Progress and opportunities for monitoring greenhouse gases fluxes in Mexican ecosystems: the MexFlux network

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Corresponding author: R. Vargas; e-mail: [email protected] Received March 15, 2012; accepted September 4, 2012 RESUMEN Para entender los procesos de los ecosistemas desde un punto de vista funcional es fundamental entender las UHODFLRQHVHQWUHODYDULDELOLGDGFOLPiWLFDORVFLFORVELRJHRTXtPLFRV\ODVLQWHUDFFLRQHVVXSHU¿FLHDWPyVIHUD (QODV~OWLPDVGpFDGDVVHKDDSOLFDGRGHPDQHUDFUHFLHQWHHOPpWRGRGHFRYDULDQ]DGHÀXMRVWXUEXOHQWRV(& SRUVXVVLJODVHQLQJOpV HQHFRVLVWHPDVWHUUHVWUHVPDULQRV\XUEDQRVSDUDPHGLUORVÀXMRVGHJDVHVGHLQYHUQDGHURSHM&22, H22 \HQHUJtDSHMFDORUVHQVLEOH\ODWHQWH (QGLYHUVDVUHJLRQHVVHKDQHVWDEOHFLGR UHGHVGHVLVWHPDV(&TXHKDQDSRUWDGRLQIRUPDFLyQFLHQWt¿FDSDUDHOGLVHxRGHSROtWLFDVDPELHQWDOHV\GH DGDSWDFLyQ(QHVWHFRQWH[WRHOSUHVHQWHWUDEDMRGHOLPLWDHOPDUFRFRQFHSWXDO\WpFQLFRSDUDHOHVWDEOHFLPLHQWR GHXQDUHGUHJLRQDOGHPHGLFLyQGHÀXMRVGHJDVHVGHHIHFWRLQYHUQDGHURHQ0p[LFRGHQRPLQDGD0H[)OX[ FX\RREMHWLYRSULQFLSDOHVPHMRUDUQXHVWUDFRPSUHQVLyQGHODIRUPDHQTXHODYDULDELOLGDGFOLPiWLFD\OD WUDQVIRUPDFLyQDPELHQWDOLQÀX\HHQODGLQiPLFDGHORVHFRVLVWHPDVPH[LFDQRVDQWHORVIDFWRUHVGHFDPELR ambiental global. En este documento se analiza primero la importancia del intercambio de CO2 y vapor de DJXDHQWUHORVHFRVLVWHPDVWHUUHVWUHV\ODDWPyVIHUD'HVSXpVVHGHVFULEHEUHYHPHQWHODWpFQLFDGHFRYDULDQ]D GHÀXMRVWXUEXOHQWRVSDUDODPHGLFLyQGHpVWRV\VHSUHVHQWDQHMHPSORVGHPHGLFLRQHVHQGRVHFRVLVWHPDV WHUUHVWUHV\XQRXUEDQRHQ0p[LFR3RU~OWLPRVHGHVFULEHQODVEDVHVFRQFHSWXDOHV\RSHUDWLYDVDFRUWR PHGLDQR\ODUJRSOD]RSDUDODFRQWLQXLGDGGHODUHG0H[)OX[

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ABSTRACT Understanding ecosystem processes from a functional point of view is essential to study relationships among climate variability, biogeochemical cycles, and surface-atmosphere interactions. Increasingly during the last GHFDGHVWKHHGG\FRYDULDQFH(& PHWKRGKDVEHHQDSSOLHGLQWHUUHVWULDOPDULQHDQGXUEDQHFRV\VWHPVWR TXDQWLI\ÀX[HVRIJUHHQKRXVHJDVHVHJ, CO2, H22 DQGHQHUJ\HJ, sensible and latent heat). Networks of (&V\VWHPVKDYHEHHQHVWDEOLVKHGLQGLIIHUHQWUHJLRQVDQGKDYHSURYLGHGVFLHQWL¿FLQIRUPDWLRQWKDWKDVEHHQ XVHGIRUGHVLJQLQJHQYLURQPHQWDODQGDGDSWDWLRQSROLFLHV,QWKLVFRQWH[WWKLVDUWLFOHRXWOLQHVWKHFRQFHSWXDO DQGWHFKQLFDOIUDPHZRUNIRUWKHHVWDEOLVKPHQWRIDQ(&UHJLRQDOQHWZRUNLH0H[)OX[ WRPHDVXUHWKH VXUIDFHDWPRVSKHUHH[FKDQJHRIKHDWDQGJUHHQKRXVHJDVHVLQ0H[LFR7KHJRDORIWKHQHWZRUNLVWRLPSURYH RXUXQGHUVWDQGLQJRIKRZFOLPDWHYDULDELOLW\DQGHQYLURQPHQWDOFKDQJHLQÀXHQFHWKHG\QDPLFVRI0H[LFDQ ecosystems. First, we discuss the relevance of CO2DQGZDWHUYDSRUH[FKDQJHEHWZHHQWHUUHVWULDOHFRV\VWHPVDQGWKHDWPRVSKHUH6HFRQGZHEULHÀ\GHVFULEHWKH(&EDVLVDQGSUHVHQWH[DPSOHVRIPHDVXUHPHQWV LQWHUUHVWULDODQGXUEDQHFRV\VWHPVRI0H[LFR)LQDOO\ZHGHVFULEHWKHFRQFHSWXDODQGRSHUDWLRQDOJRDOVDW VKRUWPHGLXPDQGORQJWHUPVFDOHVIRUFRQWLQXLW\RIWKH0H[)OX[QHWZRUN .H\ZRUGV: Environmental networks, eddy covariance, FLUXNET, greenhouse gases, long-term measurePHQWVVXUIDFHDLUH[FKDQJH

