The Ecology of Black Cotton Glades Kari E. Veblen University of California-Davis, USA (email@example.com) Making glades Research overview Introduction My research explores the ecology of abandoned boma sites in the black cotton ecosystem. In Laikipia, old boma sites, referred to as “glades,” are recognized as large treeless patches The objective of this experiment is to test methods of creating glade-like structures—areas that are (approx. 0.5-1.0 ha) of nutrient-rich grass that dot the savanna landscape (Figures 1 and 2). nutrient rich and attractive to wildlife and livestock. I am testing the effects of three factors on glade Abandoned boma sites such as these occur throughout much of eastern and southern Africa development: in various forms (Stelfox 1986, Blackmore et al. 1990, Reid and Ellis 1995). In Turkana, • fertilization with dung or commercial fertilizer Kenya, old boma sites are the mirror image of Laikipia’s old bomas: dense Acacia patches in • clearing of trees to make open areas an otherwise treeless landscape (Reid and Ellis 1995). Glades can remain on the landscape for many decades—at least 45 years in Laikipia. Understanding how glades develop over • addition of Acacia brush, which may create safe sites for the establishment and time and how plants and animals fit into their development are integral to a scientific growth of certain plant species preferred by herbivores (Figure 6). understanding of the black cotton ecosystem as a whole. Additionally, better understanding Fertilization may increase the nutritive value of the plants in the area or encourage the glades, which attract both wild and domestic animals, may be useful to livestock and wildlife establishment of lawns of Cynodon, thereby attracting wildlife or cattle. If cleared or brush-addition managers. Here I present two components of my research: 1) description of the plants, areas attract cattle or wildlife, increased defecation and/or grazing may stimulate grass production animals, and soil associated with black cotton glades as they develop over time and 2) to produce more attractive forage. Each of these three factors or some combination of them could experimental boma-building that explores how dung addition, tree-clearing and Acacia perpetuate an escalating cycle of increased nutrients and increased herbivore use, leading to brush-addition— three major components of bomas—influence glade development. glade-like structures. Methods Figure 1. Quickbird satellite image (June 2003) displayed in false color I am using a combination of 50x50 m. plots (shared with C. Riginos’ tree density experiment) and infrared, with red indicating higher plant productivity. Image covers portions of 10x10 m. plots to test the influence of dung and fertilizer addition, tree clearing and Acacia brush a) Mpala, Jessel and Segera black cotton soil. Glades appear as small red patches across the landscape. addition on glade development in the Mpala and Jessel black cotton soil (Figure 7). In 50x50 m. Recently abandoned boma plots (with a 10 m. buffer on each side), I will compare five replicates each of the following three treatments: 1) trees cleared, 2) trees cleared with 10x10 m. patch of dung at center, and 3) no tree Description of black cotton glades clearing. In 20x20 m. plots, I will compare five replicates each of the following treatments: 1) dung Cynodon plectostachyus Pennisetum stramineum Introduction addition in inner 10x10 m. area, 2) tree clearing in full 20x20 m. area, 3) Acacia drepanolobium 100 Although the vegetation, soil and animals associated with glades in red soil have been brush addition around inner 10x10 m. area, 4) brush addition+dung addition, 5) clearing +dung 80 described (Young et al. 1995, Augustine 2003), black cotton glades have not yet been addition, 6) brush addition +clearing+dung addition, 7) fertilizer addition in inner 10x10m. + 60 formally described. Because the two ecosystems differ so dramatically, we would expect clearing, and 8) control (no manipulations). In addition to making comparisons among plots of the pin hits 40 black cotton glades to be characterized by very different communities of plants and same size, I will be able to compare similar treatments of different sizes. I am regularly sampling animals, and by unique soil characteristics. I surveyed plants, animals and soil on new vegetation, dung (animal use), termite presence, and soils to test which factors are most 20 and old glades to better understand how glades develop over time in the black cotton soil. responsible for the functional traits of glades. 0 Methods Significance/application New glades Old glades I surveyed five young glades (<45 years old, Figure 2b) and five old glades (>45 years Understanding how old bomas develop into glades is of significance for understanding dynamics of Figure 4. Mean (+1 S.E.) of Cynodon old, Figure 2c) on Mpala and Jessel properties. In these glades, I measured plant cover the ecosystem and is also potentially of interest to livestock and wildlife managers. The results of and Pennisetum cover in 5 new (<45 b) yrs) and 5 old (>45 yrs) glades. Glade ~7 years old inside and outside of the glades, using a series of pin-frame measurements (Figure 3). I this study will complement my descriptive study by lending insight into the mechanisms behind also assessed animal use of these glades by identifying and counting different piles