variation in light regime when 0 °C≤Ts5≤8 °C; and (3) an NEE decrease with increase in Ts5 and PPFD when Ts5 was approximately >8 °C. The highest daily net ecosystem CO2 uptake was observed under the conditions of daily mean Ts5 of about 15 °C and daily mean PPFD of about 50 mol m−2 day−1. The results suggested that temperature is the most critical determinant of CO2 exchange in this alpine meadow ecosystem and may play an important role in the ecosystem carbon budget under future global warming conditions.

The frequency of severe droughts is increasing in many regions around the world as a result of climate change(1-3). Droughts alter the structure and function of forests(4,5). Site- and region-specific studies suggest that large trees, which play keystone roles in forests(6) and can be disproportionately important to ecosystem carbon storage(7) and hydrology(8), exhibit greater sensitivity to drought than small trees(4,5,9,10). Here, we synthesize data on tree growth and mortality collected during 40 drought events in forests worldwide to see whether this size-dependent sensitivity to drought holds more widely. We find that droughts consistently had a more detrimental impact on the growth and mortality rates of larger trees. Moreover, drought-related mortality increased with tree size in 65% of the droughts examined, especially when community-wide mortality was high or when bark beetles were present. The more pronounced drought sensitivity of larger trees could be underpinned by greater inherent vulnerability to hydraulic stress(11-14), the higher radiation and evaporative demand experienced by exposed crowns(4,15), and the tendency for bark beetles to preferentially attack larger trees(16). We suggest that future droughts will have a more detrimental impact on the growth and mortality of larger trees, potentially exacerbating feedbacks to climate change.

Current concentrations of surface ozone in many parts of the world can reduce crop yields, impair forest growth, and change plant species composition. Predicted increases in northern hemispheric background ozone concentrations are likely to increase these impacts over the first half of this century. Ozone effects on vegetation are modified by climate and CO 2 concentrations, while ozone itself can change ecosystem carbon budgets. For these reasons, surface ozone needs to be considered as an important element of global environmental change over this century.

Comparative distribution characteristic of root system and the root system carbon stocks from three forest age of S. gordejevii in Aohan sanditificational. And three plots were set by using stratified segmentation mining method to test the root biomass and the carbon ratio in different soil assays and segment, and calculate root carbon reserves, analyzing distribution characteristics of forest root carbon stocks on different S. gordejevii in different forest ages. With the increase of soil depth, S. gordejevii root biomass presents the trend of increase first then decrease, mainly in soil of 0-100cm, which accounted for more than 80% of the total; with the increase of forest age, S. gordejevii root biomass presenting a growing trend. Root distribution of carbon stocks was in a fusiform, it increase with the increase of forest age. Results provide reference data for Sandy ecosystem carbon storage estimation.

An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux from July to October, 2003. The canopy quantum yield (alpha) of alpine meadow was calculated by the linear function between the net ecosystem carbon dioxide exchange (NEE) and the photosynthetic active radiation (PAR) under low light, and how it was influenced by the temperature was also discussed. Results showed that the canopy a decreased almost linearly with temperature, with the decrease in every 1 degrees C increase of temperature similar to those measured on leaf level of C-3 plant. At the beginning, the decrease of canopy a with temperature was 0.0005 Nmol CO2-mu mol(-1) PAR; while it increased to 0.0008 Nmol CO2.mu mol(-1) PAR in September, showing a rising trend with plant growing stages. Compared with the canopy a calculated with rectangular hyperbola function, the value in the paper was lower. However, the method advanced here has the advantages in examining the relationship between a and the key environmental factors, such as temperature.

