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Human and natural impacts on forests along lower Tana river, Kenya: Implications towards conservation and management of endemic primate species and their habitat

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Seventy-three forest patches were assessed to determine the effects of human and natural impact on native forests along the Lower Tana River flood plains in Kenya between January and March 2001. Seventeen of these forests were within the Tana River Primate National Reserve (TRPNR) while 56 were outside the protected area. Cultivation and dyke construction had the most devastating human impact, which involved partial or complete forest clearing resulting in further fragmentation of forest patches [Suleman MA, Wahungu GM, Mouria PK, Karere GM, Oguge N, Moinde NN (2001) Tana River primate census and forest evaluation. A report to Kenya Wildlife Services]. Natural impacts were either die back or flooding, which appeared to cause progressive degradation of forest structure and biodiversity. Overall, forest area in the Lower Tana significantly reduced by 34.5% (P<0.001) over a 21-year period. Forest loss was greater outside the reserve (38%) than inside (29.2%) reiterating the significant role played by this protected area in habitat and species conservation. Continued forest loss increases extinction risks for the endemic primate species the Tana River Red Colobus (Procolobus rufomitratus) and the Crested Mangabey sub-species (Cercocebus galeritus galeritus). Initiation of community conservation programmes outside the reserve and introduction of sustainable micro-economic projects were recommended to enhance sustainable livelihoods and the environment.
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Abstract Seventy-three forest patches were assessed to determine the effects of
human and natural impact on native forests along the Lower Tana River flood plains
in Kenya between January and March 2001. Seventeen of these forests were within
the Tana River Primate National Reserve (TRPNR) while 56 were outside the
protected area. Cultivation and dyke construction had the most devastating human
impact, which involved partial or complete forest clearing resulting in further frag-
mentation of forest patches [Suleman MA, Wahungu GM, Mouria PK, Karere GM,
Oguge N, Moinde NN (2001) Tana River primate census and forest evaluation. A
report to Kenya Wildlife Services]. Natural impacts were either die back or flooding,
which appeared to cause progressive degradation of forest structure and biodiversity.
Overall, forest area in the Lower Tana significantly reduced by 34.5% (P< 0.001)
over a 21-year period. Forest loss was greater outside the reserve (38%) than inside
(29.2%) reiterating the significant role played by this protected area in habitat and
species conservation. Continued forest loss increases extinction risks for the endemic
primate species the Tana River Red Colobus (Procolobus rufomitratus) and the
Crested Mangabey sub-species (Cercocebus galeritus galeritus). Initiation of com-
munity conservation programmes outside the reserve and introduction of sustainable
micro-economic projects were recommended to enhance sustainable livelihoods and
the environment.
N. N. Moinde-Fockler (&)ÆG. M. Karere ÆM. A. Suleman
Department of Ecology & Conservation, Institute of Primate Research,
National Museums of Kenya, P.O. Box 24481, Karen, Nairobi, Kenya
e-mail: nmoinde@eden.rutgers.edu
N. O. Oguge
Department of Zoology, Kenyatta University, P.O. Box 43844, Nairobi, Kenya
D. Otina
Department of Botany, Nairobi University, P.O. Box 30197, Nairobi, Kenya
123
Biodivers Conserv (2007) 16:1161–1173
DOI 10.1007/s10531-006-9096-8
ORIGINAL PAPER
Human and natural impacts on forests along lower
Tana river, Kenya: implications towards conservation
and management of endemic primate species
and their habitat
Nancy Nthenya Moinde-Fockler Æ
Nicholas Otienoh Oguge ÆGenesio Mugambi Karere Æ
Daniel Otina ÆMbaruk Abdalla Suleman
Received: 9 August 2005 / Accepted: 3 July 2006 / Published online: 27 October 2006
Springer Science+Business Media B.V. 2006
Keywords Forest destruction ÆHuman and Natural impacts ÆTana River Æ
Red Colobus ÆCrested Mangabey ÆCommunity conservation
Introduction
There are major concerns towards the loss of biodiversity, particularly in tropical
forests around the equator where these hotspots are concentrated (Myers et al. 2000;
Beck et al. 2002). Deforestation of tropical forests not only jeopardizes biological
diversity but also climate systems of the world (Myers 1989; Schwartzman et al.