1. ,QWURGXFWLRQ Humankind faces new challenges to develop policies for the reduction, adaptation and mitigation of JOREDOHQYLURQPHQWDOFKDQJH7KHVFLHQWL¿FFRPmunity has the responsibility of providing information to enable the development of such policies and strategies. This includes the generation of knowledge about the components, processes and mechanisms by ZKLFKHFRV\VWHPVUHVSRQGWR FOLPDWHYDULDELOLW\ DQG WKHLQWHUDFWLRQDQGHIIHFWVRIJUHHQKRXVHJDVHV HJ, CO2, CH4, N2O) on global climate. From a functional standpoint, the interaction between climate variability, vegetation dynamics HJ, land use change), and biogeochemical cycles are necessary to understand ecosystem processes ZLWKLQWKHFRQWH[WRIJOREDOHQYLURQPHQWDOFKDQJH &KDSLQHWDO, 2002). From a socio-ecological point of view, the water and carbon cycles are critical for the regulation and supporting of ecosystem services, and therefore represent part of our natural capital 0LOOHQQLXP (FRV\VWHP$VVHVVPHQW   7KXV LWLVLPSRUWDQWWR HYDOXDWHWKHLQÀXHQFHRIWKHVH SURFHVVHV RQ DWPRVSKHULF G\QDPLFV   HVWLPDWH the potential ecosystem services provided to human SRSXODWLRQVDQG SURYLGHUHOHYDQWLQIRUPDWLRQWR GH¿QHSROLFLHVIRUPDQDJHPHQWDQGFRQVHUYDWLRQ Through the processes of photosynthesis and respiration, ecosystems play a key role in the capture and emission of CO2)LJ )XUWKHUPRUHWKHFKDUacteristics of vegetation cover also affect water vapor ÀX[HVLQWRWKHDWPRVSKHUHWKURXJKHYDSRWUDQVSLUDWLRQ )LJ DQGWKHUHIRUHWKHEDODQFHEHWZHHQVHQVLEOH

DQG ODWHQW KHDW ÀX[HV WKDW LPSDFW WKH DWPRVSKHUH )LVKHUHWDO $GGLWLRQDOO\WKHW\SHDQGH[WHQW RIYHJHWDWLRQGH¿QHVWKHSK\VLFDOSURSHUWLHVVXFKDV surface albedo, emissivity and aerodynamic roughness that can affect air temperature, precipitation, and wind VSHHG%XUEDDQG9HUPD ,QWXUQFOLPDWHLVWKH main factor determining the presence and distribution of ecosystems around the world, and establishes FRPSOH[IHHGEDFNVEHWZHHQWKHELRVSKHUHDQGJOREDO ELRJHRFKHPLFDOF\FOHV%RQDQ+HLPDQQDQG Reichstein, 2008). Current knowledge on the interactions between climate and carbon and water cycles is still limited. 7KLV KDV EHHQ LGHQWL¿HG E\ WKH ,QWHUJRYHUQPHQWDO 3DQHORQ&OLPDWH&KDQJH,3&& DVD³NH\XQFHUWDLQty” in our understanding of present and future climate ,3&&   7KH H[SHULPHQWDO HYDOXDWLRQ RI WKH interaction between weather and these cycles has PDGHVLJQL¿FDQWSURJUHVVZLWKWKHGHYHORSPHQWRI QHZPHWKRGRORJLHVWRPHDVXUHWKHPDVVHJ, water vapor, CO2  DQG HQHUJ\ H[FKDQJH HJ, sensible heat, solar radiation) at multiple spatial and temporal VFDOHV&DQDGHOOHWDO, 2000). This development has required a multidisciplinary link between earth and atmospheric sciences, functional ecology, biogeochemistry, and mathematics, which has improved WKHDSSOLFDWLRQRIPRGHOGDWDIXVLRQ9DUJDVHWDO, D 7KLVVFLHQWL¿FGHYHORSPHQWNQRZQDVWKH WKLUG VFLHQWL¿F SDUDGLJP LV FRPSOHPHQWHG E\ WKH integration of knowledge from computer systems science, which is emerging as the fourth paradigm LQVFLHQWL¿FUHVHDUFK+H\HWDO, 2009).