Short- and long-term patterns of net ecosystem carbon balance (NECB) for small, relatively uniform forest stands have been examined in detail, but the same is not true for landscapes, especially those with heterogeneous disturbance histories. In this paper, we explore the effect of two contrasting types of disturbances (i.e., fire and tree harvest) on landscape level NECB by using an ecosystem process model that explicitly accounts for changes in carbon (C) stores as a function of disturbance regimes. The latter were defined by the average disturbance interval, the regularity of the disturbance interval (i.e., random, based on a Poisson frequency distribution, or regular), the amount of C removed by the disturbance (i.e., severity), and the relative abundance of stands in the landscape with unique disturbance histories. We used the model to create over 300 hypothetical landscapes, each with a different disturbance regime, by simulating up to 200 unique stand histories and averaging their total C stores. Mean NECB and its year-to-year variability was computed by calculating the difference in mean total C stores from one year to the next. Results indicated that landscape C stores were higher for random than for regular disturbance intervals, and increased as the mean disturbance interval increased and as the disturbance severity decreased. For example, C storage was reduced by 58% when the fire interval was shortened from 250 years to 100 years. Average landscape NECB was not significantly different than zero for any of the simulated landscapes. Year-to-year variability in landscape NECB, however, was related to the landscape disturbance regime; increasing with disturbance severity and frequency, and higher for random versus regular disturbance intervals. We conclude that landscape C stores of forest systems can be predicted using the concept of disturbance regimes, a result that may be a useful for adjusting estimates of C storage to broad scales that are solely based on physiological processes.

Introduction 156 Overview 156 Harmful Changes in Earth’s Climate and Carbon Fluxes 156 Failure of Emission Reduction Strategies 157 Alternative Focus on Ecosystem Carbon Sinks 157 Grassland Potential and Restorative Grazing 158 Need for Sustainable Solutions 159Role of Rangelands in Ecosystem Health 161 Soil Health and Ecosystem Function 161

We used a 72-year chronosequence to study the loss and recovery of ecosystem C pools following stand-replacing wildfire in Michigan, USA, jack pine (Pinus banksiana Lamb.) forests. We quantified the amount of C stored in aboveground plant biomass, standing dead timber, downed dead wood, surface organic soil, and mineral soil in 11 jack pine stands that had burned between 1 and 72 years previously. Total ecosystem C ranged from a low of 59 Mg C·ha–1 in the 4-year-old stand to 110 Mg C·ha–1 in the 72-year-old stand. Changes in total ecosystem C across the chronosequence conformed to theoretical predictions, in which C stocks declined initially as decomposition of dead wood and forest-floor C exceeded production by regenerating vegetation, and then increased asymptotically with the development of a new stand of jack pine. This pattern was well described by the following "gamma" function: total ecosystem C (Mg·ha–1) = 112.2 – 39.6 × age0.351 × exp(–0.053 × age01.039); mean-corrected R2 = 0.976. Using the first derivative of this parameterized gamma function, we estimated that jack pine stands function as a weak source of C to the atmosphere for only ca. 6 years following wildfire, and reach a maximum net ecosystem productivity of 1.6 Mg C·ha–1·year–1 by year 16. We attribute the rapid transition from carbon source to carbon sink in these ecosystems to two factors: (i) stand-replacing wildfires in these xeric forests leave behind little respirable substrate in surface organic horizons, and (ii) jack pine is able to rapidly reestablish following wildfires via serotinous cones. Jack pine stands remained net sinks for C across the chronosequence; however, net ecosystem productivity had declined to 0.12 C ha–1·year–1 by year 72. Carbon sequestration by mature jack pine ecosystems was driven primarily by continued growth of overstory jack pine, not by accumulation of detrital C.

