Orthopteran assemblages in early succession stages of clear–cuts and grasslands in fragmented beech forests

Ústav ekológie lesa, Slovenská akadémia vied, Štúrova 2, 960 53 Zvolen, Slovakia [asliacka@savzv.sk; kristin@savzv.sk]

Received 9 August 2012 ~ Accepted 24 October 2012 ~ Published 16 December 2012

Abstract

Fragmented forest landscape is composed from a variety of habitats influenced by succession. Deforested plots, showing distinct differences from the surrounding forests, were colonised by heliophilous insects, such as orthopterans. We studied the structure of Orthoptera assemblages in four clear–cuts and in four forest grassland habitats in two mountains of Central Slovakia. The Orthoptera were recorded by the sweeping method at monthly intervals in May – October 2010. Our research aims were to find out i) which species were able to colonise new–established deforested plots in deciduous forests dominated by beech, ii) differences in Orthoptera assemblage structure between the clear–cuts and grasslands (assumed main source habitats for clear–cut colonisation). Altogether 27 Orthoptera species were recorded in the one– and two–year–old clear–cuts, while only 21 in the grasslands. In the clear–cuts was evident dominance of Caelifera, while in the grasslands, the proportions of Ensifera and Caelifera were nearly the same. There were distinct differences in the species composition, abundance and frequency in Orthoptera assemblages structure between the grasslands and clear–cuts. Just 90.5% of the grassland species were also recorded in the clear–cuts, while only 70.4% species from the clear–cuts we also found in the grasslands. The clear–cuts were colonised by several grassland species and species of bare ground. The species composition of clear–cuts and grasslands varied among the localities, probably due to different clear–cut age, microclimate and vegetation structure in the two habitats.

Key words

Ensifera, Caelifera, deforestation, heliophilous insects, central Europe.

Dispersional patterns of orthopterans in forest complexes and also in fragmented forest landscape with small patches of grasslands, is facilitated by the presence of ecotones, corridors and scattered shrub and tree greenery (Guido & Gianelle 2001; Deans et al. 2005). The number of Orthoptera species generally increases with the size of forest meadows and clear–cuts (Krištín & Hrúz 2005; Theuerkauf & Rouys 2006). However, also small meadows and pastures can provide appropriate amounts of food and favourable conditions promoting the reproduction of heliophilous orthopteran species (Marini et al. 2008; Fabriciusová et al. 2011). On the other hand, big forest grasslands are often exposed to disturbances such as mowing and grazing (Báldi & Kisbenedek 1999).

In case when the grasslands adjacent to forests are managed in an extensive way, the local orthopterans recede in refuges in the forest ecotones. The succession of forest vegetation at margins of forest grasslands acts, up to the certain moment, positively on the species composition in Orthoptera (Marini et al. 2009a, b; Fabriciusová et al. 2011; Fartmann et al. 2012). Encroaching of forest meadows with woody plants has reducing effect on the size of permanent grasslands and may even lead to extinction of small forest meadows serving as important refuges for rare species (Gavlas 2003; Krištín & Hrúz 2005). Deforested plots created by forest disturbances in mixed (Laußmann 1993; Dalbeck 2011) and coniferous forests (Bergmann & Chaplin 1992; Clayton 2002; Jenni et al. 2007) were colonised by heliophilous Orthoptera. Little is known about habitat–associated (clear–cuts, grasslands) differences in the orthopteran assemblages in fragmented deciduous forests.

In this study we investigated: i) which species are able to colonise deforested plots in deciduous forests with dominant beech; ii) whether there are differences in the structure of Orthoptera assemblages between clear–cuts and grasslands in fragmented beech forests.

We assumed: a) less species in the clear–cuts (aged 1–2 years) than in the grasslands (expected main source habitats for clear–cuts colonisation); b) Ensifera more abundant in the deforested areas than in the grasslands; c) similar species phenology (seasonality in occurrence) in the clear–cuts and the grasslands.

