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

Authors


Dr N.A.D. Bourn, Butterfly Conservation, Manor Yard, East Lulworth, Dorset BH20 5QP, UK (fax +44 1929 400210; e-mail nbourn@butterfly-conservation.org).

Summary

  • 1Many 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.
  • 2The 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.
  • 3A 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.

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