Dissertations / Theses on the topic 'Agroforestry'

The potential of agroforestry in the British uplands depends largely on the ability of system components to efficiently use resources for which they compete. A typical system would comprise conifers planted at wide spacing, with sheep grazing pasture beneath. Computer models were developed to investigate the growth of trees and pasture in a British upland agroforest system, assuming that growth is primarily a function of light intercepted. Some of the implications of growing trees at wide spacing compared to conventional spacings, and the impact of trees on the spatial and annual production of pasture, were examined. Competition for environmental resources between trees and pasture was assumed to be exclusively for light: below-ground interactions were ignored. Empirical methods were used to try and predict timber production in agroforest stands based on data for conventional forest stands, and data for widely-spaced radiata pine grown in South Africa. These methods attempted to relate stem volume increment to stand density, age, and derived competition measures. Inadequacy of the data base prevented successful extrapolation of growth trends of British stands, although direct extrapolation of the South African data did permit predictions to be made. A mechanistic individual-tree growth model was developed, both to investigate the mechanisms of tree growth at wide spacings, and to provide an interface for a pasture model to examine pasture growth under the shading conditions imposed by a tree canopy. The process of light interception as influenced by radiation geometry and stand architecture was treated in detail. Other features given detailed consideration include carbon partitioning, respiration, the dynamics of foliage and crown dimensions, and wood density within tree stems. The predictive ability of the model was considered poor, resulting from inadequate knowledge and data on various aspects of tree growth. The model highlighted the need for further research into the dynamics of crown dimensions, foliage dynamics, carbon partitioning patterns and wood density within stems, and how these are affected by wide spacing. A pasture model was developed to investigate growth beneath the heterogeneous light environment created by an agroforest tree canopy. Pasture growth was closely related to light impinging on the crop, with temperature having only a minor effect. The model highlighted the fact that significant physiological adaptation (increased specific leaf area, decreased carbon partitioned below-ground and changes in the nitrogen cycle) is likely to occur in pasture shaded by a tree canopy.

Tropical rain forests around the world suffer from deforestation, which is caused mainly by small-scale farmers. These farmers largely employ slash-and-burn methods to clear the land for agricultural settlement. Agroforestry systems are widely found in the humid tropics, where they could have great potential to increase the productivity of farming systems and sustain continuous crop production and they are also supposed to conserve biodiversity. As a group of freshwater invertebrates, dragonflies (Odonata) are commonly used as ecological indicators of freshwater ecosystems. The main objective of the study is to assess the impact of land use changes on dragonflies (Odonata) species richness and diversity, namely primary and secondary forest, cocoa agroforest and slash-and-burn agriculture in the Tropical Africa. We hypothesize, that the species richness and diversity of dragonflies decrease with disturbance of the ecosystems, along the land-use changes gradient.

Agroforestry as a sustainable production system has been recognized as a land use system with the potential to slow encroachment of agriculture onto forested lands in developing countries. However, the acceptance of nontraditional agroforestry systems has been hampered in some areas due to the risk-averse nature of rural agriculturalists. By explicitly recognizing risk in agroforestry planning, a wider acceptance of agroforestry is possible. This thesis consists of a collection of three papers that explore the potential of modern stock portfolio theory to reduce financial risk in agroforestry planning. The first paper presents a theoretical framework that incorporates modern stock portfolio theory through mathematical programming. This framework allows for the explicit recognition of financial risk by using a knowledge of past net revenue trends and fluctuations for various cropping systems, with the assumption that past trend behavior is indicative of future behavior. The paper demonstrates how financial risk can be reduced by selecting cropping systems with stable and/or negatively correlated net revenues, thereby reducing the variance of future net revenues. Agroforestry systems generally entail growing simultaneously some combination of plant and/or animal species. As a result, interactions between crops usually cause crop yields within systems to deviate from what would be observed under monocultural conditions, thus requiring some means of incorporating these interactions into mathematical models. The second paper presents two approaches to modeling such interactions, depending on the nature of the interaction. The continuous system approach is appropriate under conditions where yield interactions are linear between crops and allows for a continuous range of crop mixtures. The discrete system approach should be used where nonlinear interactions occur. Under this second approach, decision variables are defined as fixed crop mixtures with known yields. In the third paper, the techniques presented above were applied to a case study site in Costa Rica. Using MOTAD programming and a discrete system approach, a set of minimum-risk farm plans were derived for a hypothetical farm. For the region studied, results indicate that reductions in risk require substantial reductions in expected net revenue.

This thesis deals with the perceptions of agroforestry among farmers in Babati, north- central Tanzania. The focus is on which resources farmers perceive that they need to adopt agroforestry and which risks that are connected with agroforestry adoption. It is also to see how farmers perceive that the access to resources changes after agroforestry adoption and how their livelihoods change. The data has been collected through qualitative interviews with agroforestry farmers, conventional farmers and extension officers. After that the data has been analyzed through the sustainable livelihood approach and a risk perception theory. The results show that some of the obstacles or risks that farmers perceive with agroforestry adoption are high input costs, dependency on short-term benefits, competition between trees and crops and lack of education from extension services. Without financial capital and human capital in terms of knowledge there might be too many risks connected with adoption. If agroforestry however is adopted the farmers perceive that the access to firewood, timber and fruits increase which increase their incomes and therefore financial capital. They also perceive that the fruits improve food security and that the timber improves the housing. The firewood is also perceived to improve the situation for women as they do not have to walk as far to collect the firewood. Agroforestry is also perceived to provide environmental services like erosion prevention and increased soil fertility, therefore it increases natural capital. Some trees can also be used as natural pesticides. The increased soil fertility or the access to natural pesticides, however does not seem to affect the use of industrial fertilizers or pesticides. Agroforestry is also not perceived to have any effects on biodiversity or water quality. Even if agroforestry may not be a good choice for all farmers, it can for some farmers increase their ability to cope with stress and shocks like future climate change. This is because the agroforestry system can work as a buffer against increased climatic variability.

