TITLE: Council 2000 forest understorey flux data AUTHORS: Dr. Jason Beringer # Dr. F.S. Chapin III @ Catherine Copass @ # School of Geography and Environmental Science PO Box 11A Monash University Clayton, Victoria, 3800 AUSTRALIA Ph: +61 3 9905 9352 Fax: +61 3 9905 2948 Email: Jason.beringer@arts.monash.edu.au @ Institute of Arctic Biology 311 Irving I Bldg University of Alaska Fairbanks Fairbanks, AK, 99775-7000 USA DATA SET OVERVIEW: There were three flux and climate towers operating at Council, Seward Peninsula, during 2000. Two towers were located at the tundra and forest sites. The third tower was a mobile tower and covered four different surface types (Tall shrub, tundra ISS2, burned tundra, heath and shallow thaw lake). The data presented here is an additional eddy covariance system that was established beneath the forest tower at Council at 2m above the ground. This system measured below canopy fluxes from the ground surface and ground shrubs. The data set was collected in conjunction with overstorey fluxes, mini lysimeter measurements of soil evaporation and sap flow measurements of tree transpiration. The forest tower fluxes and climate can be found in the files 'cfore_2f and cfore_2c' and details of the tower are given. CFORE - SPRUCE FOREST Location: N 64o 54.456' W 163o 40.469' Elevation: 275 feet Slope: 3.3% (3o) Aspect: 140 o TN Grid orientation (A1-A11): 058o TN Data dates: 13/5-29/8 Average LAI: 2.7 Average vegetation height: 6.1m Sonic Anemmeter:120 oTN Sonic Height: 11.20 m DATA COLLECTION AND PROCESSING: Data were collected at Council (N64o50.499' W163o41.591') on the Seward Peninsula, located approximately 70 miles to the northeast of Nome. The Peninsula itself encompasses a diversity of landscape and ecosystem types created by the various climatic and topographical settings. The climate of the Peninsula is annually slightly wetter and warmer than the north slope of Alaska [Fleming et al. 2000]. In the summer, climate is somewhat continental with relatively cool and windy conditions along the coast with the inland climate being relatively hotter and drier. The Council area provides an excellent field site to investigate a variety of high-latitude ecosystem types that may be important in future climate change in close proximity. It also allowed us to examine what may happen under a changing vegetation regime brought about by future warmer and wetter conditions. Seven different vegetation/surface types were selected for study along a gradient from Heath through to mature white spruce (Picea glauca) forest. The seven sites were termed heath, tundra, burned tundra, replicate tundra ISS2, tall shrub, shallow lake and forest. These sites were located within a 5 km radius of Council. This region of tundra and forest is representative of the contrast in vegetation that may be observed across northern treeline [Lafleur et al. 1992]. Leaf area index (LAI) was measured in these sites at peak season biomass using optical techniques (Licor Inc., model LAI-2000). See Copass data Surface energy exchanges Three towers were deployed to obtain microclimatic and eddy-covariance measurements in order to characterize the radiation, energy and trace gas exchanges above the different vegetation types. Simultaneous measurements of radiation, energy and trace gas exchanges were made at both the tundra and forest sites over the entire growing season using the eddy covariance technique [Eugster et al. 1997]. The tundra tower was used as a reference tower to compare with the various mobile sites because it had the most complete data set. The third mobile tower was deployed to collect measurements consecutively at the tall shrub, ISS2, burn, heath and lake sites but during the same period as the tundra site. Comparisons are made between the reference and mobile towers in a method developed by Eugster et al. [1997]. We used 10 m towers at all sites except the forest site where the tower was 20 m. Radiation measurements were made as close as practical to the top of the towers to minimize the potential of shading from above and to maximize the surface area within the effective sensor footprint [Schmid 1997]. Eddy-covariance measurements were made at varying heights above the vegetation (Table 1). Three dimensional wind velocities were measured using a 3-D ultrasonic anemometer (Gill Solent, model HS) and were co-ordinate rotated [McMillen 1988]. Turbulent fluctuations of CO2 and H2O were measured using a closed path infrared gas analyser (Licor, model LI-6262). The CO2 and H2O time series