KSURainfall Manipulation Plot Study

 

Rainfall, Temperature, and Invasive Species Treatments

Experimental manipulations of rainfall and temperature are conducted in a split-plot design, with rainout shelters (whole plots) assigned to one of two rainfall treatments, and subplots assigned to one of two warming treatments.

Rainfall

shelter picture

Ambient precipitation regime
In six of the 12 RaMPs, intercepted water is reapplied to the plots each time a natural rainfall event occurs.  Rain gauges outside the RaMPs and an in-line flow meter to the sprinkler system allows us to confirm that precipitation amounts applied inside the RaMPs equal the amounts of rain falling outside.

Altered temporal rainfall patterns
The other six RaMPs receive this treatment, which imposes a predicted climate change regime of longer inter-rainfall dry periods and larger rain events relative to current precipitation patterns. Assuming a typical growing season rainfall pattern, we lengthen the intervals between rainfall events by 50 percent, with an event defined as >5 mm precipitation in a 24 hr period.  Thus, a 2-week period between natural rainfall events (occurring an average of 4 times per growing season, Fahnestock and Knapp 1994) would be lengthened to 3 weeks. Any rain falling during these increased dry periods is stored and applied later as a single, large event at the end of the dry interval. Thus, individual storm events are larger and intervening dry periods longer relative to ambient patterns, but the total amount of precipitation received over the course of the growing season is the same as in the ambient treatment.

Warming

Each RaMP and unsheltered plot contains 4, 2 x 2m subplots.  Two of the subplots receive
20-25 W m-2 of downward infrared radiation to the soil surface/plant canopy year round from infrared lamps suspended 1.2 m above the canopy.  A sheet metal housing identical in size to the lamps is suspended above a third sub plot to control for the presence of the lamp housing, and the fourth subplot is unaltered.  Lamp height is increased periodically as the canopy height increases.

Invasive Species

To assess invasibility, we will focus on establishment and persistence of several target exotic invaders, including a C3 grass (Bromus inermis), a C4 grass (Sorghum halpense), and a C3 legume (Melilotus officinalis or Coronilla varia).  Seeds will be collected from field populations, and seeds of each species will be added to 0.1m2 subplots located in four 1.0m2 species composition subplots (two heated, two unheated) within each RaMP, after spring burning.  One heated and unheated 1.0m2 plot will be dedicated to destructive sampling throughout the growing season, the others for monitoring of seedling establishment.  Seedling establishment and growth (using destructive (biomass) and nondestructive (height) measurements), as well as light availability, will be monitored biweekly throughout growing season.  At the beginning and end of the growing season, cover of resident species will be estimated.  Biomass will be harvested at the end of the growing season.  The seed addition study will be repeated over several years to assess invasion success across a broader range of soil moisture availability.  All invasive species will be removed at the conclusion of this study to maintain the integrity of the plant community for future studies.

 

Last Updated 2-11-2011
NSF NRI DOE Konza