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3. (GG\ FRYDULDQFH (& WHFKQLTXH 7KHHQHUJ\DQGPDVVH[FKDQJHEHWZHHQWKHELRVSKHUH and atmosphere can be studied through different methods depending on the characteristics of the ecosystem and the spatial and temporal scales RI LQWHUHVW &DQDGHOO HW DO, 2000). At the scale RI H[SHULPHQWDO SORWV LH, square meters), gas H[FKDQJHFKDPEHUVSURYLGHLQIRUPDWLRQRQPLFURELDO and plant ecophysiological processes that control WKH H[FKDQJH RI ZDWHU YDSRU DQG &2 2 9DUJDV HW DO, 2011a). However, the spatial sampling is OLPLWHG PDNLQJ LW GLI¿FXOW WR H[WUDSRODWH UHVXOWV to larger spatial scales, and undesirable effects of FRQ¿QHPHQWDQGPDQLSXODWLRQPD\DOVREHLQKHUHQW WR WKH PHWKRGRORJ\ 3XPSDQHQ HW DO, 2004). For scales between 100 to 1000 m2 ZKLFK DUH PRVW representative of an ecosystem) micrometeorological techniques are a useful approach to monitor HFRV\VWHP H[FKDQJH SURFHVVHV RI ZDWHU YDSRU CO2, other biogenic gases, and aerosols. Among micrometeorological techniques, the EC has been the most widely used for estimating NEE by direct PHDVXUHPHQWRIYHUWLFDOÀX[HVRIPDVVDQGHQHUJ\ DFURVVDKRUL]RQWDOSODQHDERYHWKHFDQRS\$XELQHW HW DO, 2000; Baldocchi, 2003). This technique is LQ VLWX and non-destructive, and can be applied to time scales ranging from fractions of an hour WR \HDUV LW LV WKHUHIRUH LGHDO WR FDSWXUH WKH ÀX[ dynamics across different weather conditions from diurnal cycles to long-term environmental changes %DOGRFFKL  7KH WHFKQLTXH LV DOVR VXLWDEOH for understanding the response of ecosystems to disturbance, management history and comparative studies between ecosystem functional types, or for GLIIHUHQW VXFFHVVLRQDO VWDJHV %DOGRFFKL   +RZHYHU LWV LPSOHPHQWDWLRQ LV FRPSOH[ EHFDXVH WKHVWXG\VLWHVKRXOGEHLQDUHODWLYHO\ÀDWWHUUDLQ and be homogeneous in terms of vegetation and soil. The installation and operation of instruments, as well as processing and data analysis require special attention for correct results representing the HFRV\VWHP3DSDOHHWDO, 2006). %ULHÀ\WXUEXOHQWH[FKDQJHVRIPRPHQWXPKHDW water vapor, CO2, and in general any scalar, can be PDWKHPDWLFDOO\ GH¿QHG DV WKH FRYDULDQFH EHWZHHQ WKH LQVWDQWDQHRXV GHYLDWLRQV RU ÀXFWXDWLRQV RI WKH VFDODULQTXHVWLRQHJ, temperature, concentration of water vapor or CO2 PL[LQJUDWLR DQGYHUWLFDOZLQG YHORFLW\RYHUDVSHFL¿FWLPHLQWHUYDOHJ, 30 min).

