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

Abstract

Nutrient-poor grasslands are considered regional biodiversity hotspots and therefore of high conservation value (Blab & Kudrna 1982; Bignal & McCracken 1996; Sanchez-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. These results emphasize the high conservation value of Transylvanian steppe-like grasslands and their seral stages of abandonment. Since each of the four taxonomic groups reacted differently to grassland abandonment, a mosaic consisting of extensively grazed areas and the grassland's seral stages of succession should be preserved. The second chapter analyses the effects of abandonment and manmade habitat alterations of steppe-like grasslands only on diurnal and nocturnal Lepidoptera communities considering the xerophilous character of the typical species of these habitats and their Red List status. Like the species richness and diversity of diurnal Lepidoptera the number of xerophilous and Red List species peaked in later successional stages with bushes and in abandoned vineyards and was low in forests and Pinus plantations. In contrast, xerophilous and Red List species of moths showed their highest richness in early successional stages, emphasizing also the significance of this successional stage for conservation. Species richness, diversity, xerophilous and Red List species were not correlated between diurnal and nocturnal Lepidoptera. Correspondence analyses (DCA) and classifications after Renkonen revealed for both diurnal and nocturnal Lepidoptera a clear separation between forests, Pinus plantations and the rest of the vegetation types. In contrast to diurnal Lepidoptera, classification of nocturnal Lepidoptera showed another important feature, as it clustered successional stages and abandoned vineyards according to locality in the first place, emphasizing the importance of regionally. The observed species reactions confirm that diurnal Lepidoptera react strongly to environmental change and hence are good indicators of habitat change. Several specific diurnal Lepidoptera like Pseudophilotes bavius hungaricus, endemic to Transylvania's steppe-like grasslands, Muschampia cribrellum and M. tesselum, typical xerotermophilous species, would require special conservation attention, since they occur just in highly isolated, relic populations. The investigated habitat types are also relevant as potential recolonization sources for areas where some species (e.g. Chazara briseis) are highly threatened and have dramatically declined. The response of plants, gastropods and diurnal and nocturnal Lepidoptera to abandonment of hay meadows in subalpine semi-natural grasslands in Transylvania was different too (chapter three). Each stage of succession harbored the maximum species richness for one taxonomic group: extensive hay meadows for vascular plants, abandoned hay meadows for diurnal Lepidoptera, birch forest for nocturnal Lepidoptera and mature forests for gastropods. Similar to the results from the steppe-like grasslands, no decline in plant species richness in early successional stages was recorded, due to a delayed succession and/or a small scale mosaic of abiotic conditions. A high structural diversity found in later successional stages favors the diversity of invertebrates. The number of red listed plant and diurnal Lepidoptera species was not correlated with successional age. Similar results were found in a study on plants in semi-natural grasslands in Finland (Pykala et al. 2005). In contrast to open-land species, the number of red-listed nocturnal Lepidoptera species increased with successional age. This study showed too that one taxonomic group is a poor indicator for the overall diversity (Baur et al, 1996; Niemela and Baur 1998). These results show the high conservation value of subalpine hay meadows and their seral stages of abandonment in Transylvania. The fourth chapter describes the effect of intensified grazing on plants and gastropods in the alpine grasslands in two areas of the Southern Carpathians (Bucegi, calcareous, and Fagaras, silicious mountains). Alpine grasslands in the Southern Carpathians harbor an extraordinary high diversity of plants and invertebrates, including Carpathic endemics, which are now threatened by the high grazing pressure. Our study showed that plant and gastropod species richness are reduced in grazed sites compared with sites only occasionally grazed by wildlife in the Bucegi mountains. The effects of intensive sheep grazing on plant and gastropod communities were less pronounced on the acid soils of the Fagaras mountains. This is due to the fact that plants and gastropods are generally less species rich on acidic soil. However the species composition and abundance in plants were altered in a particular way, suggesting that intensive sheep grazing affects the vegetation composition also on silicious bedrock. Grazed and ungrazed sites did not differ in the proportion of endemic plants and gastropods, but total cover of Carpathic endemic plants was reduced in grazed sites in the Bucegi mountains. This might be explained by the fact that different endemic plant and gastropod species react differently to grazing pressure. Our study confirms the high biodiversity of alpine grasslands and shows the detrimental effects of intensified sheep grazing. General conclusion The present thesis documents the high biodiversity of semi-natural grasslands and their successional stages of abandonment at different altitudes: lowland steppe-like grasslands, subalpine mown meadows and alpine pastures in Transylvania, Romania. Not only early but also late successional stages seem to be of high conservation value due to the high species diversity found and their composition in open-land, endemic, xerophilous and red-listed species. Climax forests are less diverse and harbor less endemic and threatened species. Investigated taxonomic groups differed in their responses to the abandonment of semi-natural grasslands in lowland steppe-like grasslands and subalpine meadows. Thus one taxonomic group is a poor indicator for the overall diversity. The abandonment of formerly extensively used vineyards resulted in a highly precious habitat, with high diversity and many threatened, endemic and red-listed species. The Pinus plantations have changed the habitat quality and will have a devastating effect on the unique and indigenous diversity of steppe-like grasslands as soon as the canopy closes. This thesis also shows that the intensification of sheep grazing is a major threat to diversity and to endemic and threatened species of plants and gastropods in alpine pastures in Fagaras and Bucegi mountains.