Numerous scholars describe agroforestry as an extraordinary food production system that generates viable ecosystems and accommodates regenerative capabilities. Agroforestry may therefore be a promising solution to the future environmental challenges facing food production. This multifunctional land management system is practised in temperate and tropical regions alike, however, it exists to a remarkably limited extent in Sweden. This research points to the complexities in agricultural and forestry policy as a main barrier for wider agroforestry adoption. The foundation of inquiry is thus to analyze various Swedish legislatives and support systems that either facilitate or adverse agroforestry practice, through the lens of political ecology. The research findings derive from a qualitative study, consisting of conducted interviews with key stakeholders in Swedish agricultural and forestry policy. The study contends that a core obstacle for agroforestry development is the dualistic approach to governmental sectors, i.e. forestry and agriculture, and the lack of coordination between them, since agroforestry cannot be classified as neither . A perpetual policy prioritized towards large-volume crop yields, rapid production, large scale investments, calculative assessments and a competitive business sector is moreover identified. The research asserts that these hegemonic discourses permeating policy, consequently act as a disincentive for agroforestry adoption due to the ofttimes long implementation period, high initial investment and uncertain food market for agroforestry produce. In addition, the study illustrates that cultural expectations of landscape mainly give trees a cultural and environmental value, therein neglecting the multifunctionality of woody vegetation - which hence suggest a lack of a holistic approach to food systems. The thesis finally argues that these hegemonic discourses concerning assessment and management of land, together influence the design of state policy and farmers’ attitude towards agroforestry systems. Overall, current policy regulations portray a rather static and incomplete way of managing the dynamic symbiosis of multifunctional food systems.

While the light regimes of closed forest strands and open pasture have been quantitatively described and modelled, agroforestry involves greater complexity and spatial variability. This research involved intensive measurement of quantum flux density (QFD) above and below re-spaced tree strands of Sitka spruce (Picea sitchensis [Bong.] Carr.) and hybrid larch (Larix x eurolepis Henry) in conjunction with measurement of tree growth. QFD was also measured above and below pasture growing in boxes in imported soil sunk to ground level beneath the trees. The Monteith hypothesis that crop growth in unstressed conditions is linearly related to the amount of QFD intercepted by its canopy was found to hold for above ground growth of trees at agroforestry spacings. The overall dry matter: QFD quotient (e) for Picea sitchensis across the range of tree frequencies was 0.32 g mol^-1 which is lower than typical values reported for agricultural crops, young container grown trees of Salix viminalis and Populus trichocarpa and closed-canopy Picea sitchensis, but comparable with previous estimates for a range of mature tree stands. e was unaffected by tree spacing, but was significantly higher for the tall tree stand which had been pruned. The mean annual QFD transmitted to the understorey varied from 39% to 96% of that in the open across the agroforestry treatments. The mean transmittance was similar but spatial variability of QFD was significantly higher in tree stands with crown to ground level when compared with stands having similar crown dimensions but which had been pruned to approximately 1.3 m height. More than 90% of seasonal pasture growth could be explained by a regression of growth on incident QFD.

Air pollution can lead to environmental impacts. Over the past decades there have been some success stories reducing pollutant emission, namely sulphur dioxide (SO2). However, impacts on ecosystems from atmospheric nitrogen (N) pollution are still seen as a major threat for European biodiversity. Across Europe over 70% of Natura 2000 sites are at risk for eutrophication with over 70% of the Natura 2000 area in Europe (EU28( exceeding critical loads for nutrient nitrogen deposition. Agricultural ammonia is a key contributor to the threat to these sites due to the close proximity of agricultural activities and protected sites. Source attribution modelling using an atmospheric transport model showed that agricultural livestock production in the UK is the dominant nitrogen source for N disposition across the UK Natura 2000 network. Nearly 90% of all sites had livestock as their dominant source, contributing 32% of the total nitrogen deposition across the whole network. 76% of all Special Areas of Conservation (SAC) sites exceeded their critical load for nutrient nitrogen, representing 74% of the entire SAC area. The extent of exceedance is also notable with many sites experiencing depositions of >50 kg N/ha/yr over the critical load. the situation for acidity critical load exceedance is less sever, by 51% of sites are still exeeded. Legislation to regulate pollutant emissions to air and protect biodiversity are often not integrated, and there has been no common European approach for determining the impacts of nitrogen deposition on individual Natura sites, or on conservation status. Off-site sources of air pollution present difficulties in assessing and attributing impacts, because deposition can result from local sources (1-2 km), or very far away sources (>1000 kms). Managing nitrogen losses on the farm and improving the efficient use of nitrogen are key components for overall reduction in NH3 emissions. Many nitrogen management options are available to abate ammonia from agricultural activities. On the one hand, technical and management measures include controlling emissions from manure storage and spreading, livestock feeding strategies, and improving housing systems. Trees, on the other hand, are effective scavengers of both gaseous and particulate pollutants from the atmosphere, making tree belts potentially effective landscape features to support ammonia abatement strategies. Using a coupled deposition and turbulence model the recapture efficiency of tree planting around ammonia sources was estimated. Using different canopy structure scenarios, tree depths and differing leaf area density (LAD) and leaf are index (LAI) were adjusted for a main canopy and a backstop canopy. Recapture efficiency for ammonia ranged from 27% (trees planted around housing systems), up to 60% (under-story livestock silvopastoral systems). Practical recapture potential was set at 20% and 40% for housing and silvopastoral systems respectively. Model results from scaling up to national level suggest that tree planting in hot spot areas of ammonia emissions would lead to reduced N deposition on nearby sensitive habitats. Scenarios for on-farm emission control through tree planting showed national reductions in nitrogen deposition to semi-natural areas of 0.14% (0.2 kt N-NHx) to 2.2% (3.15 kt N-NHx). Scenarios mitigating emissions from cattle and pig housing yielded the highest reductions. The afforestation strategy showed national-scale emission reductions of 6% (8.4 kt N-NHx) to 11% (15.7 kt N-NHx) for 25% and 50% afforestation scenarios respectively. Increased capture by the planted trees also generated an added benefit of reducing long-range transport effects, including a decrease in wet deposition of up to 3.7 kt N-NHx (4.6%) and a decrease in export from the UK of up to 8.3 kt N-NHx (6.8%). Agroforestry measures for ammonia abatement were shown to be cost-effective for both planting downwind of housing and in silvopastoral systems, when costs to society were taken into account. Planting trees was also cost-effective from a climate change perspective. Comparing the cost per kg of NH3 abated showed that planting trees is a method of ammonia emission mitigation comparable with other (technical) measures. The costs for planting trees downwind of housing were calculated at €2.6-7.3/kg NH3. Agroforestry for ammonia abatement offers multiple benefits for the farmer and synergistic effects for society as a whole including i) carbon sequestration. ii) visibility screening around housing units, iii) imporved animal welfare for silvopastoral systems, iv) reducing critical load exceedance on protected sites, v) price advantage of 'woodland chick' productions, vi) supporting the Industrial Emission Directive (IED) requirements for emission reduction, vii) supporting national afforestation policies. The results of this work support the notion that in the emerging discussion about the values of ecosystem services and the role of nature-based solution to tackle persistent environmental challenges, tree planting has a large potential in rural and urban environments.

