The LTER dry heath (Toolik DH) site was set up in 1989.  The experimental design is three blocks of 5 x 20 meter plots with randomly assigned treatments within each block. Treatments include control (CT), and nitrogen 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).  Starting in 2012 NH4NO3 fertilizer was no longer available for purchase.  We switched to NaNO3 and NH4Cl as a nitrogen source for all subsequence years.

Exclosure plots were set up at the dry heath site in July 1996 on extra 5 x 20 meter plots within the three-block design.  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). Control plots from the 1989 plots can be used as control values for years in which the NFCT plots were not sampled.

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.
Gough, L., P.A. Wookey, and G.R. Shaver. 2002. Dry heath arctic tundra responses to long-term nutrient and light manipulation. Arctic, Antarctic, and Alpine Research. 34: 211-218.
Shaver, G.R., J.A. Laundre, A.E. Giblin, and K.J. Nadelhoffer. 1996. Changes in live plant biomass, primary production and species composition along a riverside toposequence in Arctic Alaska, U.S.A. Arctic and Alpine Research. 28: 363-379.

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. 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. 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%.