2000). In addition to high species diversity and endemism, tropical forests are also
home to rural communities in need of economic sustainability. Conservation of
tropical forest is thus one of the greatest human challenges involving a delicate
balance between complex-fragile ecosystems, and impoverished populations.
Consequently, shifting cultivation remains the biggest threat to tropical forests
(Myers 1987) and has exacerbated the natural fragmentation of landscapes affecting
whole ecosystems and biotas (Bender et al. 1998).
The lower Tana riverine forests are unique because they support a high diversity of
plants and animals species that exist in a semi-arid environment, which has an annual
rainfall of £400 mm and show floristic similarities to the western and coastal ever-
green forests (Marsh 1976). Of great importance, they provide remaining habitats for
two endangered primates: (1) the Tana River Red Colobus (Procolobus rufomitra-
tus), and (2) the Tana River Crested Mangabey (Cercocebus galeritus galeritus). Five
other primate species are among faunal and flora taxa represented here (Suleman
et al. 2001). This ecosystem is, however, under severe threat due to intense shifting
cultivation practiced by the Pokomo people. These forests have been subjected to
increasing destruction of forest cover due to clear cutting, burning and slashing
mainly for agriculture as well as forest deterioration due to harvesting and utilization
of different forest products (Decker 1994; Medley 1993).Currently, the ecosystem is
highly fragmented and exists as isolated patches of various sizes (Karere et al. 2004).
One of the direct effects of forest loss since the 1960s has been the notable decline in
the two endangered primate populations (Marsh 1986; Homewood 1975; Decker
1994). As a management measure, a 169 km
2
area—the Tana River Primate National
Reserve (TRPNR)—was set up in 1976 to protect the two endangered primates
species (Marsh 1976). Conservation of these primates and their habitat has since been
of high priority nationally and internationally (IUCN 1996).
Aside from the human effects, natural impacts have also had an enormous role in
influencing the conditions of the forest here due to dependence on the river seepage
for tree survival. The Tana riverine forest ecosystem is highly dynamic being
maintained by a balance between forest patches dying off and regeneration driven
by regular natural shifts in the course of the river. The Tana River has changed its
course several times (Andrews et al. 1975; Butynski and Mwangi 1994a). This is
evident by the presence of old river channels, ox-bow lakes and remnant forests
around the flood plain due to seasonal flooding regimes (Hughes 1984). According to
Hughes (1990), it is evident that the forest patches are ground water dependent and
the frequency and duration of flooding of the Tana flood plain affects the distribu-
tion and composition of the forests along the lower Tana region. This dynamic
nature of the Tana River has consequently led to drying of trees due to either lack of
water (natural die-back) or flooding.
1162 Biodivers Conserv (2007) 16:1161–1173
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We examined the impacts of human activities and natural causes on forest patches
in and out of the TRPNR. Herein, we discuss the implication of these impacts on
conservation and management of the red colobus and crested mangabey and their
habitat.
Methods
Study site
There are currently more than 80 forests distributed in scattered patches on both
side of the Tana River varying in sizes along the lower Tana Region (Butynski and
Mwangi 1994). The TRPNR, contains 27 of these forest patches, and straddles the
lower Tana River and is located entirely within the lower Tana River flood plain
(150¢S, 4010¢E) (Fig. 1). The TRPNR, has only 9.5 km
2
out of its total area under
forest cover (Medley 1990) and the rest of the reserve is covered by shrubs and grass.
The Tana Delta Irrigation project (TDIP), situated south of the reserve is a large
rice irrigation project administered by the Tana and Athi River Development
Authority (TARDA) and is located at the northern end of the Tana Delta near
Garsen (Fig. 1). The plan of the project is to eventually encompass 160 km
2
and
currently covers areas that include 21 of the riverine forest patches in the Lower
Tana Region. Despite the low human density in the Tana district, there are pockets
of high human population concentrating along the Lower Tana River. The Pokomo
are the dominant tribe along the River (Kenya Wildlife Service 1996) and are
sedentary agriculturists who cultivate land within the flood plain. They practice flood
recession and riverbank farming around the along the Tana River, which provides
the only source of land in the region that is suitable for arable agriculture because
this farming system depends both on floodwater to irrigate their crops, and on the
depositions of fertile sediments that the floods bring (IUCN 2003). This form of
shifting cultivation along the Lower Tana River, unlike other cultivation systems in
tropical wet environments, is largely dictated by the availability of floods, where
establishments of farms and their permanence are dictated by soil fertility. The
Orma, Somali and Wardei are exclusively pastrolists and make use of in the dry
semi-arid areas above the flood plain.