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)RU H[DPSOH WKH YHUWLFDO WXUEXOHQW ÀX[ RI &22 is GH¿QHGDVWKHFRYDULDQFHEHWZHHQWKHÀXFWXDWLRQV of vertical wind speed and CO2PDVVGHQVLW\Z¶F¶) PXOWLSOLHGE\WKHDYHUDJHDLUGHQVLW\ a %DOGRFFKL   ,I WKH QHW ÀX[ LV SRVLWLYH LH, towards the atmosphere) the ecosystem is a net source, but on the FRQWUDU\LIWKHÀX[LVQHJDWLYHWKHQWKHHFRV\VWHP functions as a sink. 7RPRQLWRUÀX[HVRIJUHHQKRXVHJDVHV*+*V  and energy using this technique, the installation of a micrometeorology tower with particular equipment located at a suitable height is required, to ensure the UHSUHVHQWDWLYHQHVVQHHGHGIRUWKHH[FKDQJHVXUface in all directions. The height and position of the tower in turn depend on the height of the vegetation as well as the predominant wind direction and the average wind speed. A basic EC system to measure ÀX[HVRI&22 consists of a three-dimensional sonic anemometer and a CO2 analytical sensor. Fast-response CO2 analyzers are based on the principle of absorption of infrared radiation by trace gases, and often measure CO2 and water vapor at the same time. Also an EC system includes basic equipment WR PHDVXUH K\GURPHWHRURORJLFDO YDULDEOHV HJ, precipitation, temperature, relative humidity, soil temperature and moisture), and the surface available

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intended to grow in coming years, as new sites will be established within strategic ecosystems to ensure the long-term operation of the network. The new sites, in addition to consistency with the assumptions for EC technique, should ideally be located at sites WKDWUHSUHVHQWWKHYDULDELOLW\RI0H[LFDQHFRV\VWHPV DQGRUDWHFRV\VWHPVDQGUHJLRQVPRVWYXOQHUDEOHWR environmental or land use change. 5. :DWHU YDSRU DQG &22 ÀX[HV LQ WHUUHVWULDO HFRV\VWHPV RI 0H[LFR 0H[LFDQ HFRV\VWHPV SURYLGH ULFK RSSRUWXQLWLHV WR validate previous observations across ecosystems. 6RPHH[DPSOHVRIUHODWLRQVKLSVWKDWFRXOGEHWHVWHG and validated are those observed between phenology and CO2ÀX[HV5LFKDUGVRQHWDO, 2010), control of *33 RQ 56 9DUJDV HW DO, 2011b), or the role of GURXJKW DQG ZDWHU SXOVHV 7KRPH\ HW DO, 2011). :KDWIROORZVDUHH[DPSOHVIURPPHDVXUHPHQWVDW 0H[)OX[VLWHVWRLOOXVWUDWHWKHGLYHUVLW\RISDWWHUQV and magnitudes of CO2ÀX[HV )RUH[DPSOHWKH2MXHORVVLWHORFDWHGLQDVHPLDULGJUDVVODQG7DEOH,,, LVLGHDOIRULQYHVWLJDWLQJ the effect of precipitation pulses on NEE during the summer that result in higher CO2 emissions. Data from this site show that before precipitation events, QRFWXUQDO 1(( YDOXHV 5HFR E\ GH¿QLWLRQ  ZHUH  2 μmol CO2 m2 s–1 while after precipitation, pulses increased to values > 5 μmol CO2 m2 s–1)LJ 7KH implications of these observations rely on climate change scenarios characterized by changes in frequency and intensity of precipitation and pulses.

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These changes in precipitation patterns can substantially affect carbon sequestration in semiarid rangelands by reducing or increasing water stress ZLWKLQWKHHFRV\VWHP7KRPH\HWDO, 2011, Vargas HWDO, 2012b). $QRWKHUH[DPSOHFRPHVIURPVWXG\LQJWKH1RUWK American Monsoon, which is a regional phenomenon that provides most of the annual rainfall over large DUHDVRIQRUWKHUQ0H[LFR9LYRQLHWDO, 2010). Data from the Tesopaco site, a tropical deciduous forest 7DEOH,,, VKRZVWKHLQÀXHQFHRIWKHPRQVRRQRYHU the seasonal trend of the normalized difference vegHWDWLRQLQGH[1'9,GHULYHGIURP02',6REVHUYDWLRQV 1((DQG(7)LJ DVDPDUNHGYDULDELOLW\ LQWKHGLUHFWLRQDQGPDJQLWXGHRIÀX[HVDFURVVWKH growing season. It is estimated that this forest can sequester up to 374 g CO2 m-2 during the monsoon VHDVRQ3pUH]5XL]HWDO, 2010). In urban sites, CO2ÀX[PHDVXUHPHQWVKDYHEHHQ used to evaluate emission inventories and develop PLWLJDWLRQ VWUDWHJLHV ZKLOH HQHUJ\ ÀX[HV FDQ EH useful for urbanization planning through a better

