the objective of this study was to develop a microcomputer-based planning model for guiding individual investors in choosing between alternative forestry investments as well as other nonforestry investments in the thunder bay district. this model has a special focus on alternative thinning regimes in red pine plantations for these reflect stand response to changes in stand density. the model was built from stand-level growth, yield, and product models for southern ontario. the planning model was constructed as an interactive computer program which allows inputs and thinning treatments to be entered at the terminal. the model inputs involve stand, site, and economic variables; while thinning treatments are mainly age of first thinning, thinning weight, thinning cycle, thinning intensity, thinning frequency, and rotation age. the outputs of the model are in the form of physical and economic returns as well as stand volume development over time. the model allows evaluation of 'what if alternatives which enable physical and economic returns to be examined under varied market and environmental conditions. a lack of adequate data for model construction restricted this planning model to stands of ages 20 - 45 years, basal area of 10 m[superscript 2]/ha and above, and site indices of 16 to 26 m. the model was tested with data from the rockland plantation of southern ontario and the hogarth plantations of the thunder bay district the tests for the rockland plantation were based on mean ratios of simulated to observed total volume means and r[superscript 2] values. such tests were not possible with the hogarth plantations because there was not enough data for the tests. instead, for the hogarth plantations curves representing three points each for the simulated and observed basal area data were drawn for comparisons. the results with the rockland plantation gave a mean ratio of 1.05 and r[superscript 2] value of 0.96. the tests with the hogarth plantations also showed consistent results. the data used in both tests were very limited for any strong conclusion. rigorous tests are necessary to confirm these preliminary results. the model was finally tested for physical and economic information based on alternative thinning treatments. the results of this test showed that returns from alternative thinning regimes depend on: age of first thinning; thinning weight; thinning cycle; thinning frequency; thinning intensity; and average stand diameter. further studies on the influences of individual factors on physical and economic returns are suggested.