Abstract
The paper focuses on a research carried out during two consecutive growing seasons (2011 and 2012) in a willow tree stand (Salix schwerinii × S. viminalis, variety Tordis) and a grass stand of miscanthus (Miscanthus × giganteus Greef et Deuter). Both of the species can be used for energy production. The evaluation was carried out in a research centre located in Kolíňany (Nitra district area, SW Slovakia). Biodiversity of the ground flora within the two crops stands was jointly assessed through the multivariate statistical method of Principal Components Analysis (PCA). The results showed that almost all spontaneous vascular plant species have a weedy character, they have no specific environment requirements, they are stress tolerant, and their propagules are often present in agricultural ecosystems or in vegetation of rural landscape (field margins, strip boundaries, abandoned fields, orchards, etc.). Good examples of synanthropic species observed in the stands are Cirsium arvense, Equisetum arvense, Convolvulus arvensis etc., while several other typical species of usually non-synanthropic, habitats, e.g. Symphytum officinale, Persicaria lapathifolia, Calystegia sepium were also observed. Many juvenile shrub and wood species occurring in E1 and E2 layers also belonged to the semi-natural vegetation, e.g. Sambucus nigra, Rosa canina agg., Crataegus laevigata. The presence of potentially invasive and expansive plant species is evaluated as a negative factor.