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measuring instruments and measurement methods; DQG GHYHORSTXDOLW\DVVXUDQFHDQGFRQWURO4$ 4& SURFHGXUHVRIUDZGDWDDQGSRVWSURFHVVLQJRI FRPSXWHG ÀX[HV LH JDS¿OOLQJ VHULHV SDUWLWLRQ 1((LQWR*33DQG56 7KLV4$4&PXVWFRPSO\ ZLWKLQWHUQDWLRQDOVWDQGDUGV3DSDOHHWDO, 2006) to generate useful and consistent datasets for regional and global synthesis studies. 7RIDFLOLWDWHV\QWKHVLVVWXGLHVDQGPD[LPL]HGDWD use, the data storage and standardized post-processLQJFRXOGEHSURYLGHGE\H[LVWLQJF\EHULQIUDVWUXFWXUHLQGLIIHUHQWLQVWLWXWLRQVRI0H[)OX[PHPEHUV HJ, University of Alberta, Canada with its EnYLUR1HW SODWIRUP  ,QLWLDOO\ D VSHFL¿F 0H[)OX[ database will contain the products of site-level meaVXUHPHQWVLH, raw data) along with the processed data obtained following standardized protocols 3DSDOHHWDO 0H[)OX[KDVDGRSWHGDSROLF\ of submitting information from each study site to this database within a period of one year from its incorporation to the network. Only principal investigators will submit raw and processed data, and these will be freely available to the network memEHUVXQGHUDIDLUXVHSROLF\)LQDOO\0H[)OX[ZLOO promote training of human resources in the area of micrometeorological and biophysical measurements RIHQHUJ\DQG*+*ÀX[HV

7KHVKRUWWHUPFKDOOHQJHVIDFLQJ0H[)OX[DUH  developing protocols and standardization among sites IRUUHGXFLQJXQFHUWDLQWLHVLQWKHÀX[PHDVXUHPHQWV  HVWDEOLVKLQJUXOHVIRUDUFKLYLQJDQGSURFHVVLQJ GDWDZLWKLQWKH0H[)OX[GDWDEDVH HVWDEOLVKLQJ clear and fair use data policies for all members acFRUGLQJWRWKHIXQGLQJVRXUFHIRUHDFKSURMHFWLH, GRPHVWLFDJHQFLHVDQGLQWHUQDWLRQDOIXQGLQJ DQG  the study sites must invest in measuring a common set of biological and physical parameters to describe the HFRV\VWHPHJ, vegetation structure, phenology, soil properties, management history) to better interpret REVHUYHGÀX[HV/DZHWDO, 2008). ,QWKHORQJWHUP0H[)OX[QHHGVDFRQWLQXRXVLQteraction with institutions and networks at the national and international levels. Important collaborations have been identified with the scientific networks VSRQVRUHGE\WKH&RQVHMR1DFLRQDOGH&LHQFLD\7HFQRORJtD&RQDF\W VXFKDVWKH5HG7HPiWLFDGHO$JXD 5(7$&ZDWHUUHVHDUFKQHWZRUN 5HG7HPiWLFDGH (FRVLVWHPDV(FR5HGHFRV\VWHPVUHVHDUFKQHWZRUN  and Red Temática de Medio Ambiente y SustentabilLGDG5(0$6HQYLURQPHQWDOVXVWDLQDELOLW\UHVHDUFK network). Additionally, there is a strong link with the 3URJUDPD 0H[LFDQR GHO &DUERQR 30& 0H[LFDQ FDUERQSURJUDP WKH5HG0H[LFDQDGH,QYHVWLJDFLyQ (FROyJLFDD/DUJR3OD]R0H[/7(50H[LFDQORQJ

