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Abstract

Land degradation is a major problem in the semi-arid environments of Sub-Saharan Africa. Fighting land degradation is essential to ensure the sustainable and long-term productivity of the habited semi-arid lands. In Kenya, grass reseeding technology has been used to combat land degradation. However, despite the use of locally adapted perennial grass species namely Cenchrus ciliaris (African foxtail grass), Eragrostis superba (Maasai love grass) and Enteropogon macrostachyus (Bush rye) failure still abound. Therefore, more land is still being degraded. The aim of this study was to determine the main factors which contribute to failures in rehabilitating denuded patches in semi-arid lands of Kenya. A questionnaire was administered to capture farmer perceptions on failures on rangeland rehabilitation using grass reseeding technology. Rainfall data was collected during the study period. Moreover, rehabilitation trials using the three grasses were done under natural rainfall. Results from this study show that climatic factors mainly low amounts of rainfall to be the main contributor to rehabilitation failures. 92% of the respondents asserted that reseeding fails because of low rainfall amounts received in the area. The study area received a total of 324 mm of rainfall which was low compared to the average annual mean of 600mm. Reseeded trial plots also failed to establish due to the low amounts of rainfall received. This showed how low rainfall is unreliable for reseeding. Other factors namely destruction by the grazing animals, pests and rodents, flush floods, poor sowing time, poor seed quality, lack of enough seed and weeds also contribute to rehabilitation failures in semi-arid lands of Kenya.
African Journal of Environmental Science and Technology Vol. 4(7), pp. 430-436, July 2010
Available online at http://www.academicjournals.org/AJEST
ISSN 1991-637X ©2010 Academic Journals
Full Length Research Paper
The challenges of rehabilitating denuded patches of a
semi-arid environment in Kenya
Kevin Z. Mganga1*, Moses M. Nyangito1, Nashon K. R. Musimba1, Dickson M. Nyariki1, Agnes
W. Mwangombe2, Wellington N. Ekaya3, William M. Muiru2, Daniele Clavel4, Judith Francis5,
Ralph von Kaufmann6 and Jan Verhagen7
1Department of Land Resource Management and Agricultural Technology University of Nairobi, P. O. Box 29053-00625,
Nairobi, Kenya
2Department of Plant Science and Crop Protection, University of Nairobi, Kenya.
3RUFORUM, Uganda.
4CIRAD, France.
5CTA, Netherlands.
6FARA
7Wagengen University, Netherlands.
Accepted 28 April, 2010
Land degradation is a major problem in the semi-arid environments of Sub-Saharan Africa. Fighting
land degradation is essential to ensure the sustainable and long-term productivity of the habited semi-
arid lands. In Kenya, grass reseeding technology has been used to combat land degradation. However,
despite the use of locally adapted perennial grass species namely Cenchrus ciliaris (African foxtail
grass), Eragrostis superba (Maasai love grass) and Enteropogon macrostachyus (Bush rye) failure still
abound. Therefore, more land is still being degraded. The aim of this study was to determine the main
factors which contribute to failures in rehabilitating denuded patches in semi-arid lands of Kenya. A
questionnaire was administered to capture farmer perceptions on failures on rangeland rehabilitation
using grass reseeding technology. Rainfall data was collected during the study period. Moreover,
rehabilitation trials using the three grasses were done under natural rainfall. Results from this study
show that climatic factors mainly low amounts of rainfall to be the main contributor to rehabilitation
failures. 92% of the respondents asserted that reseeding fails because of low rainfall amounts received
in the area. The study area received a total of 324 mm of rainfall which was low compared to the
average annual mean of 600mm. Reseeded trial plots also failed to establish due to the low amounts of
rainfall received. This showed how low rainfall is unreliable for reseeding. Other factors namely
destruction by the grazing animals, pests and rodents, flush floods, poor sowing time, poor seed
quality, lack of enough seed and weeds also contribute to rehabilitation failures in semi-arid lands of
Kenya.
Key words: Land degradation, grass reseeding, rehabilitation failures, low rainfall.
INTRODUCTION
Land degradation is a global problem facing us today.