The purpose of this study was to assess the correlation between (1) selected seedling conditions and (2) the participating farmers' knowledge of planting techniques and the seedling mortality of trees supplied by the Pan American Development Foundation's Agroforestry Outreach Project in Haiti. During the spring of 1990 planting season, 18 sample farmers and the trees they received were studied to determine the correlation of several seedling conditions with seedling mortality. Rootball condition, leaf drop, plant turgor, and internal box temperature were measured during seedling transportation from nursery to the field. The farmers' knowledge of planting techniques was determined by a test over a planting guide. The most significant findings were that the seedling mortality was not strongly correlated to either the individual conditions measured or the farmers' knowledge of planting techniques. Collectively, these seedling conditions accounted for approximately 25 percent of the total variation in the seedling mortality.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on December 19, 2007) Includes bibliographical references.

This study reports the results of experiments on growth and physiology of an agricultural annual (French bean) and a young tree (poplar) in relation to limited soil water. Competition and complementarity between the species were evaluated in a model agroforestry experiment. The experiments were carried out in a greenhouse and growth cabinet with plants grown in pots containing sandy-loam compost. The species studied were Phaseolus vulgaris cv. Argus and Populus trichocarpa X P. deltoides cv. Raspalje. The main aim of the study was to characterise the responses of both species to different soil water supply regimes, shoot water supply by roots and chemical signalling from the roots in drying soil and to show how these responses could be used in the selection of suitable agroforestry for dry regions. Bean and poplar plants showed differential growth responses although both the species performed better in mixed stands than in monoculture when soil water was severely limited. Beanplants were more competitive than poplar, although both species showed complementarity in exploration for soil water. As the soil dried leaf water potential declined. Stomatal conductance of both species was more closely related to pre-dawn leaf water potential than to mid-day leaf water potential, indicating the importance of soil water status. Experiments with both vertically and horizontally divided root systems showed that bean and poplar plants with at least half of their root system in moist soil were able to maintain leaf water status as well as plants with all their root systems in moist soil. Furthermore, stomatal conductance and leaf expansion of both species were affected directly by soil drying independent of leaf water potential.

Enligt FAO kommer världsbefolkningen stiga till över nio miljarder till år 2050 och efterfrågan på livsmedel öka med 70 procent. Framtiden med dess ökade befolkningsmängd och efterfrågan på en hållbar livsmedelsproduktion kräver ett livsmedelssystem som ger hög avkastning, men inte påverkar miljön negativt. Syftet med denna studie är att undersöka agroforestry som potentiellt jordbrukssystem i tempererade områden, med fokus på åkermark. Studien innehåller en litteraturstudie samt intervjuer med två svenska lantbrukare. Agroforestry innebär integrering av träd och buskar i jordbrukslandskapet. Träd integrerade på jordbruksmark har lång tradition i Europa, men har försvunnit under de senaste decennierna i och med en ökad mekanisering under efterkrigstiden. Agroforestrysystemen beskrivs i vetenskapliga studier ha potential att ge en rad olika ekosystemtjänster och fördelar som ökad biologisk mångfald, ökad kolinlagring, högre produktivitet, förbättrat näringsflöde samt bättre skadedjurs- och ogräsbekämpning. Dessa ekosystemtjänster och fördelar är betydande i och med dagens klimatutmaningar. Men att anlägga agroforestrysystem innebär även svårigheter då systemen kostar och tar tid att anlägga. En risk är att interaktioner mellan träd och grödor kan bli negativa. Det saknas fortfarande tillräcklig mycket forskning gällande agroforestry i tempererade områden. Idag är agroforestry relativt okänt bland lantbrukare. Att det finns en tveksamhet hos dem kan även ha historiska orsaker. Information kring systemen har dock givit en mer positiv bild av agroforestry vilket tyder på att tveksamhet kan bero på att lantbrukare idag generellt inte har tillräckligt med kunskap och information kring systemen. Det är viktigt att överväga möjligheterna och svårigheterna för vidare integrering av agroforestry. Mer forskning och kunskap samt ökat jordbrukspolitiskt stöd och ekonomisk stimulans tillsammans med noggrann planering av systemen krävs för att agroforestry ska kunna utnyttjas till sin fulla potential i framtidens jordbruk.

Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on January 4, 2008) Includes bibliographical references.

Resource capture and utilisation were studied in two agroforestry systems at the International Centre for Research in Agroforestry (ICRAF) Research Station at Machakos, Kenya. The agroforestry systems examined contained two contrasting tree species, leucaena (Leucaena leucocephala (Lam.) de wit) and grevillea (Grevillea robusta), and the C3 and C4 crops, cowpea (Vigna unguiculata) and maize (Zea mays, Katumani composite). The leucaena-based trial was established in November 1989 and the trees were grown with ten maize crop rows on either side of a pruned hedgerow (HM) or unpruned tree row (LM). A sole maize control (SM) was also grown. Paired sets of treatments were irrigated to eliminate below-ground competition for water (HMI, LMI and SMI respectively). Interception of photosynthetically active radiation (PAR) by leucaena and maize was measured on a row-wise basis in all treatments at 7-10 day intervals using a sunfleck ceptometer. Sap flux was measured for the maize and both pruned and unpruned leucaena using heat balance gauges. Results are presented for the 1992 April-July rainy season. Total PAR interception was 30 % greater in LM and LMI than in the SM and SMI sole maize treatments. However, little more than 30 % of the light intercepted by the LM and LMI systems was captured by the crop component, and competition for light alone reduced maize yields by over 30 %. Total water uptake by the LM leucaena and maize comprised 60 % of the seasonal rainfall (237 mm) as compared to 30 % for sole maize. However, as for light interception, only 30 % of the water transpired in LM was used by the intercropped maize, and competition from the trees for soil water reduced maize yields at distances of over 6 m from the leucaena. The leucaena was more effective at resource capture, yet less efficient in resource utilisation since it exhibited a lower dry matter:radiation quotient and a lower transpired water:dry matter ratio than maize. Thus the leucaena in the agroforestry systems captured more of the resources that could have been used more effectively by the maize, causing the performance of the mixture to be sub-optimal; these results suggest that the two components would be best grown separately. Intensive monitoring of resource capture and use by trees and crops was subsequently transferred to the Complementarity In Resource Use on Sloping land trial (CIRUS). Although it had been intended to study both trials during the long rains of 1993, the leucaena trees were almost completely defoliated by psyllid (Heteropsylla cubana) infestation shortly before the onset of the rains: in subsequent seasons, CIRUS was studied in preference to the leucaena trial as the trees had only partially recovered. CIRUS was designed to investigate the effects of competition and the extent of complementarity between grevillea and associated crops using the following treatments; sole crops (Cg) of cowpea during the short rains and maize during the long rains, dispersed-planted trees with (CTd) and without crops (Td), and across (CTa) or on-contour-planted (CTc) tree rows with crops. Light interception and water use were monitored using a similar measurement regime to that employed in the leucaena trial. Results are presented for the 199213 and 1993/4 short rainy seasons; the failure of the 1993 long rains forced the abandonment of experimental measurements during this season. Light interception by the Td and CTd grevillea increased greatly between the two short rainy seasons. Thus, total seasonal interception of PAR was three times greater in sole cowpea than in sole grevillea during the 1992/3 short rains, but by the following short rainy season was over 50 % greater in the grevillea than in the cowpea. Cumulative interception of PAR by the CTd grevillea and cowpea combined was more than twice that of the sole cowpea and over 40 % greater than that for sole grevillea during the 1993/4 short rains. Experiments involving artificially imposed shade showed that there was no reduction in total above-ground dry matter production in cowpea until 75 % shading was imposed. To quantify the degree of below-ground complementarity in water use between grevillea and cowpea, sap flux was measured using heat balance gauges attached to the stems of young grevillea (10-18 months old), both before and after excavating the crop rooting zone (upper 60 cm of soil) around the stem base. The crop rooting zone was removed to establish the capability of the grevillea to extract water from deeper horizons. After excavation, the trees maintained sap fluxes of up to 85 % of the unexcavated values. During both short rains, soil evaporation was by far the largest component of the water balance in all treatments. However, continued extraction of water by the trees during the dry season greatly increased resource capture~ thus total water uptake was three times greater for the sole trees than for the sole crop when dry season water use was included. During the 1993/4 short rains, water use was greatest in the CTd treatment, in which 25 % of the total seasonal rainfall was transpired by the trees and crops. Although transpiration by the CTd trees exceeded interception losses, the latter may have had a greater effect on crop growth by reducing the total quantity of water available within the system. The existence of below-ground complementarity and the shade tolerance of the cowpea suggest that deep-rooted tree species and certain C3 crops may be combined successfully in the semi-arid tropics, but the sensitivity of crop yield to any reduction in water availability within the system demonstrates the need for caution when implementing such systems. The results obtained are discussed in relation to previous research on intercropping and agroforestry and their implications for the successful adoption of agroforestry systems in the semi-arid tropics.