334

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term ecological research network), and international networks such as the North American Carbon Program &DUER1$ DQG7URSL'U\0H[)OX[LVH[SHFWHGWR KDYHDIXQGDPHQWDOUROHZLWKLQ)/8;1(7VLQFH0H[ican ecosystems are underrepresented and this limits the production of synthesis studies across regions, ZKLFKDUHLPSRUWDQWIRUVFLHQWL¿FXQGHUVWDQGLQJDQG SROLF\PDNLQJDFURVV1RUWK$PHULFD+DUPRQHWDO, 2011; Masek HWDO, 2011; Vargas HWDO, 2012a). We also suggest that long-term measurements ZLWKLQ 0H[)OX[ VKRXOG LQFRUSRUDWH RWKHU *+*V pollutants, aerosols and stable isotopes as technology EHFRPHVPRUHDFFHVVLEOHDQGPRUHVFLHQWLVWVMRLQWKH network. This new information could be integrated into models of ecosystem processes to update and validate previous observations and parameters. 0H[)OX[¶VORQJWHUPFKDOOHQJHLVWRVHHNWKHLQWHJUDWLRQRIUHVHDUFKHUVLQ¿HOGVRIFOLPDWHPRGHOLQJ mathematics, biogeochemistry, and social science related to policy making. Finally, we believe that it is essential to develop multi-institutional training DQG¿QDQFLQJPHFKDQLVPVIRUWKHPDLQWHQDQFHDQG operation of the study sites and secure the continuity RI0H[)OX[7KLVZLOORQO\EHDFKLHYHGLIWKHUHLV political will and evidence of the usefulness of value added products from the network for policy-making DQGVFLHQWL¿FDGYDQFHPHQW $FNQRZOHGJHPHQWV The authors acknowledge funding from Conacyt (FR5HG&RQDF\W IRUPHHWLQJVWKDWKDYHIDFLOLWDWed discussions between researchers and students. 59 LV JUDWHIXO IRU IXQGLQJ IURP &RQDF\W &LHQFLD Básica-152671). TA and CW thanks SEP-Conacyt. ASA and EGC thank the Inter-American Institute for Global Change Research, Tropi-Dry, supported by the National Science Foundation. EGC also acknowledgHVIXQGLQJIURPD&RQDF\W8&0H[XVVFKRODUVKLS CW gratefully acknowledges funding from Conacyt Ciencia Básica. EV acknowledges support from INE, MCE2, SMA-GDF and Singapore National Research Foundation trough SMART. GA and JLA acknowledge support from USAID and USFS. 5HIHUHQFHV Aubinet M., A. Grelle, A. Ibrom, U. Rannik, J. Moncrieff, T. Foken, A. S. Kowalski, P. H. Martin, P. Berbigier, C. Bernhofer, R. Clement, J. Elbers, A. Granier, T. Grunwald, K. Morgenstern, K. Pilegaard, C. Reb-

PDQQ:6QLMGHUV59DOHQWLQLDQG79HVDOD (VWLPDWHVRIWKHDQQXDOQHWFDUERQDQGZDWHUH[FKDQJH RIIRUHVWV7KH(XUR)OX[PHWKRGRORJ\$GY(FRO5HV 30, 113-175. Baldocchi D., E. Falge, L. H. Gu, R. Olson, D. Hollinger, S. Running, P. Anthoni, C. Bernhofer, K. Davis, R. Evans, J. Fuentes, A. Goldstein, G. Katul, B. Law, X. H. Lee, Y. Malhi, T. Meyers, W. Munger, W. Oechel, K. T. Paw, K. Pilegaard, H. P. Schmid, R. Valentini, S. Verma, T. Vesala, K. Wilson, and S. Wofsy, 2001. FLUXNET: A new tool to study the temporal and VSDWLDOYDULDELOLW\RIHFRV\VWHPVFDOHFDUERQGLR[LGH ZDWHUYDSRUDQGHQHUJ\ÀX[GHQVLWLHV%$P0HWHR URO6RF 82, 2415-2434. Baldocchi D. D., 2003. Assessing the eddy covariance WHFKQLTXHIRUHYDOXDWLQJFDUERQGLR[LGHH[FKDQJHUDWHV of ecosystems: Past, present and future. *ORE&KDQJH %LRO 9, 479-492. Baldocchi D., 2008. Breathing of the terrestrial biosphere: OHVVRQVOHDUQHGIURPDJOREDOQHWZRUNRIFDUERQGLR[LGH ÀX[PHDVXUHPHQWV\VWHPV$XVW-%RW 56, 1-26. Beer C., M. Reichstein, E. Tomelleri, P. Ciais, M. Jung, N. Carvalhais, C. Rodenbeck, M. A. Arain, D. Baldocchi, G. B. Bonan, A. Bondeau, A. Cescatti, G. Lasslop, A. Lindroth, M. Lomas, S. Luyssaert, H. Margolis, K. W. Oleson, O. Roupsard, E. Veenendaal, N. Viovy, C. Williams, F. I. Woodward and D. Papale, 2010. TerresWULDOJURVVFDUERQGLR[LGHXSWDNH*OREDOGLVWULEXWLRQ and covariation with climate. 6FLHQFH 329, 834-838. Bonan G. B., 2008. Forests and climate change: Forcings, IHHGEDFNVDQGWKHFOLPDWHEHQH¿WVRIIRUHVWV6FLHQFH 320, 1444-1449. Bond-Lamberty B. and A. Thomson, 2010. Temperature-associated increases in the global soil respiration record. 1DWXUH 464, 579-582. Burba G. G. and S. B. Verma, 2005. Seasonal and interannual variability in evapotranspiration of native tallgrass prairie and cultivated wheat ecosystems. $JU)RUHVW 0HWHRURO 135, 190-201. Canadell J. G., H. A. Mooney, D. D. Baldocchi, J. A. Berry, J. R. Ehleringer, C. B. Field, S. T. Gower, D. Y. Hollinger, J. E. Hunt, R. B. Jackson, S. W. Running, G. R. Shaver, W. Steffen, S. E. Trumbore, R. Valentini and B. Y. Bond, 2000. Carbon metabolism of the terrestrial biosphere: A multi-technique approach for improved understanding. (FRV\VWHPV 3, 115-130. &KDOOHQJHU$DQG-6REHUyQ/RVHFRVLVWHPDVWHUrestres. In &DSLWDOQDWXUDOGH0é[LFR&RQDELR(G  &RPLVLyQ1DFLRQDOSDUDHO&RQRFLPLHQWR\8VRGHOD %LRGLYHUVLGDG0p[LFRSS 87-108. Chapin F. S., P. A. Matson and H. A. Mooney, 2002. 3ULQFLSOHVRIWHUUHVWULDOHFRV\VWHPHFRORJ\. Springer, New York, 392 pp.

