EN
The paper presents the assumptions of the portfolio theory and the possibilities of its application in the forestry to diversify the species composition of the stand. The decision problem concerns the rationalization of the species share, ensuring the optimal ratio of annual production value from 1 ha in the stand (financial effect) to the expected level of risk. The adopted measure of the assessment of the value of production and the risk of its achievement is the Sharpe index, which is an approximate measure of the correlation between the income of one investment and its market, and therefore a measure of systematic risk. The paper presents the theoretical foundations of the mentioned optimization problem and examples of research results of American and European scientists regarding applications of portfolio theory in the forestry. The research results indicate that the portfolio theory in forestry focuses on making investment decisions in conditions of high uncertainty. The main criteria for selecting these decisions are income and risk. Diversification of the share of various investments is the source of the so−called risk diversification effects, e.g. the share of particular species in the composition of the stand, the assortment structure and other natural and economic factors that cause a reduction in the total risk with the same income or an increase in the total income with the same risk. The paper indicate that in forest management it is possible and justified to use the simplified Sharpe model, in the form of a univariate indicator, to analyze and make decisions rational from the point of view of natural and economic investment. This solution was applied to various portfolios, including the diversification of the species composition of tree stands. The key indicator when assessing the size of risk and related (predicted) income is the so−called the beta coefficient, determined using the modified Sharpe formula.