A survey of arthropods associated with exotic multipurpose trees and food crops used in agroforestry and indigenous tree species (Tamarindus indicus) grown in the wild was conducted in 1990 and 1991. The exotic multipurpose tree species (MPTs) used were: Gliricidia septum, Leucaena leucocephala and Cassia siamea growing in an alley cropping system and the food crops were Vigna unguiculata, Zea mays, and Cajanus cajan. The consequences of growing taxonomically related plant species in agroforestry systems were considered. Insecticidal knockdown technique was used to sample arthropods from the foliage. 92 species of arthropods belonging to 48 Families were found to be associated with tree species and the crops. Of these, 27 species were on MPTs, 3 species on crops, 12 species on the chosen wild tree, 13 species were shared amongst MPTs and crops while 14 species were shared between MPTs and the wild tree. A further 19 species were shared between all the groups of plant species (MPTs, crops and the wild tree) with 4 species being shared between the wild and the crop. The effect of tree pruning on arthropod communities on trees was also investigated and the results showed that pruned trees supported a richer arthropod fauna than unpruned trees. Through simulated defoliation, the impact of insect defoliators on four MPTs was also investigated. There was a considerable reduction in overall growth rate, height and diameter increment depending on the level of defoliation. Several stress factors often predispose plants to insect attack. Pruning, as a stressing agent was investigated in relation to infestation of Cassia siamea by the stem borer Xyleutes capensis. Out of the 200 pruned trees surveyed, 90 % showed the signs of borer attack, compared with only 31.5 % of unpruned trees. The role MPTs can play in aggravating infestation of stored pulses by a bruchid beetle, Callosobruchus chinensis was investigated by comparing its survival on seeds of three MPTs and Cajanus cajan. Whereas the bruchid was able to oviposit on both the MPT and crop seeds, no larval emergence was observed in any of the MPTs showing that the MPTs may not support reproduction and development of C. chinensis in the field.

The aim of the study was to establish whether clones could be selected for single or multipurpose products by conducting studies involving the evaluation of phenotypic characteristics and their influence on biomass production using Sesbania sesban (L.) provenances and clones. The study initially examined the extent of genetic variation in phenotypic characteristics and biomass production in S. sesban provenances at Maseno, in Kenya. The study showed that significant differences existed between provenances and that it was possible to select of outstanding individual trees in the best provenances for testing on different sites as clones. Significant allometric relationships were established between dry mass, and tree dimensions for the different tree components. Stem diameter at 0.15 m provided a reliable estimation of biomass in the provenances. The provenance repeatabilities (0.31-0.41) and potential genetic gain (40%) highlight the expected returns due to selection. Plant growth analysis results helped in understanding the growth of young S. sesban clones in the field at Maseno, particularly the distribution of biomass into components. Clones performed similarly in the initial stages of growth and differences were only detected when competition set in. Clone net assimilation ratios were found to be sensitive to moisture stress. Leaf area was found to be the major determinant of clonal differences and was a good indicator of plant growth and productivity. The results from the genetic variation and productivity study of S. sesban clones grown at Maseno, Kisii and Machakos revealed a differential response of the clones to different environmental conditions. Although there was lack of genotype by environmental interaction among clones, biomass production was higher at Maseno and Kisii than Machakos. S. sesban clones differed greatly in absolute biomass but showed similar percentage distribution of dry mass among the different tree components with branches being a major preferred sink.

As urbanisation increases choices in how to use green areas within cities growin importance, determining how several urban sustainability issues will play out. In urban environment the role for forest, both inside and at the city borders, is most important for the well-being of city inhabitants from several species, as well as provider of numerous ecosystem services necessary for anthropogenic development. Despite this,urban green areas are often given a lower priority in city developing processes compared to new structures, meaning them being transformed into built environments. This makes a higher awareness of what urban forests provides, and can provide, evident. Thus, this bachelor thesis presents the idea of urban agroforestry. The focus is towards agroforestry systems as they can be adapted and applied in a Swedish context. Firstly, literature review is used for investigating the concepts of urban forest, ecosystem services and agroforestry, defining and connecting them. Some of the critique towards the ecosystem services concept is lifted, as well as some specific ecosystem services directly connected to urban forest. Also, recent Swedish development in the agroforestry field is mapped and briefly described. Further, knowledge from this is adapted to the settings in Östersund, developing suggestions for construction of actual urban agroforestry systems. This part describes the local possibilities for urban agroforestry, as well as suitable urban forest areas, species and things to take into consideration in terms of risk assessment. Finally, the thesis also presents some suggestions for how to account for the change in ecosystem services in a more mathematical way. This is followed by discussion of both general findings and the local agroforestry potential, as well as some suggestions for focus points in further studies. This study shows that despite the cold climate in Sweden, urban agroforestry provides an interesting potential for preservation of ecosystem services as well as reconstruction of historical landscapes. It further suggests that urban agroforestry systems within Östersund should be focused on cultural services rather than high yields, by this aiming to connect to numerous local interests seen as defining for the region.