were lagged against the sonic temperature series so that they were in phase with each other. Scalar quantities were linearly detrended and bell tapered [Stull 1988]. A 3 mm internal diameter "Bev-A-Line" intake tube was used for the gas analyzer with an aspiration rate of approximately 7 L.min-1 that ensured turbulent flow in the sample line [Philip 1963]. In addition, 1.5 m of insulated copper tubing was placed inline to minimize temperature-induced density fluctuations [Leuning and Judd 1996]. The observations were logged at 10 Hz to a nearby laptop PC. The w'T' cospectra for each site followed the idealized cospectra [Kaimal et al. 1972] and the w'CO2' and w'H2O' were spectrally corrected following [Eugster and Senn 1995]. Spectral correction factors for water vapour were less than 1.4 during daylight hours. The energy balance closure ((Q/Rn) was generally less than 15% as a fraction of net radiation during the daylight hours indicating satisfactory measurement techniques and confidence in the measured fluxes [Eugster et al. 1997]. Climate sensors were measured every 30-seconds and 10-minute averages were recorded on a data-logger (Campbell Scientific Inc., model CR10X). The mean daily temperature, wind speed, vapour pressure deficit, soil moisture and soil bulk density for each site are given in table 1. Incoming and reflected shortwave as well as incoming and emitted long-wave radiation were measured using a pair of pyranometers (Eppley Labs Inc., model PSP) and pyrgeometers (Eppley Labs Inc., model PIR) respectively. An independent estimate of net radiation above each surface was made using a Frischen type net radiometer (REBS, model Q*7.1) with a wind-speed-dependant dome cooling correction applied to the results [Radiation and Energy Balance Systems 1995]. Profiles of air temperature and water vapor content above and below the level of the sonic anemometer were measured using temperature/relative humidity probes (Vaisala, model HMP45C). Wind speed at the radiometer height was measured using a cup anemometer (R.M. Young, model 03101). Ground heat flux was estimated via the combination method [Fuchs and Tanner 1968] using heat flux plates (REBS, model HFT3) and soil temperature measurements (REBS, model PRT) at four representative locations. Ground heat fluxes for each tower site were estimated using the area-weighted average of ground heat fluxes measured in each of the representative microsite types sampled (e.g., lichen-dominated vs. moss-dominated microsites) [McFadden et al. 1998]. Observations of energy and moisture exchange were made in conjunction with vegetation biomass and structure, soil thermal characteristics, permafrost characteristics (Romanovsky) and parameters important in catchment-scale hydrological processes (Hinzman). Measurements were taken over the 2000 summer growing season between 13/5 and 29/8. The time system used here is local Alaskan Daylight Time (ADT), which is (UTC -8 Hours). Throughout this paper the term daily refers to the 24-hour period from midnight to midnight and daytime refers to the period when net radiation is positive. Solar noon at Council was around 15:00. DATA FORMAT: There is only one file that contains flux data from the spruce understory fore_und These files are saved in two formats *.xls being an Excel4 worksheet and *.txt being a comma delineated text file. The files contain one or more of the following parameters and the parameter names are given at the top of each column. The following table gives the parameter definitions. Note that in each flux file there is a VALIDY column which is a flag to indicate good quality data. Data with a 8 is identified as good data. UNDERSTOREY FOREST FLUX TTIME -9999 TIME1 Excel alaska time JOSSTIME -9999 8.3 JOSS UTC time FRN2 -9999 8.3 Net radiation 760cm (Wm-2) UMEANWD -9999 8.3 Mean horizontal wind direction of sonic (205cm) (m.s-1) UMEANWS -9999 8.3 Mean horizontal wind speed of sonic (205cm) (m.s-1) UMEANT -9999 8.3 Mean absolute (virtual corrected) sonic temperature (oC) UMEANP -9999 8.3 Mean Licor internal pressure (Kpa) UMEANH2O -9999 8.3 Mean Licor weight fraction water vapour (g.kg-1) UMEANCO2 -9999 8.3 Mean Licor weight fraction CO2 (ug.g-1) UUSTAR -9999 8.3 Friction velocity (m/s) UL -9999 8.3 Monin-Obukov length (m) U_LE -9999 8.3 Corrected latent heat flux (Wm-2) U_H -9999 8.3 Sensible heat flux (Wm-2) U_FC -9999 8.3 Corrected CO2 flux (ug.g-1.m-2) U_G -9999 8.3 Average surface soil heat flux (Wm-2) U_VALIDY -9999 8.3 Validy is sum of other valid so if all valid then validy=8