The objective of this study was to dynamically simulate the response of vegetation distribution, carbon, and fire to the historical climate and to two contrasting scenarios of climate change in California. The results of the simulations for the historical climate compared favorably to independent estimates and observations, but validation of the results was complicated by the lack of land use effects in the model. The response to increasing temperatures under both scenarios was characterized by a shift in dominance from needle-leaved to broad-leaved life-forms and by increases in vegetation productivity, especially in the relatively cool and mesic regions of the state. The simulated response to changes in precipitation were complex, involving not only the effect of changes in soil moisture on vegetation productivity, but also changes in tree-grass competition mediated by fire. Summer months were warmer and persistently dry under both scenarios, so the trends in simulated fire area under both scenarios were primarily a response to changes in vegetation biomass. Total ecosystem carbon increased under both climate scenarios, but the proportions allocated to the wood and grass carbon pools differed. The results of the simulations underscore the potentially large impact of climate change on California eco- systems, and the need for further use and development of dynamic vegetation models using various ensembles of climate change scenarios.

The controversy on how to measure fine root production of forests (P) most accurately continues. We applied four different approaches to determine annual rates of P in an old-growth temperate Fagus sylvatica–Quercus petraea stand: sequential soil coring with minimum–maximum calculation, sequential coring with compartmental flow calculation, the ingrowth core method, and a recently developed root chamber method for measuring the growth of individual fine roots in situ. The results of the four destructive approaches differed by an order of magnitude and, thus, are likely to introduce large errors in estimating P. The highest annual rates of P were obtained from the sequential coring approach with compartmental flow calculation, intermediate rates by sequential coring with minimum–maximum calculation, and low ones by both the root growth chamber and ingrowth core approaches. A carbon budget for the stand was set up based on a model of annual net carbon gain by the canopy and measurements on carbon sink strength (annual leaf, branch and stem growth). The budget implied that a maximum of 27% of the net carbon gain was available for allocation to fine root growth. When compared to the carbon budget data, the sequential coring/compartmental flow approach overestimated annual fine root production substantially; whereas the ingrowth core and root growth chamber approaches grossly underestimated P rates. With an overestimation of about 25% the sequential coring/minimum–maximum approach demonstrated the best agreement with the carbon budget data. It is concluded that the most reliable estimate of P in this temperate forest will be obtained by applying the sequential coring/minimum–maximum approach, conducted with a large number of replicate samples taken on a few dates per season, in conjunction with direct root growth observation by minirhizotrons.

Ecosystem carbon (C) uptake in terrestrial ecosystems has increased over the past five decades, but with large interannual variability (IAV). However, we are not clear on the attribution and the processes that control the long-term trend and IAV of land C uptake. Using atmospheric inversion net ecosystem exchange (NEE) data, we quantified the trend and IAV of NEE across the globe, the Northern Hemisphere (NH), and the Southern Hemisphere (SH), and decomposed NEE into carbon uptake amplitude and duration during each year from 1979–2013. We found the NH rather than the SH determined the IAV, while both hemispheres contributed equivalently to the global NEE trend. Different ecosystems in the NH and SH had differential relative contributions to their trend and IAV. The long-term trends of increased C uptake across the globe and the SH were attributed to both extended duration and increasing amplitude of C uptake. The shortened duration of uptake in the NH partly offsets the effects of increased NEE amplitude, making the net C uptake trend the same as that of the SH. The change in NEE IAV was also linked to changes in the amplitude and duration of uptake, but they worked in different ways in the NH, SH and globe. The fundamental attributions of amplitude and duration of C uptake revealed in this study are helpful to better understand the mechanisms underlying the trend and IAV of land C uptake. Our findings also suggest the critical roles of grassland and croplands in the NH in contributing to the trend and IAV of land C uptake.

