Grazing management of calcareous grasslands and its implications for the conservation of beetle communities

Published source details Woodcock B.A., Pywell R.F., Roy D.B., Rose R.J. & Bell D. (2005) Grazing management of calcareous grasslands and its implications for the conservation of beetle communities. Biological Conservation, 125, 193-202.
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Summary

In the UK and eslewhere in Europe, grazing of livestock is frequently used in the management of grasslands. The study summarised assessed the effect of different grazing regimes on clacareous grassland on beetle guild species composition in association with changes in plant community structure.

Study site: The study was conducted at the Salisbury Plain Training Area (SPTA), a military training ground in Wiltshire, southern England. Grazing was reintroduced after an abscence of 50 years (2,990 ha) to reduce sward height and control scrub invasion. Cattle and sheep were grazed at high densities for short periods (10-14 days) in temporary pens (up to 8.2 ha) on a two year rotation.

Experimental design: In May 2003, five replicate 100 x 100 m plots were established and the following grazing treatments randomly applied:

1) Control (ungrazed for about 50 years);
2) Recently introduced rotational cattle (2-3 years);
3) Recently introduced rotational sheep (2-3 years);
4) Longer term rotational cattle (10 years);
5) Longer term rotational sheep (10 years).

Core sampling areas (30 x 100 m) were established within each plot in order to avoid disturbed areas (e.g. caused by military or rabbit activity) or scrub.

Vegetation sampling: Twenty five plots were established in July 2003 (five 2 x 2 m quadrats at 20 m intervals along the central line) the sampling areas. Percentage cover of all vascular plants and bryophytes were estimated and communities classified. Within each quadrat a random 40 x 40 cm area of biomass was removed, sorted and dried. In addition, on four occasions (May, June, July and September) vegetation height was assessed using a drop disk.

Invertebrate sampling: In 2003, adult beetles were collected on three occasions (28-31 May, 22-29 June and 9-11 September) at positions corresponding to the quadrats for 15 x 10 second intervals using a suction sampler. For each treatment on each date an area of 1.32 m² was sampled. Collected beetles were identified to species with exceptions of Aleocharinae (Staphylinidae), Ptilidae, Lathrididae, Nitidulidae and Crytophagidae. Beetles identified were representative of the following guilds:

1) Polyphagous/predatory species;
2) Opportunistic phytophagous/spermatophagous species;
3) Mycetophagous species;
4) Above and below ground feeding phytophagous species.

The majority of beetles collected were common grassland species. No significant difference in total abundance, species richness, diversity and evenness between treatments was found but species composition and guild structure was affected (Table 1, attached). No significant differences were recorded between cattle and sheep grazing. The high density, short duration rotational grazing system used at the SPTA was equivalent to a longer term extensive (low intensity) grazing regime and forbs flourished with the reduction of otherwise highly competative graminoid species.

Proportional abundance of phytophagous beetle species was significantly higher in the longer term grazed areas but lower in short term and ungrazed areas (Table 1). This was attributed to a shift from dominant grasses (e.g. oat-grass Arrenatherum elatius and cock's-foot Dactylis glomerata), towards a sward richer in herbs (food resources). Abundance of predatory/polyphagous species was significantly lower in longer term grazed areas and higher in the short term and ungrazed areas. Some Carabids and Staphylinids associated with tussock forming grasses declined over time as demonstrated by the change in plant community structure from predominantly MG1 Arrenatherum elatius (NVC plant community) in the ungrazed areas (four out of five) to CG3 upright brome Bromus erectus (NVC plant community) in the longer term grazed areas (eight out of 10).

The study suggests that where maintenance of a continuous grazing herd is not possible, short bursts of intensive grazing every other year may be used as an alternative grazing regime to potentially obtain similar outcomes.

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