The United Nations Convention to Combat Desertification
(UNCCD, 2003) defines desertification as a process of
land degradation in the arid, semi-arid and dry sub-humid
*Corresponding author. E-mail: kzowe@yahoo.com.
areas, resulting from various factors including both
climatic variation and change in human activities. Land
degradation manifests in forms of impoverishment and
depletion of vegetative cover, loss of biological and eco-
nomic productivity, wind and water erosion, salinization
and deterioration of physical, chemical and biological soil
properties. The drylands of the world, comprising the
hyper-arid, arid, and semi-arid regions with annual
Mganga et al. 431
Table 1. Agro-climatic zones of Kenya, excluding areas above 3000m altitude (Biamah, 2005).
Zone R/E
o
* (%) Classification R (mm) E
o
(mm)
I > 80 Humid 1100 - 2700 1200 - 2000
II 65-80 Sub-humid 1000 - 1600 1300 - 2100
III 50-65 Semi-humid 800 - 1400 1450 - 2200
IV 40-50 S.humid - S.arid 600 - 1100 1500 - 2200
V 25-40 Semi-arid 450 - 900 1650 - 2300
VI 15-25 Arid 300 - 560 1900 - 2400
VII < 15 Very arid 150 - 350 2100 - 2500
Notes: * R – Average rainfall; Eo- Average annual evaporation.
moisture deficits greater than 50% are considered the
most threatened by land degradation.
These drylands are estimated to cover 47% of the earth’s
surface (GEF/IFAD, 2002). In these areas, land degradation
of which desert encroachment is only a small part is
widespread and thus very important.
The semi-arid to weakly arid areas of Africa are
particularly vulnerable as they have fragile soils, localized
high population densities and generally a low input form
of agriculture. Degradation is evident in a decline in soil
productivity, loss of biodiversity and increasing rate of soil
erosion (Beukes and Cowling, 2003; van den Berg and
Kellner, 2005; Visser et al., 2007). Africa is particularly
threatened because the land degradation process affects
about 46% of the land surface area of the continent
(WMO, 2005). It has been estimated that approximately
30-40% of Kenya’s arid and semi-arid lands are quickly
degrading and that another 2% has completely been lost
through this process (Keya, 1991). In Kenya, high rates
of soil loss of up to 50 tonnes per hectare per year from
degraded grazing lands in semi arid areas are common
(Nyangito et al., 2009). According to Graetz and Tongway
(1986) grazing contributes about 34.5% of the total soil
degradation. High rates of degradation can partly be
attributed to the nature of the soils in the arid and semi-
arid lands of Kenya. The main problems associated with
these soils are high levels of salinity and sodicity, poor
drainage, soil erosion, soil compaction, soil crusting and
low fertility. Surface crusting properties are enhanced by
rainfall of high intensity and short duration that is common in
semi-arid areas (Biamah, 2005). The problem of land
degradation is difficult to grasp in its totality. The use of
indicators of degradation is more appropriate in trying to
understand the land degradation problem. Indicators are
variables and only show that land degradation has taken
place. According to the United States Climate Change
Technology Program, USCCTP (2005), the indicators of
land degradation include poor soil cover, dominance of
undesirable plant species, low soil quality, or in the
extreme, erosion of top soil. According to Snel and Bot
(2005), the indicators of land degradation can be grouped
into three broad categories; biophysical indicators
(degradation of soil, water and vegetation cover), socio-
economic indicators (poverty and food insecurity) and
institutional indicators (failures in the public/government,
private/market, civil/community sectors and civil strife).
The problem of land degradation can partly be reversed
through revegetation. Grass reseeding technology has
been used successfully as a means of rehabilitating
degraded rangelands in East Africa (Jordan, 1957;
Bogdan and Pratt, 1967; Musimba et al., 2004). Despite
the widespread success of grass reseeding technologies
in combating land degradation in the semi-arid environ-
ment of East Africa, failure still abounds. The aim of this
study was to determine the main factors which contri-
buting to rehabilitation failures using grass reseeding
technology in a semi-arid environment in south eastern
Kenya.
MATERIALS AND METHODS
Study area
This study was carried out in the semi-arid district of Kibwezi of
Kenya located about 200 km southeast of the capital city Nairobi,
along the Nairobi-Mombasa highway. The Kamba agropastoralists
are the main ethnic inhabitants in the study area (Nyangito et al.
