These data sets describe the composition, biological characteristics, and physiological processes of the vegetation found within the FIFE experimental area. There are 15 data sets in this group. These data sets range in scope from those that characterize the vegetation of the FIFE site (vegetation species reference, leaf angle data sets, vegetation biophysics, vegetation species, biomass transect, leaf water potential, and leaf chlorphyll) to those which assess biological and physiological responses to different experimental treatments or environmental features (root biomass, plant production, mow biohysics, mow exotech, soil gas flux, photosynthesis box, photosynthesis leaf, and soil carbon dioxide flux). In all cases, the focus is on the biological component and an assessment of that component. These data are useful because they provide the background information that is necessary to link the biological features of the site to the remote sensing measurements of these same features. The measurements of the physiological processes (photosynthesis and respiration) or physiologically active constitutents (plant photosynthetic pigments) provide the links between the indirect measurements of these elements (e.g., leaf area index, NDVI, greenness, etc.) and the physiological activity of the canopy during the growing season.

This data set addresses the effects of intensity and frequency of grazing upon the production and standing crop of native and disturbed prairie. This is done by simulating grazing on experimental plots that have been treated with fertilizer, burned, cultivated, or never treated (native). Grazing is simulated by clipping at different intervals and at different heights. The data set contains biomass (standing crop) and production (standing crop + cumulative harvest since start of growing season) for grasses and forbes in these experimental plots, and it also contains the nitrogen and the phosphorus content of the grasses in these plots.

Measurements of canopy reflectance were made using an exotech instrument at sites which had been treated (burned or fertilized), and at sites which were used in the grazing and simulated grazing experiments. Reflectance measurements were made at the 4 wavebands found on the Landsat MSS sensor (.5-.6 micrometers, .6-.7 micrometers, .7-.8 micrometers, and .8-1.1 micrometers). All measurements were made within a day of the treatment or sampling event. Measurements were made only during the daylight hours.

This data set addresses the effects of grazing by herbivores. Experimental exclosures were placed in areas that were regularly grazed. The vegetation within these exclosures was periodically clipped to ground level and the biomass (standing crop) determined for both grass and non-grass components of the clippings. The vegetation in regularly grazed areas immediately outside the exclosures was also clipped to the ground and the biomass determined. From these measurements calculations of consumption were made at each sampling interval. The data set provides both the consumption and standing crop at several intervals during the growing season, and the cumulative consumption and production since the beginning of the growing season for grasses, non-grasses, and the two combined.

Measurements of below-ground biomass (production and standing crop) for the FIFE site were made at several locations over the growing reason. Many of the sampled sites had been manipulated by burning, grazing, simulated grazing, and fertilization. At some locations only standing crop measurements were made at the end of the growing season while at others production measurements were made over the growing season. The below-ground production and standing crop measurements are partitioned into five fractions: live and dead roots for both forbes and grasses (four fractions), and a rhizome fraction which was primarily grass rhizomes.

This data set contains biomass and nitrogen concentration data for live and dead above-ground plant material collected along transects in watersheds within the FIFE experimental area. Basic information describing the topography of the sampling sites along each transect is also included. The transects were located in watersheds that had undergone burning and grazing treatments. All are located within the northwest quadrant of the FIFE area. Five transects were run at each of four different times (once during each IFC) in 1987. Total nitrogen content was measured for live, dead, and woody plant materials, and the total nitrogen content of all above-ground fractions was computed.

Measurements of leaf water potential (a measure of the water equilibrium/balance within a plant) are provided for three grass species common to the FIFE experimental area. These data give a measure of the water stress within a plant over a day in June of 1988, and in June, July, and August of 1989 at six different sites within the FIFE area.

This data set addresses rates of in situ denitrification, maximum rates of denitrification and effect of competition between nitrogen sources within the root zone. Measurements of soil respiration, denitrification, and total nitrogen content made under four different experimental treatments are located in this data set. Soil cores were treated in one of four ways: 1) acetylene, 2) acetylene and water, 3) acetylene, water and nitrate were added, or 4) they were left untreated (control). Soil moisture measurements were also taken when the soil cores were collected. Measurements were made at four times during 1987, once during April, May, June, and October.