Data collection
Human and natural impact
Data was collected on human and natural impacts while concurrently conducting a
primate census between January 2001 and March 2001. The forest fragments that
were surveyed varied in size from approximately 500 ha to less than 2 ha. A pre-
orientation workshop was held in which all participants familiarized themselves with
data collecting techniques and in order to minimize inter-observer variations
(Suleman et al. 2001; Karere et al. 2004). The evaluating team was divided into
several observer groups consisting of two members each. The name of the forest,
reference number, date and names of observers were entered onto the data sheets.
Biodivers Conserv (2007) 16:1161–1173 1163
123
The observer groups walked parallel to each other (approximately 50–100 m apart,
depending on the shape and size of the forest) along pre-determined routes in the
forest with the aid of compasses. The observers identified and examined human
activities, natural impacts and their frequency of occurrence. Human activities and
natural impacts were categorized as follows:
Fig. 1 Distribution of forest patches along the Lower Tana River from Nkanjonja to Onkolde
1164 Biodivers Conserv (2007) 16:1161–1173
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(1) Resource utilization is defined as human practices that do not necessarily result
in partial/complete forest cover removal but resulted into deterioration of forest
stature. These activities included:
Tree harvesting, which included cutting plant parts for various human utilizations
such as thatching, wine tapping, constructions of animal traps and sometimes fire-
wood collection. Thatching and wine tapping involved the chopping off the crowns
of trees and tapping of the sap, respectively. Animal trapping involved the use of
snares. Firewood collection involved gathering dried twigs and to a lesser extent
cutting young stems and branches.
Honey harvesting, which involved digging a hole on a tree stem where bees had a
natural hive or cutting the whole tree to harvest the honey.
Logging, which includes cutting trees for construction of canoes, beehives, fur-
niture, building materials and charcoal burning. Charcoal burning involved burning
of felled logs under earth mounds from various tree species.
(2) Land use practices are defined as human activities that resulted to partial or
complete removal of forest canopy cover. These were identified as follows:
Cultivation entailed the complete or partial clearances of areas of forest for
agriculture through slash and burn techniques, which affected all species. This
practice sometimes also causes fragmentation of the affected forest patch.
Dyke construction for rice irrigation by the Tana Athi Development Agency
(TARDA) which generally destroyed natural vegetation across 50–60 m wide swaths
resulting in losses of forest area and further fragmentation of affected forest patches.
(3) Natural Impacts are as a result of excess flooding and natural die back
resulting in progressive degradation of forest structure and biodiversity and eventual
loss of forest cover. Indicators of natural impacts included:
Excess flooding made evident by swampy forest conditions caused by very heavy
rain such as the El Nino
˜Southern Oscillation (ENSO) that occurred in 1998, causing
the river water to overflow its banks and the excess water remains stagnant for a long
period of time in the adjacent forests. This caused the tree roots to suffocate due to
lack of aeration and consequently resulted to senescence.
Natural dieback made evident by the drying up of canopy trees and fallen trees
due to river dynamism resulting to insufficient ground water seepage to forest
adjacent to old river courses.
Forest status
Data obtained from human and natural impact evaluation was used to provide
overall assessment of the status of forests surveyed. Each observer group recorded
levels of forest disturbance, based on the frequency and effects of human activities
and natural impacts on a forest. Disturbance levels were categorized as detailed by
Muoria et al. (2002) from level 1 to 4 as follows:
Level 1: Little or no destruction. More specifically little or no human resources
utilization and no land use practices and natural impacts observed.
Otherwise forest could be pristine.
Level 2: Moderate destruction. Human resource utilization are being observed at a
higher frequency as compared to level 1 but less frequently observed than in
level 3.
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Level 3: Extensive human disturbances and natural impacts. Higher frequency of
resource utilization, partial clearing of forest cover due to difference land
use impacts such as cultivation and dykes or complete or partial flooding or
dieback resulting to overall degradation of forest structure and biodiversity.
