The main objectives of this thesis are: i) to assess the genetical variation in Nigerian oil palm (Elaeis guineensis Jacq.) populations with respect to the fatty acid composition of their oil; and ii) to assess the value of the Nigerian material to the breeder in oil palm improvement programmes. Two hundred families, the progeny of 200 (5 from each of 40 populations) individual palms from which seeds were collected in Nigeria were planted in a completely randomised design in two independent blocks of six seedlings per family. A set of fifty families were planted in another experiment at three locations in order to detect the presence of genotypeenvironmental interaction. Data on fatty acid composition from the above experiments is presented and compared with data for current breeding material, the related species (E.oleifera) and the interspecific hybrid (E.oleifera x E • guineens is) • There is substantial phenotypic variation for fatty acid traits in the Nigerian material. Part of the variation observed is genetically determined but heritability estimates are generally low and the populations studied do not differ greatly for these traits. Genotype-environment interaction was not detected with respect to fatty acid composition in the material studied. The Nigerian material offer much greater scope for breeding high yielding oil palms with modified fatty acid composition than the current breeding material. However, the interspecific hybrids (E.oleifera x E.guineensis) offer even better prospects for improvement of fatty acid composition.

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Rapidly increasing population densities in Malawi have put a huge strain on the existing agricultural land and the surrounding woodland. Smallholder agriculture is the dominant economic activity of Malawi’s rural population and many farmers have been forced to cultivate marginal lands with less fertile soils, making conditions much more difficult to grow crops. Natural woodland is under increasing pressure from the opening of new lands for cultivation and the increased demand for firewood, timber and other woody resources, with rural households historically obtaining most of their complementary inputs and saleable commodities from nearby areas of forest (Arnold, 1997a). Despite this increasing pressure, woodlands are not being cleared indiscriminately; selected indigenous species are left standing in fields and around households. These are joined by exotic species that are planted and maintained. These trees provide products and services that are vital, yielding food, firewood, building materials and medicine, replenishing soil fertility and protecting against soil erosion. Following a Boserupian approach, this study attempts to establish the reality of a trajectory of enhanced on-farm tree planting and management as population pressure mounts and as part of a more general process of agricultural intensification. The study examines the combination of factors (social, economic, political and environmental) that either stimulate or discourage on-farm tree planting on smallholdings in Malawi, highlighting how woodland resource use changes over a gradient of land use intensity. This study gives a detailed insight into the way that tree planting and management in the smallholder farming system in Malawi works and identifies a trend of increased tree planting/management alongside an increase in agricultural intensification. However, there is no single ‘path’ of intensification; the link between agricultural change and tree planting is complex and there are many trajectories of intensification that a farmer may follow, dependent on his/her social or economic circumstances. The study recommends that agroforestry interventions give rigorous consideration to the needs of the local community, and the suitability of trees to address those needs, before embarking

