Ecotonal blue and black grama: ecophysiological responses to precipitation changes

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Ecotonal blue and black grama ecophysiological
responses to precipitation changes

• Chuck Buxbaum

Dept of Biology, UNM
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• Blue grama
• Colorado shortgrass steppe dominant
• Slow growing
• Long-lived
• Grazing resistant
• Drought sensitive
• Seed dispersal
• May-Sept. establishment
• Deep rooting
• Fine soils

• Black grama
• Chihuahuan Desert dominant
• Quick growing
• Not-so-long-lived
• Grazing sensitive
• Drought resistant
• Vegetative reproduction
• July establishment
• Shallow rooting
• Varied soils

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Is coexistence stable?
No
Yes
Competitive exclusion
Resource partitioning
Hypothesis Blue and Black grama coexistence is
stable Prediction Different resource use,
temporally spatially
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• Responses to different amounts of precipitation
• Hypotheses
• Blue grama will respond more positively to
  increased precipitation
• Black grama will not decline as rapidly with
  decreased precipitation
• Treatments 0, 100, 200 precipitation

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• Responses to different seasons of precipitation
• Hypotheses
• Blue grama will respond more positively to
  winter/spring precipitation
• Black grama will respond more positively to
  summer precipitation
• Precipitation treatments
• no rain, cold season rain, warm season rain,
  control

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• Conclusions (Part I)
• 2-year growth responses similar between species
• Plant phosphorus correlated with growth response,
  but not nitrogen
• Black grama more nutrient-use efficient
• Interaction between treatment and species
  suggested by multivariate analysis

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no rain/gracilis
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• Conclusions (Part II)
• 2-year growth responses differ -- Blue grama
  uses winter precipitation.
• plant nutrient concentrations are highest in
  winter drought treatment.
• some interaction between treatment and species
  suggested by multivariate analysis.
• PRECIPITATION IS UTILIZED DIFFERENTLY BY BLUE AND
  BLACK GRAMA

Coexistence is stable
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Thank you to Jim Gosz, Bob Parmenter, Cliff
Dahm, Bruce Milne, Carl White, Deb Peters, Les
McFadden, Carol Treadwell, John Craig, Doug
Moore, Greg Shore, John Dewitt, Luis Guzman,
Charles Curtin, Tamara Hochstrasser, Ray Romero,
Susan Geer, the US FWS and many others. Funded
by Sevilleta LTER summer R.A. program
(1995-1996), Albuquerque Daylily Society, UNM
Biology GRAC, and Sandia Preparatory School
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Landscape evolution of the Llano de Manzano
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