The ecology of large herbivores in the Miombo woodlands of South East Tanzania
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Date
1979
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
The University of of Nairobi
Abstract
The studies described in this thesis arose from an
ecological survey of part of the eastern side of the Selous
Game Reserve in south east Tanzania from 1967 to 1975*
The intensive study area contained two major, ecologically
distinct, habitats, an area of tall grass miombo woodlahd and
a smaller area of short grass scattered tree grassland.
Several species of large grazing ungulate utilised thefce
habitats, namely: buffalo, hartebeest, impala, sable, warthog,
wildebeest and zebra*
Seasonal changes in the environment
such as the six month drought and widespread annual fires affect
the pattern of habitat utilisation exhibited by each species.
This thesis examines such utilisation and shows that each
species has developed its own ecological and feeding
strategies in order to maximise nutrient inputs and reproductive
success in what is seasonally a harsh environment
In many ways the miombo (Brachystegia) woodlands
remain the least studied of the East African habitats
This
lack of data on the miombo in general and the Selous Game
Reserve in particular means much of the thesis is taken up
by descriptions of the physical and biotic environment of the
study area.
Following an introductory chapter the thesis is
divided into three parts.
Part one, with three chapters,
describes the physical environment: geology, soil, climate,
water and prehistory; the vegetation: community description,
distribution and species composition, floristics and
vegetation dynamics; and range factors of productivity
and forage nutrient content
Part two contains chapters on animal numbers, distribution patterns, feeding and
nutrition and a chapter examining growth and reproduction as
indices of population performance
Part three concludes
the thesis with a chapter reviewing the miombo woodlands
and the Selous as a wildlife habitat and a final chapter
discussing management policy for the Selous Game Reserve.
The study area is low lying (100 - 700m asl) with a
single rainy season from late November to early May (average
760mm p.a.)
Despite a long hot dry season, surface water is
relatively plentiful
Habitat distribution is primarily
controlled by geology and soil type with major modifications
by fires and past human activity.
The upland Karoo and post
karoo sandstones give rise to infertile acidic red sandy
soils which carry a climax-thicket formation
These have
been degraded into woodland by fire and settlement activity
Lower down the drainage slope the flat Pleistocene river
terrace of grits and sands has produced a hard alkaline
sodic soil carrying short grass scattered tree grassland
The drainage sump of recent alluvial clay carries tall
floodplain grasses
The vegetation is diverse, collections to date totalling
over 1200 vascular plants including 150 grass species.
The woodland vegetation shows strong affinities to the
Zambezian flora,and the thicket, riverine and alkaline
communities show affinities to the East African coastal
flora o
The thesis contains species lists and a vegetation
community map.
Fire has opened up the thickets producing tall grass woodlands of various types.
Grasses, mainly Andropogonae,
are coarse tussock perennials with very low nutritive values when
dry*
No burning allows the spread of woody and climbing species
which engulf the grass layer and rapidly reduce grazing values*
Late dry season fires reduce woody elements and plant diversities and
leave coarse grass growth thoughout the dry season*
Cooler early dry
season fires maintain mixed woodland communities and a mixture of
grass species and, where water tables allow, rapidly produce a flush
of nutritious regenerating grass growth*
Crude protein content of
such growth can reach 20% although standing crop is low*
The alkaline soils carry a short grass sward of mixed annual
perennial species of high nutritive values in the rains*
There is
no flush after burning and dry season grazing values are low*
Chapter 5 discusses techniques of animal census in detail*
A vehicular ground sample census using fixed systematically
placed transects was used for common ungulates*
Rainy season
densities on the short grass habitats are as follows:
Impala 28*7/km2, wildebeest 27,2/km2, zebra l6*2/km^ and warthog
9*4/km2#
Wildebeest and impala densities have remained unchanged
for six years, zebra and warthog densities have increased
significantly*
Less detailed data are given for other species*
Distribution data have been collected at several different scales
from Tanzania wide, to the Selous, to the study area, to the different
facets of a miombo valley-ridge catenary system* It is ‘shewn that 'salile *nd'‘L±ch’fcnrteins
.'S*
: ns
hartebeest are restricted to tall grass woodland habitats,
wildebeest and impala must have access to short grass areas
in the rains and that buffalo, zebra and warthog, are more
habitat tolerant but achieve higher densities on short grass
habitats .
Within the study area virtually all impala, warthog,
wildebeest and zebra concentrate on the short grass areas
in the rains, moving into the woodlands following the onset
of burning
Within the woodland habitat wildebeest and
impala concentrate on the green flush of the valleys and
avoid the unburnt areas and ridge tops.
Sable and hartebeest
are distributed throughout all categories and warthog and
zebra are intermediate showing some selection of valley and
green areas
The onset of the November rains signals a return
to the short grasslands
Studies of feeding behaviour showed buffalo, hartebeest
and wildebeest to
be total grazers whilst sable and impala
took significant proportions of browse in the dry season and
warthog diet changed to perennial monocot
roots and rhizomes.
Feeding studies concentrated on wildebeest and impala and
much data was obtained from post morterm analysis.
By
assuming that extrapolation of data from other large ungulate
studies was unlikely to cause large relative errors
it was
possible to make estimates of protein and energy intakes and
of theoretical nutrient needs for these two species.
the rainy season both species had inputs greater than
During theoretical requirements for maintenance, i e
i
positive nutritional balance.
they were in
As the dry season progressed T
both male and female wildebeest which remained on the dry
short grass habit entered a period of negative nutritional
balance•
However wildebeest moving to fresh flush in the
woodlands were shown (albeit on less evidence) to maintain
a positive balance.
Impala at the onset of the dry season
changed their diet to nutrient rich browse components and
so maintained a positive nutritional balance.
These two
!
strategies of habitat change and dietary change have resulted
in peak nutritional inputs at different times of year.
Impala have peak inputs in September and wildebeest in
i
December
periods.
Onset of parturition coincides with these peak
The nutritional load of gestation is minimal
compared to that of lactation.
Calving season therefore allows
lactation and wearing of calves at the nutritional optimum
time of year.
Other species show different strategies,
which allow a separation of niche space reducing competition
for food resources
Chapter eight shows that individual
growth rate, body condition and fecundity rates are as
high or higher than other populations in Africa., and that
populations here are well adapted to the ecological conditions
of this part of the Selous Game Reserve.
This chapter discusses
why the wildebeest population is stationary when nutrition is
adequate, condition is good and fecundity is high.
Predation by lion is put forward as a major limiting factor*
The concluding chapters look at the miombo woodlands
throughout Africa as wildlife reserves and suggest that
only when tall grass woodlands are adjacent to other habitats such as short grassland or floodplains do animal densities reach
levels high enough to warrant major conservation inputs*
The
importance of fire in providing dry season graze is stressed and
fire management polices for the Selous are discussed*
Past,
present and future human impacts on the wilderness values of the
Selous are examined and a plea is made for definite land use
policy statements for south east Tanzania and the reserve*
Description
Keywords
Ecology, Herbivores, Miombo, Woodlands, South east, Tanzania