Abstract
Demographic variability in the tree component of savannas, arising from both spatial and temporal variability in fire, herbivory, and climate, is thought to be a key driver maintaining tree-grass co-existence in savannas. Modeling work has shown that this variability can be vital to the persistence of savanna as a biome and that variability in climate, herbivory and fire affect tree establishment. However, empirical evaluations of the idea that savanna tree establishment is variable have so far been limited to tests of the effects of major events (such as the East African rinderpest epidemic) on tree establishment. The degree to which tree establishment varies in savannas under less extreme variability in climate, herbivory and fire remains unknown. We tested whether establishment of adult trees was constant or episodic using tree ring counting of three Acacia species in Hluhluwe iMfolozi Park in South Africa. Patterns of establishment of adult trees were analyzed at three spatial scales for temporal and spatial patchiness. Establishment of adult trees was not constant for any of the three species of Acacia, and all three species showed significant spatial patchiness and larger-scale temporal variability in establishment patterns. Spatial patchiness highlights the importance of landscape processes like fire and herbivory, while larger-scale temporal variability indicates that climatic variability also structures tree demography. These results suggest that current tree cover in savannas is a product of ecological history and is not necessarily determined by current ecological processes. An historical perspective is essential for interpreting patterns of tree cover in savannas, in models of the effects of climate, fire and herbivory (especially elephants), in experimental work, and in analyses of continental patterns of tree cover alike.
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Claims 6
Claim · model-written summary
Establishment of adult Acacia trees was not constant for any of the three species.
- Outcome
- establishment of adult treese1
- Qualifier
- not constant for any of the three speciese1
- Setting
- Hluhluwe iMfolozi Park in South Africae0
AcaciaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We tested whether establishment of adult trees was constant or episodic using tree ring counting of three Acacia species in Hluhluwe iMfolozi Park in South Africa”
e1“Establishment of adult trees was not constant for any of the three species of Acacia”
Claim · model-written summary
All three Acacia species showed significant spatial patchiness in tree establishment.
- Outcome
- spatial patchinesse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We tested whether establishment of adult trees was constant or episodic using tree ring counting of three Acacia species in Hluhluwe iMfolozi Park in South Africa”
e1“all three species showed significant spatial patchiness and larger-scale temporal variability in establishment patterns”
Claim · model-written summary
All three Acacia species showed larger-scale temporal variability in establishment patterns.
- Outcome
- larger-scale temporal variability in establishment patternse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We tested whether establishment of adult trees was constant or episodic using tree ring counting of three Acacia species in Hluhluwe iMfolozi Park in South Africa”
e1“all three species showed significant spatial patchiness and larger-scale temporal variability in establishment patterns”
Claim · model-written summary
Spatial patchiness of Acacia establishment highlights the importance of landscape processes such as fire and herbivory.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We tested whether establishment of adult trees was constant or episodic using tree ring counting of three Acacia species in Hluhluwe iMfolozi Park in South Africa”
e1“Spatial patchiness highlights the importance of landscape processes like fire and herbivory”
Claim · model-written summary
Temporal variability in Acacia establishment indicates that climatic variability structures tree demography.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We tested whether establishment of adult trees was constant or episodic using tree ring counting of three Acacia species in Hluhluwe iMfolozi Park in South Africa”
e1“larger-scale temporal variability indicates that climatic variability also structures tree demography”
Claim · model-written summary
Current tree cover in savannas is a product of ecological history rather than only current processes.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We tested whether establishment of adult trees was constant or episodic using tree ring counting of three Acacia species in Hluhluwe iMfolozi Park in South Africa”
e1“current tree cover in savannas is a product of ecological history”