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

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.
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 (Pykälä 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;
Niemelä 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.