-
X. Lee,
M.L. Goulden,
D.Y. Hollinger,
A. Barr,
T.A. Black,
G. Bohrer,
R. Bracho,
B. Drake,
A. Goldstein,
L. Gu, [......],
T. Meyers,
R. Monson,
W. Munger,
R. Oren,
K.T. Paw U,
A.D. RIchardson, H.P. Schmid,
R. Staebler,
S. Wofsy,
L. Zhao
Nature 02/2013; 479:384-387. · 36.28 Impact Factor
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D. Y. HOLLINGER,
S. V. OLLINGER,
A. D. RICHARDSON,
T. P. MEYERS,
D. B. DAIL,
M. E. MARTIN,
N. A. SCOTT,
T. J. ARKEBAUER,
D. D. BALDOCCHI,
K. L. CLARK, [......],
D. DRAGONI,
M. L. GOULDEN,
L. GU,
G. G. KATUL,
S. G. PALLARDY,
K. T. PAW U, H. P. SCHMID,
P. C. STOY,
A. E. SUYKER,
S. B. VERMA
[show abstract]
[hide abstract]
ABSTRACT: Vegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site-years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two-stream albedo submodel provided accurate predictions of boreal needle-leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two-stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r2=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r2=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two-stream albedo model and foliage nitrogen concentration. These nitrogen-based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.
Global Change Biology 01/2010; 16(2):696 - 710. · 6.86 Impact Factor
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J. Xiao,
Q. Zhuang,
B.E. Law,
J. Chen,
D.D. Baldocchi,
D.R. Cook,
R. Oren,
A.D. Richardson,
S. Wharton,
S. Ma, [......],
S.G. McNulty,
T.P. Meyers,
J.W. Munger,
A. Noormets,
W.C. Oechel,
K.T. Paw U, H.P. Schmid,
G. Starr,
M.S. Torn,
S.C. Wofsy
Remote Sensing of Environment 01/2010; 114�
�:576-591. · 4.57 Impact Factor
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D. Y. Hollinger,
S. V. Ollinger,
A. D. Richardson,
T. P. Meyers,
D. B. Dail,
M. E. Martin,
N. A. Scott,
T. J. Arkebauer,
D. D. Baldocchi,
K. L. Clark, [......],
D. Dragoni,
M. L. Goulden,
L. Gu,
G. G. Katul,
S. G. Pallardy,
K. T. Paw, H. P. Schmid,
P. C. Stoy,
A. E. Suyker,
S. B. Verma
[show abstract]
[hide abstract]
ABSTRACT: Vegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site-years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two-stream albedo submodel provided accurate predictions of boreal needle-leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two-stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r2=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r2=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two-stream albedo model and foliage nitrogen concentration. These nitrogen-based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.
Global Change Biology. 01/2010; 16(2):696-710.
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[show abstract]
[hide abstract]
ABSTRACT: In this study, we compare 10 years (1998-2007) of carbon budget
estimates obtained with two independent methods: the micrometeorological
approach based on eddy-covariance measurements, and the biometric method
based on carbon stock increment measurements in a mixed deciduous forest
in the Morgan-Monroe State Forest, Indiana, USA. Even though the
cumulative estimates of both methods for the ten-year period are within
1% of each other, differences between biometric estimates of net
ecosystem productivity (NEP-BM) and the corresponding eddy covariance
based estimates (NEP-EC) were large in some years (up to 100%). We focus
our analysis on the inter-annual variability in NEP and on the
differences between the two methods and what processes they represent.
We interpret our results in terms of ecosystem response to inter-annual
and seasonal meteorological variability, extreme weather events (like
late-spring or early-fall frost and intense and prolonged droughts), and
consequences for allocation to different carbon pools. This work
confirms the importance of long-term experiments in which results from
both approaches are used to reduce overall uncertainty of NEP estimates,
increase the understanding of carbon partitioning among different
compartments of the forest ecosystem, and helps to explain observed
inter-annual variability.
03/2009; 11:3315.
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S V Ollinger,
A D Richardson,
M E Martin,
D Y Hollinger,
S E Frolking,
P B Reich,
L C Plourde,
G G Katul,
J W Munger,
R Oren,
M-L Smith,
K T Paw U,
P V Bolstad,
B D Cook,
M C Day,
T A Martin,
R K Monson, H P Schmid
[show abstract]
[hide abstract]
ABSTRACT: The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth's climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO(2) uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO(2) uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle-climate models.
