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R 2 = 0.90. Increasing burn “preference”. Figure 1. Relationship between body size and overall preference for burned sites (patchy and continuous combined). Pure browsers, giraffe and steinbuck, are shown in orange and were excluded from the regression.
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Increasing burn “preference”
Figure 1. Relationship between body size and overall preference for burned sites (patchy and continuous combined). Pure browsers, giraffe and steinbuck, are shown in orange and were excluded from the regression.
Preference for burn pattern related to body size
Average dung per 40 m2
Spatial ecology of fire:
Herbivore preferences for burns of varying size and patchiness
Ryan Sensenig Graduate Group in Ecology, University of California, Davis
Large herbivores are known to select burn sites for improved grazing efficiency, enhanced nutrient quality, and increased visibility. Few studies have addressed (a) the magnitude of attraction for species of varying body size and (b) whether the scale of the burn affects their response.
While most species showed some preference for burned areas, smaller bodied animals showed the most dramatic response (Figure 1). Hare dung was 25 X’s more abundant in burns than unburned areas, Grants and Impala dung 6 X’s more abundant, and oryx and hartebeest 2-3 X’s more abundant. However, dung of the largest species (zebra, eland, and elephant) were at greater densities in unburned controls than in burned sites.
As shown in Figure 3, grazers seem to select burn sizes related to their body size. Hare had highest dung densities in the smallest burns and Grants gazelle the highest in 9 ha burns. Eland, hartebeest, and giraffe had highest dung means in 9 ha burns, though less dramatically. The largest species avoided burns and showed a slight tendency to select the largest burn sizes.
Figure 3. Ratio of dung in burn sites to dung in control plots for different burn sizes. Colored lines indicate species where burn sizes are significantly different (p = 0.05, white filled dots are different.)
These findings suggest that grazers respond to burns differently depending on their body size and burn scale. Differences may relate to predator avoidance strategies; small species require cover for hiding and larger species select open areas with increased visibility. Alternatively, larger animals may not be able to obtain enough food in burns and require unburned grass nearby (oryx, hartebeest, zebra).
This study suggests that burning will benefit the smaller species in Laikipia the most, and that burns need not be large to have a significant impact. This may be an important realization when balancing the use of fire with preservation of whistling thorn for elephants and other browsers. Further analysis is ongoing to understand how visibility, grass quality, and rainfall affect grazing selection of burned areas.
During March of 2004 and 2005 we burned more than 480 hectares across five different properties in Laikipia (Jessel, Ol Pejeta, Mpala, Segera, and Sweetwaters). We completed a total of 18 different burns which varied in their size (81, 9 and 1 hectares). Eleven of these burns were “continuous” burns and seven were “patchy” burns as shown below.
Species preferences for patchy versus continuous burns varies with body size (Figure 2). The smallest species showed preferences for patchy burns, as did the larger antelope (oryx and hartebeest). Grants gazelle and impala showed preferences for continuous burns. The largest species showed no preference between patchy, continuous, or unburned areas.
Special thanks to Jessel, Mpala, Ol Pejeta, and Segera Ranches. Support and assistance from Peter Jessel, Giles Prettejohn, JohnHenry Ruggieri, Richard Vigneand Ken Wreford-Smith has been vital to the project and is greatly appreciated. Assistance from MRC, Nathan Gregory, and Isaac Kimathi has been invaluable. Thanks to James Ekiru, Patrick Etelej, John Mpaiyan, and Callistus for their hard work.
Grazer use of burned sites was assessed by counting dung pellets in burned and unburned areas. The first survey was completed in April/May, about 1 month after the burn, and 2 additional surveys in June and August.
Funding provided by a National Science Foundation Graduate Research Fellowship, a National Science Foundation Dissertation Improvement Grant, UC Davis, the Global CRSP, and a NSF to Truman P. Young.
Figure 2. Mean dung piles in patchy burns, continuous burns, and unburned control plots from 3 surveys. (MANCOVA, Wilk’s Lambda = 0.008)