2009). The district lies between the latitudes S and 3ºS, and
longitude 37º36¹ E and 38º30¹E, respectively and has a total area
of 3400 km² (CBS, 2000). The most dominant soils in the semi-arid
area are Luvisols, Lixisols, Acrisols, Alisols, Ferralsols, Planosols,
Solonchaks, Solonetz, Vertisols and Fluvisols (Biamah, 2005).
These semi-arid soils are considered problematic because of their
physico-chemical properties limit that their use for agriculture
(Biamah, 2005). They generally have low organic matter content
and an unstable structure.
The climate is typical semi-arid and the district is representative
of many other zones with similar ecological conditions throughout
Kenya, characterized by low and unreliable supply of soil moisture
for plant growth. The semi-arid lands of Kenya occupy
approximately 30% of the total land area and are classified into two
agro-climatic zones (ACZ), IV and V, on the basis of the ratio of
rainfall to open water evaporation (R/Eo) (Table 1) (Biamah, 2005).
These areas have average annual rainfall, evaporation and
temperatures of 600, 2000 mm and 23°C respectively (Michieka
and van der Pouw, 1977; Braunn, 1977). Rainfall comes in high
intensities and is usually concentrated at the beginning of the long
or short rains. The natural vegetation in the area is woodland and
savanna, with several tree species, mainly Acacia sp (A) such as
Acacia tortilis (Forsk) Hayne and Acacia mellifera (Vahl) Benth,
432 Afr. J. Environ. Sci. Technol.
Commiphora africana (A. Rich) Engl, Adansonia digitata Linn and
Tamarindus indica L. Shrubs include Apis mellifera, Apis senegal
(L) willd and Grewia spp. (Nyangito et al., 2009). Perennial grasses
such as Cenchrus ciliaris, Enteropogon macrostachyus and Chloris
roxburghiana can dominate but many succumb to continuous abuse
over long periods. Eragrostis superba is also commonly found in
the district (Musimba et al. 2004).
Seed viability estimation in the laboratory
Seed viability of perennial grasses commonly used for reseeding
was estimated. Viability tests of freshly harvested and two year old
seeds were determined as described by Tarawali et al. (1995).
Random samples of 100 seeds of each set of the three grass
species used; Cenchrus ciliaris, Enteropogon macrostachyus and
Eragrostis superba were put on wet Whitman filter paper in a Petri
dish. The Petri dishes were then placed at room temperature (30°C)
in the study area. The seeds were monitored for a period of 14
days. All germinated seeds were expressed as a percentage of
total number of seeds at the end of this period. Seeds which did not
germinate within this period were dimmed dormant.
Site preparation and experimental design of reseeded plots
Land preparation involved the creation of micro-catchments. The
micro-catchments were done using an ox-driven plough in rows
across the slope. Each micro-catchment measured approximately
15cm deep. Spacing between micro-catchments was 30 cm. The
micro-catchments were created to promote better germination of
seeds and establishment of seedlings (van der Merwe and Kellner,
1999; Snyman, 2003; Visser et al., 2007). Slope (%) was estimated
using the dumpy level and stuff method (Mnene, 2006) and was
found to be 1.5% (range 0.00 - 2.11).
The plots were arranged in a Complete Block Design (CBD). Three
blocks measuring 15 x 10 m were demarcated in the site. Fencing
was done using locally available Acacia branches and Commiphora
poles to keep of grazers from trampling over the grass seedlings,
with a buffer zone of 3m around the perimeter as recommended by
Ekaya et al. (2001) to minimize external influence. The 3 blocks
were laid horizontally next to each other separated by 5 m spacing.
Each block was further divided into 6 plots each 5 x 5 m. The seeds
of the grasses were sown along the created micro-catchments as
pure stands; Cenchrus ciliaris, Enteropogon macrostachyus and
Eragrostis superba and as two grass mixtures; Cenchrus ciliaris-
Enteropogon macrostachyus, Cenchrus ciliaris-Eragrostis superba
and Enteropogon macrostachyus-Eragrostis superba. The seeds
were covered with light amount of soil. The whole process; site
preparation and sowing was completed before the on-set of the
rainy season. .
