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The steeplebush is a shrub growing naturally in North America. In Europe this species has been cultivated as an ornamental plant since the 18th century. It has been observed in spontaneously developing secondary localities in such countries as Belgium, Denmark, Sweden, Norway and Germany. In Poland there are three regions in which Spiraea tomentosa is known to be a permanently established anthropophyte: Puszcza Drawska, Bory Niemodlińskie and Bory Dolnośląskie forests. The greatest number of localities of this shrub can be found in the extensive area of the latter, where its expansion has caused significant changes in the natural environment and problems in woodland management. Therefore a research was carried out to find what conditions made the steeplebush ready for invasion and what types of plant communities were especially susceptible to it. The information about the distribution of S. tomentosa in the Bory Dolnośląskie Forest (SW Poland) was collected during field observations in the years 2011−2014. We also verified and used the results of a survey made in 2011 in three forest districts located in the study area: Ruszów, Węgliniec and Wymiarki. The analysis concerned the frequency of the steeplebush in the forest environment in terms of the forest habitat type, species composition, and stand growth stage as well as in non−forest environments like meadows, peatland, margins of drainage ditches, etc. Phytocoenoses in the habitats of humid mixed coniferous forests and humid coniferous forests with mature tree stands dominated by birches or alders were found to be forest communities the most susceptible to colonisation by S. tomentosa. Especially susceptible to steeplebush invasion were also forest cultures on those habitats. Much fewer steeplebush localities were recorded on fresh and mixed coniferous forests as well as fresh broadleaved forests. In a non−forest environments the steeplebush was mostly noted on margins of drainage ditches. The extensive system of such man−made environmental structures in the Bory Dolnośląskie Forest was found to be the most important factor favouring the expansion of S. tomentosa. Thus, the invasion of the discussed species is primarily determined by a large proportion of humid habitats in a single compact woodland complex connected by a dense network of drainage ditches.
Black cherry (Prunus serotina Ehrh.) belongs to quite common and the best known invasive woody plants of alien origin occurring in central Europe. On the other hand, little is known about the degree of settling of another North American representative of the Prunus genus from the Padus subgenus – the chokecherry (P. virginiana L.). A considerable morphological similarity of the above-mentioned taxon to P. padus L. is a cause of fairly significant problems associated with its identification. It is not easy to distinguish these related indigenous species, common in forests, as well as in mesophilous thickets in the area of entire Europe. That is why P. virginiana is usually unnoticed and, consequently, it is overlooked in floristic studies. On the basis of the data derived from a variety of sources, mostly collected by the authors in the course of their field trips, supplemented with information from literature, as well as unpublished notes obtained from different persons, information concerning the distribution of secondary P. virginiana sites in Poland is summed up. The article presents a list of 28 such sites together with a map on which their locations have been marked. The discussed species was observed most frequently in the forest environment on eutrophic as well as mesotrophic broad-leaved forest sites in shrub thicket areas at the edge of dense forests. It was also found in broad-leaved and pine coniferous forest underbrush as well as in mid-field thickets. It was established that in Poland, it was not only fully settled in on semi-natural sites but it also encroached upon forest phytocoenoses of natural character. In order to draw attention to possibilities of P. virginiana occurrence in other, hitherto unrecognised synanthropic sites, some remarks and observations concerning morphological features and phenological properties of this taxon in field conditions were included.
Dispersal distance and burial mode of acorns are two of the most important characteristics in renewal processes of oaks that result from the food hoarding ecology of the Eurasian Jay Garrulus glandarius. To obtain the dispersal distance and to locate precisely the caches with scattered acorns we used radio-tracked transmitters with flexible 13 cm long sticking out antennae injected into drilled acorns. From mid-September to mid-October acorns of Pedunculate Oak Quercus robur with transmitters were mixed with untagged acorns and exhibited on five feeders distributed from each other at a distance of at least 1.3 km (max. 3.8). We obtained information on 121 tagged acorns scattered by Jays in two consecutive years (2014 - 42 records, 2015 - 79 records). For both seasons, mean dispersal distance was 115.7 metres (SE = 9.2). The maximum detected distance was 456 m, the minimum was 3 m. Most of the acorns (52.6%) were deposited by Jays up to 100 m from the source. Dispersal distance differed significantly between the two years of research and between feeders. Mean dispersal distance was much higher in 2014 (166 m, N = 42) than in 2015 (86 m, N = 72) and differed between seasons while the seed crop was similar and low. Only four acorns (3.5%) were found on the litter with no signs of hiding, which suggests accidental loss during transport (dyszoochory). Most of the cached acorns (44.6%) were deposited in the Scots Pine Pinus silvestris litter or moss cushions no deeper than 0.5 cm. The additional covering of caches with pieces of bark or leaves were noted accidentally in nine cases (9.8%).
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