The study plots were situated in deciduous forests with dominance of beech (> 70%) in the Kremnické vrchy Mts and the Javorie Mts (Western Carpathians, Central Slovakia). In each mountain region, there were established two west–facing research plots in clear–cuts (aged 1–2 years) and two in grasslands, as the potential main source habitats for colonisation of the clear–cuts. The clear–cuts were in the direct contact with forest roads, and at the same time, isolated with min. 50 m wide forest from the surrounding grassland and open habitats. The clear–cut pairs (in each locality) exhibited only minimal differences in their abiotic characteristics (age, size, aspect, altitude). Each grassland pair in each mountain unit was situated in one valley, to guarantee similar vegetation structure and abiotic characteristics (Fig. 1).

The clear–cuts in the Kremnické vrchy Mts (48° 38’ 19” N; 19° 4’ 3” E; CC1, CC2; 486–541 m a. s. l.; 8,580 m2 and 9,174 m2; Fig. 1) were created by cutting in April – May 2009 applied in a 100–year–old beech ecosystem with admixed Abies alba. In September 2010, the plot was grown with natural regeneration (Fagus sylvatica, Carpinus betulus, Tilia spp., with an average height of 45 cm) covering 50–70% of the area of the two clear–cuts. Herbs and grasses (15–40 cm) covered 10–30%. The rests were bare soil plots or low vegetation under 10 cm (5–20%). In August, the vegetation reached (e.g. species of the genus Cirsium spp.) a maximum height of 130–170 cm.

The grasslands (GR1 and GR2; 328–362 m a. s. l.; each 10,000 m2; Fig. 1) were at one side adjacent to the forest. The plot GR1 was primarily characterised with the species Thymus vulgaris, Argimonia eupatoria, Vicia cracca, Dianthus carthusianorum, Euphorbia cyparissias, Achillea millefolium, Hypericum perforatum, Fragaria spp., Potentilla erecta, Trifolium medium, Galium verum, Trifolium arvense, Clinopodium vulgare, Knautia arvensis, Centaurea scabiosa, Lotus corniculatus, Carex hirta, Festuca rubra, Anthericum ramosum. From the shrubs, typical was the presence of Juniperus communis, Rosa canina, Prunus spinosa.

The vegetation on plot GR2 mainly consisted of the species Galium verum, Clinopodium vulgare, Argimonia eupatoria, Euphorbia cyparissias, Potentila spp., Plantago major, Cichorium intybus, Plantago lanceolata, Fragaria spp., Thymus vulgaris, Knautia arvensis, Daucus carota, Ononis spinosa, Centaurea phrygia, Achillea millefolium, Polygala vulgaris, Allium oleraceum, Vicia cracca, Cirsium arvense, Calamagrostis epigeios, Alopecurus pratensis, Brachypodium pinnatum, Agrostis capillaris, Carex hirta, Dactylis glomerata, Convolvulus arvensis, Arrhenatherum elatior, Trisetum flavescens. The plot edge was created by a stand of Pinus sylvestris. The height of vegetation on GR1 and GR2 was max 60 cm, as the stands were grazed by cattle and mowed once a year. The meadows were situated 2400–2900 m southeast from the studied clear–cuts (Fig. 1).

The clear–cuts in the Javorie Mts were created by deforestation in January – February 2010 (48° 31’ 38” N; 19° 15’ 48” E; CC3–CC4; 459–520 m a. s. l.; 13,188 m2 and 11,149 m2; Fig. 1). The original forest consisted of Fagus sylvatica (75%), Quercus spp./Carpinus betulus oak/hornbeam (25%) without developed herb understorey. The regeneration (oak/hornbeam/beech) tall on average 50 cm covered 30–50% of the clear–cut area. Herbs and grasses tall 15–150 cm were present on 20–40% of the area. The areas without vegetation cover and with vegetation lower than 10 cm made 10–50%.