The impacts of historical droughts and heat-waves on ecosystems are often considered indicative of future global warming impacts, under the assumption that water stress sets in above a fixed high temperature threshold. Historical and future (RCP8.5) Earth system model (ESM) climate projections were analyzed in this study to illustrate changes in the temperatures for onset of water stress under global warming. The ESMs examined here predict sharp declines in gross primary production (GPP) at warm temperature extremes in historical climates, similar to the observed correlations between GPP and temperature during historical heat-waves and droughts. However, soil moisture increases at the warm end of the temperature range, and the temperature at which soil moisture declines with temperature shifts to a higher temperature. The temperature for onset of water stress thus increases under global warming and is associated with a shift in the temperature for maximum GPP to warmer temperatures. Despite the shift in this local temperature optimum, the impacts of warm extremes on GPP are approximately invariant when extremes are defined relative to the optimal temperature within each climate period. The GPP sensitivity to these relative temperature extremes therefore remains similar between future and present climates, suggesting that the heat- and drought-induced GPP reductions seen recently can be expected to be similar in the future, and may be underestimates of future impacts given model projections of increased frequency and persistence of heat-waves and droughts. The local temperature optimum can be understood as the temperature at which the combination of water stress and light limitations is minimized, and this concept gives insights into how GPP responds to climate extremes in both historical and future climate periods. Both cold (temperature and light-limited) and warm (water-limited) relative temperature extremes become more persistent in future climate projections, and the time taken to return to locally optimal climates for GPP following climate extremes increases by more than 25% over many land regions.

The northern terrestrial net ecosystem carbon balance (NECB) is contingent on inputs from vegetation gross primary productivity (GPP) to offset the ecosystem respiration (Reco) of carbon dioxide (CO2) and methane (CH4) emissions, but an effective framework to monitor the regional Arctic NECB is lacking. We modified a terrestrial carbon flux (TCF) model developed for satellite remote sensing applications to evaluate wetland CO2 and CH4 fluxes over pan-Arctic eddy covariance (EC) flux tower sites. The TCF model estimates GPP, CO2 and CH4 emissions using in situ or remote sensing and reanalysis-based climate data as inputs. The TCF model simulations using in situ data explained > 70% of the r2 variability in the 8 day cumulative EC measured fluxes. Model simulations using coarser satellite (MODIS) and reanalysis (MERRA) records accounted for approximately 69% and 75% of the respective r2 variability in the tower CO2 and CH4 records, with corresponding RMSE uncertainties of &leq; 1.3 g C m−2 d−1 (CO2) and 18.2 mg C m−2 d−1 (CH4). Although the estimated annual CH4 emissions were small (< 18 g C m−2 yr−1) relative to Reco (> 180 g C m−2 yr−1), they reduced the across-site NECB by 23% and contributed to a global warming potential of approximately 165 ± 128 g CO2eq m−2 yr−1 when considered over a 100 year time span. This model evaluation indicates a strong potential for using the TCF model approach to document landscape-scale variability in CO2 and CH4 fluxes, and to estimate the NECB for northern peatland and tundra ecosystems.

International audience; Feedbacks between the terrestrial carbon cycle and climate change could affect many ecosystem functions and services, such as food production, carbon sequestration and climate regulation. The rate of climate warming varies on diurnal and seasonal timescales. A synthesis of global air temperature data reveals a greater rate of warming in winter than in summer in northern mid and high latitudes, and the inverse pattern in some tropical regions. The data also reveal a decline in the diurnal temperature range over 51% of the global land area and an increase over only 13%, because night-time temperatures in most locations have risen faster than daytime temperatures. Analyses of satellite data, model simulations and in situ observations suggest that the impact of seasonal warming varies between regions. For example, spring warming has largely stimulated ecosystem productivity at latitudes between 30° and 90° N, but suppressed productivity in other regions. Contrasting impacts of day- and night-time warming on plant carbon gain and loss are apparent in many regions. We argue that ascertaining the effects of non-uniform climate warming on terrestrial ecosystems is a key challenge in carbon cycle research.

