Effects of grassland management on plants and invertebrates in Transylvania, Romania : a threat to local biodiversity hotspots

摘要

Nutrient-poor grasslands are considered regional biodiversity hotspots and therefore of high conservation value (Blab & Kudrna 1982; Bignal & McCracken 1996; Sánchez-Zapata et al. 2003). Nutrient-poor grasslands in Transylvania and the Carpathians, Romania, harbor a variety of endemic and sub-endemic species of plants and invertebrates which are threatened by non-sustainable agriculture or abandonment. The aim of this thesis was to investigate biodiversity and species compositions in traditionally cultivated grasslands and to compare it with that of intensified and abandoned grasslands in Romania in three different regions of Transylvania: lowland steppe-like grasslands, the subalpine region and the alpine region of the southern Carpathians. In order to give a more accurate picture of the diversity in these regions we investigated not only one taxonomic group, but four: vascular plants, terrestrial gastropods and diurnal and nocturnal Lepidoptera. Another aim of this study was to foresee future development of the investigated grasslands as a consequence of political change, and to suggest management strategies and programs to prevent the loss of precious semi-natural habitats. Chapter one describes the species richness, species abundance, proportion of open-land, endemic and threatened vascular plants, gastropods, and diurnal and nocturnal Lepidoptera in six different vegetation types (extensively used pastures and their early and late successional stage of abandonment, climax forest and two man-made habitat alterations, abandoned vineyards and Pinus plantations) all originating from steppe-like grasslands in Transylvania, Romania. We found a high plant and invertebrate species richness in the investigated steppe-like grasslands and their seral stages of abandonment. In climax forests, the final stage of natural grassland succession, diversity of all groups of organisms examined was significantly reduced. Furthermore, many of the rare and threatened grassland species of plants and Lepidoptera were replaced by common mesophilous species because of the reduced light. The abandonment of the extensively used vineyards created a valuable habitat for plants and invertebrates. Pinus plantations (a recent grassland alteration) have changed habitat quality and will have a devastating effect on the unique, indigenous diversity of these steppe-like grasslands as soon as the canopy closes. Effects of patch scale variable (i.e., habitat characteristics, including the type of grassland management, abandonment, and afforestation) were pronounced on the species richness and abundance of the investigated invertebrate groups. The proportion of open-land plant and gastropod species, that are of primary concern in Romania (loras 2003) decreased with successional age. All investigated vegetation types harbored threatened species. Endemic species were found in all vegetation types except mature forests and Pinus plantations. The four taxonomic groups differed in their response to the abandonment of steppe like grassland, except that species richness of plants and diurnal Lepidoptera were positively correlated. This confirms the study of Hawkins and Porter (2003). They concluded however, that plant diversity does not directly influence butterfly diversity but that both groups of organisms respond to similar environmental conditions.ududThese results emphasize the high conservation value of Transylvanianudsteppe-like grasslands and their seral stages of abandonment. Since each ofudthe four taxonomic groups reacted differently to grassland abandonment, audmosaic consisting of extensively grazed areas and the grassland's seraludstages of succession should be preserved.udThe second chapter analyses the effects of abandonment and manmadeudhabitat alterations of steppe-like grasslands only on diurnal andudnocturnal Lepidoptera communities considering the xerophilous character ofudthe typical species of these habitats and their Red List status.udLike the species richness and diversity of diurnal Lepidoptera the numberudof xerophilous and Red List species peaked in later successional stages withudbushes and in abandoned vineyards and was low in forests and Pinusudplantations. In contrast, xerophilous and Red List species of moths showedudtheir highest richness in early successional stages, emphasizing also theudsignificance of this successional stage for conservation. Species richness,uddiversity, xerophilous and Red List species were not correlated betweenuddiurnal and nocturnal Lepidoptera. Correspondence analyses (DCA) andudclassifications after Renkonen revealed for both diurnal and nocturnaludLepidoptera a clear separation between forests, Pinus plantations and the restudof the vegetation types. In contrast to diurnal Lepidoptera, classification ofudnocturnal Lepidoptera showed another important feature, as it