A new method is used for evaluation of the stability of tree against the wind and to testing the theoretical stability models. The base principle of the uniform couple method is the relative identical environment conditions (site, stand and airflow) by using a couple of one damaged tree and two undamaged trees (the most close). Using the index statistical method it was possible to evaluate the direction of influences of the biometrical and qualitative tree parameters. Height and the ratio between height and diameter of the damaged tree were higher than the same parameters of undamaged trees in 73 % and 83 % of the paars, respectively. The influence of defects, especially the root decay, is the most important in the stability of tree against the wind. Over 50 % of damaged tree have defects. The method of uniform couple is an alternative to destructive methods for testing, in site condition, by mechanical methods, the stability of tree and to validate the theoretical models.

The paper describes and advocates for a tradable permits system designed for forest logging wherever uneven aged structures are needed to create and/or preserve. The main reason for advocating for tradable permits is the landowner's risk seeker behaviour whenever the auction price exceeds too much the reservation price. The main idea is to allocate a given number of ecological points per cubic meter of timber, to each company operating within an area. According to a simple formula, this number is re-computed at the end of the year, taking into account all damages reported by the Environment Authority. Ideally, a firm which makes no damages, keeps all its ecological points and it is able to have additional revenue from selling logging rights to other competing companies. Effectively, the winning firm is the one that has kept the most ecological points and will set up the price for ecological points required by other companies to operate in the forthcoming year. The ecological company is able to get an additional income, which is proportional to the gap between the two re-computed ecological points assigned to each harvested cubic meter of timber and the difference between the volume it harvested and the volume harvested by all other competitors.