Assessment activity and surveillance of the forests health, held at the global, regional and local level, has continuously developed, culminating in the current period with interdisciplinary and extensive scientific researches, that evaluate the effects of the main factors on forest ecosystems state, in particular, air pollution and climate change. Scientific researches have shown that among trees ecophysiological processes, forest life processes and meteorological parameters there are direct dependences, particularly in the case of trees supply with water during the growing period (May-July), with major influences for critical months (July and August), which have a decisive impact on growth, vitality and production of organic matter in forests. Dry years, from the beginning of the third millennium can lead to a decrease of mesophilic forests area (beech, sessile oak and penduculate oak), which will tend to retreat towards the center of the area (central Europe) in favor of thermophilic forests with pubescent oak. It was determined that a most significant negative impact of climate aridization will feel the forest ecosystems from Southern and central regions of country (conditioned by the mean air temperature (July-August), monthly rainfall (May-August), evapotranspiration and geographic latitude), and less - the Northern part of the country (Forestry Aridity Index calculated for 3 experimental stations revealed variations of this index between 7.8 - 8.3 - in the Central part of country, and 8.4 - 8.6 - for Southern part of country). At the same time the impact of climate change will determine the spatial and temporal dynamics of pests and pathogenic species. The phenomenon of climate aridization was expressed also through the impact of the Microsphaera alphitoides disease, intensity of “mildew” attack being based on the climatic conditions of the study region. Obtained data, for confirmation, were correlated with indications of bioindicators, present in the study region.