Level 4: The highest scale of destruction where larger portions or all of the forest area
had been cleared. Clearing of all or large portion of forest area for cultivation
or the combinative impact of cultivation and natural dieback or cultivation
and flooding resulting to high portions or complete loss of forest area.
Observer groups derived the overall disturbance level in each forest from the
average of the disturbance indices recorded. Therefore, the disturbance level that
was assigned to each forest was an overall qualitative and accumulated assessment of
all human activities and/or natural impacts indicators that had been observed.
Changes in forests sizes
Satellite imagery for the year 2000 and 1979 topographic maps of the study area were
used as sources of land cover information and were digitized using MapInfo Version
5.5 (MapInfo Corporation 1985–1999) to obtain forest sizes. Differences in forest
sizes between the 2 years were used to determine changes in size of the forests.
Results
Anthropogenic activities in the forest patches along the Tana River
The main human activities observed were logging, tree harvesting and cultivation
(Table 1).
Logging was observed in 69 forests and accounted for 39% of human activities,
tree harvesting in 45 (25%), and cultivation in 43 (24%). Honey harvesting and dyke
constructions were observed in 16 (9%) and 6 (3%) forests visited, respectively.
Where observed, cultivation and dyke construction had the most devastating effects
on forest cover due to partial or complete vegetation clearance. The most affected
species due to tree harvesting were Borassus aethiopuim,Phoenix reclinata and
Hyphaene compressa. While the most preferred tree species for construction of
canoes and beehives were Diospyros kabuyeana, Ficus sycomorus, Mimusops fruti-
cosa and Mangifera indica. Bee keeping appeared more sustainable than honey
harvesting because although the hives are constructed from a felled tree, the hive can
be used for a long period of time while harvesting of honey from standing natural
tree hives looked very destructive. Furniture was constructed from Spyrostachys
venenifera, while building materials were obtained largely from Phoenix reclinata.
Table 1 Frequencies and
proportional occurrence of
categorized human activities
in 73 forest patches along the
Lower Tana River basin
Activities Frequency %
Logging 69 39
Tree harvesting 45 25
Cultivation 43 24
Honey harvesting 16 9
Dyke construction 6 3
Total 179 100
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Eight forest patches, severely impacted by cultivation alone were Nkanjonja
(no. 1), Wenje Complex (nos. 2a–c), Baomo East (no. 20), Baomo North (no. 21),
Baomo South (no. 22), Lazima East (no. 42), Hewani East 1 (no. 59) and Hewani
West 2 (no. 2) (Fig. 1). Four forests affected by dyke construction alone were Kulesa
East 1 (no. 48a), Wema East 1 (no. 56), Hewani East 2 (no. 60) and Mitapan 2 (no. 70)
(Fig. 1). Three forests, Hewani East 1, Hewani East 3 and Hewani West 2 (numbers
59, 61 and 62, respectively) were heavily impacted by human activities and yet
satellite imagery indicated an increase in area by 8.2% to 161 ha.
Excess flooding in forest patches along the Tana River
Six forest patches affected by excess flooding included Kipendi 1 (3a), Kipendi 2
(3b), Maroni West 1 (4a) and Maroni West 2 (4b), and are all along channel 2, the
current river course (Fig. 1).
Natural die back in forest patches along the lower Tana River
Along the old river channel (channel 1), only one forest patch, Maziwa North (forest
no. 51), was affected by natural die back (Fig. 1). Four other forest patches affected
by dieback are near the current river channel (Fig. 1). They include Wema East 4
(no. 68), Hewani South 1a (no. 63a), Hewani South 2 (no. 64) and Bvumbwe South 2
(no. 66b) (Fig. 1).
Forests impacted by both natural impacts and human activities along the lower
Tana River
Forests impacted by both natural dieback and cultivation were Matalani South (no.
33), Sera (no. 41), Giritu woodlands (no. 45) and Maziwa South (no. 52) (Fig. 1).
Flooding and cultivation impacted only Maroni East 1 (5a) and Maroni East 2 (no.
5b) (Fig. 1). Two forest patches impacted by both dieback and dyke constructions
were Bvumbwe North (no. 65) and Lango La Simba (67a) (Fig. 1).