Background Trends in Alaska ecosystem carbon fluxes were predicted from inputs of monthly MODerate resolution Imaging Spectroradiometer (MODIS) vegetation index time-series combined with the NASA-CASA (Carnegie Ames Stanford Approach) carbon cycle simulation model over the past decade. CASA simulates monthly net ecosystem production (NEP) as the difference in carbon fluxes between net primary production (NPP) and soil microbial respiration (Rh). Results Model results showed that NEP on a unit area basis was estimated to be highest (> +10 g C m-2 yr-1) on average over the period 2000 to 2010 within the Major Land Resource Areas (MRLAs) of the Interior Brooks Range Mountains, the Arctic Foothills, and the Western Brooks Range Mountains. The lowest (as negative land C source fluxes) mean NEP fluxes were predicted for the MLRAs of the Cook Inlet Lowlands, the Ahklun Mountains, and Bristol Bay-Northern Alaska Peninsula Lowlands. High levels of interannual variation in NEP were predicted for most MLRAs of Alaska. Conclusions The relatively warm and wet years of 2004 and 2007 resulted in the highest positive NEP flux totals across MLRAs in the northern and western coastal locations in the state (i.e., the Brooks Range Mountains and Arctic Foothills). The relatively cold and dry years of 2001 and 2006 were predicted with the lowest (negative) NEP flux totals for these MLRAs, and likewise across the Ahklun Mountains and the Yukon-Kuskokwim Highlands.

The terrestrial biosphere is a key component of the global carbon cycle and its carbon balance is strongly influenced by climate. Continuing environmental changes are thought to increase global terrestrial carbon uptake. But evidence is mounting that climate extremes such as droughts or storms can lead to a decrease in regional ecosystem carbon stocks and therefore have the potential to negate an expected increase in terrestrial carbon uptake. Here we explore the mechanisms and impacts of climate extremes on the terrestrial carbon cycle, and propose a pathway to improve our understanding of present and future impacts of climate extremes on the terrestrial carbon budget.

The legends for Figures 2 and 3 were incorrectly switched. The legend that appears with Figure 2 should be with Figure 3 and the legend that appears with Figure 3 should be with Figure 2. The figures themselves are in correct order.

Satellite remote sensing was combined with the NASA-CASA (Carnegie Ames Stanford Approach) carbon cycle simulation model to evaluate the impact of the 2010 drought throughout China. Results indicated that net primary production (NPP) for 2010 declined most notably in the provinces of Xinjiang, Hebei, and Zhejiang, predominantly in cropland and mixed forest areas. Annual NPP in the most drought-impacted areas of southwestern China declined by an average of 13% compared to the previous 10-year average. The greatest decline in total ecosystem carbon gain during 2010 (compared to 2000 to 2009) was detected in the provinces of Yunnan (-28.1 Tg C), Tibet (-18.8 Tg C), and Guizhou, (-6.3 Tg C) predominantly in cropland, grassland, and mixed forest areas. Despite these drought impacts over the southwest and northern regions, the CASA model estimated that China gained total ecosystem carbon in 2010 at double the mean annual rate (computed for the period 2000 to 2009). Cropland and forest areas of Heilongjiang and Inner Mongolia remained productive in 2010 and these regions were estimated, along with several other provinces, to offset and exceed declines in plant production and total ecosystem carbon losses in the most drought-impacted areas of Tibet, Guizhou, Yunnan, Xinjiang, and Zhejiang provinces.

Research involves analysis and field direction of AmeriFlux operations, and the PI provides scientific leadership of the AmeriFlux network. Activities include the coordination and quality assurance of measurements across AmeriFlux network sites, synthesis of results across the network, organizing and supporting the annual Science Team Meeting, and communicating AmeriFlux results to the scientific community and other users. Objectives of measurement research include (i) coordination of flux and biometric measurement protocols (ii) timely data delivery to the Carbon Dioxide Information and Analysis Center (CDIAC); and (iii) assurance of data quality of flux and ecosystem measurements contributed by AmeriFlux sites. Objectives of integration and synthesis activities include (i) integration of site data into network-wide synthesis products; and (ii) participation in the analysis, modeling and interpretation of network data products. Communications objectives include (i) organizing an annual meeting of AmeriFlux investigators for reporting annual flux measurements and exchanging scientific information on ecosystem carbon budgets; (ii) developing focused topics for analysis and publication; and (iii) developing data reporting protocols in support of AmeriFlux network goals.

