In the framework of completion of a system of larch research sites in the Ore Mountains (Krusne Hory) also Nos. 29 and 30 research sites were laid out in 1970 comprising the issues of the clones originated by free pollination and the issues of hybrid combination from controlled cross-breeding. Research site 29 contains 16 issues of Larix decidua originated from free pollination, while research site 30 contains 11 hybrid combinations originated from controlled cross-breeding, of which 8 are inter-species cross-breeds (Larix decidua x L. leptolepis and L. decidua x L. gmelini) and further 5 issues originated from free pollination. The research sites are situated on a plateau of the Ore Mountains at the elevation of 810 m above sea level. The locality is classified typologically as dwarf hornbeam spruce forest on mountain humus to peat podsols. It has been heavily damaged by industrial immissions particularly SO2, and ranked in the highest danger zone A. The issues were planted on plots sized 8 x 8 by the double grid method in four repetitions. For every experimental variant 4 x128 seedlings were planted on the research sites. The measurements and appraisal were carried out at the age of 18 years. Mortality was recorded; the height and the diameter of all seedlings were measued, the shape quality and the state of health of the trunk were assessed visually. The results were processed by current methods of mathematical statistics (variance analysis, Ducan's multiple sequence test). In agreement with the experiente of forest practice with the planting on calamity-cleared sites in the Ore Mountains the larches on research sites have shown considerable mortality and slow growth, However, the indivudals which have overcome the growth phases of the first few years show a satisfactory growth in comparison with other species used and are characterized by a good state of health. The shape of the trunk and the crown of the larches on exposed sites in the Ore Mountains is influenced negatively y snow pressure, hoar frost, ice accruation and, to a considerable extent, also by the damage caused by animals. In spite of these drawbacks, however, the quota of individuals with a trunk of satisfactory quality on the individual sites is satisfactory in the majority of cases. It has been ascertained by mathematical statistical analysis that there are no statistically significant differences between the investigated variants on both sites in respect of mortality, state of health and trunk shape. In respect of these characteristics all investigated issues must be considered equivalent. On the basis of mean heights and diameters it was possible to identify the most valuable issues on both sites and determine their sequence. The issue of the 1-6-18 clone from the High Tatra has shown good growth characteristics exceeding distinctly the average of the whole .........