Forest status
Out of the 73 forest fragments evaluated, 28 had little or no disturbance while 21
were heavily disturbed. Of the heavily impacted forests, six were in the reserve and
15 outside the protected area (Table 2).
Causes of forest area loss in forest patches along the Tana River
Natural dieback alone impacted on Maziwa North (no. 51) and Hewani South 1a
(no. 63a) resulting to area loss of 28.9% and 22.4%, respectively (Table 3). Of the
forest patches impacted by flooding alone, Maroni West 2 (no. 24b) and Kipendi 2
(no. 3b) had the highest habitat loss of 85% and 57.1%, respectively (Table 2).
Baomo East (no. 20) and Nkanjonja (no. 1) forests were most affected through
cultivation with losses of 80.7% and 50.1%, respectively. Construction of irrigation
dykes greatly impacted on Kulesa East 1 (no. 48a) resulting in loss of 71.7% of
forested area (Table 3).
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Four forest patches were affected by a combination of cultivation and natural
diebacks. Matalani South (no. 33), Sera (no. 41), Giritu woodlands (no. 52) and
Maziwa South (no. 45) forests had area loss of 99, 75.8, 71.1, and 46.8%, respectively
(Table 3). Maroni East 1 (no. 5a) and Maroni East 2 (no. 5b) were affected by both
cultivation and flooding resulting to a total forest area loss of 50% each (Table 3).
Table 2 Intensity of destruction of forests and their current areas in and out of the Tana River
National Primate Reserve using a scale of 1–4
Destruction levels Forests in reserve Forests out of reserve
Numbers Area (ha) % Numbers Area (ha) %
1 6 469.1 35 22 744.1 27
2 5 486.8 29 12 421.4 21
3 0 0.0 0 7 362.3 13
4 6 595.0 35 15 509.1 39
Total 17 1550.9 100 56 2036.9 100
Scale 1, little or no destruction; scale 2, moderate levels of destruction; scale 3, extensive human
destruction with no section of forest completely cleared; scale 4, highest levels of destruction with
sections of the forest completely cleared
Table 3 Changes in forest sizes and their respective causes in the lower Tana River between 1979
and 2000
Forest patch No. Area (ha) Change in
area (%)
Factors leading to loss of area
1979 2000 Cult. Dyke D/back Flooding
Nkanjonja 1 168.8 84.2 50.1 +
Wenje complex 2a–c 683.6 534 21.9 +
Kipendi 1 3a 55.9 37.4 33.1 +
Kipendi 2 3b 34.5 14.8 57.1 +
Maroni West 1 4a 69.1 30.9 55.3 +
Maroni West 2 4b 27.4 4.1 85.0 +
Maroni East 1,2 5a–b 133.6 54.3 59.4 + +
Baomo East 20 73.7 14.2 80.7 +
Baomo North 21 46.1 30.2 34.5 +
Baomo South 22 261.4 99 62.1 +
Matalani South 33 240.3 2.3 99.0 + +
Sera 41 204.1 59 71.1 + +
Lazima East 42 15.5 8.9 42.6 +
Giritu 45 327.5 79.2 75.8 + +
Kulesa East 1 48a 68.1 19.3 71.7 +
Maziwa North 51 61.2 43.5 28.9 +
Maziwa South 52 40 21.3 46.8 + +
Wema East 1 56 30 28.1 6.3 +
Hewani East 2 60 7.9 4.2 46.7 +
Hewani South 1 63a 20.1 15.6 22.4 +
Bvumbe North 65 260.6 136.5 47.6 + +
Lango la Simba 67a 86.4 79.2 8.3 + +
Mitapani 2 70 105.3 76.7 27.2 +
Total 3021.1 1476.9 48.9
Four factors driving change were identified as cultivation (cult.), dyke construction (dyke), natural
dieback (D/back) or flooding. Forests affected by the various factors are specifically indicated by a
positive (+) sign
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Overall forest area reduced significantly from 5,439 ha to 3,564 ha (t= 3.807,
n= 76, P< 0.001) accounting for a 34% decrease between 1979 and 2000 (Table 4).
The loss of forest area outside the reserve was 38% from 3,283 ha to 2,037 ha
(t= 2.929; n= 57; P< 0.005) and 28.1% from 2,156 ha to 1,551 ha (t= 2.522; n= 21;
P< 0.02) in the protected area (Table 4).