The grasslands of a large forest meadow (ca 3 ha; western part of the meadow GR3, valley, eastern part of the meadow GR4; 478–497 m a. s. l.; ca 20,000 and 30,000 m2; Fig. 1) in oak–hornbeam forests were managed by mowing (July 2010). The meadows were situated west from clear–cuts and there were isolated with a wide (80–200 m) forest stand. In the year 2010, these meadows were rather flooded, due to very high precipitation amount. For these two grasslands were characteristic the species Sanguisorba minor, Hypericum perforatum, Euphorbia cyparissias, Galium verum, Calamagrostis epigejos, Centaurea phrygia, Mentha spp., Prunella vulgaris, Lysimachia vulgaris, Alopecurus pratensis, Agrostis capillaris, Daucus carota, Helictotrichon pubescens, Juncus effusus, Potentilla erecta, Alopecurus spp., Carex spp., Dianthus carthusianorum, Achillea millefolium, Luzula campestris, Lotus corniculatus, Cruciata glabra, Lysimachia nummularia, Leontodon hispidus, Trifolium medium, Campanula patula, Holcus lanatus.

Orthoptera were collected (and released) at one–month intervals in May – October 2010 (always towards the end of month), by sweeping throughout vegetation (Gardinger et al. 2005). We used (250 sweepings/plot/visit) a sweeping net with a solid protective frame, circle–shaped, 35 cm diameter. The sweeping line was driven across a wide spectrum of microhabitats, representative for each clear–cut and grasslands: grasses, herbs, Rubus spp., shrubs (natural regeneration of clear–cuts, grassland ecotones) and bare soil in clear–cuts. We registered all captured individuals, and individuals identified visually and acoustically under the sweeping net.

During the season 2010, on all eight plots, we caught altogether 2,497 orthopterans, from which we identified 2,177 individuals belonging to 29 species (Table 1). The Orthoptera were identified and classified according to Kočárek et al. (2005). Not identified individuals were young nymphs of the genus Tettigonia (2), Tetrix (131) and nymphs Acrididae, especially the genus Chorthippus (187).

We evaluated the following parameters: the numbers of Orthoptera, Ensifera and Caelifera species, total abundance from six collections, relative frequency of the species on four grasslands and four clear–cuts (Fig. 2), seasonal variations in the species number in all clear–cuts and in all grasslands (mean ± SD; Fig. 3).

Figure 1. Position of four clear-cuts (CC1–CC4) and four grasslands (GR1–GR4) in beech forests in two mountains in Central Slovakia.

The total Orthoptera species number recorded in clear–cuts and grasslands in fragmented beech forests during one year was 29 (14 Ensifera, 15 Caelifera). In the clear–cuts were found 27 Orthoptera species (12 Ensifera, 15 Caelifera), in the grasslands 21 (11 Ensifera, 10 Caelifera). On the clear–cuts dominated Caelifera species, in the grasslands with dispersed shrub vegetation the proportions of Ensifera and Caelifera were very similar.

The Orthoptera species composition showed differences among the habitats (Table 1). In the clear–cuts, there occurred eight species not recorded in the grasslands (Meconema thalassinum, Pholidoptera aptera, Platycleis grisea, Tetrix undulata, Chorthippus albomarginatus – 1 individual, Chorthippus vagans, Calliptamus italicus and Oedipoda caerulescens). In the clear–cuts, there occurred additional grassland species characteristic also for the studied grass stands, such as Metrioptera roeselii, Gryllus campestris, Euthystira brachyptera, C. albomarginatus, Chorthippus apricarius, Chorthippus dorsatus, Chorthippus parallelus, Chrysochraon dispar, Stenobothrus lineatus. The species we have recorded altogether in the clear–cuts represented 90.5% of the species recorded in the grasslands. In the clear–cuts in the Kremnické vrchy Mts (CC1, CC2) we recorded 25 species from which eight were absent in the clear–cuts in the Javorie Mts (CC3, CC4; Table 1). In the clear–cuts in Javorie we observed 19 species with two (Tettigonia viridissima, M. roeselii) lacking in the clear–cuts in the Kremnické vrchy Mts (Table 1).

