Seasonal pattern of regional carbon balance in the central Rocky Mountains from surface and airborne measurements

[1] High-elevation forests represent a large fraction of potential carbon uptake in North America, but this uptake is not well constrained by observations. Additionally, forests in the Rocky Mountains have recently been severely damaged by drought, fire, and insect outbreaks, which have been quantified at local scales but not assessed in terms of carbon uptake at regional scales. The Airborne Carbon in the Mountains Experiment was carried out in 2007 partly to assess carbon uptake in western U.S. mountain ecosystems. The magnitude and seasonal change of carbon uptake were quantified by (1) paired upwind-downwind airborne CO2 observations applied in a boundary layer budget, (2) a spatially explicit ecosystem model constrained using remote sensing and flux tower observations, and (3) a downscaled global tracer transport inversion. Top-down approaches had mean carbon uptake equivalent to flux tower observations at a subalpine forest, while the ecosystem model showed less. The techniques disagreed on temporal evolution. Regional carbon uptake was greatest in the early summer immediately following snowmelt and tended to lessen as the region experienced dry summer conditions. This reduction was more pronounced in the airborne budget and inversion than in flux tower or upscaling, possibly related to lower snow water availability in forests sampled by the aircraft, which were lower in elevation than the tower site. Changes in vegetative greenness associated with insect outbreaks were detected using satellite reflectance observations, but impacts on regional carbon cycling were unclear, highlighting the need to better quantify this emerging disturbance effect on montane forest carbon cycling.

[1]  J. Randerson,et al.  An atmospheric perspective on North American carbon dioxide exchange: CarbonTracker , 2007, Proceedings of the National Academy of Sciences.

[2]  K. Davis,et al.  Regional carbon dioxide fluxes from mixing ratio data , 2004 .

[3]  Estimates of regional surface carbon dioxide exchange and carbon and oxygen isotope discrimination during photosynthesis from concentration profiles in the atmospheric boundary layer , 2002 .

[4]  W. J. Steenburgh,et al.  A Climatological Study of Thermally Driven Wind Systems of the U.S. Intermountain West. , 2002 .

[5]  E. Cook,et al.  Long-Term Aridity Changes in the Western United States , 2004, Science.

[6]  S. Running,et al.  Numerical Terradynamic Simulation Group 7-2010 Simulations show decreasing carbon stocks and potential for carbon emissions in Rocky Mountain forests over the next century , 2018 .

[7]  Dusanka Zupanski,et al.  An ensemble data assimilation system to estimate CO2 surface fluxes from atmospheric trace gas observations , 2005 .

[8]  B. Santer,et al.  Human-Induced Changes in the Hydrology of the Western United States , 2008, Science.

[9]  T. A. Black,et al.  A model‐data intercomparison of CO2 exchange across North America: Results from the North American Carbon Program site synthesis , 2010 .

[10]  Larry Mahrt,et al.  Flux Sampling Errors for Aircraft and Towers , 1998 .

[11]  John C. Lin,et al.  A near-field tool for simulating the upstream influence of atmospheric observations: The Stochastic Time-Inverted Lagrangian Transport (STILT) model , 2003 .

[12]  Daniel M. Ricciuto,et al.  Estimates of net CO2 flux by application of equilibrium boundary layer concepts to CO2 and water vapor measurements from a tall tower , 2004 .

[13]  S. Running,et al.  Global products of vegetation leaf area and fraction absorbed PAR from year one of MODIS data , 2002 .

[14]  Steven W. Running,et al.  Ecosystem Disturbance, Carbon, and Climate , 2008, Science.

[15]  Y. Goto,et al.  Characteristics of CO2 flux over a forest on complex topography , 2003 .

[16]  A. Betts,et al.  Coupling between CO2, water vapor, temperature, and radon and their fluxes in an idealized equilibrium boundary layer over land , 2004 .

[17]  Eddy Moors,et al.  Diurnal and vertical variability of the sensible heat and carbon dioxide budgets in the atmospheric surface layer , 2008 .

[18]  David D. Parrish,et al.  NORTH AMERICAN REGIONAL REANALYSIS , 2006 .

[19]  S. Running,et al.  Carbon sequestration studied in western U.S. mountains , 2002 .

[20]  D. Lenschow,et al.  A Multiscale and Multidisciplinary Investigation Of Ecosystem–Atmosphere CO2 Exchange Over the Rocky Mountains of Colorado , 2010 .

[21]  W. Kurz,et al.  Mountain pine beetle and forest carbon feedback to climate change , 2008, Nature.

[22]  R. Monson,et al.  The contribution of beneath‐snow soil respiration to total ecosystem respiration in a high‐elevation, subalpine forest , 2006 .

[23]  Maosheng Zhao,et al.  Drought-Induced Reduction in Global Terrestrial Net Primary Production from 2000 Through 2009 , 2010, Science.

[24]  N. Metropolis,et al.  The Monte Carlo method. , 1949 .

[25]  A. Stohl,et al.  Validation of the lagrangian particle dispersion model FLEXPART against large-scale tracer experiment data , 1998 .

[26]  A. Holtslag,et al.  Regional carbon dioxide and energy fluxes from airborne observations using flight-path segmentation based on landscape characteristics , 2009 .

[27]  Beniamino Gioli,et al.  The CarboEurope regional experiment strategy , 2006 .

[28]  D. R. Bowling,et al.  Integration of Process-based Soil Respiration Models with Whole-Ecosystem CO2 Measurements , 2008, Ecosystems.

[29]  Russell K. Monson,et al.  Coupling between carbon cycling and climate in a high-elevation, subalpine forest: a model-data fusion analysis , 2007, Oecologia.

