Protecting the resource: an assessment of mitigation methods used to protect large trees from African elephant impact in a savanna system
Data files
Sep 18, 2023 version files 61.14 KB
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Cook_et_al_2023_WildlifeBiology_DataDepository.xlsx
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README.md
Abstract
African elephants (Loxodonta africana) can alter the structural components of savanna ecosystems, often through the reduction of the large tree (>5 m height) cover component. Elephant impact can be amplified in small, protected areas, or areas where water is readily available to elephants. One management option is to protect large trees directly using applied mitigation methods to limit elephant impact. In this paper, we assessed and compared the effectiveness and logistical requirements of four mitigation methods that have been applied to protect large trees from elephant impact in South Africa’s Greater Kruger National Park - namely African honeybees (Apis mellifera scutellata) in beehives; creosote oil in glass jars, concrete pyramids arranged in circles around trees, as well as wire-netting the trees’ main stems. For each method, elephant impact levels and tree mortality rates were measured over a 2–5-year period depending on the method in use. Sample sizes ranged from 43 to 59 trees per mitigation method, with a comparable control, which was a tree of the same species and morphological dimensions but lacking any mitigation application. Beehives were the most effective method at reducing tree loss, significantly reducing tree mortality from 34% (6.8%/year) in control trees to only 10% (2%/year) over the five-year experimental period. However, beehives were the most expensive method to apply to a tree, although this cost can be compensated through honey sales. Concrete pyramids reduced tree loss when the combined pyramid radius was >1.5 m in length, whilst wire-netting was effective against bark-stripping by elephants but was still vulnerable to heavier forms of impact such as uprooting and stem snapping. Creosote jars did not prevent elephants from impacting treated trees. Our results provide managers with a toolkit for protecting large trees against elephant impact, commenting on both the efficacy and the logistical constraints for each method.
README: Protecting the resource: an assessment of mitigation methods used to protect large trees from African elephant impact in a savanna system
In this study, we assess the effectiveness of four mitigation methods that have been used to protect marula (Sclerocarya birrea) trees from African elephant (Loxodonta africana) impact in the Associated Private Nature Reserves (APNR) in South Africa. The four mitigation methods included beehives, creosote jars, concrete pyramids and wire-netting. Each 'treated' tree was compared with control (no protection) trees, with the levels of impact assessed and compared between the method and control trees.
Description of the data and file structure
The datasets are divided into the following sections:
1) Elephant impact scores
Impact scores were measured at the start and end of each method's experiment. Impact scores were assessed according to the following assessment table:
Table 1. Elephant impact scoring system for impact on large trees, as defined by Walker (1976) and modified by Greyling (2004).
Impact-type | Impact-type severity classes |
---|---|
1 | 2 |
Bark-stripping | No impact |
Primary branch breakage | No impact |
Uprooting | No impact |
Main stem snapping | No impact |
Secondary branch breakage | No impact since baseline assessment |
Time was measured as 0 (Project start) and 1 (Project end).
This data was used to assess how each method protect the trees against various forms of elephant impact.
Greyling, M. D. 2004. Sex and age related distinctions in the feeding ecology of the African elephant, Loxodonta africana. PhD Thesis, University of the Witwatersrand, Johannesburg, South Africa.
Walker, B. H. 1976. An approach to the monitoring of changes in the composition and utilization of woodland and savanna vegetation. South African Journal of Wildlife Research – 6: 1-32.
2) Survival analyses
Survival analyses data includes the method name (Method), whether it is a control or treated tree (Treatment), the number of years that the tree survived (Time) and whether the tree survived (0) or was killed (1) (Status). This data was used to assess the effectiveness of each method at prolonging the persistence of marula trees in the APNR. Each method was compared against its control trees.
3) Regression
The regression data was used to assess how tree survival was affected by the type of mitigation, tree height (m), as well as stem diameter (cm). The tree height and stem diameter values have been logged. Mortality is recorded as 0 (tree alive) or 1 (tree dead).
The Excel file contains a metadata tab for each data tab, complete with variable descriptions.
Sharing/Access information
Further information regarding the dataset can be obtained by contacting the lead author (Robin Cook; robincook@elephantsalive.org) or the Director of Elephants Alive (Dr. Michelle Henley; michelephant@savetheelephants.org).
Code/Software
All statistical analyses were conduced in R-studio. The following R-packages were used for the survival analyses: survival package, Therneau 2022
Therneau, T. T. 2022. survival: Survival Analysis. R package version 3.4-0.