Proceedings of the National Academy of Sciences 01/2009; 105(49):19336-41. · 9.68 Impact Factor
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Jingfeng Xiao,
Qianlai Z,
D.D. Baldocchi,
B.E. Law,
A.D. Richardson,
J. Chen,
R. Oren,
G. Starr,
A. Noormets,
S. Ma, [......],
T.P. Meyers,
R.K. Monson,
J. W. Munger,
W.C. Oechel,
K.Tha Paw U, H. P. Schmid,
R. L. Scott,
G. Sun,
A.E. Suyker,
M.S. Torn
Agricultural and Forest Meteorology. 01/2008; 148(11):1827-1847.
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Dennis D Baldocchi,
T A Black,
P S Curtis,
E Falge,
J D Fuentes,
A Granier,
L Gu,
A Knohl,
K Pilegaard, H P Schmid,
R Valentini,
K Wilson,
S Wofsy,
L Xu,
S Yamamoto
[show abstract]
[hide abstract]
ABSTRACT: We tested the hypothesis that the date of the onset of net carbon uptake by temperate deciduous forest canopies corresponds with the time when the mean daily soil temperature equals the mean annual air temperature. The hypothesis was tested using over 30 site-years of data from 12 field sites where CO(2) exchange is being measured continuously with the eddy covariance method. The sites spanned the geographic range of Europe, North America and Asia and spanned a climate space of 16 degrees C in mean annual temperature. The tested phenology rule was robust and worked well over a 75 day range of the initiation of carbon uptake, starting as early as day 88 near Ione, California to as late as day 147 near Takayama, Japan. Overall, we observed that 64% of variance in the timing when net carbon uptake started was explained by the date when soil temperature matched the mean annual air temperature. We also observed a strong correlation between mean annual air temperature and the day that a deciduous forest starts to be a carbon sink. Consequently we are able to provide a simple phenological rule that can be implemented in regional carbon balance models and be assessed with soil and temperature outputs produced by climate and weather models.
International Journal of Bioclimatology Biometeorology 08/2005; 49(6):377-87. · 2.25 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Quantifying net carbon (C) storage by forests is a necessary step in the validation of carbon sequestration estimates and in assessing the possible role of these ecosystems in offsetting fossil fuel emissions. In eastern North America, five sites were established in deciduous forests to provide measurements of net ecosystem CO 2 exchange (NEE) using micro-meteorological methods, and measures of major carbon pools and fluxes, using a combination of forest mensurational, eco-physiological, and other biometric methods. The five study sites, part of the AmeriFlux network, ranged across 10 • of latitude and 18 • of longitude, but were all of similar age, canopy height, and stand basal area. Here we present a cross-site synthesis of annual carbon storage estimates, comparing meteorological and biometric approaches, and also comparing biometric estimates based on analyses of autotrophic carbon pools and heterotrophic carbon fluxes (net ecosystem production, NEP) versus those based on measurements of change in two major carbon pools (C). Annual above-ground net primary production (ANPP) varied nearly two-fold among sites and was strongly correlated with average annual temperature and with annual soil nitrogen mineralization (N min). Estimates of NEP ranged from 0.7 Mg C per hectare per year in northern lower Michigan to 3.5 Mg C per hectare per year in central Indiana, and were also well correlated with N min . There was less variation among sites in estimates of C (range, 1.8–3.2 Mg C per hectare per year). In general, C more closely matched NEE than did NEP, but there was no systematic pattern among sites in over-versus under-estimation of the biometric compared to the meteorologically based measures. Root and soil carbon dynamics were significant sources of uncertainty in our biometric measures and represent a prerequisite area of study needed for accurate estimates of forest carbon storage.