Disturbances have been recognized as a key factor shaping terrestrial ecosystem states and dynamics. A general model that quantitatively describes the relationship between carbon storage and disturbance regime is critical for better understanding large scale terrestrial ecosystem carbon dynamics. We developed a model (REGIME) to quantify ecosystem carbon storage capacities (E[x]) under varying disturbance regimes with an analytical solution E[x] = U {center_dot} {tau}{sub E} {center_dot} {lambda}{lambda} + s {tau} 1, where U is ecosystem carbon influx, {tau}{sub E} is ecosystem carbon residence time, and {tau}{sub 1} is the residence time of the carbon pool affected by disturbances (biomass pool in this study). The disturbance regime is characterized by the mean disturbance interval ({lambda}) and the mean disturbance severity (s). It is a Michaelis-Menten-type equation illustrating the saturation of carbon content with mean disturbance interval. This model analytically integrates the deterministic ecosystem carbon processes with stochastic disturbance events to reveal a general pattern of terrestrial carbon dynamics at large scales. The model allows us to get a sense of the sensitivity of ecosystems to future environmental changes just by a few calculations. According to the REGIME model, for example, approximately 1.8 Pg C will be lost in the high-latitude regionsmore » of North America (>45{sup o} N) if fire disturbance intensity increases around 5.7 time the current intensity to the end of the twenty-first century, which will require around 12% increases in net primary productivity (NPP) to maintain stable carbon stocks. If the residence time decreased 10% at the same time additional 12.5% increases in NPP are required to keep current C stocks. The REGIME model also lays the foundation for analytically modeling the interactions between deterministic biogeochemical processes and stochastic disturbance events.« less

[1] In temperate regions, the budburst date of deciduous trees is mainly regulated by temperature variation, but the exact nature of the temperature dependence has been a matter of debate. One hypothesis is that budburst date depends purely on the accumulation of warm temperature; a competing hypothesis states that exposure to cold temperatures is also important for budburst. In this study, variability in budburst is evaluated using 15 years of budburst data for 17 tree species at Harvard Forest. We compare two budburst hypotheses through reversible jump Markov chain Monte Carlo. We then investigate how uncertainties in budburst date mapped onto uncertainties in ecosystem carbon using the Geophysical Fluid Dynamics Laboratory's LM3 land model. For 15 of 17 species, we find that more complicated budburst models that account for a chilling period are favored over simpler models that do not include such dependence. LM3 simulations show that the choice of budburst model induces differences in the timing of carbon uptake commencement of ∼11 days, in the magnitude of April–May carbon uptake of ∼1.03 g C m−2 day−1, and in total ecosystem carbon stocks of ∼2 kg C m−2. While the choice of whether to include a chilling period in the budburst model strongly contributes to this variability, another important factor is how the species-dependent field data gets mapped onto LM3's single deciduous plant functional type (PFT). We conclude budburst timing has a strong impact on simulated CO2 fluxes, and uncertainty in the fluxes can be substantially reduced by improving the model's representation of PFT diversity.

Chapitre 13; In this chapter we first provide a historic overview of – and outline some of the peculiarities associated with – grassland eddy covariance flux measurements, elaborate on the additional terms that need to be quantified when estimating the grassland net ecosystem carbon balance and finally discuss some of the challenges associated with upcoming nitrous oxide and methane flux measurements in managed grasslands.

Evidence is mounting to suggest that the transfer of carbon through roots of plants to the soil plays a primary role in regulating ecosystem responses to climate change and its mitigation. Future research is needed to improve understanding of the mechanisms involved in this phenomenon, its consequences for ecosystem carbon cycling, and the potential to exploit plant root traits and soil microbial processes that favor soil carbon sequestration.

