The thesis presents an investigation of tree, pasture and cattle interactions in multistrata silvopastoral systems on seasonally dry pastures in Colombia. The research began with a participatory appraisal of the existing silvopastoral practices in the region and farmers' attitudes towards the trees already in the landscape. A survey was conducted involving 54 farms in the Caribbean region of Colombia (West of the Magdalena River) and revealed much greater and more deliberate use of trees on pastures than had previously been recognized. This confirmed that asking farmers about their current knowledge and practice is an essential prerequisite to design of research that is relevant to their needs. Farmers' knowledge about trees and scientific consideration of the trees present in pastures highlighted the importance of different functional roles of trees, occupying different strata, particularly with respect to production of fruit for cattle fodder as well as leaf browse. A preliminary single tree plot experiment measuring the effects of 10 tree species on pasture productivity and soil moisture revealed that the overall pasture dry matter in the vicinity of trees was different for different tree species. This confirmed that choice of tree species for use in silvopastoral systems may have a large impact on understorey productivity particularly in the dry season and, therefore, is an important management consideration for farmers. A large systems experiment was designed, based on the results of the farmer survey, to investigate the effect of planting trees of different stature and productive function (sources of leaves, fruit or timber) into pasture. The experiment was established on 30 ha of cattle-grazed pasture, using four treatments of differing structural complexity made up of combinations of vegetative layers or strata (pasture layer-Dichanthium aristatum and Brachiaria mutica, shrub layer-Crescentia cujete, Gliricidia sepium and Leucaena leucocephala, arboreal tree 1ayer-Albizia saman, Cassia grandis and Guazuma ulmifolia and timber tree layer-Pachira quinata, Swietenia macrophylla and Tabebuia rosea), plus a pasture control. The target density of plants was higher for lower stratum species (625, 156 and 39 trees ha-1 for shrubs, arboreal and timber trees respectively) and a substitutive design was used where multiple strata were combined. High survival and fast growth of trees planted into pasture demonstrated that productive associations of trees on grazed pasture could be established. Higher growth rates of shrubs and arboreal trees were observed when they were mixed with other strata than when grown alone with pasture. In contrast, there was no detectable effect of the addition of trees on either pasture biomass or compostion over a two-year period. However, pasture biomass and composition were both heavily influenced by season, with markedly less biomass in the dry season. This demonstrated that high tree densities could be established in this environment without immediate reductions in pasture productivity. There was also evidence of differences in diet quality amongst treatments. In terms of the nutritive value of components, the potential degradability of Dichanthium aristatum was higher when it was grown in the more complex systems containing shrubs and trees than in the pasture control. This was associated with higher nitrogen content of dry season diets including tree leaf material which may have enhanced rumen function. Estimation of feed intake using the n-alkane technique indicated that up to about half of the dry season diet could be provided by shrub fodder confirming that browse species have large potential as a food source for ruminants, on seasonally dry pasture. The overall impact of adding trees to pasture was to increase animal productivity. Milk yield per cow in the dry season was higher in agroforestry treatments than in the pasture control, consistent with higher quality diets in agroforestry treatments. There was also a marked increase in milk yield per hectare irrespective of season as a result of higher stock carrying capacity on agroforestry plots, consistent with higher overall forage biomass productivity in plots with trees or shrubs. The research has revealed considerable potential for using trees to improve and sustain cattle productivity on seasonally dry pastures. These results are discussed in the light of ongoing development of silvopastoral systems in the Caribbean region of Colombia.