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ŠUMARSKI LIST 5-6/2022 str. 51     <-- 51 -->        PDF

abundance of spring ephemeral geophytes; however, a general impression persists that it has exerted only a minor impact, if any, on native species diversity (Hejda, 2012). Impatiens parviflora is a very successful invasive plant with the ability to extend its range extremely rapidly. It is able to form dense stands even in undisturbed forests with a closed canopy (CABI, 2020b). The seeds are dispersed by birds or other animals and by water; however, they can also be dispersed by humans during the transport of contaminated soil and timber (CABI, 2020b).
Data collection – Prikupljanje podataka
We surveyed the occurrence of native and alien plant species in Illyrian oak-hornbeam forest patches: 25 on Apaško polje and 23 on Dravsko polje. Detailed flora inventarisation was performed by recording vascular plants during the exploration of each entire forest patch. To ensure the maximum coverage of species in a patch we recorded species in the entire patch perimeter (edge), along existing walking paths inside the forest patch, and finally by crossing each forest patch diagonally for additional accuracy. For patches with larger area, we increased the inventarization effort comparably. We recorded the presence of all vascular plants found in each patch and classified them as native or alien according to Martinčič et al. (2007) and Jogan et al. (2012). Based on the native species composition of each patch, environmental characteristics including nutrients, moisture, light and temperature were estimated from mean Ellenberg`s species indicator values (Table 1; Ellenberg et al., 1992).
Patch landscape metrics were determined using ArcGIS (Table 1; ESRI, 2014). We measured the perimeter and area on satellite images. Additionally, we extracted land use shares in a 200 m buffer around each forest patch from Corine Land Cover 2018 (CLC) data layer (EEA, 2018) and categorised these as follows: urban areas, roads, arable land, forest area and meadows. To obtain patch complexity, we calculated the patch indices P/A ratio and SHPI. P/A ratio is determined as the perimeter (p) – area (a) ratio ( P/A ratio = p/a, P/A ratio > 0) and SHPI (Patton 1975) as SHPI =p/(2(√πa), SHPI > 1).
Variables indicating human pressure were determined at the time of flora sampling in terms of the presence of any sort of waste (household waste, bulky waste), garden waste or walking paths in the forest patch (Table 1). These variables have been chosen because alien plant propagules can be introduced into the studied forest patches with waste, especially garden waste (Šipek and Šajna, 2020 and references therein). Additional human presence was indicated by the presence of walking paths in a patch, since paths can serve as corridors for the spread of alien plants propagules attached to clothing (anthropochory). Other human related disturbances such as tree felling were not carried out in the time of recording.
Data analysis and modelling – Analiza i modeliranje podataka
Patch metrics for each patch and land cover shares in the 200 m buffer surrounding each patch as well as environmental characteristics obtained as mean Ellenberg`s species indicator values for native flora belonged to continuous variables (Table 1). They were compared between forest patches where the species of interest was present or absent using the stat_compare_means function and method t-test in package “ggpubr”.