A digital model of pattern and productivity in an agroforestry landscape

Agroforestry is an approach to land-use which offers much promise in addres sing many of the inter-related problems associated with rural development a nd land degradation (Scherr, 1992; Nair, 1993). This research incorporates remotely sensed agroforestry landscape information within a computerized mo del that relates spatial structure at the field and landscape scale to maiz e production. Remote sensing, cartographic modeling as well as landscape ec ological theory and methods of analysis figure prominently in the work. The study area is in the coffee zone on the southern footslopes of Mount Kenya . The research tests the hypotheses that: there is a correlation between la ndscape, field structure and crop production. Specifically, it is hypothesi zed that spatial configuration at the field scale, (e.g. patch size, shape and adjacency relationships etc.) as well as at the landscape scale (densit y of trees and hedgerows) can be significantly correlated with productivity . The central hypothesis is that spatial variability across the landscape, at scales both at and beyond that of the field, can explain a significant a mount of the variability in yields. In order to carry out the work, a recen t innovation in remote sensing, the Compact Airborne Spectrographic Imager (CASI), has been used in the project. The CASI was used to acquire a detail ed digital image of the site at a high spatial resolution (1.75 m pixel siz e). Six spectrally narrow width bands were acquired with the purpose of det ermining chlorophyll density as well as crop type and vigor. Findings indic ate that the spatial measures that were undertaken at the landscape scale d o not explain enough crop variability to be statistically significant. Rath er, it is far better explained at the individual field level. Here it was d emonstrated that the distance from shelter plantings is inversely and curvi linearly related to crop vigor as measured by the relationship between the Near Infra Red and Red wavelengths. Findings indicate that the positive eff ects of trees in the study landscape are limited to within 25 m of the cano py and may increase production as much as 32% at the optimal distance. An o ptimum hedgerow inter-distance of 40 m is suggested in order to maximize cr op vigor. The impact of both the existing conditions as well as two possibl e alternatives are evaluated for their total landscape wide impacts on maiz e yields and wood production. It was determined that removal of the existin g hedgerows (50% of all the trees in the area) by a disturbance such as a p est outbreak would cause a 5% reduction in maize production. A second alter native, which identified under-utilized planting niches throughout the land scape, is predicted to result in a modest increase in maize production and a doubling of wood products. (C) 1998 Elsevier Science B.V. All rights rese rved.