Planting trees on agricultural land either as farm woodlands or agroforestry (trees integrated with farming) is one option for reducing the level of atmospheric carbon dioxide. Trees store carbon as biomass, and may increase carbon storage in the ground. A review of the literature outlined uncertainty relating to changes in carbon storage after planting trees on agricultural land. The aim of this thesis is to deter¬mine the impact of tree planting on arable and pasture land in terms of above and belowground carbon storage and thereby address these uncertainties, and assess the implications for the Woodland Carbon Code: a voluntary standard for carbon storage in UK woodlands. Measurements of soil organic carbon to a depth of 1.5 m were taken at two field sites in Bedfordshire in the UK: a 19 year old silvoarable trial, and a 14 year old silvopasture and farm woodland. On average 60% and 40% of the soil carbon (rel¬ative to 1.5 m) was found beneath 0.2 and 0.4 m in depth respectively. Whilst tree planting in the arable system showed gains in soil organic carbon (12.4 t C ha−1 at 0–40 cm), tree planting in the pasture was associated with losses of soil organic carbon (6.1–13.4 t C ha−1 at 0–10 cm). Evidence from a nearby mature grazed woodland indicate that these losses may be recovered. No differences associated with tree planting were found to the full 1.5 m, though this may be due to a lack of statistical power. Measurements of above and belowground biomass, and the root distribution of 19 year old poplar (Populus spp.) trees (at the silvoarable trial) and ash (Fraxinus excelsior) trees ranging from 7 to 21 years (at several field sites across Bedfordshire) were made, involving the destructive harvest of 48 trees. These measurements suggest that Forestry Commission yield tables overestimate yield for poplar trees grown in a silvoarable system. An allometric relationship for determining ash tree biomass from diameter measurements was established. The biophysical model Yield-SAFE was updated to take into account root growth, and was parameterised using field measurements. It was successfully used to describe existing tree growth at two sites, and was then used to predict future biomass carbon storage at the silvoarable trial. Measurements indicate that losses in soil carbon at relatively shallow depths can offset a large proportion of the carbon stored in tree biomass, but assessing changes on a site by site basis may be prohibitively expensive for schemes such as the Woodland Carbon Code.

