Individual study: Effects of seasonal sheep grazing on the Heteroptera and Auchenorhyncha of chalk grassland at Aston Rowant National Nature Reserve, Oxfordshire, England
Morris M.G. (1973) The effects of seasonal grazing on the Heteroptera and Auchenorhyncha (Hemiptera) of chalk grassland. Journal of Applied Ecology, 10, 761-780
For conservation purposes, semi-natural grasslands are typically manged by grazing to maintain a herb-rich sward. Here, the effects of sheep grazing at different seasons of the year on Heteroptera and Auchenorhyncha, two characteristic groups (suborders) of Hemiptera found in calcareous grasslands, were studied at Aston Rowant National Nature Reserve in Oxfordshire, southern England.
Experimental design: In October 1966, two replicates of four grazing treatments were established on two adjacent south-west to west facing hillsides. Each treatment plot in replicate 1 was 2 acres (0.81 ha) in area, and in the replicate 2, 3 acres (1.21 ha). Sheep stocking density on grazed plots was 3 animals/acre (7.41 ha). Each plot was grazed for 3 months, plots 1 and 5 from January to March (winter), plots 3 and 7 from April to June (spring), plots 4 and 8 from July to September (summer) and plots 2 and 6 from October to December (autumn). Vegetation control plots comprised a 'small' fenced exclosures within each plot (no sheep grazing); these were not considered large enough as controls for hemipterans, so two ungrazed/very occasionally sheep-grazed adjoining areas were selected for this purpose.
Hemipteran sampling: Vacuum net samples were taken at the beginning and in the middle of each grazing period from plots and the two ungrazed areas from 16 May 1969 to 11 August 1971, and from the grazed plots on 13 August 1968. A 'D-Vac' was used to sample 2 m² of grassland per plot. Between 11 and 14 August 1971 the procedure was modified to obtain information about the distribution of Hemiptera in the grassland plots.
Vegetation sampling: Vegetation height was measured at randomly selected points on each plot, each spring summer and autumn (1969-1971).
A total of 35 Heteroptera and 49 of Auchenorhyncha species were recorded, but many present in only small numbers. Fewest larvae were taken on the spring-grazed plots. The average number of larvae/treatment (taken in July) was: Heteroptera: winter - 34, spring - 1, summer - 5, autumn - 8, ungrazed - 14; Auchenorhyncha: winter- 255, spring - 77, summer - 282, autumn - 264, ungrazed - 256.
Abundance of Heteroptera and Auchenorhyncha (larvae and adults) and species diversity, tended to be higher on the autumn- and winter-grazed plots than those subject to spring or summer grazing. The ungrazed areas supported greater numbers of individuals and more species. Auchenorhyncha species diversity differed little between treatments.
Conclusions: The author considers that to maintain diversity of Heteroptera and Auchenorhyncha, autumn or winter sheep-grazing is preferred to spring or summer sheep-grazing, but that consideration needs to be taken for other flora and fauna.
Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28197312%2910%3A3%3C761%3ATEOSGO%3E2.0.CO%3B2-A