Agricultural and Forest Meteorology 01/2002; 113:3-19. · 3.39 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Quantifying net carbon (C) storage by forests is a necessary step in the
validation of C sequestration estimates and in assessing the possible
role of these ecosystems in offsetting fossil fuel emissions. In eastern
North America, five sites were established in deciduous forests to
provide measurements of net ecosystem CO2 exchange using
micro-meteorological methods (NEE), and measures of major C pools and
fluxes, using a combination of forest mensurational, eco-physiological,
and other biometric methods. The five study sites, part of the AmeriFlux
network, ranged across 10° of latitude and 18° of longitude, but
were all of similar age, canopy height, and stand basal area. Here we
present a cross-site synthesis of C storage estimates, comparing
meteorological and biometric approaches, and also comparing biometric
estimates based on analyses of autotrophic C pools and heterotrophic C
fluxes (net ecosystem production, NEP) versus those based on
measurements of change in two major C pools (Δ C). Annual
above-ground net primary production varied nearly two-fold among sites
and was strongly correlated with average annual temperature and with
annual soil nitrogen mineralization (Nmin). Estimates of NEP
ranged from a low of 0.3 Mg C ha-1 yr-1 in
northern Michigan to a high of 3.5 Mg C ha-1 yr-1
in central Indiana, and were also well correlated with Nmin.
There was less variation among sites in estimates of Δ C (range,
1.8 - 3.2 Mg C ha-1 yr-1). In general, Δ C
more closely matched NEE than did NEP, but there was no systematic
pattern among sites in over- versus under-estimation of the biometric
compared to the meteorologically based measures. Root and soil C
dynamics were significant sources of uncertainty in our biometric
measures and represent a prerequisite area of study needed for accurate
estimates of forest C storage.
AGU Fall Meeting Abstracts. 11/2001; -1:03.
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Dennis Baldocchi,
Eva Falge,
Lianhong Gu,
Richard Olson,
David Hollinger,
Steve Running,
Peter Anthoni,
Ch Bernhofer,
Kenneth Davis,
Robert Evans, [......],
Walt Oechel,
K T Paw,
Kim Pilegaard, H P Schmid,
Riccardo Valentini,
Shashi Verma,
Timo Vesala,
Kell Wilson,
Steve Wofsy,
F Richardson
[show abstract]
[hide abstract]
ABSTRACT: FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of car-bon dioxide, water vapor, and energy between the biosphere and atmosphere. At present over 140 sites are operating on a long-term and continuous basis. Vegetation under study includes temperate conifer and broadleaved (deciduous and evergreen) forests, tropical and boreal forests, crops, grasslands, chaparral, wetlands, and tundra. Sites exist on five con-tinents and their latitudinal distribution ranges from 70°N to 30°S. FLUXNET has several primary functions. First, it provides infrastructure for compiling, archiving, and distributing carbon, water, and energy flux measurement, and meteorological, plant, and soil data to the science community. (Data and site information are available online at the FLUXNET Web site, http://www-eosdis.ornl.gov/FLUXNET/.) Second, the project supports calibration and flux intercomparison activities. This activity ensures that data from the regional networks are intercomparable. And third, FLUXNET supports the synthesis, discussion, and communication of ideas and data by supporting project scientists, workshops, and visiting scientists. The overarching goal is to provide infor-mation for validating computations of net primary productivity, evaporation, and energy absorption that are being generated by sensors mounted on the NASA Terra satellite. Data being compiled by FLUXNET are being used to quantify and compare magnitudes and dynamics of annual ecosystem carbon and water balances, to quantify the response of stand-scale carbon dioxide and water vapor flux densities to controlling biotic and abiotic factors, and to validate a hierarchy of soil–plant–atmosphere trace gas ex-change models. Findings so far include 1) net CO 2 exchange of temperate broadleaved forests increases by about 5.7 g C m −2 day −1 for each additional day that the growing season is extended; 2) the sensitivity of net ecosystem CO 2 exchange to sunlight doubles if the sky is cloudy rather than clear; 3) the spectrum of CO 2 flux density exhibits peaks at timescales of days, weeks, and years, and a spectral gap exists at the month timescale; 4) the optimal temperature of net CO 2 exchange varies with mean summer temperature; and 5) stand age affects carbon dioxide and water vapor flux densities.
©2001 American Meteorological Society. 01/2001; 82.