The greater increase in daily minimum temperature than daily maximum temperature has been widely observed at global scale. A growing body of evidence suggests that this asymmetrically diurnal warming has great impacts on aboveground ecological processes. However, little is known about the effect of the asymmetrically diurnal warming on belowground biotic organisms. This study was conducted as part of a field manipulative experiment with day (6:00 a.m.–6:00 p.m.), night (6:00 p.m.–6:00 a.m.) and diurnal warming (24 h) in a temperate steppe, to assess shifts in soil microbial community composition and physiology in response to asymmetrically diurnal warming. Our results show that contrasting hydro-thermal conditions of the two experimental years (2006–2007) reshaped microbial community structure and modified C use patterns in the grassland ecosystem. Consistent with our hypothesis, day and night warming had different effects on some specific microbial groups and microbial C utilization potential. Significant reductions in the relative proportion of total bacteria, gram-positive bacteria and arbuscular mycorrhizal fungi and microbial C utilization potential, were observed under conditions of night warming only. The close association of microbial C utilization patterns with ecosystem C exchange and coupled responses of plant and microbe to night warming highlight physiological continuity in plant–microbe–soil system.

Recent studies of carbonate ecosystems suggest a possible contribution of subterranean ventilation to the net ecosystem carbon balance. However, both the overall importance of such CO2 exchange processes and their drivers remain unknown. Here we analyze several dry-season episodes of net CO2 emissions to the atmosphere, along with soil and borehole CO2 measurements. Results highlight important events where rapid decreases of underground CO2 molar fractions correlate well with sizeable CO2 release to the atmosphere. Such events, with high friction velocities, are attributed to ventilation processes, and should be accounted for by predictive models of surface CO2 exchange., This research was funded by the Andalusian regional government projects GEOCARBO (P08‐RNM‐3721) and GLOCHARID, including European Union ERDF funds, with support from European Community’s Seventh Framework Programme (FP7/2007‐2013) under grant agreement 244122 and Spanish Ministry of Science and Innovation projects PROBASE (CGL2006‐11619/HID) and (Carbored‐II; CGL2010‐22193‐C04‐02).

Increasing temperatures are expected to increase decomposition rates in soils, potentially reducing ecosystem carbon storage. Research now indicates that — in a tropical montane forest — soil carbon stocks are unaffected by higher temperatures despite substantially increased rates of CO2 release from the soil.

Climate-herbivory interactions have been largely debated vis-a-vis ecosystem carbon sequestration. However, invertebrate herbivores also modify emissions of plant biogenic volatile organic compounds (BVOCs). Over the shorter term, they do this by the induction of de novo synthesis of a plethora of compounds; but invertebrates also affect the relative proportions of constitutively BVOCs-emitting plants. Thus, invertebrate-BVOCs interactions have potentially important implications for air quality and climate. Insect outbreaks are expected to increase with warmer climate, but quantitative understanding of BVOCs-invertebrate ecology, climate connections and atmospheric feedback remain as yet elusive. Examination of these interactions requires a description of outbreaks in ecosystem models, combined with quantitative observations on leaf and ecosystem level. We review here recent advances and propose a strategy for inclusion of invertebrate-BVOCs relationships in terrestrial ecosystem models.

Seloste vaitoskirjasta: Fen ecosystem carbon gas dynamics in changing hydrological conditions. Dissertationes Forestales 67.

