The Ecology of Black Cotton Glades
Kari E. Veblen
University of California-Davis, USA (keveblen@ucdavis.edu)
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
•
clearing of trees to make open areas
•
addition of Acacia brush, which may create safe sites for the establishment and
Kenya, old boma sites are the mirror image of Laikipia’s old bomas: dense Acacia patches in
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
growth of certain plant species preferred by herbivores (Figure 6).
time and how plants and animals fit into their development are integral to a scientific
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
a)
I am using a combination of 50x50 m. plots (shared with C. Riginos’ tree density experiment) and
Figure 1. Quickbird satellite image (June 2003) displayed in false color
infrared, with red indicating higher plant productivity. Image covers portions of
Mpala, Jessel and Segera black cotton soil. Glades appear as small red
patches across the landscape.
Recently abandoned boma
10x10 m. plots to test the influence of dung and fertilizer addition, tree clearing and Acacia brush
addition on glade development in the Mpala and Jessel black cotton soil (Figure 7). In 50x50 m.
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
Cynodon plectostachyus
Pennisetum stramineum
addition in inner 10x10 m. area, 2) tree clearing in full 20x20 m. area, 3) Acacia drepanolobium
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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
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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. +
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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
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
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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
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
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
pin hits
Introduction
0
New glades
b)
Glade ~7 years old
clearing. In 20x20 m. plots, I will compare five replicates each of the following treatments: 1) dung
Old glades
Figure 4. Mean (+1 S.E.) of Cynodon
and Pennisetum cover in 5 new (<45
yrs) and 5 old (>45 yrs) glades.
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
of new versus old glades.
INSIDE
OUTSIDE
Brush only
NEW GLADES
dung density (x1000)
100
80
60
OLD
40
20
Glade > 45 years old
• New glades in the black cotton soil were dominated by the mat-forming Cynodon
plectostachyus (Star grass), followed by dominance by the taller bunch grass,
Dung only
Pennisetum stramineum, in old glades (Figure 4).
Dung + clear
• Cynodon plectostachyus almost never occurred outside of glades.
Dung + clear
100
OLD GLADES
dung density (x1000)
c)
0
120
Clearing only
Results and conclusions
80
60
40
20
• Bracharia, Lintonia, Themeda, and Mezianum grass species, which dominate
outside of glades, were almost never found inside glades.
• Total dung density of all herbivores was higher inside new glades than outside
(Figure 5). Zebra dung density was highest outside of glades, while Grant’s gazelle
Brush + dung
Figure 3. Ten-point pin-frame used to assess
plant cover. Observers count how many times
each plant species is hit by a vertical pin
(maximum 10 hits for each species).
dung was highest inside glades. Elephants appear to strongly prefer new glades,
0
None
Brush, clear, dung
All
herbivores
Cattle+
buffalo
Zebra
Grant's
gazelle
Elephant
Figure 5. Herbivore dung count data inside
and outside of new (<45 yrs) and old (>45
yrs) glades.
Figure 2. Successional sequence of abandoned
black cotton boma vegetation: (a) a newly
abandoned boma, (b) a new glade (~7 years)
covered with Star grass, Cynodon plectostachyus,
and (c) an old glade (>45 years) covered with
Pennisetum stramineum.
References:
Augustine, D. J. 2003. Long-term, livestock-mediated redistribution of nitrogen and phosphorus in an East African savanna.
Journal of Applied Ecology 40:137-149.
Blackmore, A. C., M. T. Mentis, and R. J. Scholes. 1990. The origin and extent of nutrient-enriched patches within a nutrientpoor savanna in South Africa. Journal of Biogeography 17:463-470.
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.
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
in Laikipia, Kenya. African Journal of Range and Forage Science 14:94-102.
Young, T. P., N. Patridge, and A. Macrae. 1995. Long-term glades in acacia bushland and their edge effects in Laikipia, Kenya.
Ecological Applications 5:97-108.
and cattle show a slight preference for new glades.
None
• Relative to non-glade soils, glade soils were high in phosphorus and potassium, but
low in magnesium, calcium, sodium and clay content. Nitrogen was high in all
Fert + clear
glades, but highest in new glades.
Because cattle and wildlife are important players in the black cotton ecosystem and also
appear to use glades especially heavily, herbivore activity may influence the rate at which
=dung
=N fertilizer
=Acacia brush
=trees/uncleared
glades make the transition from Cynodon- to P.stramineum-dominance. For example:
• A plant that has been damaged by herbivory may be at a competitive disadvantage
for resources such as water or light. In such a case, heavier grazing of Cynodon
would lead to a faster takeover by P. stramineum.
• Herbivores may export nutrients out of glades when they graze on high-nutrient
Figure 6. Experimental Acacia drepanolobium
brush addition to simulate boma fence.
glade grasses. If Cynodon competes better in high-nutrient environments, then
Figure 7. Schematic diagram of treatments for
glade-making experiment testing the effects of
dung and fertilizer addition, brush addition, and tree
clearing on glade development. Large plots are
50x50m., and small plots are 20x20m. Small focal
plots included within larger plots are 10x10m.
herbivores exporting nutrients may speed the transition from Cynodon to P.
stramineum.
I am using the KLEE experiment (Young et al. 1998) and conducting additional
experiments on Mpala, Jessel and Segera properties to try to understand how the effects
of herbivores influence the nature of competition and interactions between the two glade
grass species.
Acknowledgements:
Many thanks are owed to the following for their help in the field: Frederick Erii, John Lochukuya, Jackson Ekadeli, Patrick Etelej,
Corinna Riginos, James Ekiru, Jake Goheen, Ali Hassan, Dan Kelly, John Lemboi and Simon Lima. Thank you to Truman
Young for advice, support and field assistance. Thank you to Mpala Research Centre, Mpala Ranch and Peter Jessel for
permission to use field sites and for logistical support. Funded by NSF and U. California-Davis Jastro Shields grant.