A survey of the biomass distribution within the above-ground component of the standing crop at 58 sites within the FIFE experimental area was made over the growing season. This data set contains standing crop information at sample plots located near each of these 58 sites. At each site 20 biomass fractions were reported; wet and dry weight for grass and non- grass stems and leaves (eight fractions), wet and dry weight of standing dead and canopy litter (four fractions), plant segment area indices for the leaf, stem, and litter for grasses and non-grasses (five fractions), the total wet and dry weight of the living vegetation (two fractions), and the total leaf area index for the grasses and non-grasses (one fraction).

A survey of the species composition and cover abundance at 65 sites within the FIFE experimental area was made throughout the growing season. The cover abundance and the average cover for 211 species found within the experimental plots that were located near these 65 sites are contained in this data set.

This data set is a look-up table for the LTER species codes and plant types used in the vegetation biophysics data set. The data set contains a list of species names, their associated LTER codes and types, and a short description of each species.

Direct measurements of leaf angle distribution for 11 common species of prairie vegetation are contained in this data set. The percentage leaf area within a specific azimuth or zenith angle for a leaf and the total leaf area is present.

Measurements of photosynthetic respiration and bulk stomatal resistance of plant canopy were made using a plexiglass chamber equipped with a LI-COR CO₂ gas analyzer. Measurements of incident Photosynthetically Active Radiation (PAR) were made throughout the day within and outside the chamber. These data were collected from Sites 6 (2132-PSB), 16 (4439-PSB), 28 (6943-PSB), 36 (2655-PSB), and 44 (2043-PSB) during July 1, 1987 through October 12, 1987, which fell within FIFE IPCs 1-4. One site (2132-PSB) was located within the northwest quadrant of the FIFE site, well within the Konza LTER site, while the others were distributed within the rest of the FIFE area. The results showed that estimated values of net CO₂ flux varied between about 0.25 and 1.0 [mg][m^-2][sec^-1] during IPC-2 and IPC-3, and around zero during IPC-4. Resistances ranged from 80 [sec][m^-1] to 300 [sec][m^-1] during IPC-2 and IPC-3, rising to very high values (greater than 1000 [sec][m^-1] ) during IPC-4.

Photosynthesis measurements were made at 5 irradiances (100, 45, 20, 5 and 0 percent sunlight) throughout the day using three species of C4 grasses (Big bluestem, Indian grass, and Switchgrass) common to the FIFE site. These measurements were made in the field on leaves attached to growing plants. Measurements were made at three stations (3414-JNO, 1608-JNO, and 3225-JNO) within the FIFE site. Data was collected at these stations during all four IFCs in 1987; however, the data from IFC 4 in October of 1987 is not contained here since most of the leaves measured during this IFC were dead. Photosynthesis-Irradiance responses for these species were typical of C4 plant species. However, the measurements of maximum photosynthesis were less than those found for cultivated species. Measurements of stomatal conductance and osmotic potential are also available at the different times of day.

Chlorophyll-a, chlorophyll-b, and beta-carotene content of leaves collected from two research treatment areas (B and 1D) within the Konza LTER area portion of the FIFE site (northwest quadrant) and from FIFE Site 16 (Sitegrid 4439-ECV) located in the center of the FIFE site are contained within this data set. Data are available from June 15, 1989 through August 11, 1989 during FIFE IFC 5. Data is available from treatment area B for June and August, treatment area 1D for June, July and August and for Site 16 only in August. This data set contains the optical densities, and the weight and area of the plant sample associated with each optical density. The weights and area of plant material used for each sample were not identical for each sample. Therefore, to use these data, the optical densities must be converted to a unit of plant material, either leaf area or plant weight. Information about the angle of the hillslope and direction of the slope relative to due North is also available for most samples. Lastly, in most cases, samples were taken from three depths within the canopy; top, middle and bottom. This data is stored in the "Grab Bag" section.

The flux of the carbon dioxide (CO₂) from the surface of the soil is an important component of the carbon budget of a prairie ecosystem. In this data set, a prototype gas exchange system and sensor were used to determine the soil surface flux of carbon dioxide and associated parameters at the three FIFE supersites (2133-LCN, 4439-LCN, 8739-LCN) during IFC 5 in July and August 1989. Measurements of soil moisture, soil temperature, air temperature, leaf area index of the plant material growing at the location of the flux measurements, water conductance, and relative humidity are also present in this data set.

