Field Site
Our long-term field studies are conducted at the University of Kansas Field Station
(KUFS) located in eastern Kansas in the prairie-forest ecotone region of the central
USA. KUFS and is located just north of Lawrence, Kansas. Historically, the area was
dominated by tall-grass prairie and savanna vegetation prior to settlement. Experiments
1 and 2 were established in a 20+ hectare former cool-season hay field that had been
maintained as grassland by periodic mowing since abandonment from hay production in the
early 1980’s. At the start of our studies in 2000, the field was dominated by introduced
C3 hay-grasses, Bromus inermis (Smooth Brome) and Schedonorus arundinaceus (Tall
Fescue).
Design and Setup:
In preparation for experiment 1 a 70 x 120 m rectangular area of the field was
sprayed with glyphosate herbicide summer 2000 and then plowed and disked March-April
2001. In mid-April 2001 we established 96 4 x 5 m experimental plots, laid out in a 12 x
8 plot grid. The plot array was divided into 6 rectangular blocks of 16 plots, arranged
to control for spatial effects associated with a slight field slope. Each block was
further divided into two clusters of 8 plots. Blocks were separated by 12 m buffers,
clusters nested within blocks were separated by 10 m buffers, and plots nested within
clusters were separated by 2 m buffers. To the array of plots we applied 16 unique
treatment combinations (n = 6) in a 4 x 2 x 2 factorial nested design. Nested in each
cluster of each block, the first two factors were fully crossed in a 4 x 2
configuration: nitrogen (N) fertilizer added to plots as ammonium-nitrate at four levels
(0, 4, 8 and 16 g N m-2 yr-1); and phosphorus (P) added as superphosphate at two levels
(0 and 8 g P m-2 yr-1). In each block, one of the two clusters of eight plots was
randomly selected to receive multi-species seed additions (sowing treatment) to
experimentally enhance the pool of species available to plots. To accomplish sowing,
seeds of 50+ native and naturalized species were sown in April 2002 and 2003. All sown
species are members of the regional pool, chosen to represent a range of life histories,
functional guilds, historical origins and habitat affinities. Seeds were sown at rates
ranging from 10-320 seeds m-2 yr-1 year; depending on availability. To maintain plots as
grassland, a schedule of spring prescribed burns was initiated in 2005 on a return
frequency of once every three years.
Data Collection:
Core data consists of plant species % cover and plant biomass data collected during
annual vegetation surveys/harvests of all experiment plots. The annual core data
time-series currently spans 2001-2015.
Percent cover - Cover surveys of vegetation are conducted annually in late June -
early July by taking ocular estimates of percent cover for each species rooted within in
two permanently-marked 1 x 1 m sampling quadrats in each plot (192 quadrats in all).
Plant biomass - Biomass harvests of all plots are conducted annually in mid-late
July. From each plot, one 0.1 x 2 m strip of aboveground plant material is harvested
with electric clippers. Biomass is clipped at ground level and all litter collected.
Samples are separated into live and litter fractions. All biomass fractions are dried to
constant mass at 70C in a forced-air oven and then weighed
