An evaluation of three quick methods commonly used to assess sward height in ecology

Abstract

Summary 1.Many ecological studies and applications involve measuring the height of grassland swards. An evaluation was made of the practicality, accuracy and comparability of using the sward stick, drop disc and direct methods of measurement. Each method proved to be appropriate for measuring swards that contain a wide range of heights, each was quick to perform, and recorder effects were negligible. Yet each had strengths and weaknesses. 2. The sward stick gave the most variable results: it was considered the best method for recording the architecture of the sward surface, and hence invertebrate niches, but was poor for measuring short turf. The drop disc was the worst method for recording microheterogeneity in sward architecture and was completely unsuitable for measuring variation in short turf. But in medium-tall swards, it was considered to be the best method for measuring productivity, vertebrate herbivory and for large-scale monitoring of land managed for conservation and under agri-environment schemes. The direct method gave the most consistent and accurate results compared with an independent parameter, soil temperature. It was the only method suitable for measuring variation in short turf. 3. A serious problem exists when research results, recommendations and assays involve measurements made by more than one method. The sward stick consistently gave higher absolute values than either of the other methods and, apart from in short turf (for which it is unsuitable), the drop disc gave values that were 73% and up to 40% lower, respectively, than those obtained using the sward stick and direct methods. This can lead to major misapplications of ecological results and recommendations in conservation and agri-environmental projects.

Effects of sheep grazing on abundance and predators of field vole (Microtus agrestis) in upland Britain

“…Cover of plant species in each quadrat was assessed and height of vegetation was measured using the drop-disc method (Stewart et al, 2001). Abundance in broad habitat types was assessed by comparing VSI for each of the four habitats.…”

Invertebrates in field margins: taxonomic group diversity and functional group abundance in relation to age

“…This measurement was performed at five points 10 m apart by lowering a 30 cm diameter, 200 g vinyl drop disc from 2 m over a wooden rule. This method is well suited for medium to tall swards (Stewart et al 2001). The vegetation cover was estimated in winter as well as summer.…”

Influence of sward structure on daily intake and foraging behaviour by horses

“…The distribution of grass heights in the pastures (measured with a drop disc of 100 cm 2 , 2.7 g; Stewart et al, 2001) was assessed twice a week, by observations on the diagonals every 3 m (sample sizes were between 257 and 397 per pasture). We grouped grass heights into classes (1 to 4 cm, 5 to 8 cm, 9 to 16 cm, 17 to 24 cm, 25 to 32 cm, 33 to 40 cm, 41 to 48 cm, 49 to 56 cm, 57 to 64 cm, 65 to 72 cm and .72 cm) before statistical analyses.…”