The LTER moist acidic tussock (MAT) site was set up in 1989. The experimental design is four blocks of 5 x 20 meter plots with randomly assigned treatments within each block. Treatments include control (CT), nitrogen added (N), phosphorus added (P), and nitrogen plus phosphorus (NP). Fertilizer is added annually following snowmelt in June as 10 g/m2 nitrogen (as NH4NO3) and 5 g/m2 phosphorous (as triple superphosphate). A passive warming experiment is conducted annually plastic covered greenhouses (GH) and warming amended N plus P as described above (GHNP). Shade houses reduce ambient light penetration to the ground by 50% (SHCT) and are also imposed on plots where N and P are added as above (SHNP). Exclosure plots were set up at the MAT site in July 1996 on extra 5 x 20 meter plots within the four-block design of the 1989 LTER acidic tussock experimental plots. On each plot a 5 x 10 meter section was fenced with large mesh (4-inch square mesh) and within this fence a 5x5-meter plot was fenced with a small mesh (1/2-inch square mesh). In each block two fenced plots were setup: a plot with no fertilizer and a plot with annual fertilization treatments as described above. Thus the treatments created are no fence, no fertilizer (NFCT); small mesh fence, no fertilizer (SFCT); large mesh fence, no fertilizer (LFCT); no fence, N plus P (NFNP); small mesh fence, N plus P (SFNP); and large mesh fence, N plus P (LFNP). In 1997 pH manipulation plots were established by creating one new 5 x 20 m plot adjacent to each of the original four blocks described above. Each plot was divided into two 5 x 10 m sections. Lime (L) is added annually at the rate of 150 g/m2 to raise pH in one half of the plot, and elemental sulfur (S) is added annually at the rate of 50 g/m2 to decrease pH in the other half of the plot.
In 1997 experimental plots were established at the LTER moist non-acidic tussock (MNT) site with the same methods as those used at MAT. CT, N, P, NP, L and S treatments are replicated in three blocks. GHCT and GHNP treatments are replicated in two blocks.

Calculations: All percent cover values were summed within each plot, and then each value was divided by the total to generate a percent cover value standardized to 100%.

Reference Citations: Gough, L. and S.E. Hobbie. 2003. Responses of moist non-acidic arctic tundra to altered environment: productivity, biomass, and species richness. Oikos 103:204-216.

Sampling Description.

Permanent monitoring areas were established in all treatment plots in 1998. Eight 1 m2 plots are sampled in each treatment in each block each year at the end of July. A 1 m2 quadrat is aligned 0.2 m inside of the plot at the site of a flag marking the first measurement. Within this quadrat, aerial percent cover of all vascular plants are noted by species as is all other ground cover. Categories include moss (all species lumped), lichen (all species lumped), litter, and standing dead Betula nana. Tussocks of Eriophorum vaginatum may be recorded as dying, dead, or eaten (indicating consumption by voles). Bare ground, frost boil, and water are also recorded. As an indicator of vole activity, the percent cover of the plot comprised of vole burrow holes, vole trails, and vole litter (small pieces of dead plant material) are also recorded. Finally, tussocks of Eriophorum vaginatum are counted. To standardize cover among plots, all percent cover values were summed within each plot, and then each value was divided by the total to generate a percent cover value standardized to 100%.