clusteredudsuccessional stages and abandoned vineyards according to locality in the firstudplace, emphasizing the importance of regionally. The observed speciesudreactions confirm that diurnal Lepidoptera react strongly to environmentaludchange and hence are good indicators of habitat change. Several specificuddiurnal Lepidoptera like Pseudophilotes bavius hungaricus, endemic toudTransylvania's steppe-like grasslands, Muschampia cribrellum and M.udtesselum, typical xerotermophilous species, would require specialudconservation attention, since they occur just in highly isolated, relicudpopulations. The investigated habitat types are also relevant as potentialudrecolonization sources for areas where some species (e.g. Chazara briseis)udare highly threatened and have dramatically declined.udThe response of plants, gastropods and diurnal and nocturnal Lepidopteraudto abandonment of hay meadows in subalpine semi-natural grasslands inudTransylvania was different too (chapter three). Each stage of successionudharbored the maximum species richness for one taxonomic group: extensiveudhay meadows for vascular plants, abandoned hay meadows for diurnaludLepidoptera, birch forest for nocturnal Lepidoptera and mature forests forudgastropods. Similar to the results from the steppe-like grasslands, no declineudin plant species richness in early successional stages was recorded, due to auddelayed succession and/or a small scale mosaic of abiotic conditions. A highudstructural diversity found in later successional stages favors the diversity ofudinvertebrates. The number of red listed plant and diurnal Lepidoptera speciesudwas not correlated with successional age. Similar results were found in audstudy on plants in semi-natural grasslands in Finland (Pykälä et al. 2005). Inudcontrast to open-land species, the number of red-listed nocturnal Lepidopteraudspecies increased with successional age. This study showed too that oneudtaxonomic group is a poor indicator for the overall diversity (Baur et al, 1996;udNiemelä and Baur 1998). These results show the high conservation value ofududsubalpine hay meadows and their seral stages of abandonment inudTransylvania.udThe fourth chapter describes the effect of intensified grazing on plantsudand gastropods in the alpine grasslands in two areas of the SouthernudCarpathians (Bucegi, calcareous, and Fagaras, silicious mountains). Alpineudgrasslands in the Southern Carpathians harbor an extraordinary high diversityudof plants and invertebrates, including Carpathic endemics, which are nowudthreatened by the high grazing pressure.udOur study showed that plant and gastropod species richness are reducedudin grazed sites compared with sites only occasionally grazed by wildlife in theudBucegi mountains. The effects of intensive sheep grazing on plant andudgastropod communities were less pronounced on the acid soils of the Fagarasudmountains. This is due to the fact that plants and gastropods are generallyudless species rich on acidic soil. However the species composition andudabundance in plants were altered in a particular way, suggesting that intensiveudsheep grazing affects the vegetation composition also on silicious bedrock.udGrazed and ungrazed sites did not differ in the proportion of endemic plantsudand gastropods, but total cover of Carpathic endemic plants was reduced inudgrazed sites in the Bucegi mountains. This might be explained by the fact thatuddifferent endemic plant and gastropod species react differently to grazingudpressure.udOur study confirms the high biodiversity of alpine grasslands and showsudthe detrimental effects of intensified sheep grazing.udGeneral conclusionudThe present thesis documents the high biodiversity of semi-naturaludgrasslands and their successional stages of abandonment at differentudaltitudes: lowland steppe-like grasslands, subalpine mown meadows andudalpine pastures in Transylvania, Romania. Not only early but also lateudsuccessional stages seem to be of high conservation value due to the highudspecies diversity found and their composition in open-land, endemic,udxerophilous and red-listed species. Climax forests are less diverse and harborudless endemic and threatened species.udInvestigated taxonomic groups differed in their responses to theudabandonment of semi-natural grasslands in lowland steppe-like grasslandsudand subalpine meadows. Thus one taxonomic group is a poor indicator for theudoverall diversity.udThe abandonment of formerly extensively used vineyards resulted in audhighly precious habitat, with high diversity and many threatened, endemic andudred-listed species.udThe Pinus plantations have changed the habitat quality and will have auddevastating effect on the unique and indigenous diversity of steppe-likeudgrasslands as soon as the canopy closes.udThis thesis also shows that the intensification of sheep grazing is a majorudthreat to diversity and to endemic and threatened species of plants andudgastropods in alpine pastures in Fagaras and Bucegi mountains.