Data Set Summary
| Item | Value |
|---|---|
| Dataset ID: | hum_den |
| Dataset Title: | SGS-LTER Effects of nitrogen availability on the growth of native grasses and exotic weeds: Plant density on the Central Plains Experimental Range, Nunn, Colorado, USA 1997-2008 |
| Abstract: | It was hypothesized that decreasing nitrogen availability would create a disadvantage for the dominant exotic species and provide an advantage for the native species, returning the community to a vegetative structure more characteristic of undisturbed sites. experiment on a historic study site. Prior researchers added treatments to this site consisting of control, water, nitrogen, and water plus nitrogen from 1971 to 1975 (Lauenroth et al. 1978). The historic experiment was a factorial combination of four treatments with two replicates, with each experimental unit being 1 ha in size. Researchers sampled the experimental plots for plant density, cover, and biomass production through 1974, and then again from 1982 to 1991. The initial sampling from 1970 to 1974 showed that the water and water plus nitrogen treatments had the strongest effect on plant community structure, both treatments increased biomass, and exotic weed species were noted on the water plus nitrogen treatment. Later sampling from 1982 to 1991 showed a ten-fold increase in exotic weed species on the water plus nitrogen plots as compared to the controls (Milchunas and Lauenroth 1995), a community change that has persisted on this site due to a chronic elevation of soil nitrogen caused by a plant tissue/soil organic matter feedback mechanism (Vinton and Burke 1995). Six new treatments were superimposed on the historic study site. The six new treatments were: control, sugar, lignin, sawdust, lignin and sugar, and sawdust and sugar. The additions provided 350 g carbon m-2 yr-1, resulting in 1,061 g m-2 of lignin, 777 g m-2 sawdust, and 833 g m-2 sugar being added to the study plots in from 1998 to 2004. This study has a split-plot completely randomized design. Three randomly transects are located within each 1 ha historic treatment, each one of these three transects was divided evenly into six 9 m2 plots, to which one of the six new treatments was randomly assigned. The entire experiment consisted of two blocks of four historic treatments, and 3 transects of six new treatments for a total of 144 sample plots. Transect plots within each historic plot are statistically psuedoreplicates, resulting in two true replicates of each new treatment, one in each of the two historic replicate plots. Density and basal cover by species within a centrally located 1m2 plot within each 9 m2 new treatment plot, was recorded since 1997 and canopy cover was collected since 2007. |
| Methods: | Density sampling (number of individuals of each species/m2): Count all the individuals for each species in a 1 m2 quadrat in the center of each of the 144 – 4 x 4 m plot. The corners of the center of the plot are marked by 4 nails. If a nail is missing or out of place, use the measurements along the diagonals to locate the corner of the plot and re-install the nail. For bunchgrass (i.e. STCO) count the individual plants, not the tillers. For single stemmed grasses (i.e. AGSM), count each tiller. For all dicots and sedges, count individuals. Count by 1’s up to 30. After 30, begin counting by 10’s. Use a string or wire to divide the quadrat into quarters, which will make counting more manageable. Basal Cover Sampling (m2/m2): Use a 10 point frame to estimate cover in each 1 m2 quadrat in which density was estimated. The point frame should be placed in 4 different locations, along each diagonal, as shown in the diagram, in each quadrat. Flip a coin to decide which direction the points should face. You may use the same directions for every diagonal in every quadrat. This will provide a total of 40 point contacts for each quadrat. The categories to records are plant species (use codes), litter, bare ground, and rocks. Be very critical about what the contact is. The accuracy of the methods is determined by how carefully contacts are made. Record only what the exact tip of the point touches at the soil surface. You may need to ignore a hit on a leaf to reach the soil surface. Do not penetrate the soil surface. All points must hit inside the quadrat. Canopy cover sampling (added in 2007): Locate each of 4 quadrats centered on a diagonal of the 1 m2 plot half way between the center and a corner of the plot (see figure). In each quadrat, estimate canopy cover (the projection of the canopy of all the individuals of each species onto the soil surface) using the following set of cover classes record the projected canopy cover. For each Daubenmire quadrat you will record on the Canopy Cover datasheet the cover class (1, 2, 3, 4, 5, or 6) for each group of species. |
| Principal Investigator: | Indy Burke |
| Long Term Contact: | Indy Burke: iburke@uwyo.edu |
| Public Access Status: | open |
| Begin Date: | 7/1/1997 |
| End Date: | 10/31/2008 |
| Sample Frequency: | |
| Long Term Experiment?: | Yes |
| Keywords: | density, disturbance, fertilization, nitrogen, plants, water, organic matter, inorganic matter |
| Geographic Location: | Bounded by (40.857500N,-104.785833W) and (40.800278S,-104.730556E). Altitude Range: 1645.0 to 1675.1 Meters above sea level |
| Related Datasets: | (none) |
| Related Publications: |
Lowe, P.. 2000. Nitrogen availability effects on exotic invasive species. M.S. Thesis. Colorado State University. Advisor(s): W.K. Lauenroth |
Metadata
Download Data Set
Note: Standard Excel files are limited to around 64,000 rows. Several of our data sets are much larger than that – if your download takes a long time to initialize, check the excel file for the last row. If the last row is at or in excess of 64,000, please contact us to arrange for alternative access to the larger tables.
