---TITLE: Toolik Litter Study ---AUTHORS: -Jeff Welker (PI), Jace Fahnestock (co-PI) -Natural Resource Ecology Lab, Colorado State University, Fort Collins, CO 80523-1499 -telephone 970-491-1796; facsimile 970-491-1965; e-mail jwelker@nrel.colostate.edu -data questions: jace@nrel.colostate.edu ---DATA SET OVERVIEW: -During winter in the Arctic, plant litter is scoured from exposed hills and ridges by wind and snow and is redistributed to other portions of the landscape. Since tundra ecosystems are often nutrient limited, the redistribution of litter during winter may be an important mechanism of carbon and nutrient transfer in Arctic ecosystems. The data set presented here represents part of a study that examined the ecological consequences of allochthonous litter deposition in tundra communities near Toolik Lake, Alaska. The study indicates that wintertime litter redistribution is an important mechanism of nutrient transfer across the Arctic landscape, increasing C and nutrient inputs to some portions of the landscape while decreasing their availability in other areas. Accumulation of windblown litter modifies the physical and chemical environment of patchy areas of the landscape and significantly alters some important biological processes such as respiration. Data are for control and litter plots and include net ecosystem CO2 exchange (umol m-2 s-1), photosynthesis (umol m-2 s-1), respiration (umol m-2 s-1), soil temperature at 5 cm (degrees C), and various dates for key phenological events (snow free, first green leaf visible, first flower petal visible, first flower open, first petal drop, last petal drop, first color change, and seed dispersal) for six important dry heath tundra plant species. The data span the time period of 19960619 to 19980826 UTC. ---INSTRUMENT DESCRIPTION: -Gas exchange was measured with a LI-COR LI-6200 infrared gas analyzer (IRGA) coupled to a transparent (30 cm x 30 cm x 30 cm) chamber. The chamber is placed on pre-selected control or litter plots at the time of measurement. Each plot is surrounded by a permanent 30 cm by 30 cm base, inserted into the tundra in late 1995, to which the chamber is sealed at the time of each measurement. Measurements of carbon dioxide exchange are corrected for prevailing atmospheric pressure and temperature within the IRGA. -Temperature was collected in control or litter plots using HOBO dataloggers. Measurements were collected every four hours and averaged for each day. -Phenological events were measured by visibly documenting each event as it occurred in each plot. The first plant of each species in each plot to undertake a given phonological event was documented. ---DATA COLLECTION and PROCESSING: -Gas exchange data are generally collected over 24-hour periods at various dates during the growing seasons. Three consecutive 30-second measurements of net carbon dioxide exchange are taken on each plot at the time of measurement to ensure steady state conditions within the chamber. The chamber is subsequently covered with an opaque cloth and three more measurements of respiration (photosynthesis eliminated by covering the chamber) are taken. Photosynthesis is calculated as the difference between net flux and respiration. There are three replicate control and two replicate litter plots. The three consecutive measurements are averaged for each plot and the data for the plots are subsequently averaged to produce a mean carbon dioxide exchange estimate for each treatment for each time period. In this notation, negative numbers indicate net carbon loss by the tundra to the atmosphere during the measurement time period while positive numbers indicate net carbon gain by the tundra during the measurement period. Thus, respiration is always negative and photosynthesis is always positive or zero. ---DATA FORMAT: -Data are in an Microsoft Excel spreadsheet. Data for phenological events are Julian date. Headings are Date/time for gas exchange measurements, Net ecosystem CO2 exchange for control plots, 1 SE for NEE-Control, NEE for litter plots, 1 SE for NEE-Litter, Photosynthesis for control plots, 1 SE for Photo-Control, Photosynthesis for litter plots, 1 SE for Photo-Litter, Respiration for control plots, 1 SE for Resp-Control, Respiration for litter plots, 1 SE for Resp-Litter, Date for temperature data, Temperature for control plots, Temperature for litter plots, Species for which phenological events were documented, Snow-free_CTL, Snow-Free_Litter, First-leaf-visible_CTL, First-leaf-visible_Litter, First-flower-visible_CTL, First-flower-visible_Litter, First-flower-open_CTL, First-flower-open_Litter, First-petal-drop_CTL, First-petal-drop_Litter, Last-petal-drop_CTL, Last-petal-drop_Litter, First-color-change_CTL, First-color-change_Litter, Seed-dispersal_CTL, Seed-dispersal_Litter. -Missing data indicated with 999.99. -DATA VERSION= 1.0 (28 February 2002) FINAL. ---DATA REMARKS: -Gas exchange data are initially stored in the LI-6200. Both BINARY and ASCII versions of the data are subsequently transferred to a PC where we primarily use Microsoft Excel to manipulate the data. Because the LI-6200 operating parameters are calibrated and set before each measurement period, we do very little manipulation of the data following collection except to average the replicate measurements and plots. The three replicate measurements on each plot help to ensure no outliers. -Temperature data are stored in the HOBO dataloggers that are periodically downloaded to a PC. ---REFERENCES: -Additional details and information regarding this study can be found in Fahnestock, JT, KL Povirk and JM Welker. 2000. Ecological significance of litter redistribution by wind and snow in arctic landscapes. Ecography 23:623-631.