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D. Baldocchi,
E. Falge,
L. H. Gu,
R. Olson,
D. Hollinger,
S. Running,
P. Anthoni,
C. Bernhofer,
K. Davis,
R. Evans, [......],
W. Munger,
W. Oechel,
K. T. Paw U,
K. Pilegaard, H. P. Schmid,
R. Valentini,
S. Verma,
T. Vesala,
K. Wilson,
S. Wofsy
Bulletin of the American Meteorological Society. 01/2001; 82(11):2415-2434.
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D. D. Baldocchi,
T A Black,
P S Curtis,
E. Falge,
J. Fuentes,
A. Granier,
L. H. Gu,
Alexander Knohl,
K. Pilegaard, H P Schmid,
R. Valentini,
K. Wilson,
S. Wofsy,
L Xu,
S. Yamamoto
International Journal of Biometeorology, v.49, 377-387 (2005).
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D. Y. Hollinger,
S.V. Ollinger,
A.D. Richardson,
T.P. Meyers,
D. B. Dail,
M.E. Martin,
N.A. Scott,
T. J. Arkebauer,
D. D. Baldocchi,
K.L. Clark, [......],
D. Dragoni,
M. L. Goulden,
L Gu,
G G Katul,
S.G. Pallard,
K. T. Paw U, H P Schmid,
P. C. Stoy,
A.E. Suyker,
S.B. Verma
[show abstract]
[hide abstract]
ABSTRACT: Vegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site-years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two-stream albedo submodel provided accurate predictions of boreal needle-leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two-stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r²=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r²=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two-stream albedo model and foliage nitrogen concentration. These nitrogen-based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.
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[show abstract]
[hide abstract]
ABSTRACT: Most satellites provide, at best, a single daily snapshot of vegetation and, at worst, these snapshots may be separated by periods of many days when the ground was obscured by cloud cover. Since vegetation carbon exchange can be very dynamic on diurnal and day-to-day timescales, the limited temporal resolution of satellite data is a potential limitation in the use of these data to estimate integrated CO2 exchange between vegetation and the atmosphere. Our objective in this study was to determine whether consistent relationships exist between midday carbon flux on clear days and daily or 8-day mean values. CO2 flux data were obtained from eight sites, covering a wide range of vegetation types, which are part of the AmeriFlux system. Midday gross CO2 exchange was highly correlated with both daily and 8-day mean gross CO2 exchange and these relationships were consistent across all the vegetation types. In addition, it did not make any difference whether the midday data were derived from the AM or PM satellite overpass times, indicating that midday depression of photosynthesis was not a significant factor in these relationships. Inclusion of cloudy days in the 8-day means also did not affect the relationships relative to single clear days. Although there was a relationship between photosynthetic rates and photosynthetically active radiation (PAR) for half hour data, this relationship tended to saturate at PAR values less than half of full sun and for many of the sites the relationship between daily total photosynthesis and PAR was very weak. Consequently, cloudy conditions had less effect on daily gross CO2 exchange than would have been expected. Conversely, the saturation of photosynthesis at moderate PAR values resulted in considerable variation in light use efficiency (LUE). LUE was higher for daily and 8-day means than it was at midday on clear days and the correlation between midday and 8-day mean LUE was relatively weak. Although these results suggest that it may not be possible to estimate 8-day mean LUE reliably from satellite data, LUE models may still be useful for estimation of midday values of gross CO2 exchange which could then be related to longer term means of CO2 exchange.
