Abstract
Despite the long history of anxiety about shifting cultivation practices by small-scale farmers in Central African forests causing deforestation, this is the first study that examines the temporal and spatial dynamics of shifting cultivation landscapes and the influence of landscape configuration on secondary vegetation regrowth in fallows. This is important not least because, within the landscape matrix, fallow vegetation is crucial to alleviate effects of losses of forest vegetation, and biodiversity as well as negative impacts on carbon balance. Moreover, fallows provide food, beverage, fuel, building and medicinal products harvested from a diversity of plant species, whose value for local livelihoods is well known.The present study addressed two overarching hypotheses:
1) socio-cultural and technical factors operating at the household level mediate
regional driving forces of land use change and differentiate spatial and temporal
patterns of land cover in shifting cultivation landscapes; and
2) landscape level factors influence successional process in fallows.
The research was carried out in three villages in the Humid Forest Zone of Southern Cameroon along a gradient of resource management domains from low population and abundant land to high population and scarce land.
Three different spatial scales of analysis where integrated: the landscape scale, the patch scale and the plot scale. The landscape scale corresponded to functional territories of villages (the area utilizable by the village). Spatial information on land cover, path networks, access rights and tenure was collected by integrating Participatory Mapping with GIS. GIS models of land rights indicated a nested configuration of social accessibility with land endowments by kin-groups presenting a high heterogeneity in terms of area and physical accessibility. Even in contexts where land was abundant spots of high population pressure occurred because of differences in land endowments. Interviews with individual farmers were conducted to investigate the importance of locational properties for selection of sites for cultivation. Accessibility from residential units, proximity to other fields, and proximity to water, make a site attractive. Ownership strategies of 'defence' or 'expansion' of landholdings are crucial. The perception of a plot's qualities is context dependent and during the crop-fallow sequence a particular plot can be selected for cultivation because it meets various different criteria. The length of the fallow cycle observed was not consistent and short and longer cycles alternated on the same land unit.
GIS based land cover change detection for three photographs spanning a period of 50 years, indicated a net agricultural expansion and intensification processes as the most important changes in the two more populated and accessible sites. These changes consisted mostly in the aggregation and intensification of the agricultural matrix with young fallow becoming the dominant class. The proportion of land likely to undergo forest recovery through the influence of neighbouring forest stands reduced. The forest in turn underwent a general degradation process because of 1) the isolation of the remnants within an agricultural matrix and their smaller size, subject to greater edge effect; 2) an increase in the human pressure for harvesting of timber and non-timber forest products and 3) the increased proportion of secondary forests derived from old fallows in the landscape.
The analysis of the sequence of land cover changes during two observation intervals (1951-1984 and 1984-2001) indicated that 1) forest regrowth and clearing are continuously and simultaneously occurring with the predominance of each varying on the basis of the location of sites within landscapes and the temporal interval over which change is observed; 2) there is a highly variable spatial grain of land cover change; 3) there is a differentiated spatial pattern for individual types of trajectory, with the spatial pattern of each, related to social and physical accessibility and population pressure.
A conceptual model was proposed to describe the landscape and agricultural factors affecting the successional process of tree species in fallows between 0 and 15 years in age. Agricultural history, and particularly the repetition of cropping cycles, affected distribution of tree species in the landscape. But spatial characteristics of the agricultural matrix and its internal fine scale heterogeneity and stability, have a significant impact, increasing with the age of the fallow. Agricultural expansion in combination with fallow shortening can result in an overall shift of fallow species composition with a loss of useful species.
| Date of Award | May 2008 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Italian Foreign Ministry |
| Supervisor | Fergus Sinclair (Supervisor) |