Summary:
The purpose of this experiment, begun
in 1982, is to measure the long-term effects of nitrogen deposition on
the species diversity, species composition, productivity and stability of vegetation
not under the stress of mammalian herbivory. The experiment is being conducted
in fields A, B, C, and D. There are 8 different levels of nitrogen addition
with other nutrients added to ensure that N remains the limiting nutrient, and
a control which receives no nutrients. The treatments are A, B, C, D, E, F,
G, H, and I , defined as "microplot" strategy and documented in fertilization
details. There are 6 replicates of the 9 treatments in fields A, B, and C and
5 replicates in field D. The treatments were randomly assigned to the plots.
In fields A, B, and C the plots are in 6 by 9 grid and are 4 by 4 meters in
size with 1 meter aisles between plots. In field D the plots are 1.5 by 4 meters
and are placed in a 3 by 17 grid. The plots are enclosed by a fence to keep
out mammalian herbivores. Gophers are trapped and removed as they appear. Nitrogen
fertilizer (NH4NO3) is applied twice per year, once in
early May and once in late June.
Methods and Data: