Individual study: Effects of between-tussock sward height on goat utilization of mat-grass Nardus stricta and floristic composition in the Cleish Hills, Fife, Scotland
Grant S.A., Torvell L., Sim E.M., Small J.L. & Armstrong R.H. (1996) Controlled grazing studies on Nardus grassland: effects of between-tussock sward height and species of grazer on Nardus utilization and floristic composition in two fields in Scotland. Journal of Applied Ecology, 33, 1053-1064
In northern Britain, the tussock-forming mat-grass Nardus stricta can be abundant in upland areas deficient in calcium. Acid grasslands rich in Nardus can occur as a result of its avoidance by grazing sheep and over recent decades research has highlighted increasing Nardus dominance. In this study, grazing of Nardus was investigated in experiments in which various pre-determined sward heights of between-tussock grasses was maintained throughout the growing season by goat-grazing.
Study site: The experiment was conducted on 0.6 ha acid grassland (soil pH 4.9-5.6, 270 m altitude) with 10-15%b Nardus cover, in the Cleish Hills (National Grid ref: NT 088950), Fife, Scotland.
Grazing treatments: The experiment was conducted over 4.5 years (May 1984 to Septemper1988). Four plots (each 0.15 ha) were stocked with goats (dairy breed x feral) during the growing season.
The four treatments (based on the control of between-tussock vegetation height) were: between-tussock grasses maintained at i) 4-5 cm, ii) 5-6 cm and iii) 6-7 cm by goats, and iv) a sheep control with vegetation maintained at 4-5 cm.
Nardus utilisation: Nardus utilisation was estimated each July and October by the proportion of tillers and leaves that had been grazed. Grazing severity was determined by measuring the lamina length of grazed leaves (20-40 random measurements in October or July each year). Leaf growth (mm/tiller/day) was recorded at weekly intervals from samples of 30 tillers in each plot from 26 April to 20 September 1988.
Floristic composition Vegetation composition was recorded in May 1989 using an inclined point quadrat. Percentage cover by species, and relative frequency were recorded.
Utilization of Nardus by goats: In the goat grazed plots the proportion of Nardus tillers and leaves that were grazed increased as the between-tussock grass length, comprising preferred forage species, was reduced. The preferred forage grasses recorded including common bent Agrostis capillaris (dominant), velvet bent A.canina, sweet vernal Anthoxanthum odoratum, creeping soft-grass Holcus mollis, smooth meadow grass Poa pratensis and sheep's fescue Festuca ovina.
Lamina length of grazed leaves was shorter where more tillers/leaves were grazed. Utilization declined over successive seasons under sheep grazing, but was sustained by goat grazing.
Nardus growth: Leaf growth was measured during the 1988 growing season. Peak growth rates occurred in late June on all four plots. Growth rates were inversely related to grazing severity, being lowest on the 4-5cm goat plot, and highest on the 6-7cm goat plot.
Conclusions: The utilization of Nardus by goats increased as the height of the preferred between-tussock grasses was reduced. Goats grazed more Nardus at 4.5 and 5.5 cm than the sheep did at 4.5 cm. The severity of Nardus achieved were at levels that cutting studies (Grant et al. 1996) indicated were likely to reduce Nardus vigour.
Grant S.A., Torvell L., Sim E.M., Small J.L. & Elston D.A. (1996) Seasonal Pattern of Leaf Growth and Senescence of Nardus stricta and Responses of Tussocks to Differing Severity, Timing and Frequency of Defoliation. The Journal of Applied Ecology, 33, 1145-1155.
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