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Davidson E. A., P. A. Matson, P. M. Vitousek, R. Riley, K. Dunkin, G. García-Méndez and J. M. Maass, 1993. Processes regulating soil emissions of No and N2O in a seasonally dry tropical forest. (FRORJ\ 74, 130-139. Fisher J. B., R. J. Whittaker and Y. Malhi, 2011. ET come home: potential evapotranspiration in geographical ecology. *OREDO(FRO%LRJHRJU. 20, 1-18. Goulden M. L., J. W. Munger, S. M. Fan, B. C. Daube and S. C. Wofsy, 1996. Measurements of carbon sequestration by long-term eddy covariance: Methods and a critical evaluation of accuracy. *ORE &KDQJH %LRO 2, 169-182. *UHHQODQG''**RRGLQDQG&6PLWK(GV  &OLPDWH YDULDELOLW\ DQG HFRV\VWHP UHVSRQVH DW ORQJ WHUP HFRORJLFDO VLWHV 2[IRUG 8QLYHUVLW\ 3UHVV 1HZ York, 480 pp. Hanson P. J., N. T. Edwards, C. T. Garten and J. A. Andrews, 2000. Separating root and soil microbial contributions to soil respiration: A review of methods and observations. %LRJHRFKHPLVWU\ 48, 115-146. Harmon M. E., B. Bond-Lamberty, J. W. Tang and R. Vargas, 2011. Heterotrophic respiration in disturbed IRUHVWV$ UHYLHZ ZLWK H[DPSOHV IURP 1RUWK$PHUica. - *HRSK\V 5HV%LRJHR 116 GRL 2010JG001495. Hastings S. J., W. C. Oechel and A. Muhlia-Melo, 2005. Diurnal, seasonal and annual variation in the net ecosystem CO2 H[FKDQJH RI D GHVHUW VKUXE FRPPXQLW\ 6DUFRFDXOHVFHQW LQ%DMD&DOLIRUQLD0H[LFR*ORE &KDQJH%LRO 11, 927-939. Heimann M. and M. Reichstein, 2008. Terrestrial ecosystem carbon dynamics and climate feedbacks. 1DWXUH 451, 289-292. +H\767DQVOH\DQG.7ROOH(GV 7KHIRXUWK SDUDGLJPGDWDLQWHQVLYHVFLHQWL¿FGLVFRYHU\Microsoft Research, Redmond, WA, 284 pp. IPCC, 2007. &OLPDWHFKDQJH7KHSK\VLFDOVFLHQFH EDVLV&RQWULEXWLRQRI:RUNLQJ*URXS,WRWKH)RXUWK $VVHVVPHQW5HSRUWRIWKH,QWHUJRYHUQPHQWDO3DQHORQ &OLPDWH&KDQJH6 6RORPRQ'4LQ00DQQLQJ= Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller, Eds.). Cambridge University Press, Cambridge, United Kingdom and New York, 996 pp. Jung M., M. Reichstein, P. Ciais, S. I. Seneviratne, J. 6KHI¿HOG 0 / *RXOGHQ * %RQDQ$ &HVFDWWL - Chen, R. de Jeu, A. J. Dolman, W. Eugster, D. Gerten, D. Gianelle, N. Gobron, J. Heinke, J. Kimball, B. E. /DZ/0RQWDJQDQL40X%0XHOOHU.2OHVRQ' Papale, A. D. Richardson, O. Roupsard, S. Running, E. Tomelleri, N. Viovy, U. Weber, C. Williams, E. Wood, S. Zaehle and K. Zhang, 2010. Recent decline in the global land evapotranspiration trend due to limited moisture supply. 1DWXUH 467, 951-954.

