Abstract
Abstract. A 44‐yr record of herbaceous vegetation change was analysed for three contrasting grazing regimes within a semi‐arid savanna to evaluate the relative contribution of confined livestock grazing and climatic variability as agents of vegetation change. Grazing intensity had a significant, directional effect on the relative composition of short‐ and mid‐grass response groups; their composition was significantly correlated with time since the grazing regimes were established. Interannual precipitation was not significantly correlated with response group composition. However, interannual precipitation was significantly correlated with total plant basal area while time since imposition of grazing regimes was not, but both interannual precipitation and time since the grazing regimes were established were significantly correlated with total plant density. Vegetation change was reversible even though the herbaceous community had been maintained in an altered state for ca. 60 yr by intensive livestock grazing. However, ca. 25 yr were required for the mid‐grass response group to recover following the elimination of grazing and recovery occurred intermittently. The increase in mid‐grass composition was associated with a significant decrease in total plant density and an increase in mean individual plant basal area. Therefore, we failed to reject the hypotheses based on the proportional change in relative response group composition with grazing intensity and the distinct effects of grazing and climatic variability on response group composition, total basal area and plant density. Long‐term vegetation change indicates that grazing intensity established the long‐term directional change in response group composition, but that episodic climate events defined the short‐term rate and trajectory of this change and determines the upper limit on total basal area. The occurrence of both directional and non‐directional vegetation responses were largely a function of (1) the unique responses of the various community attributes monitored and (2) the distinct temporal responses of these community attributes to grazing and climatic variation. This interpretation supports previous conclusions that individual ecosystems may exist in equilibrial and non‐equilibrial states at various temporal and spatial scales.
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Claims 12
Claim · model-written summary
Grazing intensity had a significant, directional effect on the relative composition of short- and mid-grass response groups.
Not reportedComparatorDirection
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e0“Grazing intensity had a significant, directional effect on the relative composition of short‐ and mid‐grass response groups”
Claim · model-written summary
Interannual precipitation was not significantly correlated with response group composition.
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e1“Interannual precipitation was not significantly correlated with response group composition”
Claim · model-written summary
Interannual precipitation was significantly correlated with total plant basal area.
Not reportedDirection
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e2“interannual precipitation was significantly correlated with total plant basal area while time since imposition of grazing regimes was not”
Claim · model-written summary
Time since imposition of grazing regimes was not correlated with total plant basal area.
- Taxon
- herbaceous vegetationt0
- Treatment
- time since imposition of grazing regimese2
- Outcome
- total plant basal areae2
Not reportedDirection
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e2“interannual precipitation was significantly correlated with total plant basal area while time since imposition of grazing regimes was not”
Claim · model-written summary
Interannual precipitation was significantly correlated with total plant density.
Not reportedDirection
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e3“both interannual precipitation and time since the grazing regimes were established were significantly correlated with total plant density”
Claim · model-written summary
Time since the grazing regimes were established was significantly correlated with total plant density.
- Taxon
- herbaceous vegetationt0
- Treatment
- time since the grazing regimes were establishede3
- Outcome
- total plant densitye3
Not reportedDirection
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e3“both interannual precipitation and time since the grazing regimes were established were significantly correlated with total plant density”
Claim · model-written summary
Response group composition was significantly correlated with time since the grazing regimes were established.
- Taxon
- herbaceous vegetationt0
- Treatment
- time since the grazing regimes were establishede4
- Outcome
- compositione4
Not reportedDirection
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e4“their composition was significantly correlated with time since the grazing regimes were established”
Claim · model-written summary
Vegetation change was reversible under intensive livestock grazing.
- Taxon
- herbaceous vegetationt0
- Treatment
- intensive livestock grazinge5
- Outcome
- Vegetation change was reversiblee5
Not reportedDirection
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e5“Vegetation change was reversible even though the herbaceous community had been maintained in an altered state for ca. 60 yr by intensive livestock grazing”
Claim · model-written summary
The mid-grass response group took about 25 years to recover after grazing was eliminated.
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e6“ca. 25 yr were required for the mid‐grass response group to recover following the elimination of grazing”
Claim · model-written summary
Recovery of the mid-grass response group occurred intermittently.
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e7“recovery occurred intermittently”
Claim · model-written summary
The increase in mid-grass composition was associated with a significant decrease in total plant density.
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e6“The increase in mid‐grass composition was associated with a significant decrease in total plant density”
Claim · model-written summary
The increase in mid-grass composition was associated with an increase in mean individual plant basal area.
Verbatim
t0“Herbaceous vegetation change in variable rangeland environments”
e6“The increase in mid‐grass composition was associated with a significant decrease in total plant density”
e7“an increase in mean individual plant basal area”