Data collection and statistical analysis
Data was collected from a total of 50 agro-pastoralists using semi-
structured questionnaires. A draft questionnaire taking into account
the objective of the study was constructed before carrying out the
field survey. Questions were dichotomous, multi-choice and open
ended to allow ease of capture of the diverse issues that were
being investigated, with necessary detail. The questionnaire was
pre-tested in a pilot survey involving 20 households, before it was
used in the main survey. The households belonged to the same
area of study but were not included in the actual survey.
Rainfall data for the study area during the study period was also
collected using a rain gauge set up at the experimental site.
Disturbed soil samples were taken from the top soil of 0 - 20 cm to
determine soil moisture. Soil moisture content was determined by
the gravimetric method as explained by Rowell (1994). Statistical
analyses were done using Statistical Package for Social Sciences
(SPSS) packages (Einstein and Abernethy, 2000). Descriptive
statistics were used to analyze data on the problems of
rehabilitating denuded patches in the semi-arid environment.
RESULTS AND DISCUSSION
Seed viability tests of the two year old set of seeds
showed that there was a difference in seed germination
between the three grass species tested. Seeds of
Enteropogon macrostachyus (under room conditions at
an average of 30°C) had the highest germination
percentage (53%). Percent germination for Cenchrus
ciliaris and Eragrostis superba was 12 and 10%,
respectively. Trends in germination percentage of the
tested grasses are illustrated in Figure 1. Percent
germination was an indicator of grass seeds viability and
capability of producing normal plants under suitable
germination conditions. The differences observed among
the grass species in terms of percent seed germination
can be explained by the intrinsic properties of the seeds
such as dormancy and integumental hardness. Seed
dormancy varies between species Veenendaal (1991).
Higher percent seed germination of Enteropogon
macrostachyus may be explained by its dormancy
mechanism which involves only the integument while the
other two species may have both the embryo and/or the
integument related dormancy (Bryant, 1985). The hairy
bristle coat of the Cenchrus ciliaris fascicles is likely to
have aided its higher germination by maintaining a high
humidity within the fascicle and thereby help reduce water
loss from the caryopsis (Sharif-Zadeh and Murdoch, 2001)
compared to that of Eragrostis superba. The freshly
harvested seeds of all the three grasses used did not
germinate. This was primarily attributed to seed
dormancy.
Rainfall total in the study area for the year 2008 was
324mm. However, most of the rain came as short lived
flushes, which lasted for a maximum of 10 days at the
beginning of the rainy season, followed by long spells of
dry periods for the remaining days of the month. The area
received a total of 39 rainy days in the whole year. This
rainfall regime resulted in initial good germination of
seeds in all the plots, but farther establishment of grass
seedling was truncated by the lack of enough moisture.
Rainfall together with soil moisture balance has an
overwhelming effect on vegetation structure, composition
and productivity. The rainfall regime witnessed during the
study period suggests that the rains in the semi-arid
lands of south eastern Kenya are usually low, erratic and
unpredictable in space and time. High variability in rainfall
amounts and distribution are common characteristics of
semi-arid rangelands (Pratt and Gwynne, 1977; Ekaya et
al., 2001), leading to low soil moisture deficits. Rainfall
trends in the study areas are illustrated in Figure 2.
According to the Kamba agro-pastoralists living in
Kibwezi district, climatic factors, namely low amounts of
Mganga et al. 433
■ Enteropogon macrostachyus ▲ Eragrostis superba ● Cenchrus ciliaris.
0
10
20
30
40
50
60
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Daily Percentage (%) Germination
Figure 1. Daily percentage seed germination of Enteropogon macrostachyus, Eragrostis superba
and Cenchrus ciliaris, under room conditions (30º C) in the study area (Set of two year old seeds).
0
200
400
600
800
1000
1200
1400
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Year
Rainfall (mm)
Rainfall
Mean Rainfall
Figure 2. Annual rainfall in the study area (1993-2008).
rainfall and recurrent droughts common in the study area
are the main factors which contribute immensely to
rangeland rehabilitation failures. Out of all the farmers
who practice reseeding, 92% have experienced rehabi-
litation failures and attributed this to low amounts of
rainfall received during the respective year. Results from
the questionnaire mirrored the results on site where there
was poor establishment despite initial good germination.