These data sets used similar and well-accepted techniques for measurement and sampling of the biota. The only unique features of these data sets was the use of herbivore exclosures in the grazing experiment thereby enabling measurement of herbivore consumption.

These data sets provide basic information about the flora of the FIFE experimental area, its composition, and the canopy cover that each species provides. The measurement and sampling techniques used for the vegetation species and vegetation biophysics data sets are well accepted. The unique data set among this group is the leaf angle data set. It is one of the few data sets that contains information on leaf direction relative to zenith and azimuth for different points on a leaf. To acquire these measurements an instrument was specifically built for this purpose (spatial coordinate apparatus). The measured leaf angles were sorted into 10 azimuth bins and 10 zenith bins; 9-degree increments for zenith measurements and 36-degree increments for azimuth measurements.

These data provide basic information about the potential for water stress in the grass canopy during the FIFE experiment, for the activity of the nitrogen cycle within the soils, the photosynthesis and respiration of the canopy at different location witin the FIFE site, and the measurements photosynthetic pigment content (chlorophyll-a and -b) at selected sites.

The data sets in this group all describe properties of the vegetative components of the FIFE experimental area. Some of these data sets describe basic properties of a species, such as the leaf angle data set, while other data sets (vegetation species, vegetation biophysics, and vegetation species reference) describe the floral composition of the FIFE area. This floral composition is measured in a variety of ways including canopy species abundance and cover, canopy height, and bulk measurements of above-ground and below-ground plant biomass in different fractions (alive, dead, litter, grass, nongrass, leaf, stem, rhizomes) over the growing season. The vegetative components are also characterized by the photosynthesis and respiration capacity of the above- and below-ground biomass of the canopy and the photosynthetic pigment content of the canopy at some of these locations.

These data sets were collected specifically to either initialize or test process models or remote sensing algorithms being developed for FIFE. The leaf-level photosynthesis and stomatal conductance data were collected to test and confirm hypotheses concerning environmental response functions related to biological assimilation and evaporation regulation mechanisms. Data sets such as leaf chlorophyll, leaf angle, plant leaf area, and above- and below-ground biomass were collected to characterize the vegetation for the process models and remote sensing algorithms. Soil CO₂ flux data were collected to establish environmental response functions for plant and soil respiration. Finally, plant productivity studies, and the effects of grazing, were studied to quantify plant productivity and its integrated response to the soils and weather variables.

A suite of studies were undertaken to address the dynamics of grazing and its role in prairie ecosystems. In each of these studies, different treatments were applied to experimental plots and then the standing crop was measured at different times over the growing season. These experimental plots examined both above-ground and below-ground (root biomass) production and biomass in grasses and non-grasses. Simulated grazing experiments (mow biophysics) were performed as were grazing experiments (plant production). The grazing experiment used exclosures to create ungrazed areas within areas which were frequently grazed. The simulated grazing experiments examined both the frequency and intensity of grazing on burned, fertilized, and native prairie sites. Canopy reflectance measurements (mow exotech) complement these data since these measurements were made at the same time and locations as the treatments.

These data sets provide basic information about the composition of the canopy at several sites within the FIFE experimental area. For that reason, they are related to all other data sets collected during the FIFE experiment that examine the canopy and its properties.

The leaf water potential data set is related to the MMR data sets. MMR measurements were made on the same plant at the same time as the water potential measurements. The photosynthetic box, leaf photosynthesis, and leaf chlorophyll data sets are all related in that they measure the basic physiological process of photosynthesis and the associated photosynthetic pigments. However, these data sets were generally not collected at the same locations or at the same times. The soil CO₂ data set is unique. There are no other FIFE data sets that contain information about below-ground respiration rates.

In reviewing the error sections written by the investigators who collected the data sets described in this chapter, the error assessments range from unknown to detailed quantitative assessments assigning error bounds to the various quantities measured. In most cases, the error discussions are qualitative in nature, describing the conditions under which the measurements might be non-representative or invalid, but with no attempt to be quantitative on a case-by-case basis. These latter kinds of assessments can, however, still be used to avoid misuse of the data.