Discussion
Human activities and natural impacts on the riverine forests along the lower
Tana River region
Our study has shown that through shifting cultivation, dyke constructions, flooding
and dieback, human activities, and natural impacts have had a devastating effect on
the status of the lower Tana riverine forests leading to loss and increased frag-
mentation of unique habitats. Anthropogenic activities in the forests persist in the
form of slash-burn agriculture, selective logging and several other deleterious uses of
forests (Table 1). The resultant change in forest structure, especially removal of
large canopy tree species, is of great concern in the conservation of the endangered
primates, the Tana red colobus (Procolobus rufomitratus) and the Tana crested
Mangabey (Cercocebus galeritus galeritus). Both species are dependent on gallery
forests for food and sleeping groves (Homewood 1976; Marsh 1981; Wahungu 1998;
Suleman et al. 2001). Shifting cultivation combined with some natural impacts
contributed to a total loss of 1,208 ha or 78.2% of affected forests that were ground
‘‘truthed.’’ Dyke construction resulted to a total loss of 210.6 ha or 13.6% of the
affected forests that were ground ‘‘truthed.’’ The most impacted forest, Matalani
south (no. 33), was affected by both cultivation and natural dieback with loss of 99%
of area and only 2.3 ha is left standing from 240.3 ha in 1979. Hewani East 1 (59),
Hewani West 2 (62) and Hewani East 3 (61) forest patches are reflected on satellite
images as indigenous forest patches but upon ground ‘‘truthing’’ it became evident
that these patches have mostly been cleared for cultivation and have been replaced
by exotic tree species. These three examples provide evidence of the importance of
ground ‘‘truthing’’ instead of only using satellite imagery to determine the true status
of forests in affected areas.
Our study recorded a loss of 34.5% of total forest area between 1979 and 2000
(Table 4). The loss outside the Tana River National Primate Reserve (1,246 ha) was
significantly (P< 0.005, t= 2.929) larger than loss within the reserve (629 ha) reit-
erating the significant role played by this protected area in habitat and species
Table 4 Comparison of forest area reduction in and out of the reserve and overall forest area
reduction along the Lower Tana River between 1979 and 2000
Location Number of forests
inspected
Area (ha) % change
1979 2000 Loss of area (ha)
Reserve 21 2156 1527 629 29.2 P< 0.020
Outside 57 3283 2037 1246 38.0 P< 0.005
Total 76 5439 3564 1875 34.5 P< 0.001
Biodivers Conserv (2007) 16:1161–1173 1169
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conservation. The loss of 29.2% of forest area within the protected area in 21 years is
nonetheless of major concern and suggests a loss rate of 29 ha per year. With only
1,527 ha of forest remaining within this reserve, these habitats constitute a biodi-
versity in risk of extinction within approximately the next five decades. The rate of
loss of forest habitats outside the reserve, at 59 ha per year, is twice that of the
protected area and the remaining 2,037 ha may disappear in approximately in three
and a half decades unless urgent conservation programmes are put in place. Twenty-
eight forest patches have experienced the highest levels of destruction (Level 3 & 4)
(Table 2). This has accounted for 1,348 ha of forest loss and has, of consequence,
severely impacted primate habitats. This equals a loss of 24.8% from the total
forested area that existed in 1979 and should be the focus of immediate conservation
effort.
The impact of flooding and natural dieback on the forests in the lower Tana River
region is enormous. Changes caused by both dieback and flooding in the Lower Tana
riverine forests do not necessary immediately remove forest cover, instead they are
more likely to cause progressive degradation of forest structure and biodiversity. In
the long-term, this progressive degradation leads to partial or complete loss of forest
cover. Thus, these impacts share the quality of being difficult to perceive by satellite
imagery and are difficult to evaluate without monitoring by ground truthing (Dale
et al. 1994). It would be important to note that a forests like Hewani South 2 and
Wema East 4 (forest nos. 64 and 68, respectively) where natural dieback occurred,
appear to have increased, while in reality the interior of the forest have been
affected by tree dieback.
