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Theories of Vegetation Theories of Vegetation ChangeChange
Mort KothmannMort Kothmann
Texas A&M UniversityTexas A&M University
Managing Plant SuccessionManaging Plant Succession
August 2003
October 2007
Fire + Herbivory
Vegetation change
Plant SuccessionPlant Succession
Plant succession is a result of the competitive Plant succession is a result of the competitive interactions of plant species and interactions of plant species and populations. Its effects are predictable. It populations. Its effects are predictable. It happens everywhere, not just on happens everywhere, not just on rangelands. Understanding plant succession rangelands. Understanding plant succession is a key concept to designing effective is a key concept to designing effective grazing management.grazing management.
Rangeland ConditionRangeland Condition
Composition of plant community at a specified Composition of plant community at a specified site site relative to potential benchmark relative to potential benchmark community community (climax or a desired plant (climax or a desired plant community) that could occur on that sitecommunity) that could occur on that site
Ecological SiteEcological Site
Distinctive kind of land with physical Distinctive kind of land with physical characteristics (climate, soils and topography) characteristics (climate, soils and topography) which differ from other sites giving rise to which differ from other sites giving rise to significantly different potential for the kinds and significantly different potential for the kinds and amount of vegetation it can produce. amount of vegetation it can produce.
(Note: this is essentially the same definition as (Note: this is essentially the same definition as Range Site except that it uses ‘land’ not Range Site except that it uses ‘land’ not ‘rangeland’)‘rangeland’)
Ecological Site DescriptionsEcological Site Descriptions
Adaptation of “poly” climax theoryAdaptation of “poly” climax theory Description of single plant community (Description of single plant community (edaphic edaphic
climax)climax) Geared towards grazing interpretationsGeared towards grazing interpretations Described at plant community scale and Described at plant community scale and
correlated to soil map unitscorrelated to soil map units
Names of Ecological (Range) Sites Names of Ecological (Range) Sites
Based on permanent Based on permanent physical features: physical features: Soil type Soil type TopographyTopography
Help users remember Help users remember significant rangeland in significant rangeland in their localitytheir locality Clay Upland, Saline, Clay Upland, Saline,
Limestone Breaks, Limestone Breaks, Claypan Savanna, Loamy Claypan Savanna, Loamy BottomlandBottomland
Time
Fire FrequencyGrazing Pressure
Probability & rate of woody plant establishment
A BC
Herbaceousretrogression
Perennialgrasses
Woodyplants
Com
mun
ity C
ompo
sitio
n
Tim
e o
r cu
ltura
l en
erg
y in
crem
ents
R
eq
uire
d to
dri
ve s
yste
m to
n
ew c
onf
igu
ratio
n
Shrubdriven succession
Graminoid-drivensuccession
A = Tall / mid-grasses
B = Mid / short grasses
C = Short grass / annuals
= Transition threshold
high lowhighhighlow
lowhigh
Archer
Juniper Replacing GrasslandJuniper Replacing Grassland
Note multiple age classes of juniper and weak stand of grasses
Prescribed BurningPrescribed Burning
FireFire
Drought – Sept 1999Drought – Sept 1999
Shrub dominated rangeland in transition towards Shrub dominated rangeland in transition towards grassland after a reclamation prescribed burngrassland after a reclamation prescribed burn
Grasses Replacing Juniper following FireGrasses Replacing Juniper following Fire
Sideoats gramma
Seasonal Vegetation DynamicsSeasonal Vegetation Dynamics(Aspect)(Aspect)
The following series of slides are photographs of The following series of slides are photographs of the same site made at 4-week intervals from the same site made at 4-week intervals from early March until mid December. Note that the early March until mid December. Note that the dominant species change as the seasons dominant species change as the seasons progress. In years with different weather progress. In years with different weather patterns, vegetation dynamics would differ.patterns, vegetation dynamics would differ.
Rolling Plains – Early MarchRolling Plains – Early March
Rolling Plains – Late MarchRolling Plains – Late March
Rolling Plains – Late AprilRolling Plains – Late April
Rolling Plains – Late MayRolling Plains – Late May
Rolling Plains – Late JuneRolling Plains – Late June
Rolling Plains – Late JulyRolling Plains – Late July
Rolling Plains – Late AugustRolling Plains – Late August
Rolling Plains – Late SeptemberRolling Plains – Late September
Rolling Plains – Mid OctoberRolling Plains – Mid October
Rolling Plains – Mid DecemberRolling Plains – Mid December