Proposal of silvicultural measures in stopping of tree of heaven (Ailanthus altissima /mill./Swingle) invasion and mitigation of consequences of colonization in degraded stands in the region of national park 'Fruška gora'

The paper analyzes the application of silvicultural measures in young stands in the area of National Park 'Fruška gora', which occurred after the clear-cutting and rep- resent the final stage in the process of regressive succession of zonal communities in the southern peripheral area of the Pannonia (Quercetum cerridis virgilianae B. & Jovanović Vukićević 1977). After clear-cutting the largest share in stands has a lime, coppice origin. Colonization and undisturbed development of invasive neophytes, tree of Heaven (Ailanthus altissima Swingle /Mill./), is a factor of their further degradation. Tree of heaven suppresses a lime from the stand structure, usually the only remaining species from natural communities that has a biological potential to sustain the further development of degraded stands. The aforementioned processes are most intense so far undermines diversity of natural forest communities. The study was conducted in the peripheral area of NP 'Fruška gora' (MU 'Gvozden-jak-lice', division 54, section g) in a stand with different participation of tree of heaven in the structure. In two permanent sample plots were measured the diameter at breast height of all trees and the height of a number of trees for the construction of height curves and calculation of wood volume of represented tree species. On the experimental plot 1 (OP-1), in the upper part of stand (170 m a.s.l.), at the age of 17 years there were seven tree species with a total of 6518 trees ha-1, with basal area of 26.24 m2ha-1 and wood volume of 219.13 m3ha-1. The most represented tree species is white lime, with 65.0% in the number of trees and 83.5% by volume, other types of natural communities are represented with 32.7% in the number of trees and 9.7% by volume, and the tree of heaven is represented with 2.3% in the number of trees and 6.8% by volume. On the experimental plot 2 (OP-2), in the lower part of stand (130 m a.s.l.), at the age of 20 years there were eight tree species with a total of 4045 trees ha-1, with basal area of 34.68 m2ha-1 and wood volume of 338.55 m3ha- 1. The most represented tree species is white lime, with 45.5% in the number of trees and 13.2% by volume, other types of natural communities are represented with 16.5% in the number of trees and 1.2% by volume. Tree of heaven is represented with 35.9% in the number of trees and 80.5% by volume and black locust with 1.9% by trees and 4.9% by wood volume. Mean and dominant diameters and heights of tree of heaven indicate dominance in growth compared to the mean and dominant diameter and height of the lime. To limit the spread of tree of heaven in the stands and, generally, in colonized edges of the NP 'Fruška gora', where the trees of tree of heaven are in the stage of fruiting, as a selection criterion for their removal is proposed the sexual dimorphism. Recorded ratio of male (without seed) and female (with seed) trees of tree of heaven, and negligible presence of mixed flowers on the male trees, provides an opportunity for the implementation of sexual dimorphism as a selection criteria in thinning to stop the spread of tree of heaven by generative way. The crown canopy of lime, and in this context, the crown canopy of grown male tress of tree of heaven, in parts of stands where it dominate, is a factor of self-thinning of tree of heaven in a lower layer of colonized stands.