Low amounts of rainfall reflected by the soil moisture
deficits hinder seed germination. Soil analysis results
showed the soil moisture content in the study area to be
as low as 6.87%. Similarly Mnene (2006) noted that when
a seed stock is healthy, the main environmental factors
that will stop seeds from germinating and establishing in
the semi-arid rangelands are soil type and moisture. 24%
of the agropastoral farmers practicing reseeding asserted
that flush floods and soil erosion contribute to reha-
bilitation failures. Rainfall in semi-arid Kenya is often of
high intensity and lasts within a very short period of time,
that is, flush floods. This coupled with the problematic
nature of the semi-arid soils characterized by high levels
of salinity and sodicity, poor drainage, soil erosion, soil
compaction, soil crusting and low soil fertility (Biamah,
2005) exposes the sown grass seeds to agents of ero-
sion notably water and wind. The water often transports
the sown grass seeds as it flows along the gradient.
Heavy storms also destroy the shallow microcatchments
meant to trap the water. Soil crusting farther hinders
seedling emergence from the soil. This combination of
climatic and edaphic factors leads to poor rates of
434 Afr. J. Environ. Sci. Technol.
germination and thus poor rates of establishment. Apart
from soils and rainfall, other factors including human
interventions (burning and grazing) and individual species
physiological differences affect germination and
subsequent growth (Mnene, 2006).
In the study area, grazing animals are kept under free
range/herding in defined household grazing areas
(Nyangito et al. 2009). This form of grazing system has
also contributed immensely to rehabilitation failures since
free grazing of livestock often cause destruction to young
grass seedlings. Results from the survey showed that
50% of the farmers who have experienced rehabilitation
failures blame it on livestock destruction. Free grazing
animals often trample on newly established grass stands
thus hindering their development to seed setting stage.
Destruction of grass seedling before seed setting leads to
the continual deprivation of the seed bank in the soil
which in the long-run leads to bare patches. Improper
stocking rates were also recognized to be a major
contributor to rehabilitation failures. This anthropogenic
influence was exacerbated by abiotic factors such as
drought. Fencing is very expensive but is often the only
way of excluding both domestic and wild herbivores from
improved pastures. 95% of the agro-pastoralists who
practice reseeding in the study area fence their
rehabilitation plots and grass enclosures using cheap and
locally available materials. However, the use of these
locally available and cheap materials notably branches
and poles of Acacia and Commiphora to keep free
roaming herbivores out of reach increases the
vulnerability of the grass seedlings to destruction in the
long run. Such materials only provide a short term
solution, since they are easily destroyed by livestock.
Continued exposure of the fence to moisture farther
weakens the fence. Moreover, some herders easily
remove the fences to allow their animals graze the newly
established seedlings and later replace it. As a rule of
thumb, to ensure successful establishment, newly esta-
blished grass stands should be protected from grazing
animals for at least two growing seasons. However, with
such prevailing conditions, this is hardly possible in agro-
pastoral production areas. Majority of the farmers, (82%),
who practice grass reseeding prepare their rehabilitation
plots and sow the grass seeds prior to the rainy season.
This ensures that the rain finds the sown seeds in the
ground. In addition, the grass seeds are normally sown at
a shallow depth and covered with minimal amounts of
soil. This guarantees that the sown seeds get enough
moisture for germination and consequent establishment.
However, 3% of the farmers interviewed asserted that
pests and rodents pose a great challenge to this form of
dry planting.
Dry season planting coincides with a period of food
scarcity for the pests and rodents. 3% of the agropastoral
farmers emphasized that rats, squirrels and other small
rodents and insects often feed on the sown seeds.
Additionally, termites often transport the seeds long
distances and store them in their food stores. Damage by
termites is a general concern in the study area since they
also affect crops and farm structures (Mnene, 2006).