One important aspect that was not evaluated during this study was the loss of
mature forest due to bank erosion. This type of evaluation would necessitate long-
term monitoring of these potential sites, which was beyond the scope of this research
study. Future studies should incorporate the impact of bank erosion and evaluating
its role as a natural impact on the forests.
As a whole, the combinative impact of cultivation and natural dieback or culti-
vation and flooding has resulted in the highest percentage forest area loss in the
Lower Tana Region. Both human and natural impacts are responsible for changes in
forest cover and forest stature. As this study has indicated, areas that have experi-
enced significant area loss due to the Tana River dynamism could be significantly
related to changes in human activities, which further complicates current and
potential conservation and management strategies in and out of the reserve.
Effects of forest degradation, destruction and fragmentation on the endangered
primate population along the Lower Tana Region
Human exploitation of forest resources can involve rapid, non-sustainable harvesting
of particular species (Gentry and Va
´squez 1988) while flooding and natural dieback
can result in a progressive degradation of forest structure and biodiversity that leaves
behind standing but biologically and economically depleted forests. The riverine
habitats on the lower Tana River are highly vulnerable to perturbations due to the
Tana River dynamism and the continual human overexploitation. An ever-increasing
human population continually exacerbates this problem. Many of the tree species
that are important to the endangered primates are also vital to the local communities
for construction of canoes, poles and other wood products (Marsh 1981; Medley
1990; Kahumbu 1992). This competition for diminishing resources is likely to result
1170 Biodivers Conserv (2007) 16:1161–1173
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in a reduction in the carrying capacity for the endangered primates in the lower Tana
region riverine forests (Kahumbu and Davies 1993).
According to the recent primate census (Karere et al. 2004), about 50% of both
the red colobus and the crested mangabeys were found outside the protected area.
The riverine forests within the protected area represents only 24% of the forest
ecosystem and may thus be inadequate to provide resources to stem the current
decline in endangered primate populations. However, the importance of the
unprotected forest patches situated outside the reserve for the survival of both
endangered primate species cannot be overemphasized. The survival of these species
depends on the future management and conservation of the majority of forest pat-
ches that are situated out of the reserve. The fact that the greatest area of forest loss
was outside the reserve implies the immediate need to initiate conservation pro-
grammes outside the protected area. That the Tana red colobus, over the last
7 years, have experienced a 15% loss in population outside the reserve (Suleman
et al. 2001; Karere et al. 2004) exemplifies these urgent needs. Previous studies
conducted in the lower Tana have shown the impact of forest destruction on the red
colobus (Marsh 1978; Decker 1989; Mbora and Meikle 2004) and the crested man-
gabey (Kinnaird 1990; Homewood 1975) populations. Forest destruction can result
in declining primate populations (Myers 1987; Gillespie et al. 1999) and in extreme
situations, extinction (Yongzu et al. 1989; Boinski 1994). Since these forest patches
do not fall under the management of the organization that manages the parks and
reserves in Kenya, i.e., Kenya Wildlife Service (KWS), management and conserva-
tion strategies should directly involve the participation of the local communities.
A prominent issue that should seriously be addressed in the Lower Tana region is
the effect of forest fragmentation on the two endangered primate species because
primates have specific responses to fragmentation making them valuable candidates
for examining its effect (Estrada and Coates-Estrada 1996; Tutin et al. 1997). Forest
fragmentation not only isolates floral and faunal population but it also impedes gene
flow between forest patches (Marsh et al. 1987). A study that was conducted on the
effect of fragmentation on the Tana river red colobus (Mbora and Miekle 2004)
suggests that this primate species may prefer more disturbed forests. However,
according to Suleman et al. (2001), the number of primate groups in any given forest
along the Tana River was significantly correlated with forest area; suggesting that
both endangered primate species along at the Lower Tana region are prone to forest
loss and fragmentation. Many primate studies at the Lower Tana region appear to
focus on the impact of human activities on these endangered species. This study
demonstrates that the effects of natural impacts are just as important, and therefore,
future studies should not only examine the long-term effects natural impacts on the
endangered primate species, but also study the combinative effects of both natural
and human impacts on these species.
