Iveta Škodová

The diversity of planted forest stands of the alien species Quercus rubra L. in Central Europe was studied. The northern red oak is a neophyte that has been cultivated in Europe since the seventeenth century as an ornamental as well as a useful tree. In 38 phytosociological relevés from Slovakia, Poland and the Czech Republic, we recorded a total of 223 vascular plant taxa, of which 10% were alien (with 9 invasive species). The stands were species-poor compared to the most native forests, with an average of 17 species per relevé, and most of the species had a low coverage value (around 5% on average). The representation of endangered species was very low, only three species were recorded. The dense canopy of Q. rubra and large cover of litter consisting mainly of fallen old red oak leaves affected the richness of the undergrowth. The mean cover of the tree layer was 84%, the mean cover of the shrub layer was 9% and the mean cover of the herb layer was 22%. The EuroVegChecklist Expert System assigned the relevés to five classes: Carpino-Fagetea sylvaticae, Alno glutinosae-Populetea albae, Rhamno-Prunetea, Epilobietea angustifolii and Robinietea.

Arable fields are among the most widespread habitats in Slovakia, but recently, there have been no studies regarding species composition and structure of weed vegetation in these fields. Therefore, we studied the structure of arable weed vegetation and detected α- and β-diversity. The dataset of 507 phytosociological relevés in different crop types contains 407 plant taxa in 46 plant families. Native plants dominated over aliens, archaeophytes dominated over neophytes, and 14 plants belonged to invasive taxa. The most common species in the dataset were Tripleurospermum perforatum, Cirsium arvense, and Viola arvensis. Weeds were mostly therophytes, b- and a-euhemerobic, competitors, and ruderals, reproducing by seeds and pollinated by insects. The β-diversity of weed vegetation decreased with elevation and temperature and was higher in the Pannonicum than the Carpaticum region. The highest β-diversity was established in fodder+fallow fields, followed by that in cereals and root-crop fields, and the smallest diversity was found in stubble. Beta-diversity increased from spring to summer and slightly decreased again in fall. Detrended correspondence analysis indicated that the major compositional turnover of weed vegetation was related to light, temperature, moisture, and elevation. Weed vegetation constitutes an important habitat in the landscape that provides refuge to many threatened plants, and this vegetation has important functions in the agro-ecosystem food chain.

The cover of introduced tree species in Europe has recently increased, due to several factors. Attempts to understand the impact of non-native edificator trees on the environmental conditions and diversity of undergrowth have so far been limited to a few studies. In this paper, we analyse the effect of one of the most commonly planted non-native tree species–black pine (Pinus nigra J. F. Arnold) in the Carpathian-Pannonian region, north of the border of its native occurrence. The objectives of our study were to determine the following: (i) How does black pine, as a non-native edificator, change the forest structure and environmental conditions in comparison to those of native communities? (ii) How does black pine change the species composition of undergrowth in comparison to that of native communities? (iii) Which factors are associated with the impact of black pine on diversity? To answer these questions, we used the twin plot method, sampling two neighbouring plots with the same environmental conditions in which one plot of the pair is in a forest with native tree species composition and the second plot is in a planted non-native Pinus nigra plantation. We found that in forests dominated by the non-native black pine, (a) the tree canopy is significantly more open; (b) the cover of the shrub layer is significantly higher; (c) the needles of black pine form a significantly thicker litter layer and (d) the cover of the herb layer is significantly lower than that in the native forest. (e) Black pine plays a vital role in modifying local climate by altering air temperature and humidity; (f) there were no significant differences in the soil pH between black pine plantations and native forests; (g) the plantations of black pine cause changes in diversity at both the species and the community level and (h) the dissimilarity between black pine plantations and neighbouring native forests decreases at higher altitudes.

Replacing native forests by alien tree plantations can lead to changes in the species composition of the understory. However, differences in the understory species spectrum can also be a part of the natural variability of forest stands. We have tested the suitability of the twin plots method for an evaluation of the impact of alien trees on the species composition of the understory. This research was conducted on an alluvial plain (SW Slovakia) that was originally covered by a hardwood floodplain forest. The study was based on 7 twin plots of black locust (Robinia pseudoacacia) and native forest plots, with a maximum distance of 100 meters between the members of the twins. The dissimilarity of the plots within the black locust forest was significantly lower than the dissimilarity between the twin plots. In addition, the dissimilarity of the plots within the hardwood floodplain forest was also significantly lower than the dissimilarity between the twin plots. Under the same environmental conditions, the higher dissimilarity of the twin plots was caused by major edificators and their impact on the understory vegetation. The twin plots method proved to be a suitable tool for analyses of the impact of alien trees on understory vegetation.