Furthermore, the Quelea quelea birds common in the
study area often invade the rehabilitation plots in
hundreds and feed on the sown grass seeds, especially
those of Eragrostis superba which is mostly preferred by
farmers because of its role in improving milk production
(Wasonga et al., 2003). This leads to poor rates of initial
germination in some patches, which often prompts the
farmers to repeat the same process, and thus waste their
time and money. That not withstanding, seedbed
preparation is important in removing soil capping,
enhance soil water infiltration and incorporate seeds into
the soil (Mnene, 2006). 29% of the farmers interviewed
cited inadequate supply of seeds of the locally adapted
species commonly used for reseeding in the study area;
Enteropogon macrostachyus, Eragrostis superba, Cenchrus
ciliaris and Chloris roxburghiana. These findings agrees
with that of Griffiths (1993) who reported that by the
1990s only 20% of farmers needs for herbage seeds
could be met by formal seed production and marketing
system in sub-Saharan Africa. This can also be attributed
to degradation of natural vegetation whereby the more
preferred vegetation type, grassland is steadily being
replaced by a more woody vegetation type. As a result
there is a shortage of supply of grass seeds commonly
harvested in the forests and open grazing areas by the
farmers. Proper seed technology is therefore necessary
at harvesting, processing and storage, especially where
communities are expected to undertake pasture seed
multiplication to meet the current shortage (Mnene,
2006).
Poor storage methods, skills and facilities to store
harvested seeds and use of poor quality seeds also
contribute to poor establishment. 29% of the agropastoral
farmers affirmed poor storage methods, skills and
facilities as a contributor to rehabilitation failures. Majority
of the farmers store their seeds in gunny bags and place
them in grass thatched granaries which are sometimes
not well done or poorly maintained. Seed quality of
domestic species is highly variable and poor in the tropics
as a result of poor harvesting and storage technology.
Dry seeds, particularly those of rangeland grasses are
known to be highly hygroscopic (Veenendaal, 1991;
Opiyo, 2007), and exposure of dry seeds to moisture has
been reported to worsen seed dormancy and often leads
to fungal infection (Chin and Hanson, 1999; Tweddle et
al., 2003). However, individual grass seed species ability
to withstand moisture varies between species. During
incidences of heavy storms, these granaries allow some
rain water to penetrate thus contaminate the stored grass
seeds. This leads to spoilage. Additionally, some of the
farmers use dormant grass seeds to reseed their
denuded patches. The seeds are either too old or too
fresh, that is, immature or not yet broken dormancy. In
this study, freshly harvested grass seeds of Enteropogon
macrostachyus, Cenchrus ciliaris and Eragrostis superba
failed to germinate under laboratory conditions. However,
two year old seeds of the same grasses germinated
under the same laboratory conditions. Competition from
weed seedlings which germinate on established sown
grass pastures can be very severe. All the farmers
interviewed cited the problem of weeds in their individual
rehabilitation plots. Semi-arid rangeland soils may
contain 3,000 -15,000 viable seeds/m2 of soil
(Hodgkinson et al., 1980). This far exceeds the
recommended sowing rates of rangeland pasture species
usually at 30 - 500 viable seeds/m2 (Heady, 1975). The
common weeds in the study area included; Solanum
incanum, Lactuca capensis, Ipomoea kituensis, Digitaria
scalarum, Eragrostis curvula, Datura stramonium, Tridax
procumbens, Barleria taitensis and Commelina
bengalensis. Results showed that out of all the men-
tioned weeds, only Ipomoea kituensis greatly affected
established grass stands. Ipomoea kituensis is a very
common and notorious weed in the semi-arid districts of
southern Kenya. It spreads very fast and thus colonizes a
wide area within a very short period, making it difficult to
eradicate. Its creeping nature engulfs the newly esta-
blished grass seedlings. Ipomoea kituensis suppresses
the growth and development of the grasses by covering
the grass seedlings and depriving them of sunlight
necessary for normal photosynthetic function. Further-
more, the weed out-competes the grass seedlings for
nutrients and water from soil due to its aggressive growth
nature.
Conclusion
The challenges facing agro-pastoralist farmers in semi-
arid Kenya, who practice grass reseeding as a means of
restoring denuded patches, are diverse. Insufficient
amount of rainfall is the main contributing factor. Low
amounts of rainfall and high rates of evapotranspiration
result into soil moisture deficits, which subjects the grass
seedlings to water stress leading to seedling mortality.
Other factors, notably destruction by grazing animals,
pests and rodents, flush floods, poor sowing time, poor
seed quality, lack of enough seed and weeds also
contribute to rehabilitation failures in semi-arid lands of
Kenya.
