Goals and Additional Design Details for E120

Additional Design Details
Biodiversity II is contained within a block of 342 plots laid out in a grid adjacent to Biodiversity I. Each plot was laid out as a 13 m x 13 m square, but only the central 9 m x 9 m is actively maintained to contain the specified species and level of plant diversity. This is the only portion sampled. Plots were planted with grassland perennial herbaceous and savanna woody species. These plant species were in either the C4 grass, C3 grass, legume, other forb, or woody functional groups. The species composition of the plots was chosen by separate random draws of the appropriate number of species (1, 2, 4, 8, or 16 plant species) from a pool of 18 species. For diversity levels 1, 2, 4, 8, and 16 species, there are 39, 35, 29, 30, and 35 replicates, respectively.

To initiate the experiment, a field at Cedar Creek Natural History Area, Minnesota, was treated with herbicide and burned in August, 1993, had 6-8 cm of soil removed to reduce the seed bank, was plowed and harrowed, then divided into plots of which 168 form this experiment. Plots for Biodiversity II were manually seeded in May 1994 using seed addition rates and methods like those of Biodiversity I. All plots received, in total, 10g/m² of seed in May 1994 with seed mass divided equally among species. Due to insufficient water resources, the plots were not irrigated in 1994. Because a dry and windy spring led to some soil and seed erosion and to poor germination, plots were re-seeded in May 1995, at half the 1994 rate, and watered once or twice weekly with an irrigation system. Two species that did not germinate in 1994 were replaced with different species in the same functional groups in the 1995, with their seeding proportionate to 10g/m². Three species (Elymus canadensis, Poa pratensis, Panicum virgatum) did not establish in one of their two original monocultures, even after reseeding, and these three plots were abandoned after 1996.

All plots were mown in July 1994 to help control weeds, and manually weeded in August 1994. They were manually weeded twice in 1995, four times in 1996, and three or four times from 1997 onward. Selective herbicides were also used through 1997. Plots that were designated to contain only legumes and/or other forbs were sprayed with Assure (Quizalofop P-ethyl (Ethyl(R)-2-[4-(6-chloroquinoxalin-2-yl oxy)-phenoxy]propionate)), a selective herbicide against grasses, twice each growing season from 1994 through 1997. The plots designated to contain just grasses were sprayed twice a year through 1997 with 2,4-dichlorophenoxyacetic acid, a selective herbicide against forbs. All plots in Biodiversity II were burned each spring in late April or early May before plant growth had begun.

There were two problems in implementing Biodiversity II. The first concerned the legume Petalostemum villosum. It had, as a seed contaminant, a congener P. candidum, causing both species to be planted, but at approximately half the desired density for each species, in plots designated for P. villosum. Moreover, seed of the legume Amorpha canescens was inadvertently substituted the legume P. villosum in 16-species plots. Second, because virtually no Solidago rigida, a non-legume forb, germinated during 1994, we reseeded all plots planted originally to Solidago rigida with the non-legume forb Monarda fistulosa. Some Solidago rigida did germinate in 1995 and occurs in plots where originally planted.

Location
The experiment occupies a 10 hectare block of land in a former "brome field" on the land that formerly was part of the Peterson farm.

Other Plots Within the Experimental Block
Plots within the experimental zone which are not used in E120 are 76 additional plots that had functional group compositions drawn from an augmented species pool, 46 plots planted to 32 species, and 48 plots designated for other uses.