Informal agroforestry is a traditional practice in Solomon Islands, mostly intercropping food crops with fruit trees. Agroforestry systems that intercrop food crops with rows of hardwood species for the purposes of timber production have not been practiced. In response to the common problem that growers of valuable hardwood species such as teak (Tectona grandis) are reluctant to thin their trees, the Australian Centre for International Agricultural Research (ACIAR) established project FST/2007/020 to develop novel silvicultural systems to overcome this problem. Flueggea flexuosa (flueggea) is a local hardwood species that is widely utilized for housing and fencing applications. The project team established several agroforestry trials testing the hypothesis that teak and flueggea could be successfully grown together with the local tree being progressively harvested for local use, effectively thinning the plantation and allowing the teak to develop through to harvestable size. The trees could be intercropped with food crops allowing for multiple land use and income generating opportunities whilst the trees grow through to maturity. The model was based on the assumption that trees and crops, when properly managed, complement each other rather than compete in the capture and efficient use of available growth resources. This system is a hybrid of the informal agroforestry traditionally practiced in Solomon Islands and the silvicultural management techniques applied to production forestry. However, teak and flueggea have not been previously grown together under an agroforestry regime and little is known of the species interaction or of the effect of growing different food and cash crops in the interrow. Traditional practices for growing food crops in Solomon Islands begin with forest clearance and burning of debris, a slash and burn system. Mounds are made using man-made hoes or picks to give crops better growing spot away from competing weeds and surface water flow during rainy seasons. Most root crops and vegetables are planted in their own blocks and kept separate from other crops. Mixing of food crops is not a usual practice in most parts of the Solomon Islands. Other crops and trees are usually planted at the boundaries of each crop’s patch or along the boundary. Most food crops reach harvesting age after 3 months. When crops are harvested, the whole plant is uprooted, plant parts and debris are piled at a location and are burnt when dry. Where the area available for gardening area is large, the harvested plot is left to fallow but if the available area is small, crops are replanted straight after harvest, leaving no time for the soil to be replenished with nutrients through decomposition of plant materials. Amongst several silvicultural trials established in Solomon Islands, this study focuses on trials established at Ringgi and Poitete which are located at the southern and northern parts of Kolombangara Island in Western Province. These silvicultural trials were established for the purpose of examining the effect of stocking rate and species mix on teak and flueggea growth and on their potential influence over the hybrid agroforestry system. Two mixed species spacing trials and one hybrid agroforestry trial of teak and flueggea were established to test the hybrid model. The two main mixed species spacing trials have 5 treatments with 4 replicates each, treatments are a combination of stocking rate and species mix. The five different treatments include teak being grown as a monoculture (Treatment 1); and then in rows interspersed with 2 rows of flueggea at different stocking rates (Treatments 2, 3, and 4); and alternating rows of teak and flueggea at standard spacing (Treatment 5). The hybrid agroforestry trial was based on the standard 4 x 3 m spacing (Treatment 5) and further intercropped with food crops. Only Treatment 3 (4 x4m) and Treatment 4 (4 x 6m) have wider planting spaces. Standard stocking is 833 stems per hectare for Treatments 1, 2 and 5, and 625 and 416 stems per hectare for Treatments 3 and 4. This research examined the interactions occurring between teak and flueggea, and between teak, flueggea and food crops grown in the inter-row with respect to competition for nitrogen (N), light and water, resource access, changes in system interactions with the development of the canopy, nutrient loss and issues of sustainability related to harvesting of food crops, biogeochemical cycling of carbon (C) and N, root architecture and growth and yield. Total carbon (TC), total nitrogen (TN) and stable isotope δ13C and δ15N, and 15N-labelled tracer were analyzed using field sampled soil, foliage, branch, stem, root and litterfall from the stands to examine soil nutrient uptake, biomass content and cycling as a result of the intraspecific and interspecific interactions with relation to tree growth and productivity of the hybrid system over time and space. Root architecture, tree mean total height (THt) and diameter at breast height (DBH) were measured and assessed over the study period. We investigated the competition between teak and flueggea for N using a 15N-labelled tracer in a field trial in a 2 year old and a 4 year old mixed species stand. The study also reports the acquisition and allocation of TC and C isotope composition (δ13C) in different tree components of teak and flueggea. Seven pairs of trees, one of each species, were isolated using an impermeable membrane 60 cm deep and 15N-labelled tracer was applied to the soil surface. The first four plots were sampled for a period of 18 months and the age of the trees at final excavation was 4 years. The final three plots were sampled for 12 months and the age of the trees at final excavation was 2 years. Each tree was measured, felled and roots excavated, divided into the components: roots, stem, branch and foliage, and then weighed for biomass, samples of each component were oven dried at 60° C to constant weight, ground to a fine powder and analysed for TN, TC, 15N enrichment, and δ13C. There was no significant difference in component 15N enrichment between teak and flueggea at both ages, suggesting that there could be equal uptake of added 15N-labelled tracer by both species. The 15N -labelled tracer concentration was greater in the foliage followed by the root, stem and branch for teak and flueggea. However, stem had significantly greater biomass and therefore had greater 15N enrichment mass (kg) than other components of teak in the 2 years trial and with teak and flueggea at 4 years trial. Approximately 55 % of added 15N tracer was recovered in the 4 years trial and 43 % was recovered in the 2 years trial, suggesting that higher uptake is possible with well-established root structure with age. Although teak had significant growth, 15N tracer uptake and enrichment were not statistically different to those of flueggea which may mean that competition in growth resources was still at minimum stage and growth rates were species specific. TN was not significantly different between teak and flueggea components at age 2 and 4 years and may indicate equal access to available N belowground and with similar allocations. TC was not significantly different between components of teak and flueggea in either age and may indicate equal access to atmospheric C and similar allocations of photosynthates. Higher δ13C in teak components than those of flueggea indicated that teak has higher water use efficiency per kg of tree and does not discriminate against 13C as strongly as flueggea during photosynthesis. Similar 13C values in tree components within the species may be the result of subsequent partitioning of the photosynthates synthesized during photosynthesis. The litter production and C and N cycling in both teak monoculture and teak and flueggea mixed species plantings in the two trials were studied over 18 months period. Leaf litter samples were collected monthly from the five treatments. Monthly litterfall production ranged from 250.51 to 541.61 kg ha-1 depending on treatment and trial. Treatment 1 produced significantly higher total litter than Treatment 4 at Ringgi but this difference will have been due to stocking rates. When based on individual tree productivity, teak in Treatment 4 at both trials produced significantly higher litter per tree than the teak in Treatments 3, 2, 5 and 1 while there was no significant difference with flueggea productivity. Although teak and flueggea TC and TN, and δ13C and δ15N varied over the study period, their mean values were not statistically different except for teak in T4 having significantly lower values at Ringgi. Teak and flueggea C/N ratios were not statistically different at both trials except for flueggea in Treatment 2 at Ringgi which was significantly higher. The highest annual TC and TN returned to the soil from total litterfall were observed in Treatment 1 followed by Treatments 3, 5, 2 and 4 for Ringgi. The highest at Poitete was Treatment 5 followed by Treatments 1, 3, 2 and 4. When comparing each treatment and using individual tree productivity, Treatment 4 produced and returned the significantly highest litter and nutrient than Treatments 3, 2, 5 and 1. Overall, individual tree productivity demonstrated that mixed species stands have significant potential for cycling higher rates of C and N than monoculture teak stand, therefore establishment of mixed species stands especially using the stocking rates of Treatment 3 and Treatment 4 is recommended as a practical measure in forest rehabilitation and agroforestry systems to realize sustainable development of community forestry in the Solomon Islands. The spatial distribution of the root systems of teak and flueggea were examined by excavating pairs of trees of each species that had been grown in isolation plots for 2 (3 pairs) and 4 (4 pairs) years. Additional trees grown without a barrier were partly excavated to ensure that the effect of the barrier on root architecture was not significant. The root architecture of both species had similar patterns of development but showed a different topology and distribution. Teak had extensive horizontal and vertical roots and occupied a larger portion of the soil volume than flueggea. Both species had similar root biomass increment of 87 % between 2 and 4 years and roots made up 20-22 % of total tree biomass at both ages. Teak and flueggea roots occupied different depths within the soil volume, which would promote nutrient uptake efficiency and therefore minimize competition. The study evaluated the effects of stocking rate and species mix on early growth of teak in a mixed species system. Intercropping with flueggea promoted diameter, height and form of teak. Teak diameter and basal area growth significantly increased with wider planting spacing though height was not statistically different to teak in single-species stands. Intercropping with flueggea resulted in teak developing smaller branches which facilitated a self-pruning habit that promoted clear wood production. Differences in teak height between all treatments were not significant though it is interesting to note that sixty months after planting, teak in T1 at Ringgi and teak in T5 at Poitete had the greatest height as had Flueggea in T5 at Ringgi though again differences in height of flueggea was not significantly throughout the treatments. Diameter and basal area were greatest at the lower stocking than at the higher stocking for teak and flueggea. Teak of T4 had the significant diameter and basal area growth than other treatments at age 60 months. Teak form was best at the pure and mixed species stands due to self-pruning while larger crown and big branches occurred at lower stocking rates. While this can be corrected with timely silviculture, a 4 x 3 m spacing would seem to optimise the benefits of higher stocking and lower maintenance. Overall, mixed species and agroforestry systems promoted reduction and delay of competition for growth resources in the early phase of the systems compared to monocultures. Both single and mixed species systems promoted similar C and N cycling in the plantation establishment phase. Growth in basal area was significantly higher at the mixed species stands at the lowest stocking rate, which also enable longer period of intercropping of food crops. However, as the present investigation was confined to the first 5 years, which is considered as establishment phase for teak, more studies are needed as the systems mature to fully understand the systems development and interactions to maturity.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Natural Sciences
Science, Environment, Engineering and Technology
Full Text

Agroforestry, though old as man, is a relatively new concept in land and natural resource management. Agroforestry "offers a means of bringing the activities of rural people into greater harmony with the environment by developing a complementary association between trees and agricultural crops" (Ffolliott and Thames, 1983). The capabilities of a people to sustain a system is a fundamental knowledge that resource managers should be equipped with. This study specifically investigated on household labor allocation in three different agroforestry systems, to qualitatively determine whether agroforestry is a viable natural resource management alternative that provides a compromise to government interests of conserving the natural resources, and supplementing and/or providing for a people's needs; and to establish the capabilities of a people to sustain agroforestry by analyzing household labor allocation patterns. The study was conducted in the Northern Philippines and data was gathered summer of 1989. Primary data gathering techniques were utilized, as well as secondary data. Agroforestry was found to be a viable land and natural resource management alternative. However, while natural resources are being managed, certain considerations should be made on: historical antecedents that give rise to the manner by which agroforestry is practiced, existing land use practices, and human activities present in the area. Aside from biophysical constraints, household labor allocation largely explains the nature of the agroforestry system. Labor allocation in Barangay Ambassador is flexible, and is affected by the availability of household labor, and the nature of the activities engaged in by the households, as well as the importance attached to the cited activities.

