The Ecology of Black Cotton Glad by pengtt


									The Ecology of Black Cotton Glades
 Kari E. Veblen
 University of California-Davis, USA (

                                                                                                                                                                                                                                                                                                                                     Making glades
                                            Research overview
     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.


                                                                                                                                                                                      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
                                                                                                                                                                                 and old glades to better understand how glades develop over time in the black cotton soil.         responsible for the functional traits of glades.

                                                                                                                                                                                 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.
                                                                                                     100                                                                                                                                                                                                                                                                                                    Brush only
                                                                                                                                                                                                                                                                                                                                                                                      Clearing only
                                                                           dung density (x1000)

                                                                                                                                                                    NEW GLADES

                                                                                                                                                                                 Results and conclusions

                                                                                                     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.
             Glade > 45 years old                                                                    100
                                                                                                                                                                                                                                                                                                                                                                                      Dung + clear
                                                                                                                                                                                     • Bracharia, Lintonia, Themeda, and Mezianum grass species, which dominate
                                                                              dung density (x1000)

                                                                                                                                                                    OLD GLADES

                                                                                                                                                                                     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
                                                                                                                                                                                                                                                                                   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).

                                                                                                                                                                                     dung was highest inside glades. Elephants appear to strongly prefer new glades,                                                                                              None
                                                                                                       0                                                                                                                                                                                                                                                                                                 Brush, clear, dung
                                                                                                               All      Cattle+              Grant's     Elephant
                                                                                                           herbivores   buffalo
                                                                                                                                             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
 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.
 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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