Catherine Muthuri

Understanding patterns of tree adoption on farms in semi-arid and sub-humid Ethiopia

Trees on farms are a widespread feature of landscapes across a large part of Ethiopia with an important role in enhancing the resilience of smallholder livelihoods through the provision of ecosystem services. Despite their importance, little is known about what trees are planted or retained from natural regeneration by different types of farmers that results in the pattern of tree cover found in the region. We address this knowledge gap through analysis of household survey data from semi-arid and sub humid areas of Oromia regional state. A set of composite variables that represent distinctive patterns of tree cover on farms were derived from principal component analysis and Pearson correlation analysis. This revealed two major tree adoption strategies: farmer managed natural regeneration (FMNR) of trees to meet subsistence needs as well as contributing to other ecosystem services; and, high value agroforestry (HVAF) involving planted trees used largely to produce fruits, timber and fodder. Regression analysis further identified fine-scale variation in ecological and socio-economic factors that affect which of these two broad strategies are adopted by farmers. Favorable climatic conditions coupled with institutional arrangements to control free grazing were pre-conditions for HVAF, whereas poor biophysical potential and sloping land provided a positive incentive for farmers to adopt FMNR. Farmers with preferences for tree species with multiple utilities and locational flexibility favored FMNR while adoption of HVAF was more asset-driven. Our findings reveal that farmers integrate many native and exotic tree species on their farms to meet their variable farm conditions, needs and asset profiles in stark contrast to most tree promotion efforts that focus on a few, usually exotic, tree species. We recommend that future agroforestry promotion should embrace a diversity of tree species appropriate to matching the fine scale variation in ecological conditions and farmer circumstances encountered in the field.

Evaluating a non-destructive method for calibrating tree biomass equations derived from tree branching architecture

Key messageFunctional branch analysis (FBA) is a promising non-destructive method that can produce accurate tree biomass equations when applied to trees which exhibit fractal branching architecture.AbstractFunctional branch analysis (FBA) is a promising non-destructive alternative to the standard destructive method of tree biomass equation development. In FBA, a theoretical model of tree branching architecture is calibrated with measurements of tree stems and branches to estimate the coefficients of the biomass equation. In this study, species-specific and mixed-species tree biomass equations were derived from destructive sampling of trees in Western Kenya and compared to tree biomass equations derived non-destructively from FBA. The results indicated that the non-destructive FBA method can produce biomass equations that are similar to, but less accurate than, those derived from standard methods. FBA biomass prediction bias was attributed to the fact that real trees diverged from fractal branching architecture due to highly variable length–diameter relationships of stems and branches and inaccurate scaling relationships for the lengths of tree crowns and trunks assumed under the FBA model.

Agroforestry solutions for buffering climate variability and adapting to change.

Th is chapter will focus on increasing the adaptive capacity of agricultural systems in tropical and subtropical regions through agroforestry. Agroforestry as a concept resists and tries to counteract the way agriculture has been segregated from forests and forestry. Understanding, using and improving agroforestry implies a focus on the interactions between trees, annual crops and domestic stock, given the local abiotic factors of climate, soils, water and nutrient balances, as well as the biotic context (pests, diseases, antagonists, predators, pollinators and dispersal agents), and the use of land, external inputs, labour and knowledge. We pose and review the hypothesis that the presence of trees increases the degree of buff ering of climate variability from the perspective of an annual food crop, and that retention and the increase of trees in agricultural landscapes can be a relevant part of climate change adaptation strategies.

Trees in agricultural landscapes enhance provision of ecosystem services in Sub-Saharan Africa

ABSTRACT The recent interest in multi-functional agricultural landscapes has not been matched with formal assessment of the roles that trees play across the spectrum of ecosystem services (ESs) provided in Sub-Saharan Africa (SSA). A structured literature review (1995–2014) assessed 350 journal articles about provision of one or more ESs by trees on farms and in agricultural landscapes in SSA. This revealed information on 15 ESs from studies in 23 countries covering arid (1% of studies), semi-arid (49%), sub-humid (26%) and humid (24%) agro-ecological zones. The majority of the studies reported provisioning (39%) and supporting (35%) followed by regulating (26%) ESs while studies on cultural services were scarce. Beneficial impacts of trees were dominating (58%), in particular in semi-arid zones where they were associated with enhancing water and nutrient cycling. A decline in some ESs was reported in 15% of the studies, while 28% found no effect of trees. Although the effects of trees were mainly positive, a decline in crop production was noted as a key trade-off against the provisions of ESs, such as modification of microclimate. This highlights the need to manage trade-offs among impacts of trees on ES provision to reduce competition and increase complementarity between trees and crops.