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The investigations here reported were designed to study the comparative physiological characteristics of Quercus robur, Betula pendula seedlings as influenced by aspects of soil and light environments. A comparative soil type experiment using a tropical fast-growing tree (Terminalia ivorensis) in addition to the temperate trees was also possible. These experiments were set up to explore the limiting factors responsible for failure of natural regeneration. The first experiment involved using an artificial growing medium (peralite) fed with different types of culture solutions for the growth of the seedlings. The role of nitrogen, phosphorus, and complete absence of nutrients on seedlings was examined. Q. robur was more sensitive to nitrogen deficiency than to that of phosphorus. Q. robur seedlings performed similarly in absence of phosphorus and in complete presence of nutrients. B. pendula seedlings on the other hand were seriously affected by the deficiency of both elements and phosphorus seemed more important than nitrogen to B. pendula seedling growth. Chemical analyses showed evidence of nitrogen deficiency in both species. In Q. robur phosphorus did not show any marked inbalance. B. pendula seedlings in a number of treatments were too small for any detailed analysis. The chemical analyses also confirmed the acorn as a main source of nutrient supply of young seedlings of Q. robur. Dry matter yield of Q. robur was not affected by soil volume variation, while B. pendula seedlings had growth performances almost proportional to the soil volume available. An attempt to distinguish the separate effects of mechanical impendance and aeration gave no clear-cut result. The soil type experiment was designed to investigate the role of soil factors on the seedling growth of Q. robur, B. pendula and T. ivorensis. Only B. pendula seemed able to grow on a calcareous soil, robur did not produce new shoots at all, while a number of T. ivorensis seedlings died on this calcareous soil. The growth of all seedlings on two other soil types (acidic) was relatively poor. These soils were generally poor in major soil nutrients especially nitrogen, phosphorus and potassium. The fourth soil type from under a rich mixture of B. pendula and Q. robur trees produced good growth of seedlings generally. The soil was rich in the major soil elements. The analysis of plant growth showed that the three species were affected by ontogenetic drift. B. pendula had the highest relative growth rates in all soil types, and Q. robur the least. Due to the nature of the different soils, the relative growth rates of the seedlings were markedly affected. On the calcareous soil, Q. robur and T. ivorensis showed no dry weight increase after transplanting. On the soil type IV the species had high growth rates which fell with time. These results indicate that soil factors may affect the distribution of Q. robur and B. pendula, although other factors were also thought to interact with soil nutrients. The effects of shade and fertilizer on the seedling growth of Q. robur and B. pendula was investigated by growing these seedlings in shaded enclosures providing 30%, 10% and 5% approximately of total daylight. The soil condition on which the seedlings were growing vas also varied by growing some seedlings in ordinary garden soil and others in garden soil mixed with a level of John Innes fertilizer. Q. robur was not influenced by the fertilizer treatment. The fertilizer addition was significant to the B. pendula seedling only in the 20% light and only towards the end of the season. The fertilizer effect was also thought to have increased the susceptibility of B. pendula seedlings to fungal attack in the light. B. pendula showed adaptation to shading by increasing specific leaf area. The experiment on various degrees of shading on B. pendula seedlings previously grown in 100% daylight helped to clarify some points about this species under shade. The results of the specific leaf area values increasing with shade confirms the fact that B. pendula might probably withstand some shading if for example it was able to put up some growth under a temporarily open canopy. The results also indicate the fact that B. pendula would respond favourably to fertilizer application at this seedling stage, if the light condition is adequate. The performance of B. pendula seedlings in 25% and 85% daylight were quite comparable. In conclusion, it was believed that light was the major important factor of the environment affecting natural regeneration of Q. robur and B. pendula seedlings in British semi-natural forests, except in certain types of soils, for example on certain calcareous soils. Further studies on these seedlings especially in relation to their herbaceous competitors was recommended.

This thesis is concerned with the way householders use their woodland and tree resources in the face of physical and socio-economic resource constraints. Its rationale is the belief that the identification of the characteristics that control the supply and demand dynamics of small holders' woodland and tree use will contribute to the understanding of how forestry interventions can more positively influence the way they manage their environment. The study takes the form of a case-study of a smallholder farming community in North Kasungu District, Central Malawi. It uses a range of research methodologies in an attempt to broaden the scope of analysis and accommodate a multi-disciplinary approach to the dynamics of household miombo utilisation. The research methods used are a participatory woodland inventory, a questionnaire survey, participatory household and household tree resource survey and a 25-month programme of monitoring household woodland and tree utilisation. The analysis is based on statistical interpretation of cross-tabulated data and supported by correlation and multivariate analysis techniques. Whilst perceptions of environmental change and utilisation constraints reflected the availability of the woody resource, the availability of household resources - particularly labour - influenced household collection and tree-planting strategies. The findings of the research indicate that socio-economic, as opposed to physical, supply constraints influence the patterns of woodland utilisation between and within household types. Resource availability and seasonality exacerbate the household differentiation, reducing the capacity of the poorer, smaller and female-headed households to adapt. The 25-month monitoring of firewood and woodland food utilisation revealed the extent of the intra-household division of labour, which was largely manifested along the lines of either age class or gender. Modelling the results of firewood collection indicated that whilst the wife remained the main collector, the relative labour supply elasticity of the household members to collection related to the marginal valuation of their labour. This was shown to be influenced by season, gender, social differentiation and employment opportunity.

This thesis describes the development and subsequent use of a computer simulation model, FENDS (Forest Ecosystem Nitrogen Dynamics Simulator), designed to investigate growth and nitrogen dynamics in managed stands of Pinus nigra var. maritima (Ait.) Melville. The literature is reviewed as three subject areas. First is the production of biomass, its partition within trees and changes which occur during stand development. Second is the cycling of nitrogen within forest ecosystems including inputs to, and losses from the system. The review ends with a description of the types of model that have been developed in relation to forestry, with emphasis placed upon the computer simulation models. An overview of the model is provided together with an account of its development. The current version is described in detail and assumptions upon which it has been based are discussed. A number of key areas for which information is lacking have been identified including: 1) allocation of growth to tree and ground vegetation components, particularly root systems; 2) turnover rates of root systems; 3) mechanisms controlling storage and remobilisation of nitrogen in trees; 4) changes in opitimum nitrogen concentrations which occur during stand development; and 5) breakdown of recalcitrant organic matter and associated nitrogen dynamics. The model has been used to simulate weeding, fertiliser applications and thinning operations and to examine potential interactions. Results from these simulations are discussed.