From the Proceedings of the 1986 Meetings of the Arizona Section - American Water Resources Association, Hydrology Section - Arizona-Nevada Academy of Science and the Arizona Hydrological Society - April 19, 1986, Glendale Community College, Glendale, Arizona

A prototype agroforestry system, which combined the low-input features and environmental benefits of the traditional Indonesian multi-species 'jungle rubber' system with high yielding rubber clones developed in monoculture plantations, was tested under on-farm conditions. Secondary forest was allowed to regenerate between weeded rows of clonal rubber. Clonal rubber establishment was studied, and the interactions between it, secondary forest species and farmer management were investigated using a combination of researcher- and farmermanaged weeding trials. In one trial, alteration of below-ground resources (using root barriers and trenches to create three soil volumes) did not affect above or below-ground growth of clonal rubber, although weeding significantly increased stem diameter and volume. It was concluded that secondary forest regrowth interfered with resource capture at the level of individual roots; interference was not due to depletion of total available resources. Shoot:root ratios and ratios of horizontally- to vertically-oriented proximal roots were not affected by weeding. Growth of clonal rubber in N-fertilised plots, in the presence of weeds, was significantly greater than in corresponding unfertilised plots, indicating that N-addition may overcome some negative effects of competition in the system. However, a bioassay of nutrient limitation showed no significant differences in root biomass or root-length density, for either rubber or weed rootingrowth into soil cores enriched with various nutrients. The second researcher-managed trial, on steep slopes, showed that the survival rate of clonal rubber was 33% higher than that of the 'seedling' rubber variety traditionally used, and that mean stem height and diameter of clonal rubber trees were significantly greater than those of seedling rubber, 21 months after planting. Damage to trees by banded leaf monkeys (Presbytis melalophos nobilis) and feral pigs (Sus barbatus) was severe, unexpected, and greater for seedling than for clonal rubber. For undamaged trees, weeding frequency within the rubber-tree row had no significant effect, indicating that the major influence on rubber tree growth was interference from secondary forest regrowth between rows, operating both aboveand below-ground. In a farmer-managed, trial, vertebrate pest damage was the major influence on clonal rubber establishment, explaining almost 70% of the variation in rubber growth. The amount of labour invested in weeding was positively correlated with rubber growth. However, fanners generally decided to completely cut back the secondary forest regrowth between rows of rubber trees, including potentially valuable trees, rather than weeding within the rows and selectively pruning inter-row trees. Farmers considered that the inter-row vegetation may harbour vertebrate pests and compete with the clonal rubber, and they had access to fruits, firewood and non-timber forest products on other land. Thus, contrary to expectations, when offered clonal germplasm, these 'progressive' farmers opted to use plantation methods to protect what they considered a valuable asset suited to monoculture, rather than maintain the traditional multispecies strategy they use with local germplasm. Thus, although clonal rubber can technically be established in a 'jungle rubber'-like system (albeit with lower growth rates than achieved in plantations), not all farmers may be prepared to adopt this type of system.

The spatial variation of tree growth and site factors was studied in a silvopastoral system at Glensaugh in Northeast Scotland. Sycamore (Acer pseudoplatanus L). Hybrid larch (Larix x eruolepsis Henry) and Scots pine (Pinus sylvestris L) were planted at 5 m x 5 m, 7.1 m x 7.1 m and 10 m x 10 m spacings on plots replicated over three blocks in a Randomised Complete Block design on a rye grass (Lolium perenne L) pasture which was grazed by sheep yearly from April to October. Included in the design were an agricultural control, forestry control and mowed plots. The agricultural control had no trees but grazed pasture and the mowed plots had trees but the pasture was not grazed, instead it was cut at intervals and left to decompose on site. The forestry control plots had no pasture and as such were not given fertiliser treatments and soil samples were not collected from them, in these the trees were planted at the standard 2 m x 2 m spacings and fenced off from the animals. Pastures received 160 kg N/ha^-1 annum^-1 in four equal applications. The objective of this work is to study at tree-scale the spatial variation of tree growth and site factors in grazed and ungrazed silvopastoral system plots. Total soil N, available Mg and Ca, as well as organic matter (OM), %C, pH in water and Calcium chloride increased significantly with distance from the tree while P decreased significantly with distance from the tree in grazed plots. The presence of trees or animals alone in a treatment did not significantly influence soil nutrient redistribution in a silvopastoral system. Therefore it takes the combined presence of trees and animals in a silvopastoral treatment for a significant redistribution of soil nutrients around the tree to occur.

This thesis examines the role of indigenous woody species in 'farmer-led' agricultural change in south east Nigeria. The study, carried out in parts of Cross River State and Akwa Ibom State, is set in the context of the recent trend among development professionals to stress the use of indigenous species and local knowledge in future development projects. Emphasising throughout the use of both indigenous knowledge and indigenous woody species, as well as participatory research techniques, the study comprised three main stages. The first stage was the selection of three study villages in different agroecological zones, one in a heavily forested area, one in a derived savanna area, and one in an area with little natural 'bush' remaining. Social surveys were carried out in the study villages to collect information concerning agricultural methods and problems, and the local use of woody species. The ethnobotanical results from this survey were documented and analysed, and the results were used in an examination of the impact of population density on the development of local natural resource management systems and indigenous agricultural innovation. Secondly, four indigenous woody species were selected in conjunction with the local communities, namely; Albizia zygia, Dialium guineense, Ridnodendron heudelotii and Uvaria chamae. A botanical study, including germination and growth trials in Calabar and phenological observations in the field, was conducted in relation to these four species. Finally, using the data collected during the social surveys, field trials and observations, an attempt was made to work with the villagers to develop ways in which some of the most pressing agricultural problems could be addressed using local knowledge and resources. As a result, a framework was developed for use in future rural development projects in the region, in an attempt to contribute to the current move by development professionals towards fuller community participation. Key words: agroforestry, indigenous woody species, 'farmer-led' innovation, germination trials, phenology, Albizia zygia, Dialium guineense, Ricinodendron heudelotii, Uvaria chamae, community participation, south east Nigeria.

