Hübriidhaavikute alustaimestik endises Aidu põlevkivikarjääris

Loodusliku mitmekesisuse säilimiseks ja negatiivsete keskkonnamõjude vähendamiseks on soovitatav ammendunud karjäärid metsastada. Leitakse, et männi kõrval, mis on üldiselt levinud puuliik karjääride metsastamisel, võiks istutada ka lehtpuid. Hübriidhaab (Populus tremula L. × P. tremuloides Michx.) võiks olla sobilik puuliik karjääride metsastamisel, sest põllumajandusmaal kasvab ta kiirelt ning on suure tootlikkusega. Käesolevas töös analüüsiti endisesse Aidu põlevkivikarjääri rajatud 21-aastaste hübriidhaavikute alustaimestikku (rohu-ja samblarinnet). Hübriidhaavikud kasvasid kas tasandatud puistangul või pealeveetud huumuskattega alal. Kontrolliti hüpoteesi, et kahe taastamisviisi vahelised erinevused taimestiku liigilises koosseisus ja taimestiku tunnustes on märgatavad ka 21-aastases puistus, ent samas on alustaimestikus toimunud mõlema taastamisviisi korral sarnased muutused, võrreldes eelmise monitooringuga keskealistes hübriidhaavikutes. Välitööde käigus koguti andmed 28 taimestiku püsiprooviruudult, millest 16 asusid puistangu alal ja 12 pealeveo alal. Ruudu suurus oli 4 m2 . Saadud andmeid võrreldi 2013. aastal kogutud andmetega. Töö tulemustest selgus, et pealeveo alal oli suurem taimestiku üldkatvus võrdluses puistangu aladega. Samuti kasvas pealeveo ala puutüvedel rohkem samblaliike. Lisaks taastamisviisile mõjutas alustaimestikku ka võrastiku avatus. Kokku leiti katsealadelt 64 soontaimeliiki, 41 samblaliiki maapinnalt ja 19 samblaliiki tüvedelt, mis näitab, et tegemist on liigirikka alaga. Puistangu ja pealeveo alade rohu- ja samblarindes olid koosseisulised erinevused. Võrreldes 2013. aasta taimestiku andmetega olid nii puistangu kui pealeveo alade taimestikus toimunud sarnased muutused, nagu maapinna ja tüve samblaliikide arvu suurenemine ja rohurinde üldkatvuse vähenemine. Rohurinde üldkatvus kahanes tugevamalt pealeveo alal, mis on seletatav tugevama valgus- ja juurkonkurentsiga rohu- ja puurinde vahel.

To maintain biological diversity and to reduce negative impacts on environment, it is recommended to restore reclaimed quarries as forests. It is found that in addition to Scots pine, which is generally used for afforestation in quarries, other deciduous trees should be planted as well. Hybrid aspen (Populus tremula L. × P. tremuloides Michx.) could be a suitable tree species for afforestation on quarry spoils, because it grows rapidly on former agricultural lands and produces a lot of biomass. The main aim of this master’s thesis was to analyse understorey vegetation cover (vascular plants and bryophytes) in 21-year-old hybrid aspen stands in reclaimed Aidu oilshale quarry. Hybrid aspens were planted either directly to the levelled quarry spoil or to another site where levelled quarry spoil was covered with previously removed topsoil. It was hypothesized that the differences in vegetation cover and vegetation diversity between the two restoration methods were noticeable in the 21-year-old stands, but at the same time similar changes had occurred in the understorey vegetation compared to the previous monitoring in middle-aged hybrid aspen plantations. Data were collected during fieldwork from 28 experimental vegetation plots. 16 vegetation plots were situated in levelled quarry spoil and 12 in site covered with soil. The size of a plot was 4 m2 . The obtained data were compared to the data collected in 2013. The results showed that area with covered soil had higher vegetation coverage compared to the quarry spoil area. There were also more bryophyte species growing on tree trunks in site covered with soil. In addition to restoration method the openness of canopy also affected understorey vegetation. Altogether 64 vascular plant species, 41 bryophyte species on the ground and 19 bryophyte species on tree trunks were found in the study area, indicating that the area hosts high species richness. There were compositional differences between quarry spoil and covered soil areas in the vascular plant layer and in the bryophyte layer. In comparison with data from 2013, similar changes took place in vegetation characteristics in both areas, such as an increase in the number of bryophytes on the ground and on tree trunks and a decrease in the total coverage of field layer. The total coverage of filed layer decreased more in areas covered with soil than in quarry spoil area, that can be explained by the stronger light and root competition between field and tree layer