Are they competing or compensating on farm? - World Agroforestry

165 Pages·2006·3.32 MB·English

Are they competing or compensating on farm?
Status of indigenous and exotic tree species in a wide range of agro-
(cid:13)
ecological zones of Eastern and Central Kenya, surrounding Mt. Kenya
Zenroku Oginosako, Parnwell Simitu, Calleb Orwa and Simon Mathenge

Are they competing or compensating
on farm?

Status of indigenous and exotic tree species in a wide range of
agro-ecological zones of Eastern and Central Kenya, surrounding Mt. Kenya

Results of vegetation, farmer and nursery surveys

Zenroku Oginosako, Parnwell Simitu, Calleb Orwa and Simon Mathenge
Correct citation: Oginosako Z, Simitu P, Orwa C and Mathenge S. 2006. Are they competing or compensating
on farm? Status of indigenous and exotic tree species in a wide range of agro-ecological zones of Eastern and
Central Kenya, surrounding Mt. Kenya. ICRAF Working Paper no. 16. Nairobi: World Agroforestry Centre.

Titles in the Working Paper Series aim to disseminate interim results on agroforestry research and practices and
stimulate feedback from the scientific community. Other publication series from the World Agroforestry Centre
include: Agroforestry Perspectives, Technical Manuals and Occasional Papers.

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© World Agroforestry Centre 2006
Working Paper no. 16

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About the authors

Zenroku Oginosako Research Scientist for the dryland agroforestry programme in East and Central
Africa, World Agroforestry Centre (ICRAF). Corresponding author.
Email contact: [email protected].
Parnwell Simitu Research Assistant for the dryland agroforestry programme in East and Central
Africa, World Agroforestry Centre (ICRAF).
Email contact:[email protected]
.
Calleb Orwa Data analysis specialist of the trees and market team, World Agroforestry Centre
(ICRAF).
Email contact: [email protected]

Simon Mathenge Taxonomist for the Herbarium of the department of Botany at the University of
Nairobi.
Email contact: [email protected]
.
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Abstract

Mt. Kenya lies at the origin of a wide variety of agro-ecological zones in Kenya, and the zones
surrounding Mt. Kenya itself comprise Kenya’s eastern and central provinces. The purpose of this
survey is to establish the current vegetation status of both indigenous and exotic tree species in this
wide range of agro-ecological zones of eastern and central Kenya, in terms of species composition
and structure type. It also aims to determine how the tree vegetation is categorized as to type of
species richness and tree abundance, as well as species composition, using some environmental
variables. In this study, a farmer survey and a nursery survey were conducted with the vegetation
survey. The purpose of the farmer survey was to know the present status of trees in order to improve
their productivity under the agroforestry systems. We collected information, such as constraints of
tree farming and agroforestry and what tree species the farmers want to plant most in their farms. A
nursery survey also collected information, such as the type of tree species they have, how they raise
tree seedlings, and seedling supply systems, in order to know the present situation of private nurseries,
family nurseries, and group nurseries.
The survey team found 459 species in 87 families at 265 plots in the target areas surrounding Mt.
Kenya. The average number of trees and shrubs per plot (1/2ha) is 204.5 and the number of species
per plot is 17.6. More than 70% of all species are indigenous tree species, and such trees are more
than 50% of all trees. Almost all zones have a higher number of exotic trees than indigenous trees,
especially in the tea-dairy, coffee-tea, and main coffee zones. The lower locations, however, have
more indigenous trees than exotic trees. A rank-abundance curve also shows that few species
dominate the landscape. Ten species, out of 459 species, represent 43.5% of all trees. Most of them
are exotic species such as Grevillea robusta, Musa sapientum and Cupressus lusitanica.
Through regression analysis we found that Embu District has a significantly greater number of trees
than the other districts, and the inner lowland zone has fewer. The ordination diagram provides further
evidence for compositional differences among districts. Species composition is especially varied
between Embu and the other four districts. Meru and Kirinyaga districts are similar in species
composition, as are Nyeri and Laikipia districts. The limited abundance of many indigenous tree
species indicates that genetic diversity and population sizes could be too low to sustain several
indigenous tree species within the agro-ecosystem unless their abundance is increased. We need to
give more attention to the direct influential mechanisms and consider the root causes. Our survey
team emphasizes ‘Conserving biodiversity, while promoting agriculture production through
agroforestry’.

Keywords: Mt. Kenya agro-ecological zones, vegetation survey, indigenous species, exotic species,
Agroforestry

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Contents

Part I.....................................................................................................................8
Results of a vegetation survey in five districts surrounding Mt. Kenya........8
1. Introduction.......................................................................................................................................................................8
2. Background........................................................................................................................................................................9
3. Profiles of survey districts, population and land use systems......................................................................................10
4. Methods and Materials...................................................................................................................................................15
4.1 Vegetation Survey........................................................................................................................................................15
4.2 Soil analysis..................................................................................................................................................................16
4.3 Farmers survey and nursery survey..............................................................................................................................16
4.4 Data analysis methodology...........................................................................................................................................17
5. Results of survey..............................................................................................................................................................18
5.1 Landscapes and vegetation types in different agro-ecological zones............................................................................18
5.2 Species richness............................................................................................................................................................22
5.3 Statistical Analyses.......................................................................................................................................................30
6. Discussion.........................................................................................................................................................................40
6.1 Biodiversity pattern on a district and agro-ecological level..........................................................................................40
6.2 Biodiversity conservation through agroforestry............................................................................................................42