International audience; This study examined the use of satellite sensor imagery for chronosequential assessment of land use and ecosystem carbon stock in slash-and-burn (S/B) regions of Laos. The segmentation approach was useful because the boundaries of S/B patches are subject to change due to natural or anthropogenic factors. Polygon-based classification using six optical bands of Landsat Enhanced Thematic Mapper Plus (ETM+) imagery showed that S/B patches could be discriminated with high accuracy (0.98). Normalized difference spectral indices, NDSI[i, j] = [Rj -Ri ]/[Rj +Ri ], using reflectances Rj and Ri at j and i nm wavelengths for S/B polygons during four consecutive years (1999-2002) showed that NDSI[2215, 830], NDSI[1650, 830] and NDSI[660, 830] ( = the normalized difference vegetation index, NDVI) values decreased significantly in S/B years compared to those under fallow conditions (by 0.21±0.04, 0.20±0.04 and 0.17±0.03, respectively). Only slight differences were found before and after the S/B year, regardless of fallow length or biomass estimated by the allometry method. Relating reflectance signatures directly to fallow biomass was unsuitable, but these NDSIs were also useful for distinguishing S/B patches. Land-use history, including the community age of fallow vegetation, can be traced on a pixel basis using a superimposed set of segmented classified images.

The future of the carbon cycle is one of the great uncertainties in projecting thefuture of climate. The response of terrestrial ecosystems remains largely un-known, and qualitative disagreement persists regarding the influence of climatechange on ecosystem carbon storage. There has been a sustained effort to un-derstand how ecosystems respond to climate and carbon dioxide (Prentice et al.2001) using observations, experiments, models, and the paleorecord. Despitethis massive research effort, and considerable effort to synthesize its results,considerable uncertainty remains. We do not have a clear paradigm for inter-preting observations of ecosystem climate responses in time and space and fortranslating that paradigm into predictive models. Many of the disagreementsoccur because it is difficult to separate the effects of processes operating ondifferent timescales. For example, low cloud cover, high solar radiation, andconsequent high temperatures may increase photosynthesis (A) in the short term.On slightly longer timescales, these conditions may favor allocation of newphotosynthate to roots, reducing leaf area relative to a cooler year. The

Atmospheric and ground-based methods agree on the presence of a carbon sink in the coterminous United States (the United States minus Alaska and Hawaii), and the primary causes for the sink recently have been identified. Projecting the future behavior of the sink is necessary for projecting future net emissions. Here we use two models, the Ecosystem Demography model and a second simpler empirically based model (Miami Land Use History), to estimate the spatio-temporal patterns of ecosystem carbon stocks and fluxes resulting from land-use changes and fire suppression from 1700 to 2100. Our results are compared with other historical reconstructions of ecosystem carbon fluxes and to a detailed carbon budget for the 1980s. Our projections indicate that the ecosystem recovery processes that are primarily responsible for the contemporary U.S. carbon sink will slow over the next century, resulting in a significant reduction of the sink. The projected rate of decrease depends strongly on scenarios of future land use and the long-term effectiveness of fire suppression.

MUCH of the carbon assimilated by plants is allocated to fine root production1–5, and the amount of carbon and nutrients subsequently returned to the soil from fine root turnover equals or surpasses that returned through leaf litter in many forests6–9. Unfortunately, limitations in traditional methods of studying roots have prevented us from thoroughly understanding the dynamic nature of fine root mortality in most forests, and better measurements of fine root longevity are needed to quantify and model more accurately ecosystem carbon and nutrient budgets8–11. We used minirhizotrons12,13 to follow the mortality of contemporaneous fine root cohorts in two sugar maple (Acer saccharum Marsh.) forests located 80 km apart (north–south) during 1989 and 1990. We report here that roots in the northern forest consistently lived the longest, principally owing to greater rates of mortality early in the life of roots at the southern site. Differences in site factors suggest that warmer soil temperatures seem to be associated with the more rapid death of roots at the southern site.

Rising levels of atmospheric CO 2 may change root production, root turnover and ecosystem carbon balance. In order to quantify these possible alterations over longer time period and at an ecosystem level a novel technique of air CO 2 enrichment was applied to a plantation of three fast growing Populus species. Root production and turnover were measured both by auger and ingrowth coring methods. In two years of this experiment, both methods applied show increased production of fine and coarse roots under elevated CO 2 conditions for all three clones utilised. These results suggest that future levels of atmospheric CO 2 will have to be taken into account when constructing a carbon budget of an ecosystem.