In Babati district, Tanzania, agro-forestry land use system has been traditionally used for hundreds of years. It is a multi layer system with trees and/or bushes integrated with crops. That knowledge has been extended in the district through the land management programme, LAMP. It is said to be a “win-win” system with both economic and ecologic benefits. For a land use system to be sustainable, three spheres have to incorporate to reach a balanced development; the economic sphere, the ecologic sphere and the social sphere. To achievesustainable development, one sphere can not develop without the others. This study aims tosee if agro-forestry in Babati district balances all three spheres, if it is a proper tool toward sustainable development. It is a qualitative case study with semi-structured interviews with farmers in Babati and one interview in Sweden. The fieldwork in Babati where held under two weeks, based on interviews with farmers who practice agro-forestry and farmers who do not, and their opinion about it. The result indicates that it employs a lot of people and that the economy among farmers in the district has improved. Most farmers say their economy is more secure, because it is a multipurpose system and most people can adopt the technologies because high costs or advanced technology are not required. Farmers benefit from the ecosystem services provided from agro-forestry, for example water catchment and decreased soil erosion which also improves the environment. Soils regain their fertility and the land use becomes more resilient when trees integrate with crops. Many farmers believe the equity between gender has improved and that condition for women improves when fuel wood can be gathered from trees on the farm instead of walking long distances to a forest. The conclusion is that agro-forestry in Babati district fulfill more or less all three sustainability spheres and is a useful tool towards sustainable development, but has not yet reached full potential, there are possibilities for improvements and to scale up for greater benefits for all three spheres.

A study of a traditional land use system was conducted at Nade, Fergusson Island, in Milne Bay Province, Papua New Guinea. An ethnobotanical inventory of useful and culturally significant plants, and a series of transects and vegetation profiles were used to identify, and map the distribution of, 15 different plant communities in the Nade landscape. Interviews were conducted with local gardeners about land use decision-making, land tenure, and ecological knowledge. The land use strategy practiced at Nade can be characterized as a polyphase agroforestry system. A spectrum of management techniques are used in the different phases, including the selecting, ignoring, transplanting and/or planting of wild, semi-domesticated, and domesticated tree species. A variety of subsistence products are available throughout the year, from the range of vegetation types. The distribution of successional phases in the landscape was found to depend on topography and soil conditions which vary within the subsistence territory of Nade. Overlying the environmentally determined pattern of the shifting mosaic are the social factors; land use decision-making based on the traditional system of susu land and plant tenure, labour-saving strategies, and agricultural tradition. The study provides baseline data for monitoring changes in the culturally modified landscapes of Fergusson Island. This in turn can be used to facilitate a land-use planning process with local people.
Forestry, Faculty of
Graduate

The work reported here aimed to provide a comprehensive database of core information to support the development and validation of process-based models of resource capture and growth in semi-arid overstorey agroforestry systems. Intensive field studies were carried out in Kenya over a 30 month period and the results obtained were combined with data from a previous project to produce a dataset spanning a 4.5 year period. This dataset was then used to verify output from the HyPAR model. Allometric procedures developed from the pipe model theory (Lott et al., 1998) were used to estimate tree growth non-destructively throughout the observation period. Significant differences in tree size between the sole (Td) and dispersed agroforestry (CTd) treatments were established during the first 130 days after planting, probably because of competition with the associated crops. The above-ground biomass and trunk length and taper characteristics of the CTd trees remained inferior to those of Td trees throughout the observation period, seriously undermining the economic potential of this agroforestry system. The biomass and grain yield of CTd understorey crops were similar to the corresponding sole crops during the first three seasons, but were negligible in three of the final four seasons, with maize yields reaching 50 % of the equivalent sole crop values only when seasonal rainfall was well above average. This observation suggests that water availability was the primary limitation for CTd maize during the final seasons of the trial, a conclusion supported by the superior performance of maize grown under net enclosures which simulated tree shade in the absence of below-ground competition. Cowpea and maize were grown concurrently in two seasons to examine the impact of grevillea on C4 and C3 crops with contrasting responses to shade; biomass and grain yield were less affected in cowpea than in maize. The tree canopy in the dispersed agroforestry (CTd) treatment reduced the daily mean quantity of radiation incident upon the understorey crops by c.30 % during the final four growing seasons, although the discontinuous nature of the tree canopy caused substantial local variation in shading intensity. Seasonal mean fractional interception was greater for the combined canopies of the CTd treatment when soil moisture status was relatively high than for either of the sole canopies, suggesting the occurrence of spatial complementarity. Tree shade had a substantial moderating influence on meristem temperature since the mean diurnal temperature range was reduced from a maximum of 20°C in sole maize to 13 °C under the trees, and maximum meristem temperature was decreased by up to 6 °C relative to sole maize. However, the non-uniform shading provided by the trees caused substantial spatial variation in thermal time accumulation and hence crop development. Grevillea continued to grow during dry seasons and was therefore able to capture off-season rainfall which might otherwise have been lost from productive use. In addition, adaptation of heat balance gauges for use on grevillea roots (Lott et al., 1996) showed that substantial quantities of water could be extracted from deep-seated reserves below the crop rooting zone during dry periods, indicating the potential for spatial and temporal complementarity. However, transpiration by grevillea greatly exceeded rainfall during the dry season, rapidly depleting residual water supplies which might otherwise have been available for crop growth. In addition, approximately two thirds of the water used by the trees during cropping seasons was extracted from the soil surface horizons by lateral roots at distances of up to 2 m from the trunk. Thus, the potential for above and below-ground complementarity may be seriously undermined by the extensive capture of water by tree roots from the crop rooting zone. Comparison of output from the HyPAR model against the observed results provided information pertinent to future model development. The model proved to be insufficiently flexible for end-users wishing to simulate the growth of different crops during the same simulation cycle, or to use model output to aid management decisions such as the timing of pruning. The allometric procedures used by the model to estimate canopy size from trunk diameter at breast height also proved incapable of accounting for reductions in canopy size resulting from pruning. Estimates of tree height are rounded to the nearest metre within the model, representing a potentially serious loss of resolution when annual increments often do not exceed 2 m. In addition, the numerous parameters required by the model would force most end-users to rely heavily on published information, potentially undermining the reliability of simulations.

This thesis aimed to examine the possibilities and benefits of implementing agroforestry projects in Sierra Leone by comparing different agroforestry systems used in a Tanzanian project that consider carbon sequestration. Farmers involved in this type of projects get income from sold carbon credits as well as from other products that an agroforestry system could provide. Sierra Leone is one of the most vulnerable countries to climate change, with most of the population living in rural conditions. It was investigated what the potential economic and environmental impact different agroforestry systems considering carbon storage could have in Sierra Leone. The study was based on empirical material from a case community Makari. The conclusions were that Sierra Leone could benefit greatly from agroforestry projects, especially at community level where it could provide additional sources of food and income. From a greater perspective it could give environmental benefits as well as securing wood commodities like fuelwood for the future. Starting up a project would however be a high risk investment with a troublesome implementation process and complications on a daily basis.