Farmland tree species diversity and spatial distribution pattern in semi-arid East Shewa, Ethiopia

Abstract Information on tree species occurring in farming systems in semi-arid agroecologies is critical for sustainable land management, biodiversity conservation and informing food security interventions. The aim of the study was to characterize the species composition, diversity, structure and spatial distribution patterns of trees in the semi-arid East Shewa Zone of Oromia, Ethiopia. A survey of 172 land parcels with a total area of 76.09 ha, and belonging to 100 randomly selected farm households was conducted in 5 semi-arid sites in East Shewa. A total of 77 tree species belonging to 32 families were identified, and the Fabaceae were the dominant group. Trees were distributed differently in the four identified land uses (homesteads, line plantings, in crop lands and woodlots). Tree diversity was the highest in line plantings and the lowest in woodlots with the Shannon diversity index of 3.1 and 1.8, respectively. The majority (70%) of the species were native, whereas the remaining 30% were exotic. The average number of tree species per parcel was 4.7 ranging from treeless condition to 36 tree species in an exceptional farm condition. The height and diameter at breast height of the 6066 recorded individuals (2 m and above) ranged from 2 to 25 m and from 1 to 86 cm, respectively. The species Acacia tortilis, Eucalyptus camaldulensis and Acacia senegal were the three dominant species in the system. Correlation analysis revealed that land-holding size had significant positive relationships with tree species abundance and basal area, but not with species richness. Interventions are suggested for increasing the currently very low tree cover through planting and managing natural regeneration for improved farming system resilience in the face of climate change.

Constraints encountered by nursery operators in establishing agroforestry tree nurseries in Burundi

A nursery operator survey was conducted to identify major constraints encountered by nursery operators for tree nursery establishment in Burundi. The survey covered two main contrasting agro-ecological zones of the country in Muruta commune and Bugesera region in Bugabira and Busoni communes. It was found that most planting materials used by nursery operators were collected from sources of unknown genetic quality. It was also noted that few tree species were raised in nurseries of Muruta and Bugesera areas. The growing medium used in individual and group nurseries was of low quality. The lack of capital and nursery material inputs was another impediment to small-scale nursery sustainability. Most nursery operators lacked sufficient technical knowledge on nursery establishment techniques and had limited skills on vegetative propagation techniques. The low involvement of non-governmental organizations and government agencies impedes the sustainability of nursery operations in the two areas of study. Finally, the low demand and price for tree seedlings do not motivate nursery operators to produce seedlings for income generation. The government intervention may develop a well-structured nursery management system to support sustainable production of high-quality seedlings. It is then necessary to organize trainings of nursery operators on source and collection techniques of germplasm or planting material. The establishment of seed orchards and seed production areas of a large number of tree species is also of great importance. The support of nursery operators in financial and material inputs may promote tree species diversity and increase seedling production. The link of tree operators to good market may improve the sustainability of tree nursery operations.

Variations in shoot and root growth of three provenances of Faidherbia albida in clay and sand soil

The variation in shoot and root seedling growth traits was compared among three Faidherbia albida (Del). A. Chev. provenances originating from Kenya (Taveta), Malawi (Bolero) and Ghana (Bolgatanga); representing east, south and west Africa, respectively. Bulked seeds from three provenances were grown in two soil types (clay and sand) at the World Agroforestry Centre nursery, Nairobi. Seedlings grown in clay soil had high shoot growth and shoot to root ratios but shorter root length, lower number of nodules and specific root length compared to seedlings in sand soil. Shoot to root ratios reduced with time and this was more pronounced in sand soil. Overall, the Bolero and Taveta provenances had higher growth than the Bolgatanga provenance. This was probably because plants grown in nutrient-rich clay soil invest more in shoot growth as compared to root growth. Longer root growth in sand soil shows a better adaptive mechanism that increases competitive ability and survival in nutrient-poor systems. Variations observed among the seedling variables such us shoot and root growth could be used for early selection for reforestation and agroforestry in predominantly clay and sand soil areas.

Testing Biodegradable Seedling Containers as an Alternative for Polythene Tubes in Tropical Small-Scale Tree Nurseries

Polythene tubes are the most commonly used seedling containers and their adoption can be attributed to high water retention that enhances seedling establishment as well as the desire for low-cost readily-available containers by nursery operators. Polythene tubes have drawbacks, however, because they adversely affect seedling root growth and are an environmental hazard. This study was conducted in Meru, Eastern Kenya, to investigate whether small-scale tree nursery operators are likely to adopt biodegradable seedling containers (cellulose papers and banana sheaths). It was hypothesised that biodegradable containers are better for seedling growth and are more environmental friendly than the widely used polythene bags. The study assessed the frequency of watering and growth (height and basal diameter) of Calliandra calothyrsus seedlings produced in various biodegradable containers under three conditions with varying watering requirements, i.e. light tree shade, shade net and polythene chambers, the first being widely used by farmers. The performance of these seedlings was later monitored in the field. Seedlings produced in biodegradable containers required more frequent watering than those in polythene bags under light tree shade and shade nets but less frequent in polythene chambers. Seedlings produced in polythene tubes had higher growth rates in the nursery, but when transplanted to the field, they were overtaken by those grown in the biodegradable containers due to transplanting shock after the polythene containers were removed. Biodegradable seedling containers can therefore be adopted in areas where water is not very limiting, and evaporation rates could be reduced and water-use efficiency improved by raising seedlings in simple polythene structures.