Part II.................................................................................................................45
Results from the farmer survey and nursery survey in 5 districts
surrounding Mt. Kenya....................................................................................45
Abstract................................................................................................................................................................................45
1. Introduction.....................................................................................................................................................................45
2. Methods and materials....................................................................................................................................................47
2.1 Selection of survey area and of informants...................................................................................................................47
2.2 Interview.......................................................................................................................................................................48
2.3 Data entry and analysis.................................................................................................................................................49
3. Result................................................................................................................................................................................49
3.1 Encountered tree species on farms................................................................................................................................50
3.2 Tree species preferred for various uses and services....................................................................................................56
3.3 Criteria used in species selection..................................................................................................................................59
3.4 Sources of knowledge on tree propagation...................................................................................................................61
3.5 Constraints to tree farming...........................................................................................................................................62
4. Discussion.........................................................................................................................................................................63
4.1 Diversity.......................................................................................................................................................................63
4.2 Uses of trees.................................................................................................................................................................64
4.3 Species niche................................................................................................................................................................64
4.4 Most preferred species..................................................................................................................................................65
4.5 Sources of knowledge...................................................................................................................................................66
4.6 Constraints of tree farming...........................................................................................................................................67

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Part III................................................................................................................68
Nursery survey..................................................................................................68
Abstract.................................................................................................................................................................................68
1. Introduction......................................................................................................................................................................68
2. Methods and materials......................................................................................................................................................69
2.1 Selection of survey area and of informants...................................................................................................................69
2.2 Interviews.....................................................................................................................................................................70
2.3 Data entry and analysis.................................................................................................................................................70
3. Result................................................................................................................................................................................71
3.1 Type of nurseries surveyed...........................................................................................................................................71
3.2 Species produced in the nurseries.................................................................................................................................72
3.3 Species demand............................................................................................................................................................76
3.4 Source of water for the nursery.....................................................................................................................................77
3.5 Compost use in the nursery...........................................................................................................................................78
3.6 Sources of plant material..............................................................................................................................................78
3.7 Sources of knowledge on nursery management............................................................................................................79
3.8 Problems associated with the management of a nursery...............................................................................................80
4. Discussion.........................................................................................................................................................................81
4.1 High demand makes good supply.................................................................................................................................81
4.2 Water source influences the fate of nursery?................................................................................................................82
4.3 Compost is necessary?..................................................................................................................................................83
4.4 Source of plant material................................................................................................................................................83
4.5 Source of knowledge and skills....................................................................................................................................84
4.6 Constraints for nursery management............................................................................................................................84
4.7 Future developments for tree nurseries.........................................................................................................................85
4.8 Conclusion and next step for natural resource management and agricultural development..........................................86
5. Acknowledgement.............................................................................................................................................................88
6. References.........................................................................................................................................................................89

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Appendix 1 94
Appendix 2 95
Appendix 3 98
Appendix 4 100
Appendix 5 111
Appendix 6 121
Appendix 7 122
Appendix 8 129
Appendix 9 130
Appendix 10 133
Appendix 11 134
Appendix 12 138
Appendix 13 145
Appendix 14 147
Appendix 15 149
Appendix 16 151
Appendix 17 156
Appendix 18 158
Appendix 19 160

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Part I
Results of a vegetation survey in five districts
surrounding Mt. Kenya

1. Introduction
Mt. Kenya, a prominent mountain located at the equator, causes a wide variety of agro-
ecological zones in Kenya. An agro-ecological zone is defined by its relevant agro-climatic
factors and differentiated by soil pattern. The aim of such zone classification is to provide a
framework for the ecological (natural) land-use potential. General agro-ecological zones were
established by FAO (1978). The target districts we surveyed comprise Kenya’s eastern and
central provinces, surrounding Mt. Kenya. No previous comprehensive survey has covered all
of these agro-ecological zones. As a world heritage site, Mt. Kenya forest is always the target
of appeals to save natural vegetation, and therefore Kenya Wildlife Service has several times
carried out vegetation surveys, using satellite images, aerial pictures and ground level surveys
(Gathara, 1999; Vanleeuwe et al. 2003). The vegetation status of agricultural fields
surrounding the mountain, however, was always dismissed and neglected by the researchers
and government officials. The World Agroforestry Centre (ICRAF) has carried out several
surveys about agroforestry potential, including fodder tree species trials, in recent decades
(Hoekstra 1988; Thijssen et al. 1993; Roothaert et al. 1997). Without an initial understanding
of the real situation of vegetation and people in the target area, ideas and plans might not be
born. The agro-ecological zone category is attached as Appendix 1.

The present survey intended to begin by establishing the current vegetation status of both
indigenous and exotic tree species in a wide range of agro-ecological zones of eastern and
central Kenya. A random vegetation survey within the target zones would assess species
inventory, which is then used to identify useful tree species for the production of timber, fuel,
fruit, fertilizer and fodder around Mt. Kenya. Diversification of species composition can lead
to enhancements of stability and productivity of ecosystems (Cottingham et al. 2001). Such
diversification of tree species on farms is one of the objectives of the World Agroforestry
Centre (ICRAF 2000). This survey also forms the basis of a vegetation map, which when
combined with satellite image analyses can be used to assess future vegetation changes
caused by such phenomena as global warming. We analyzed statistically how tree vegetation
is categorized, in terms of species richness, tree abundance, and species composition,
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