ACKNOWLEDGEMENTS
We gratefully acknowledge the Agricultural Innovations
for Drylands Africa (AIDA) for the financial support for this
research. The opportunity to use the University of Nairobi
laboratories and other facilities both in Nairobi and
Kibwezi Field Station is also highly appreciated. Last, but
not the least, we would like to thank the Kamba
agropastoral community in Kibwezi district for their active
participation and positive attitude during the study period.
Mganga et al. 435
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... Applying a native seed mix in conjunction with removing the pre-existing vegetation was revealed to be the most effective treatment combination for increasing the cover of desired species of vascular plants. Re-seeding is a commonly used restoration strategy (Pawelek et al. 2015;Baughman et al. 2016), although it may fail where environmental conditions preclude seedling establishment (Hume & Barker 1991;Mganga et al. 2010). While some seed did establish in plots without vegetation removal (to give an average of 17% cover), this more than doubled (to 42%) in plots where the vegetation was removed. ...
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... The best method of management of invasion however remains the prevention of establishment and spread (Borokini and Babalola, 2012). For semi-arid grazing lands in the Southern rangelands, rehabilitation of degraded grazing lands using natural pastures such as Cenchrus ciliaris, Enteropogon macrostachyus and Eragrostis superba is beneficial due to the competitive advantage these species possess in suppressing weeds such as Ipomoea kituiensis (Mganga et al., 2010b). Cenchrus ciliaris in particular is primarily recommended because of its allelopathic properties and deep root system hence the necessity to include the species in any reseeding initiative (Mganga, 2009). ...
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A two-year study was conducted with an overall objective of characterising the structure and function of an arid rangeland in Kenya. A plot measuring 100 × 100m was used for this study. Data on rainfall and temperature were recorded at the plot site whereas data on evaporation rates and relative humidity were obtained from the meteorological office near the study site.Herbaceous aboveground material was sampled at monthly intervals using a rectangular 0.25m2 quadrat frame. Clipped material was separated by species and classified dead or live by physical examination. A 5cm diameter metal soil corer was used to sample belowground plant material, at monthly intervals. The sampled material was washed with running water over 2mm sieves and classified dead or live using the vital staining technique. All weights and calculations were based on organic weight.Total aboveground standing crop ranged from 84.6g m−2 to 295.4g m−2, with a mean of 162.3 ± 60.6g m−2. Mean monthly aboveground standing crop for 1992 and 1993 was 142.8 ± 53.8 and 178.5 ± 63.3g m−2 respectively. The two values were significantly different (p<0.10). Aboveground biomass yield ranged from 17.7g m−2 to 242.7g m−2, with a mean of 104.3 ± 58g m−2 and a coefficient of variation of 58%. Mean aboveground standing crop was 59 ± 24g m−2 Monthly values ranged from 28.8g m−2 to 120g m−2, with a 38% coefficient of variation.The range for total belowground standing crop was from 83.3g m−2 to 232.7g m−2, and a mean of 155.2 ± 46g m−2. The values had a coefficient of variation of 30%. Mean total monthly belowground plant material yield for 1992 and 1993 was 137.6 ± 41g m−2 and 169.9 ± 46g m−2 The coefficients of variation were 59% and 28% respectively. The mean monthly belowground biomass yield was 51.6 ± 33g m−2 with a coefficient of variation of 64%. Mean monthly yield for belowground dead material was 103.7 ± 32g m−2, with a coefficient of variation of 31%. There was no significant difference (p>0.01) in the mean belowground dead material yield between 1992 and 1993.In 1992, annual NPP was 439.2g m−2, giving a net primary productivity of 1.22g m−2day−l. Monthly NPP ranged from 17.2g m−2 to 90.1g m−2 In 1993, annual NPP was 944.5g m−2, equivalent to a net primary productivity of 2.62g m−2 day−1. Monthly NPP was between 27.4g m−2 and 548.6g m−2. Over the 1992-1993 period, NPP was 1 383.7g m−2, equivalent to a productivity of 1.92g m−2day−1. Trends in monthly NPP closely followed the trend in rainfall. On the whole, herbaceous vegetation production and productivity were episodic in nature and closely linked to rainfall. The high primary productivity puts arid and semi-arid rangelands under sharp focus as CO2 sinks, whose role in the amelioration of greenhouse effect could be more important than is currently appreciated.