This article deals with the dynamics of the volume control method in forest regulation. The sustainability of harvesting a given constant volume in a simplified forest model is studied. Depending on the initial age distribution, the cut can lead to the forest exhaustion, or to an asymptotic steady-state uniform age distribution. A continuous model is formulated in terms of various kinds of partial differential equations, delay differential equations, and non-linear integral equations. Equilibrium solutions and their stability properties are determined. Discrete models are also obtained, both by direct reasoning and as approximations to the continuous case. These are used for simulation and graphical exploration of the system behavior. In addition, contrasting various discrete and continuous versions was found useful in clarifying some issues, in particular, ambiguity/redundancy problems in the relation between integral equations and delay differential equations derived from them. The basic problem of evaluating sustainability for an initial distribution remains unsolved, however. Further progress is linked to the asymptotic properties of a second-order recurrence relationship. It is hoped that the interplay between the theory of functional differential equations and this concrete and easily interpretable problem in forest management might prove fruitful in both fields.

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In the miombo woodland of Northern Zambia, the Bemba have practiced a unique shifting cultivation called Citemene. Men climb up trees and pollard the branches to open fields for agriculture. Tree branches are collected and taken to a garden from surrounding tree-cutting areas before they are set on fire in October. Newly opened Citemene fields could be recognized as white circles with black centers on LANDSAT TM images. This study examines the settlement and agricultural pattern of 8 households by applying multi-temporal LANDSAT TM images from 1984, 1989, 1992 and 1994. In 1984, the population was concentrated along the road, cultivating hybrid maize, which was introduced by the Zambian Government. Around 10 households set up seasonal dwellings during the dry season to open Citemene, but most of the villagers remained resident at the roadside. They simultaneously opened Citemene and cultivated maize although some households became dependent on maize cultivation. In 1987, the fertilizer supply became unfavorable for farmers in remote areas and they began to open Citemene actively. In 1989, approximately 30 households began to set up seasonal dwellings along the seasonal marsh, but they returned to the settlement and cultivated maize near the road during the rainy season. In 1990 a bridge was destroyed and that made it impossible for vehicles to go by the shortest way from the township to the village. The fertilizer supply was interrupted and it became difficult for them to continue the maize cultivation. Citemene became more important for maintaining subsistence, as an alternative to maize cultivation. The villagers abandoned the settlements along the road and shifted their base to the site of the seasonal dwellings. In 1994, woodland suitable for Citemene was exhausted around the new settlement and the villagers set up seasonal dwellings along the river. They prepared land for Citemene from a base of seasonal dwellings during the dry season, but they stayed at the settlement along the seasonal marsh during the rainy season. In 1997, they shifted their settlement again to seasonal dwelling area along the river. There was plenty of water at the river although they had had trouble getting water before. Not only mature woodland but also water availability is important in selecting a place for seasonal dwellings and settlement. Where the distance between the settlement and newly opened Citemene increased to 3 to 5km, they set up seasonal dwellings near the seasonal marsh or rivers. When the distance became longer than 3 to 5km from seasonal dwellings to new fields, they left the settlement for seasonal dwelling area. The villagers shifted their base with their relatives at 3 to 4years' minimum interval. These periods accord with the crop rotation of Citemene. They could furnish themselves with staple and subsidiary foods from the fields around the seasonal dwellings at least 3 to 4years after setting up seasonal dwellings and they shifted settlement to the seasonal dwelling area. After the fertilizer supply became unstable in the mid-1980's, they started actively seeking mature woodland with plenty of water. Spatial mobility was important for the Bemba to maintain their shifting cultivation and subsistence.

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Image analysis of tree crown images may provide more objective measures of crown condition which has been assessed visually in the forest health monitoring of many countries, but the commonly used interactive thresholding approach is too time-consuming to apply to large numbers of images. This study examined the usefulness of three automatic thresholding algorithms that are based on the between-class variance (VARIANCE), the classification error and the total entropy, respectively. VARIANCE had no significant difference from, and good correlation (r=0.992) with, interactive thresholding for the black pixel percentage within a region of interest, but the other two did not. VARIANCE also had high correlation (r=0.992) of the black pixel percentage between cloudy and blue sky conditions. It was concluded that VARIANCE can be successfully used for thresholding for tree crown images and can greatly reduce time for image processing, while maintaining a high level of accuracy and reproducibility. However, we need to pay attention to the quality of the original color images.

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The most important work in planning harvest schedules is to allocate spatially feasible and economically operable forest stands into harvest blocks. Stands that are more feasible and operable should have a higher priority for harvest than ones that are less feasible and operable. The main objective of this study is to analyze stand conditions and geographic factors to estimate the feasibility and operability of stands in harvest operations with a score evaluation method, and then to apply the grid-cell-based GIS method for classifying harvest priorities of stands. Estimating the feasibility and operability of stands is difficult because it involves complex natural factors such as resource structures, geography, geology, and transportation networks. Among these factors, we selected four simple factors, i.e. stand age, site class, skidding distance and slope angle, which directly affect harvest operations, to analyze harvest priorities for sugi plantations. By using the score evaluation method with four factors, we assigned each stand a value representing its feasibility, locality, and operability, and calculated the total score for the stand. By classifying the total scores into four harvest groups, we evaluated the harvest priority for each stand in the study area. A GIS grid-cell-based model was applied as an efficient means of accomplishing this work.

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