The ability of spatial expansion and conquering of new locations, suitable for growth, is one of the most important properties enabling different plant species (including forest trees) a permanent existence in a constantly changing (in space and in time) environment. In the course of evolution, plants developed several adaptations and mechanisms enabling them to capture new localities appropriate for life. The key role in this process is played by so called propagules, i.e. differently built spores, seeds and fruits. The main sources of forces and major transportation vectors for propagules are such mechanisms as: power of gravity (barochory), wind (anemochory), water (hydrochory), animals (zoochory) and man (antropochory). Among them, in case of tree species producing large seeds, containing bulky amounts of food resources, the most important role is played by zoochory. The special variant of zoochory is ornitochory, i.e. dispersion of plant propagules by birds. One of the best known and documented examples of ornitochory is dispersal of oak acorns by jays (Garrulus glandarius). The contemporary research shows that during a vegetation period one single bird is able to deposit even several thousends of acorns within the area of 10 to 100 ha. The dispersal distance in case of acorns distributed by jays is variable and depends on several factors, first of all, climatic conditions and degree of environmental heterogeneity. On average, acorns are distributed within a distance of several hundred meters from seed trees; sometimes they are disseminated at a distance of several (4−8, maximum 20) kilometers. As a rule, only a part of deposited acorns is uncovered and consumed by birds, thus at least some of them can germinate and produce new oak seedlings. It was also recently demonstrated that jays preferably put down acorns under the stand canopies composed by tree species other than oak, for instance, under Scots pine trees. Under favourable conditions, this initiates natural successional processes and leads to a significant conversion of tree stand composition. Considering a large scale and commonness of this phenomenon, it deserves an interest and attention, not in the case of natural forests only, but in the case of managed forests as well, in which the quasi−natural, successional processes, initiated by jays, can considerably contribute to a greater compositional and structural diversity of tree stands.
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