of glade development. Furthermore, my results may aid interested land managers in creating glade- animal dung found inside two 20x20 meter blocks inside each glade and along two 100m- like structures to provide nutrient-rich grazing areas for cattle or wildlife. long (and 4m-wide) transects located at 100m and at 200m away from each glade. Finally, I collected soil (at 0-30cm depth) inside and outside each glade and had the soils analyzed for nitrogen, phosphorus, potassium, calcium, magnesium, and sand/silt/clay content. I tested the data for differences in vegetation, dung, and soil inside and outside 120 Clearing only INSIDE of new versus old glades. OUTSIDE 100 Brush only Clearing only dung density (x1000) NEW GLADES Results and conclusions 80 60 • New glades in the black cotton soil were dominated by the mat-forming Cynodon 40 OLD plectostachyus (Star grass), followed by dominance by the taller bunch grass, Dung only 20 Pennisetum stramineum, in old glades (Figure 4). 0 Dung + clear 120 • Cynodon plectostachyus almost never occurred outside of glades. c) Glade > 45 years old 100 Dung + clear • Bracharia, Lintonia, Themeda, and Mezianum grass species, which dominate dung density (x1000) OLD GLADES 80 outside of glades, were almost never found inside glades. Brush + dung 60 Figure 3. Ten-point pin-frame used to assess • Total dung density of all herbivores was higher inside new glades than outside plant cover. Observers count how many times 40 each plant species is hit by a vertical pin (Figure 5). Zebra dung density was highest outside of glades, while Grant’s gazelle (maximum 10 hits for each species). 20 dung was highest inside glades. Elephants appear to strongly prefer new glades, None 0 Brush, clear, dung All Cattle+ Grant's Elephant herbivores buffalo Zebra gazelle and cattle show a slight preference for new glades. None Figure 5. Herbivore dung count data inside • Relative to non-glade soils, glade soils were high in phosphorus and potassium, but and outside of new (<45 yrs) and old (>45 low in magnesium, calcium, sodium and clay content. Nitrogen was high in all yrs) glades. Fert + clear glades, but highest in new glades. Figure 2. Successional sequence of abandoned black cotton boma vegetation: (a) a newly Because cattle and wildlife are important players in the black cotton ecosystem and also abandoned boma, (b) a new glade (~7 years) appear to use glades especially heavily, herbivore activity may influence the rate at which =dung =N fertilizer covered with Star grass, Cynodon plectostachyus, =Acacia brush =trees/uncleared and (c) an old glade (>45 years) covered with glades make the transition from Cynodon- to P.stramineum-dominance. For example: Pennisetum stramineum. • A plant that has been damaged by herbivory may be at a competitive disadvantage Figure 7. Schematic diagram of treatments for for resources such as water or light. In such a case, heavier grazing of Cynodon glade-making experiment testing the effects of References: Augustine, D. J. 2003. Long-term, livestock-mediated redistribution of nitrogen and phosphorus in an East African savanna. would lead to a faster takeover by P. stramineum. dung and fertilizer addition, brush addition, and tree Journal of Applied Ecology 40:137-149. Figure 6. Experimental Acacia drepanolobium clearing on glade development. Large plots are Blackmore, A. C., M. T. Mentis, and R. J. Scholes. 1990. The origin and extent of nutrient-enriched patches within a nutrient- • Herbivores may export nutrients out of glades when they graze on high-nutrient brush addition to simulate boma fence. 50x50m., and small plots are 20x20m. Small focal poor savanna in South Africa. Journal of Biogeography 17:463-470. plots included within larger plots are 10x10m. glade grasses. If Cynodon competes better in high-nutrient environments, then Reid, R. S., and J. E. Ellis. 1995. Impacts of pastoralists on woodlands in South Turkana, Kenya: livestock-mediated tree recruitment. Ecological Applications 5:978-992. herbivores exporting nutrients may speed the transition from Cynodon to P. Stelfox, J. B. 1986. Effects of livestock enclosures (bomas) on the vegetation of the Athi Plains, Kenya. African Journal of Ecology 24:41-45. stramineum. Young, T. P., B. D. Okello, D. Kinyua, and T. M. Palmer. 1998. KLEE: a long-term multi-species herbivore exclusion experiment Acknowledgements: in Laikipia, Kenya. African Journal of Range and Forage Science 14:94-102. I am using the KLEE experiment (Young et al. 1998) and conducting additional Many thanks are owed to the following for their help in the field: Frederick Erii, John Lochukuya, Jackson Ekadeli, Patrick Etelej, Young, T. P., N. Patridge, and A. Macrae. 1995. Long-term glades in acacia bushland and their edge effects in Laikipia, Kenya. experiments on Mpala, Jessel and Segera properties to try to understand how the effects Corinna Riginos, James Ekiru, Jake Goheen, Ali Hassan, Dan Kelly, John Lemboi and Simon Lima. Thank you to Truman Ecological Applications 5:97-108. Young for advice, support and field assistance. Thank you to Mpala Research Centre, Mpala Ranch and Peter Jessel for of herbivores influence the nature of competition and interactions between the two glade permission to use field sites and for logistical support. Funded by NSF and U. California-Davis Jastro Shields grant. grass species.
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