Conservation of the riverine forests in the Lower Tana region and the local
communities
According to Butynski and Mwangi (1994b), local people living, in the vicinity of the
Tana riverine forests are aware of the direct benefits they receive from the remaining
forests. The Pokomo, have traditional laws and norms governing land use that
determine who can clear land for cultivation and how much may be cleared (CARE-
International-Kenya 1992) known as the ‘‘Wakijo’’ (Bunger 1979; Decker 1989). It is
Biodivers Conserv (2007) 16:1161–1173 1171
123
not known, however, to what extent these laws actively protect the forest resources
or control exploitation. Decker (1989) explains that the traditional forest manage-
ment was conservative and proposed that their indifference towards forest degra-
dation is more recent phenomenon caused by the displacement of the traditional
management by the current protectionist management of the TRPNR. This was an
observation that continued to be noted during the duration of this study. The extent
to how far these traditional conservation laws are still practiced and their potential
effectiveness on the sustainability of the existing forest patches should be examined
to reinforce the present management strategies. This type of information is vital to
provide guidelines that would assist in strengthening the already existing efforts,
if any, of the local communities. The importance of the local communities’ full
participation in actively and sustainably managing these forest patches is the only
way these remaining forests can continue to persist as well as sustain their rich
biodiversity.
Acknowledgements We wish to express our gratitude to the World Bank Tana GEF Project that
funded this work and the Kenya Wildlife Service. The Senior Warden in Tana River Primate
National Reserve, Barasa Otunga and field assistants from Mchelelo Research camp who provided
invaluable assistance in logistics and data collection, respectively. Many individuals and organiza-
tions within Tana River District assisted in different ways and we are extremely grateful for making
it possible for us to accomplish the objectives of the study. We would also like to thank Dennis
Milewa for his assistance in the production of the map of the study area and Erick Fockler for his
critical editing and constructive comments.
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For the worst-case scenario of land management, gap-crossing ability and area requirements of the tropical frog imply that only 60% of the forest remaining after seven years of management is suitable habitat. Considering breeding habitat requirements and possible edge effects further reduces the suitable habitat to 39% of the remaining forest. These reductions in the proportion of suitable forest area are likely to change with rate and spatial pattern of forest loss. La deforestación agran escala está poniendo en peligro la diversidad de las selvas tropicales. Dada la insuficiencia de datos sobre las características de la historia natural de las especies tropicales, son necesarios métodos para identificar aquellas especies suceptibles a la extirpación luego de la fragmentación del bosque. 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Los efectos de la fragmentación del bosque fueron evaluados para una rana tropical, considerando no sólo la habilidad para cruzar claros y el requerimiento del área, sino también los requerimientos especializados del hábitat y los efectos de los bordes. Para el peor escenario de manejo de la tierra, la habilidad de cruzar claros y los requerimientos de superficie de la rana tropical implican que sólamente el 60% del bosque que queda después de 7 años de manejo constituye un hábitat adecuado. La consideración de los requerimientos del hábitat para cría y los posibles effectos de los bordes, reduce aún más el hábitat adecuado Ilevándolo a un 39% del bosque remanente. Estas reducciones en la proporción del área de bosque adecuada, son susceptibles a cambiar de acuerdo con la tasa y en el patrón espacial de pérdida del bosque.
Article
If logging is to be compatible with primate conservation, primate populations must be expected to recover from the disturbance and eventually return to their former densities. Surveys conducted over 28 years were used to quantify the long-term effects of both low- and high-intensity selective logging on the density of the five common primates in Kibale National Park, Uganda. The most dramatic exception to the expectation that primate populations will recover following logging was that group densities of Cercopithecus mitis and C. ascanius in the heavily logged area continued to decline decades after logging. Procolobus tephrosceles populations were recovering in the heavily logged areas, but the rate of increase appeared to be slow (0.005 groups/km(2) per year). Colobus guereza appeared to do well in some disturbed habitats and were found at higher group densities in the logged areas than in the unlogged area. There was no evidence of an increase in Lophocebus albigena group density in the heavily logged area since the time of the logging, and there was a tendency for its population to be lower in heavily logged areas that in lightly logged areas. In contrast to the findings from the heavily logged area, none of the species were found at a lower group density in the lightly logged area than in the unlogged area, and group densities in this area were not changing at a statistically significant rate. The results of our study suggest that, in this region, low-intensity selective logging could be one component of conservation plans for primates; high-intensity logging, however, which is typical of most logging operations throughout Africa, is incompatible with primate conservation.