PURPOSE
To assess the total aboveground biomass per unit area, separate the total into live and dead, grass-sedge, and forb-shrub components; and determine N and P content of aboveground foliage on treatment plots burned annually, every four years, and unburned.
LOCATIONS OF SAMPLING STATIONS
The above-ground biomass is sampled adjacent to the species composition plots in watersheds 020B, 004B, and 001D on hillsides, Tully, and Florence soils.(Fig. 22). sites are sampled and in 001C only Tully and Florence sites are sampled. A 50 meter line for above-ground biomass is located 4 m to the side of each species composition line. Canopy coverage lines are marked at each end by a 1.5 m conduit painted red, and biomass lines are marked with conduit stakes painted yellow. Additionally above ground biomass is measured in 020A and 001A (C- 30, B-30, and B-31). See maps in data set PVC02 for detailed location of sites: 001C ( Fig. 23), 020B ( Fig. 24), 001D ( Fig. 26), 004B ( Fig. 28), 002D ( Fig. 30),
FREQUENCY OF SAMPLING
The LTER watersheds are sampled in late August/September when it is estimated that peak biomass has occurred. Watersheds 020A and 001A are sampled every two weeks from May 15 to September 15.
VARIABLES MEASURED
Total aboveground biomass/unit area. Prairie vegetation is separated into live vs. dead and has grass/sedge vs. forb/shrub components. Seasonal production curves for burned and unburned tallgrass prairie are derived variables. Material is separated before oven-drying as follows:
Areas not burned that spring:
previous year grasses/sedges forbs/woody
grasses/sedges forbs/woody
Areas burned that spring:
current green current dead current green
current dead
Percent N and P in foliage (Data Set PAB01, record type 2) is determined for live grass, forbs, previous dead, and current dead from selected transects and plots that vary from year to year.
METHODS
All above ground biomass is clipped in 20 0.1 m2 quadrants per soil/watershed. At each transect, four per soil/watershed, five quadrants are clipped at each sampling date. Every quadrant clipped is marked with a plastic flag to avoid subsequent re-clipping. At the end of the season the two ends of the transect are marked with metal flags imprinted with the year clipping took place. There is sufficient room adjacent to the species composition transects for four such clipping transects insuring that an area will be re-clipped only every four years. Also, a map is kept in Bushnell Rm 216 of the locations of the clipping transects relative to the permanent species composition transects.
In addition, a growth curve for the season was obtained by clipping on a lower slope with non-rocky soil (020A and 001A) at two week intervals throughout the season (May 15-Sept. 15).
In 020A and 001A, a large area is available for clipping and re-sampling areas should not be a problem, however, all clipped plots are marked with flags. Twenty quadrats were clipped in a transect in each watershed at each sampling date.
SORTING OF THE VEGETATION
In the field, all biomass is clipped at ground level and bagged in burned watersheds but in unburned sites, it is best to sort the current year's growth from the previous years' dead biomass and bag separately. In the lab, the current year's growth bags are sorted into live grass/sedges, current year dead grass/sedges, and forb/shrub components. Beginning in 1992, woody plants are separated from forbs. The previous year's dead is also examined to make sure no live biomass accidentally was included in this category in the field. Thus, each quadrat is sorted into three components in burned watersheds and four components in unburned prairie. All sorted samples are oven-dryed at 60xC for 48 hours before weighing. A copy of the data sheet used to record weights is given in Figure 13.
To determine N and P; 20-30 grams of each tissue category (live, forbs, current dead and previous dead) are ground through a Wiley mill using a 40 mesh screen. Samples are dried for 48 hours to 70oC and approximately 0.5000 g (to the nearest 0.0001 g) is weighed into pyrex digest tubes. Nitrogen and phosphorous content are determined by Kjeldahl digestion in concentrated sulfuric acid (H2SO4) followed by calorimetric measurements using a Technican autoanalyzer. We correct the data for incomplete recovery on the basis of pine needle standard reference material values. Data are stored as percent N and P where: % N and P = ppm * cf (correction factor), cf = observed of 2x standards/literature value.