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[show abstract]
[hide abstract]
ABSTRACT: 1] We report results from the first 3 years (1999–2001) of long-term measurements of net ecosystem exchange (NEE) at an AmeriFlux site over a mixed hardwood forest in northern lower Michigan. The primary measurement methodology uses eddy covariance systems with closed-path infrared gas analyzers at two heights (46 and 34 m) above the forest (canopy height is $22 m). One objective is to contribute to a more firmly established methodology of estimating annual net ecosystem production (NEP), by systematically examining the consequences of several variations of criteria to identify periods of unreliable measurements, and to fill gaps in the data. We compared two methods to fill data gaps (about 30% of time in 1999) due to missing observations or rejected data after quality control; one using short-term ensemble averages of the daily course and the other by semiempirical parametric models based on relationships between ecosystem respiration and soil temperature and between gross ecosystem photosynthetic uptake and photosynthetically active radiation. The modeled estimates were also used to replace eddy covariance fluxes during periods of weak and/or poorly developed turbulence when eddy covariance measurements cannot be expected to represent the ecosystem exchange. Examination of the fractions of eddy covariance fluxes and storage change relative to the expected ecosystem respiration suggested a friction velocity (u *) of 0.35 m s À1 as the lower limit for the acceptance of micrometeorologically determined NEE for this site. The differences in estimated annual NEP due to different criteria of data acceptance, measurement height, or gap-filling strategies turned out to be at least as large as the interannual variations over the 3 years. After discussing various analysis strategies we conclude that the best estimate of annual NEP at our site is achieved by replacing data gaps and measurements in low-u * conditions at all times with site and period-specific parametric models, using the upper measurement level (about 2.1 canopy heights). These ''best estimates'' of annual NEP for 1999–2001 amounted to 170 (1999), 160 (2000), and 80 (2001) g C m À2 . We also discuss some problems of assigning quantitative estimates of uncertainty for annual NEP., Ecosystem-atmosphere exchange of carbon dioxide over a mixed hardwood forest in northern lower Michigan, J. Geophys. Res., 108(D14), 4417, doi:10.1029/2002JD003011, 2003.
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[show abstract]
[hide abstract]
ABSTRACT: In forest ecosystems the single largest respiratory flux influencing net ecosystem productivity (NEP) is the total soil CO 2 efflux; however, it is difficult to make measurements of this flux that are accurate at the ecosystem scale. We examined patterns of soil CO 2 efflux using five different methods: auto-chambers, portable gas analyzers, eddy covariance along and two models parameterized with the observed data. The relation between soil temperature and soil moisture with soil CO 2 effluxes are also investigated, both inter-annually and seasonally, using these observations/results. Soil respiration rates (R soil) are greatest during the growing season when soil temperatures are between 15 and 25 °C, but some soil CO 2 efflux occurs throughout the year. Measured soil respiration was sensitive to soil temperature, particularly during the spring and fall. All measurement methods produced similar annual estimates. Depending on the time of the year, the eddy covariance (flux tower) estimate for ecosystem respiration is similar to or slightly lower than estimates of annual soil CO 2 efflux from the other methods. As the eddy covariance estimate includes foliar and stem respiration which the other methods do not; it was expected to be larger (perhaps 15–30%). The auto-chamber system continuously measuring soil CO 2 efflux rates provides a level of temporal resolution that permits investigation of short-to longer term influences of factors on these efflux rates. The expense of building and maintaining an auto chamber system may not be necessary for those researchers interested in estimating R soil annually, but auto-chambers do allow the capture of data from all seasons needed for model parameterization.
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A. Noormets,
A.R. Desai,
B.D. Cook,
E.S. Euskirchen,
D.M. Ricciuto,
K.J. Davis,
P.V. Bolstad, H.P. Schmid,
C.V. Vogel,
E.V. Carey,
H.B. Su,
J. Chen
[show abstract]
[hide abstract]
ABSTRACT: Ecosystem respiration (ER) was measured with the eddy covariance technique in 14 forest ecosystems in the Upper Great Lakes Region during the growing seasons of 2002 and 2003. The response of ER to soil temperature and moisture was analyzed using empirical models. On average, ER was higher in the intermediate and young than in the mature stands, and higher in hardwood than in conifer stands. The seasonal mean temperature-normalized respiration rate (R10) ranged from 1 to 3 μmol CO2 m−2 s−1 and seasonal mean activation energy (Ea) from 40 to 110 kJ mol−1. The variation in the residuals of temperature response function of ER was best explained by soil moisture content. ER showed higher temperature sensitivity (as indicated by lower Ea) in the young than in the mature stands of coniferous forests, but not in the hardwood forests. The inclusion of soil moisture as an explicit driver of R10 explained an additional 8% (range 0–21%) of variability in ER. Significant moisture sensitivity of ER was detected in only 5 out of 20 site-years and it was associated with bimodal soil moisture distribution. Moisture sensitivity could partially be predicted from statistical moments kurtosis and interquartile range. The data implied greater moisture sensitivity with increasing stand age, possibly due to faster depletion of soil water supplies from a greater evaporative surface in the older stands. Additional limiting factors to ER were implicated.
Agricultural and Forest Meteorology.
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