In the grasslands we found only 70.4% of the species found also in the clear–cuts. The species Leptophyes albovittata and Metrioptera bicolor were recorded only in the grasslands (Table 1). In the grasslands in the Kremnické vrchy Mts we recorded 21 species, in the Javorie Mts 16 species. The species L. albovittata, M. bicolor, Tetrix subulata, Tetrix tenuicornis and Chorthippus apricarius found in the grasslands in the Kremnické vrchy Mts were not recorded in the wet grasslands in the Javorie Mts.

The most abundant species in the clear–cuts (more abundant than in grasslands) were P. griseoaptera, Tetrix tenuicornis, C. italicus, O. caerulescens, B. constrictus, T. cantans (Table 1). In the grasslands we recorded higher abundance than on clear–cuts in the species E. brachyptera, S. lineatus, C. apricarius, L. albovittata, C. parallelus, M. roeselii, C. dorsatus, Phaneroptera falcata, Decticus verrucivorus, M. bicolor, Isophya camptoxypha, T. viridissima (Table 1).

On all four clear–cuts (100% frequency), we recorded ten Orthoptera species: four Ensifera (B. constrictus, P. griseoaptera, T. cantans, M. thalassinum) and six Caelifera (E. brachyptera, C. biguttulus, C. brunneus, T. subulata, T. tenuicornis, T. undulata; Fig. 2).

In all four grasslands (100% frequency) we found nine orthopteran species, from which four were Ensifera (P. griseoaptera, D. verrucivorus, M. roeselii, T. viridissima) and five Caelifera (E. brachyptera, C. biguttulus, C. brunneus, C. apricarius, C. dorsatus; Fig. 2).

The highest number of the species per clear–cut (9–18 / clear–cut; Fig. 3) in regular monthly captures was recorded in September. In the grasslands, we did not record significant increase in the species number, probably due to unidentifiable time–dependent changes to the vegetation structure caused by mowing and grazing (Fig. 3). The species composition in the grasslands and clear–cuts displayed seasonal–dependent variations. In May – July, the most probable to catch were early spring species represented e.g. by Ensifera species (Isophya spp., B. constrictus). In August – October, these species were rare, dominated by D. verrucivorus, P. falcata, T. cantans, T. viridissima, C. italicus, C. brunneus, C. vagans, O. caerulescens.

Table 1. Species composition and abundance of Orthoptera in four clear-cuts and four grasslands in fragmented forest landscape in two mountains in Central Slovakia.

Figure 2. Frequency (%) of 29 orthopteran species in four clear-cuts (black) and in four grasslands (grey) in fragmented forest landscape (A: Ensifera; B: Caelifera).

Figure 3. Seasonal variations in Orthoptera species number (mean ± SD) in four clear-cuts (grey) and four grasslands (white) in fragmented forest landscape.

Fragmented forest landscape with a wide range of habitats (grasslands, ecotones, clearings, clear–cuts, young stands, forest roads and corridors) provides favourable conditions for a wide variety of Orthoptera species with different ecological demands (Nagy & Rácz 1996; Kati et al. 2003; Krištín & Hrúz 2005).

In our study we compared the species composition of Orthoptera assemblages between two specific habitats in fragmented forest landscape with dominant beech. We found less Orthoptera species in grasslands than in clear–cuts, which is in accordance with findings of Dalbeck (2011) on forest stands damaged by beaver and grasslands. Contrarily, Laußmann (1993) recorded more species in grasslands (11) than in clear–cuts in mixed forests (9). Similarly, Jenni et al. (2007) found more species in grasslands and ruderal stands than in shrub and tree vegetation in burnt as well as unburnt plots.

