Regular monitoring within the network of plots
Today regular Forest Focus Level I assessment in CR is done within the basic network 16 × 16 km and in selected plots of the 8 × 8 km network, in total 306 plots, regularly distributed within CR according to the forestation. The plots were selected to characterize the site and stand conditions. In the altitudes from 150 m to 1300 m more than 14 000 trees is assessed every year, representing 28 forest tree species of different age classes. In each monitoring plot basic site and stand conditions are described. In regular intervals (1–5 years) following parameters are assessed: crown condition (defoliation, colour changes etc.), social position, dendrometric parameters, phytocenology. In irregular interval also the leaf, soil and tree-ring analyses are done.
Assessment of the tree health state
Tree health state is characterized mainly with defoliation, defined as relative loss of assimilation organs in the tree crown, compared to the healthy tree living in the same stand and site conditions. It is a loss caused mainly by unsatisfactory changes in the forest ecosystem, result of the long-term, extreme air pollution by different harmful agents (SO2, NOx, F, Cl, O3, heavy metals, dust particles etc.).
Dynamics of defoliation development
Dynamics of defoliation development of the most important commercial tree species (stands over 60 years) is different at the end of the eighties, of sharp deterioration of the health state, and following period of the nineties of much lower deteriorating. In the period monitored of 1986–2004 the average defoliation value of spruce and pine had culminated in 1992, followed with stagnation In 1996 the average defoliation of these species had increased again, reaching the maximum values of 33.9 % for spruce and 38.3 % for pine. In following years defoliation was decreasing slightly, and, since1998 the average defoliation is increasing again moderately (values over 30 %). There are some visible differences among the regions in CR with respect to the long-term defoliation development. Relatively leveled trend can be observed in Ústecký kraj, Karlovarský, Olomoucký and Moravskoslezský kraj. Mostly increasing defoliation of conifers has been recorded in Středočeský, Liberecký, Královéhradecký and Pardubický kraj and in Vysočina. Gradual increase, followed with decrease again recorded in Plzeňský and Jihočeský kraj. The highest disbalance in defoliation development, connected most probably to irregularities in the development of climatic conditions, has been observed in Jihomoravsky and Zlínsky kraj. Relatively the lowes was defoliation in Olomouc region, in 2004, where defoliation classes 2-4 have represented 60 %. In contrary the highest was defoliation in Královéhradecky, Pardubicky and Jihomoravsky kraj, with the sum of defoliation classes 2-4 ( defoliation over 25 %) in 2004 was higher than 77 % in each of those regions.
For the broadleaves (stand of 60years and more) the long-term defoliation development is slightly different. Within the period studied of 1991–2004, defoliation of broadleaves was the highest in 1993 (average defoliation of oak 43.0 % and beech 22.5 %), in following years it was decreasing to the average of 27,. % for oak and 14.6 for beech %) in 1998. Than some increase was recorded again, and, since 2000, defoliation is stagnating. There are significant differences among the species. Oak is more disbalanced and of higher defoliation than beech. Gradual defoliation decrease (1997-1999) , followed with an increase again, has been recorded in the regions Jihomoravsky, Středočesky and Zlínsky kraj and in Kraj Vysočina. In other regions with higher proportion of broadleaves defoliation development was more variable. In 2004 relatively the lowest was defoliation of broadleaves (classes 2-4 ) in Zlínsky, Moravskoslezsky, Jihočesky kraj and Kraj Vysočina (17.9%). Contrarilly the highest defoliation in 2004 was in Královéhradecky kraj (classes 2-4 in 71.0 % of the stands).
Younger stands (less than 59 years) are generally less defoliated, this difference is the highest in conifers. The main tree species, spruce (Picea abies) in the category 60 and more, did not changed significantly, compared to previous years. Spruce stands less than 59 years old have recorded slight shift of the of the two age categories defoliation class 1 towards 2. Similarly less significant changes recorded in the pine stands (Pinus sylvestris) of the two age categories. The highest were changes of fir (Abies alba), in the stands 60 years and older, where the shift of the class 2, from 90.7 % to 69.2 %, together with the increase in class 1 from 9.3 % to 30.8 % has been recorded. For most of the broadleaves of the two age categories slight increase of defoliation has been recorded (shift to higher defoliation classes). Beech is an exclusion (Fagus sylvatica), of moderate decrease (shift from the class 1 towards 0). Generally increased defoliation of broadleaves can be connected to worm weather and low precipitation.