Study

Distribution and abundance of small insects and arachnids in relation to structural heterogeneity of grazed, indigenous grasslands

  • Published source details Dennis P., Young M.R. & Gordon I.J. (1998) Distribution and abundance of small insects and arachnids in relation to structural heterogeneity of grazed, indigenous grasslands. Ecological Entomology, 23, 253-264.

Actions

This study is summarised as evidence for the following.

Action Category

Use mixed stocking

Action Link
Butterfly and Moth Conservation

Reduce grazing intensity on grassland by reducing stocking density

Action Link
Butterfly and Moth Conservation

Cease grazing on grassland to allow early succession

Action Link
Butterfly and Moth Conservation
  1. Use mixed stocking

    A replicated, paired, site comparison study in 1989–1993 at an upland grassland in Scotland, UK (Dennis et al. 1998) found that plots grazed with sheep and cattle had a lower abundance of small invertebrates (including caterpillars) than plots grazed by sheep alone when grazing intensity was high, but there was no difference when grazing intensity was reduced. Heavily grazed plots with both sheep and cattle had fewer invertebrates (4–15 individuals) than plots grazed at high intensity by sheep alone (4–31 individuals). However, when grazing intensity was reduced there was no significant difference in the number of invertebrates between plots grazed by sheep and cattle (9–35 individuals) and sheep-only plots (6–39 individuals). Invertebrate abundance was highest at a fifth plot that was ungrazed (70–223 individuals). From 1989–1991, four experimental grazing plots (1–3 ha) were established. From May–October each year, the number of sheep/plot was adjusted weekly in order to maintain different sward heights (4.5 and 6.5 cm). From June–August, six yearling cattle were also grazed on two of the plots. From 1992, a fifth plot was left ungrazed. In August 1993, invertebrates were sampled from both tussocks and low sward at each of six randomly selected points/plot using a d-vac suction sampler.

    (Summarised by: Andrew Bladon)

  2. Reduce grazing intensity on grassland by reducing stocking density

    A replicated, paired, site comparison study in 1989–1993 in three upland grasslands in Scotland, UK (Dennis et al. 1998) found that two of three sites with reduced stocking density had a higher abundance of small invertebrates (including caterpillars) than sites with higher stocking density. In two out of three grasslands, the abundance of invertebrates was higher in plots with reduced stocking density (6–125 individuals) and ungrazed plots (70–250 individuals) than in plots with higher stocking density (4–70 individuals). At the third site, there was no significant difference between reduced stocking (17–78 individuals), ungrazed (35–78 individuals) and higher stocking density plots (17–55 individuals). From 1989–1991, at three sites, experimental grazing plots were established where the number of sheep was adjusted weekly in order to maintain different sward heights from May–October each year. At two sites, two 0.3-ha plots had sward kept at each of 3.0, 4.5 (high stocking density) or 6.0 cm (reduced stocking density). At the third site, four 1–3 ha plots had sward kept at each of 4.5 and 6.5 cm, but from June–August six cattle were grazed on half of the plots. Separate plots which had been ungrazed for one, four or 25 years were also monitored at each site. In August 1993, invertebrates (insects and arachnids) were sampled from both tussocks and low sward at each of six randomly selected points/plot using a d-vac suction sampler.

    (Summarised by: Andrew Bladon)

  3. Cease grazing on grassland to allow early succession

    A replicated, paired, site comparison study in 1989–1993 in three upland grasslands in Scotland, UK (Dennis et al 1998) found that in two of three sites ungrazed grassland had a higher abundance of small invertebrates (including caterpillars) than sites with low or high grazing intensity. In two out of three grasslands, the abundance of invertebrates was higher in plots which had been ungrazed for 1 and 25 years (70–250 individuals) than in plots with low (6–125 individuals) or high (4–70 individuals) grazing intensity. At the third site, there was no significant difference between a plot which had been ungrazed for four years (35–78 individuals) and sites grazed at low (17–78 individuals) or high intensity (17–55 individuals). From 1989–1991, at three sites, experimental grazing plots were established where the number of sheep was adjusted weekly in order to maintain different sward heights from May–October each year. At two sites, two 0.3-ha plots had sward kept at each of 3.0, 4.5 (high intensity) or 6.0 cm (low intensity). At the third site, four 1–3 ha plots had sward kept at each of 4.5 and 6.5 cm, but from June–August six cattle were grazed on half of the plots. Separate plots which had been ungrazed for one, four or 25 years were also monitored at each site. In August 1993, invertebrates (insects and arachnids) were sampled from both tussocks and low sward at each of six randomly selected points/plot using a d-vac suction sampler.

    (Summarised by: Andrew Bladon)

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