PARENT SESSION
Oral Session #46: Disturbance Ecology.
Presiding: M. Slocum
Tuesday, August 6. 1:00 PM to 4:45 PM. Grand Ballroom East, Radisson.

Consequences of shrub expansion and removal in mesic grassland: resource patterns and herbaceous production.

Lett, Michelle^*,1, Knapp, Alan¹, ¹ Kansas State University, Manhattan, KS

ABSTRACT- In tallgrass prairie, fire suppression permits the formation of shrub "islands" within the grassland matrix, significantly reducing herbaceous cover and production. A shrub removal study was initiated at Konza Prairie to assess the effect of Cornus drummondii on light, water, and nitrogen availability and to determine which resource(s) most strongly limits recovery of the dominant grass Andropogon gerardii. Despite increased leaf N, photosynthesis of A. gerardii and graminoid production under shrub cover were significantly reduced, due to a 90% reduction in light (PPFD) under intact shrub islands relative to open prairie. Recovery of A. gerardii photosynthesis and graminoid production following shrub removal was mediated by light and nitrogen, as seasonal mean PPFD, leaf N, and soil available N were significantly greater in removal sites (73%, 1.7%, and 19 g g^-1, respectively) relative to intact shrub islands (18%, 1.5%, and 5 g g^-1, respectively) the first year following removal. By year two, resource levels in removal sites decreased to levels typical of open prairie. An increase in net photosynthesis in A. gerardii with increasing leaf N was not seen in intact shrub islands or in shrub removal sites, reflecting light limitation and N saturation, respectively. These results indicate that patterns of resource availability change as shrub cover increases in tallgrass prairie and that shrub removal results in short-term increases in resources, enhancing the recovery of herbaceous cover and production.

KEY WORDS: shrub expansion, shrub removal, tallgrass prairie, Cornus drummondii