Health status of forest stands on permanent research plots in the Krkonoše Mts.

Damage to beech, mixed (beech with spruce to spruce with beech) and spruce stands in the Krkonose Mts. is described on the basis of evaluation of transition matrices describing the probability of a change in the assess- ment of defoliation of particular trees in defoliation classes. The condition and development of health status were evaluated in the long run on PRP 1-32 in the Krkonose Mts. by foliage and degrees of defoliation. Features describing the health status of the tree crown (damage by snow, frost, wood-decaying fungi, and insects) were also evaluated. Average defoliation, standard deviation of defoliation, estimation of minimum defoliation, and frequency of the tree number in defoliation classes were calculated for each plot, and each year. Three characteristic periods were distinguished according to different trend of foliage dynamics: period of the first symptoms of damage (1976-1980) - a decrease in foliage on average max. by 1% per year, period of great damage (1981-1988) - annual defoliation on average around 3-16%, period of damage abatement (1989-2009) - annual defoliation on average between 0% and 4%. The incomparably higher resistance of autochthonous st ands to air pollution stress culminating in the eighties of the last century was demonstrated unambiguously.