KLEE: the Kenya Long-term Exclosure Experiment
Truman Young, Frederick Erii, Kari Veblen, Corinna Riginos, Felicia Keesing
Livestock and wildlife share much of their range in
African savannas.
To understand the interactions
between livestock and wild herbivores (and other
indigenous biodiversity), we have established a longterm herbivore exclusion experiment in the Laikipia
ecosystem.
Using different kinds of barriers, we
differentially exclude various combinations of cattle,
large wild herbivores, and ‘mega-herbivores’ (giraffes
and elephants) from 18 four-hectare plots (Figure 1).
Established in 1995, this project is the first controlled,
replicated exclusion of different combinations of
rangeland herbivores. We are monitoring soils, trees,
herb layer vegetation, plant defense, grass productivity,
use by large mammals, and populations of rodents,
birds, & invertebrates. We report here 1) evidence of
competition between cattle and wildlife, 2) evidence that
elephants may mitigate the competition between cattle
and zebras, and 3) an examination of the fate of a
savanna when all large herbivores have been removed.
The pathology of no herbivory
African savannas have coexisted and co-evolved with large herbivores for
millions of years, and with livestock for millennia. The total exclusion
treatment in the KLEE plots at first developed rank grass cover and thick
thatch. This was followed by a severe drought (in an “La Nina” year), during
which there was severe reduction of living and dead biomass, and the death
of larger grass plants suppressed by rankness (Figure 5). Large numbers of
herbs appeared in the bare areas among the remnant grasses.
In
subsequent years, large areas of the exclusion plots converted to a herbdominated community, with reduced grass cover (Figure 6). We attribute
these “pathological” changes in the total exclusion plots to the novel
conditions for which some of its dominant species were ill-adapted. In the last
couple of years, it appears that the grasses may be slowly returning to
dominance on the total exclusion plots.
15 0
10 0
50
Notice in Figure 4 that the presence of elephants reduced
both grass and zebra use when there were no cattle
(because they all eat grass), but increased grass and
zebras in the presence of cattle. It appears that elephants
removed key forage plants (Commelina), causing cattle to
eat less (and remove less grass). In other words, in the
presence of cattle, elephants facilitate (increase) zebras.
This was a completely unexpected result.
Open treatments (MWC)
30
20
10
0
<5cm
Grant's
Eland
Elephant
>5cm
All sizes
Basal diameter
0
Hartebeest
Species
Figure 6. After the death of
grasses in the drought, herbs
came to dominate large areas
of the exclusion plots, where
they continue to cover twice
the ground as in the control
plots.
Grasses-MWC
Figure 2. Excluding cattle increases wildlife use
150
Grasses-O
No large herbivores
90
Large herbivores
80
70
60
Elephants (M) reduce
grass and zebra use
when cattle are absent
Elephants increase
grass and zebra use
when cattle are present
50
40
30
20
10
Sep-04
Sep-03
Sep-02
Sep-01
Sep-00
Sep-99
Sep-98
Sep-97
Sep-96
Sep-95
0
Data from Felicia Keesing
Figure 3. Density of rodents in the presence or
absence of large herbivores. Plots without large
herbivores have about twice as many mice, even
through pronounced fluctuations in abundance.
Doctoral and Masters students supported by KLEE:
Bell Okello, Ph.D. Candidate, University of Natal
David Kinyua, no degree, University of Nairobi
Michelle Gadd, Ph.D., University of California
Todd Palmer, Ph.D., University of California
Wilfred Odadi, M.Sc. Moi Univ.; and Ph.D. candidate, Egerton
Silvanos Otieno, M.Sc., University of Nairobi
Charles Warui, Ph.D., Rhodes University
Ryan Sensenig, Ph.D. candidate, University of California
Kari Veblen, Ph.D. candidate, University of California
Isaac Kimathi, M.Sc., University of Nairobi
Corinna Riginos, Ph.D. candidate, University of California
Lucy Ngatia, M.Sc. candidate, University of Nairobi
Figure 4. In plots with cattle, there is less grass and fewer
zebras than in plots without cattle.
Grasses-MWC
cover
Percent
Forbs-O
100
Pouched mice ha -1
1.
Removing cattle increases Grant’s gazelles,
hartebeest, eland, elephant and zebra (Figs 2 & 4).
2. Removing wildlife (zebras, mostly), increases
rangeland savanna use by elephants, and increases
forage intake rates of cattle.
3. Removing large herbivores doubles the numbers of
mice (Figure 3). We estimate that half of the grass you
would expect to be available to cattle (or zebras) after
the removal of zebras (or cattle) is instead being eaten
by increased numbers of mice.
4. In contrast, grasshoppers do not increase, regardless
of which other grass eaters we exclude. We suspect
that this is because the number of grasshoppers is
determined more by their predators than by their food.
Cattle excluded
Dung density (/ha)
Many species share the grasses and herbs of the Laikipia
savannas, but the only way to know if they are competing
is to remove certain herbivores, and see whether others
increase. The KLEE experiment now has evidence that
there is competition among most, but not all, of these
rangeland herbivores:
2)
Cattle allowed
20 0
Do elephants sometimes mitigate the
competition between cattle and zebras?
Grass density (#/m
Competition among herbivores
Figure 5. After being suppressed by
rank growth, larger grass plants died
during the 2000/1 drought in plots
without herbivores, but not in the
plots grazing by native herbivores
and livestock.
Total exclusion (O)
Forbs-MWC
100
50
Outreach
La Nina drought
El Nino rains
0
1996
1998
2000
2002
2004
Year
Acknowledgements: The exclosure plots were
built and have been maintained by grants from the
James Smithson Fund of the Smithsonian Institution
(to Alan P. Smith), The National Geographic Society,
The National Science Foundation, and the African
Elephant Program of the U.S. Fish and Wildlife Service
(to T.P. Young). We also appreciate the generosity of
the late George Small and the support of Nick
Georgiadis and John and Ken Wreford Smith. The
plots are currently maintained by the KLEE field crew:
Fred Erii, John Lochukuya, Jackson Ekadeli, Patrick
Etelej, Kari Veblen, Corinna Riginos, and Dan Kelly.
In addition to
writing “KLEE Corner” for
the LWF Newsletter, we
have published over 30
scientific articles from this
research
project
(list
available )