Theories of Vegetation Change Mort Kothmann Texas A&M University

Managing Plant Succession August 2003 October 2007 Fire + HerbivoryVegetation change

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.

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 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

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. 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’)

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

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

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

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

Prescribed Burning

Fire

Drought – Sept 1999

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

Grasses Replacing Juniper following Fire Sideoats gramma

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.

Rolling Plains – Early March

Rolling Plains – Late March

Rolling Plains – Late April

Rolling Plains – Late May

Rolling Plains – Late June

Rolling Plains – Late July

Rolling Plains – Late August

Rolling Plains – Late September

Rolling Plains – Mid October

Rolling Plains – Mid December