We recorded more Orthoptera species in marginal parts of grasslands with shrub vegetation and in ecotones, in accordance with Marini et al. (2009a, b), Fabriciusová et al. (2011), Fartmann et al. (2012). In the clear–cuts were dominant Caelifera, while in the grasslands the species proportions of Ensifera and Caelifera were very similar. Lower species number recorded in the grasslands was probably caused by changes to vegetation patterns (Ingrisch & Köhler 1998; Guido & Gianelle 2001; Picaud & Petid 2007), microclimate (Schmidt & Schlagbauer 1965), excessive rainfall and flooding of the habitats in the study year (Brust et al. 2007).

Some of the species occurring in the grasslands, e.g. L. albovittata, M. roeselii, M. bicolor did not colonise the clear–cuts, probably due to the badly fitting vegetation structure, which is in accordance with findings of Dalbeck (2011) in the forest damaged by beaver. For the clear–cuts were characteristic considerably fragmented microhabitats, often featuring a strong ecotonal character, which provided suitable conditions for the species preferring ecotones (Detzel 1998; Krištín & Hrúz 2005; Vadkerti & Szövényi 2005). The high proportion of shrubby vegetation and natural regeneration had positive influence especially on Ensifera species, several of them associated with shrubs and trees (Detzel 1998; Ingrisch & Köhler 1998).

The microclimate and shrubs in clear–cuts provided suitable conditions for the species P. griseoaptera, exhibiting in our study significantly higher abundance from all the species in all clear–cuts. On the clear–cuts with a high proportion of natural regeneration we recorded more Caelifera species than in grasslands, which we may explain by drier character of clear–cuts and higher proportion of bare ground in them. Contrarily, Marini et al. (2009a)recorded the grasshopper (Caelifera) species numbers in grassland habitats decreasing with developing succession of woody plants.

On the clear–cuts we found characteristic species C. brunneus, C. vagans, similar as did Laußmann (1993), Jenni et al. (2007), Hochkirch et al. (2008). Similar as Detzel (1998), in the clear–cuts we recorded such species as T. subulata, T. undulata and T. tenuicornis, less grassland species as E. brachyptera, C. dispar, C. parallelus, C. biguttulus. Only in the clear–cuts (surprisingly, not in grasslands) we recorded species of erosion plots such as C. italicus and O. caerulescens, in accordance with Jenni et al. (2007). These species probably originated in some of not checked open habitats in the surroundings.

The seasonal occurrence of Orthoptera species varied in accordance with the species development (Detzel 1998). We have found that for recording all the Orthoptera species in the clear–cuts, there were necessary two collections in the turn of June / July and August / September. For example, in June we recorded the species B. constrictus, I. camptoxypha which are rare in August – October. On the other hand, in June most of the species of the genera Tettigonia, Phaneroptera, Chorthippus were caught in nymphal stages, equally as the species C. italicus and O. caerulescens, with the adults recorded in July / September.

The low number of the species recorded in the grasslands in May was probably caused by the high precipitation amount in April – May and subsequent grasslands flooding (e.g. Brust et al. 2007); and by the changes to the vegetation structure by mowing in July (Guido & Gianelle 2001; Fabriciusová et al. 2011).

Our study puts forward some interesting findings. In the one– and two–year–old clear–cuts we recorded more orthopteran species (27) than in the surrounding meadows (21). So we suppose than in the first two years of succession, the pioneer habitats of clear–cuts are colonised very quickly from the various surrounding habitats and homogeneous meadows were only one of potential source habitats. Consequently, the future research should focus on mapping and data collection from all potential source habitats at distance up to 300, or 500 m, based on the knowledge of mobility of the recorded species (e.g. Burrows & Morris 2003). In the clear–cuts were dominant Caelifera. In the grasslands, the proportions of Ensifera and Caelifera were very similar, probably due to the presence of dispersed shrub and tree vegetation. The clear–cuts were colonised by several grassland species and species of habitats with bare ground. In addition, the Orthoptera assemblage structure exhibited considerable differences in the species abundance and frequency between the clear–cuts and grasslands.

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