In general, the data in this group are of reasonably good quality. The one exception is the mow exotech data set which has potentially serious flaws concerning calibration, sun angle, distance of canopy from the measuring device, and stability of instrument during measurement. Most data sets in this group used standard measurement and sampling techniques, therefore, they do not suffer from the problems associated with new instrumentation and techniques. Only two data sets in this group used experimental or new instrumentation (leaf angle data and photosynthesis box data) and the data from both of these are thought to be reliable.Another aspect of the error discussions is scale. Measurements in this chapter span scales from the leaf level, a few hundreths of a square meter, to the plot level at tenths of a square meter. To obtain useful quantitative error estimates at other scales, the user of these data will need to take into consideration the scale at which the errors are quoted, and how these errors might translate between scales. For example, how do quoted errors in measuring plot-level dry biomass of 0.01 grams, scale from the plot level (0.1 m^2) to the pixel level (1 km^2)? Such estimates will be necessary for comparing pixel-level spectral estimates of biomass to measured ones. Sampling theory exists that permits such scale extrapolation, and in some cases, the quantitative error measurements quoted here, can provide inputs to such extrapolations.

As described in Section VII of this chapter, many of the data sets collected in the biological characterization of vegetation effort were designed specifically to either initialize or test process models or remote sensing algorithms being developed for FIFE. A major result of this data collection effort lies outside the results summary of this section and are treated in the other sections of this document. In contrast, there were some important science findings from the measurements described in this section that stand alone; they will be summarized here.

During the 1989 year, Polley, et al. made measurements ofthe components of soil and canopy CO₂ flux due tophotosynthesis and respiration (SOIL CO₂ FLUX). They showed that, over the 20 days of the 1989 observation period (late in the growing season), the assimilation of carbon through gross photosynthesis, as measured by the flux stations, was nearly balanced by the loss of carbon by the soil and plant through respiration. Only during the cooler periods of 1989 was the plant in net positive carbon balance.

Measurements made of leaf photosynthesis by Polley, et al.(PHO_LEAF) supported earlier physiological studies by Ball, 1987, showing that net assimilation of CO₂ and stomatal conductance are tightly linked. This result provided the physiological foundation linking remotely sensed estimates of absorbed photosynthetically active radiation, assimilation of CO₂, and surface biological control of evapotranspiration. This result is ultimately the lynchpin of the remote sensing of surface energy balance. These data also provide the means for exploring the detailed mechanisms of assimilation and evaporation at the leaf level and their response to light absorption, leaf temperature,water potential, nitrogen concentration, and internal CO₂ concentration.

The data sets MOW_EXO, and MOW_BIOP, and PLANTPRO delineate the effects of grazing and other management practices on vegetation productivity and show that canopy biomass is tightly coupled to surface topography through its effect on soil depth and thus water holding capacity. The data from mowed plots show that canopy and nitrogen content will be affected by grazing intensity and frequency, and set limits on how fast the canopy can recover from phytomass loss, thus defining the inherent dynamical frequency of prairie grass response to a major disturbance (roughly four days in the cool early season, stretching to longer periods when conditions are warmer).

Turner, C.L., T.R. Seastedt, and M.I. Dyer. 1993. Maximization of aboveground production: the role of defoliation frequency, intensity, and history. Ecol. Appl. 3:175-186.

Groffman, P.M., C.W. Rice, and J.M. Tiekje. 1993. Denitrification in a tallgrass prairie landscape. Ecology (In Press).

Polley, H.W., J.M. Norman, T.J. Arkebauer, W.A. Walter-Shea, D.H. Greegor, and B. Bramer. 1992. Leaf gas exchange of Andorpogon gerardii Vitman, Panicum virgatum L., and Sorghastrum nutans (L) Nash in a tallgrass prairie. J. Geophys. Res. 97:18,837-18,844.

Norman, J.M., R. Garcia, and S.B. Verma. 1992. Soil surface CO₂ fluxes and the carbon budget of a grassland. J. Geophys. Res. 97:18,845-18,853.

Kim, J., S.B. Verma, and R.J. Clement. 1992. Carbon dioxide budget in a temperate grassland ecosystem. J. Geophys. Res. 97:6057-6063.