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Theories of Vegetation Change

Theories of Vegetation Change. Mort Kothmann Texas A&M University. Managing Plant Succession. October 2007. August 2003. Fire + Herbivory. Vegetation change. Plant Succession.

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Theories of Vegetation Change

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  1. Theories of Vegetation Change Mort Kothmann Texas A&M University

  2. Managing Plant Succession October 2007 August 2003 Fire + Herbivory Vegetation change

  3. Plant Succession Plant succession is a result of the competitive interactions of plant species and populations. Its effects are predictable. It happens everywhere, not just on rangelands. Understanding plant succession is a key concept to designing effective grazing management.

  4. Rangeland Condition • Composition of plant community at a specified site relative to potential benchmark community (climax or a desired plant community) that could occur on that site

  5. Ecological Site • Distinctive kind of land with physical characteristics (climate, soils and topography) which differ from other sites giving rise to significantly different potential for the kinds and amount of vegetation it can produce. (Note: this is essentially the same definition as Range Site except that it uses ‘land’ not ‘rangeland’)

  6. Ecological Site Descriptions • Adaptation of “poly” climax theory • Description of single plant community (edaphic climax) • Geared towards grazing interpretations • Described at plant community scale and correlated to soil map units

  7. Names of Ecological (Range) Sites • Based on permanent physical features: • Soil type • Topography • Help users remember significant rangeland in their locality • Clay Upland, Saline, Limestone Breaks, Claypan Savanna, Loamy Bottomland

  8. Graminoid-driven succession Shrub driven succession Perennial grasses Herbaceous retrogression A = Tall / mid-grasses B = Mid / short grasses C = Short grass / annuals = Transition threshold A B C Time or cultural energy increments Required to drive system to new configuration CommunityComposition Woody plants Time low high Grazing Pressure high low high Fire Frequency high Probability & rate of woody plant establishment low Archer

  9. Juniper Replacing Grassland Note multiple age classes of juniper and weak stand of grasses

  10. Prescribed Burning

  11. Fire

  12. Drought – Sept 1999

  13. Shrub dominated rangeland in transition towards grassland after a reclamation prescribed burn

  14. Grasses Replacing Juniper following Fire Sideoats gramma

  15. Seasonal Vegetation Dynamics(Aspect) The following series of slides are photographs of the same site made at 4-week intervals from early March until mid December. Note that the dominant species change as the seasons progress. In years with different weather patterns, vegetation dynamics would differ.

  16. Rolling Plains – Early March

  17. Rolling Plains – Late March

  18. Rolling Plains – Late April

  19. Rolling Plains – Late May

  20. Rolling Plains – Late June

  21. Rolling Plains – Late July

  22. Rolling Plains – Late August

  23. Rolling Plains – Late September

  24. Rolling Plains – Mid October

  25. Rolling Plains – Mid December

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