Forest ecosystems are threatened by numerous damaging factors. In recent years, an increasing negative impact on forest ecosystems is attributed to climate change. Continuous monitoring of forest conditions is of great importance for detecting changes in forest ecosystems and determines the cause and effect relationships between the resulting changes and factors that affect forests. The first symptom of forest dieback is the appearance of defoliation and discoloration of trees and therefore their monitoring is of great importance. This paper presents the results of several years of monitoring of trees defoliation and discoloration of sessile oak, English oak, spruce, fir and beech. Assessment was carried out on five plots. In addition, impact of biotic and abiotic factors harmful to the condition of the trees was evaluated and analyzed. Most conspicuous defoliation of trees was found in trees of sessile oak and English oak. In these two species was noted a low percentage of trees without defoliation, and was recorded and drying of individual trees. The most favorable situation is found for the beech in which the percentage of trees without defoliation and discoloration was very high. Investigation showed a very strong insect, disease and drought influence on the results of assessments of the status of trees and their variation.