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Law B. E., T. J. Arkebauer, J. L. Campbell, J. Chen, O. Sun, M. Schwartz, C. van Ingen and S. Verma, 2008. 7HUUHVWULDOFDUERQREVHUYDWLRQV3URWRFROVIRUYHJHWD WLRQVDPSOLQJDQGGDWDVXEPLVVLRQGlobal Terrestrial Observing System, FAO, Rome, 88 pp. /H 4XpUp & 0 5 5DXSDFK - * &DQDGHOO * 0DUland, L. Bopp, P. Ciais, T. J. Conway, S. C. Doney, R. Feely, P. Foster, P. Friedlingstein, K. Gurney, R. A. Houghton, J. I. House, C. Huntingford, P. Levy, 05/RPDV-0DMNXW10HW]O-32PHWWR*3 Peters, I. C. Prentice, J. T. Randerson, S. W. Running, J. L. Sarmiento, U. Schuster, S. Sitch, T. Takahashi, N. Viovy, G. R. van der Werf and F. I. Woodward, 2009. 7UHQGVLQWKHVRXUFHVDQGVLQNVRIFDUERQGLR[LGH1DW *HRVFL 2, 831-836. Mahecha M. D., M. Reichstein, N. Carvalhais, G. Lasslop, H. Lange, S. I. Seneviratne, R. Vargas, C. Ammann, M. A. Arain, A. Cescatti, I. A. Janssens, M. Migliavacca, L. Montagnani and A. D. Richardson, 2010. Global convergence in the temperature sensitivity of respiration at ecosystem level. 6FLHQFH 329, 838-840. Masek J. G., W. B. Cohen, D. Leckie, M. A. Wulder, R. Vargas, B. de Jong, S. Healey, B. Law, R. Birdsey, R. $ +RXJKWRQ ' 0LOGUH[OHU 6 *RZDUG DQG : % Smith, 2011. Recent rates of forest harvest and conversion in North America. -*HRSK\V5HV%LRJHR, 116*.GRL-* Millennium Ecosystem Assessment, 2005. (FRV\VWHPVDQG KXPDQZHOOEHLQJV\QWKHVLV. Island Press, Washington, D.C., 139 pp. Mittermeier R. A. and M. C. Goettsch, 1997. 0HJDGLYHUVL W\(DUWK¶VELRORJLFDOO\ZHDOWKLHVWQDWLRQV. 1st English HG&(0(;0H[LFRSS Papale D., M. Reichstein, M. Aubinet, E. Canfora, C. Bernhofer, W. Kutsch, B. Longdoz, S. Rambal, R. Valentini, T. Vesala and D. Yakir, 2006. Towards a standardized SURFHVVLQJRI1HW(FRV\VWHP([FKDQJHPHDVXUHGZLWK eddy covariance technique: algorithms and uncertainty estimation. %LRJHRVFLHQFHV 3, 571-583. Pérez-Ruiz E. R., J. Garatuza-Payán, C. J. Watts, J. C. Rodríguez, E. A. Yépez and R. L. Scott, 2010. Carbon GLR[LGHDQGZDWHUYDSRXUH[FKDQJHLQDWURSLFDOGU\ IRUHVWDVLQÀXHQFHGE\WKH1RUWK$PHULFDQ0RQVRRQ 6\VWHP1$06 -$ULG(QYLURQ 74, 556-563. Pumpanen J., P. Kolari, H. Ilvesniemi, K. Minkkinen, T. Vesala, S. Niinisto, A. Lohila, T. Larmola, M. Morero, M. Pihlatie, I. Janssens, J. C. Yuste, J. M. Grunzweig, S. Reth, J. A. Subke, K. Savage, W. Kutsch, G. Ostreng, W. Ziegler, P. Anthoni, A. Lindroth and P. Hari, 2004. Comparison of different chamber techniques for measuring soil CO2HIÀX[$JU)RUHVW0HWHRURO 123, 159-176.

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