Abstract
Context
Studies of tree cover and spatial pattern in tropical savannas often focus on coarse-scale effects of climate, disturbance, and herbivory. Local hydrological, topographic, or edaphic factors, however, play an important role in determining resource availability for trees, but we often lack data for these variables at fine spatial resolution. River networks can serve as a proxy for some of these effects.
Objectives
Our objective was to characterize the relationship between distance to rivers and tree cover and spatial pattern, and to provide a first-order assessment of the total fraction of tree cover associated with river networks in a savanna ecosystem.
Methods
We explored the relationship between tree cover amount and patchiness as a function of distance to rivers in Serengeti National Park, Tanzania. We used segmented regression to identify the proportion of trees most likely to be influenced by river-associated resources.
Results
Both tree cover and tree patchiness declined systematically with distance to rivers, with tree cover declining up to about 100 m from river beds. Assuming that trees closer than this threshold are influenced by rivers (e.g., through greater access to groundwater), between a third and half of all Serengeti trees may be classifiable as ‘river-associated trees.’
Conclusions
Our results suggest that river networks may play a greater role in determining the amount and spatial pattern of tree cover in savanna ecosystems than previously considered, with potentially important consequences for savanna dynamics, and perhaps drought resilience.
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Data availability
All data are available at the Github page listed below.
Code availability
All code used in the analysis is available at https://github.com/rholdo/Holdo_Onderdonk_2022.
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Acknowledgements
We thank Jason Donaldson and Jules NeSmith for comments on the manuscript.
Funding
This work was supported by the Odum School of Ecology at the University of Georgia and by the National Science Foundation through Grant BCS-1461728.
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Both authors conceived the study. DAO collected the data. RMH conducted the statistical analysis and wrote the first draft of the manuscript. Both authors contributed to the final version.
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Holdo, R.M., Onderdonk, D.A. Savanna tree abundance and spatial patterns are strongly associated with river networks in Serengeti National Park, Tanzania. Landsc Ecol 37, 1113–1123 (2022). https://doi.org/10.1007/s10980-021-01380-x
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DOI: https://doi.org/10.1007/s10980-021-01380-x