[30]  R. Monson,et al.  Longer growing seasons lead to less carbon sequestration by a subalpine forest , 2010 .

[31]  C. Sweeney,et al.  Interactive comment on “ Assessing filtering of mountaintop CO 2 mixing ratios for application to inverse models of biosphere-atmosphere carbon exchange ” , 2011 .

[32]  Ernst Linder,et al.  Estimating diurnal to annual ecosystem parameters by synthesis of a carbon flux model with eddy covariance net ecosystem exchange observations , 2005 .

[33]  Richard A. Birdsey,et al.  Tree age, disturbance history, and carbon stocks and fluxes in subalpine Rocky Mountain forests , 2008 .

[34]  R. Monson,et al.  Model‐data synthesis of diurnal and seasonal CO2 fluxes at Niwot Ridge, Colorado , 2006 .

[35]  M. Reichstein,et al.  Net regional ecosystem CO2 exchange from airborne and ground‐based eddy covariance, land‐use maps and weather observations , 2007 .

[36]  Regional carbon dioxide fluxes from mixing ratio data , 2004 .

[37]  R. Monson,et al.  Carbon sequestration in a high‐elevation, subalpine forest , 2001 .

[38]  S. Wofsy,et al.  The CO2 Budget and Rectification Airborne Study: Strategies for Measuring Rectifiers and Regional Fluxes , 2013 .

[39]  Mathias Disney,et al.  Impact of land cover uncertainties on estimates of biospheric carbon fluxes , 2008 .

[40]  C. Tucker,et al.  Increased plant growth in the northern high latitudes from 1981 to 1991 , 1997, Nature.

[41]  J. Aber,et al.  A generalized, lumped-parameter model of photosynthesis, evapotranspiration and net primary production in temperate and boreal forest ecosystems , 1992, Oecologia.

[42]  William K. M. Ahue.  Regional Carbon Fluxes and Boundary Layer Heights from the Airborne Carbon in the Mountains Experiment 2007 , 2010 .

[43]  D. Schimel,et al.  The Role of Mid-latitude Mountains in the Carbon Cycle: Global Perspective and a Western US Case Study , 2005 .

[44]  P. Blanken,et al.  A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado , 2009 .

[45]  Alfredo Huete,et al.  Terrestrial Carbon Sinks for the United States Predicted from MODIS Satellite Data and Ecosystem Modeling , 2006 .

[46]  J. William Munger,et al.  Exchange of Carbon Dioxide by a Deciduous Forest: Response to Interannual Climate Variability , 1996, Science.

[47]  Philippe Ciais,et al.  Weak Northern and Strong Tropical Land Carbon Uptake from Vertical Profiles of Atmospheric CO2 , 2007, Science.

[48]  G. Bonan.  Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests , 2008, Science.

[49]  Christoph Gerbig,et al.  What can tracer observations in the continental boundary layer tell us about surface-atmosphere fluxes? , 2005 .

[50]  R. Monson,et al.  Estimating transpiration and the sensitivity of carbon uptake to water availability in a subalpine forest using a simple ecosystem process model informed by measured net CO2 and H2O fluxes , 2008 .

[51]  Natascha Kljun,et al.  Climatic controls on the carbon and water balances of a boreal aspen forest, 1994–2003 , 2007 .

[52]  A. Taylor,et al.  Widespread Increase of Tree Mortality Rates in the Western United States , 2009, Science.

[53]  Darrel L. Williams,et al.  BOREAS in 1997: Experiment overview, scientific results, and future directions , 1997 .

[54]  John C. Lin,et al.  Estimating regional carbon exchange in New England and Quebec by combining atmospheric, ground-based and satellite data , 2006 .

[55]  M. Raupach,et al.  Boundary layer budgets for regional estimates of scalar fluxes , 1996 .

[56]  R. Monson,et al.  The contribution of advective fluxes to net ecosystem exchange in a high-elevation, subalpine forest. , 2008, Ecological applications : a publication of the Ecological Society of America.

[57]  J. Berry,et al.  Climatic controls of interannual variability in regional carbon fluxes from top‐down and bottom‐up perspectives , 2010 .

[58]  B. Stephens,et al.  A preliminary investigation of boundary layer effects on daytime atmospheric CO2 concentrations at a mountaintop location in the Rocky Mountains , 2009 .

[59]  Xiangming Xiao,et al.  Spatial analysis of growing season length control over net ecosystem exchange , 2005 .

[60]  D. Baldocchi.  ‘Breathing’ of the terrestrial biosphere: lessons learned from a global network of carbon dioxide flux measurement systems , 2008 .

[61]  B O B B,et al.  Estimating diurnal to annual ecosystem parameters by synthesis of a carbon flux model with eddy covariance net ecosystem exchange observations , 2005 .

[62]  Ankur R. Desai,et al.  Climatic and phenological controls on coherent regional interannual variability of carbon dioxide flux in a heterogeneous landscape , 2010 .

[63]  Bruce K. Wylie,et al.  Integration of CO 2 flux and remotely-sensed data for primary production and ecosystem respiration analyses in the Northern Great Plains: potential for quantitative spatial extrapolation , 2005 .

[64]  J. Hicke,et al.  Cross-scale Drivers of Natural Disturbances Prone to Anthropogenic Amplification: The Dynamics of Bark Beetle Eruptions , 2008 .

[65]  Eric A. Davidson,et al.  Spatial and temporal variability in forest–atmosphere CO2 exchange , 2004 .

[66]  John C. Lin,et al.  ``Designing Lagrangian experiments to measure regional-scale trace gas fluxes'' , 2007 .

[67]  J. Aber,et al.  Forest biogeochemistry and primary production altered by nitrogen saturation , 1995 .