The influence of management regime and altitude on the population structure of Succisa pratensis: implications for vegetation monitoring
Published source details
Bühler C. & Schmid B. (2001) The influence of management regime and altitude on the population structure of Succisa pratensis: implications for vegetation monitoring. Journal of Applied Ecology, 38.
Published source details Bühler C. & Schmid B. (2001) The influence of management regime and altitude on the population structure of Succisa pratensis: implications for vegetation monitoring. Journal of Applied Ecology, 38.
Despite a 90% decline in wetlands over the last 100 years in Switzerland, devil's-bit scabious Succisa pratensis, remains a typical species of calcareous fens, and was found in 46 of 48 randomly chosen fens within eastern Switerland. Often it forms large populations, and the growth form and late flowering of this perennial plant probably requires traditional low-intensity mowing or grazing for continued persistence. As part of a study investigating vegetation monitoring techniques, the density and frequency distribution of four phenological stages of devil's-bit scabious in 24 calcareous fens in eastern Switzerland was studied. These fens differed in management type (either mown or cattle-grazed) and altitude (classified as low, medium or high).
Study sites: Twenty-four sites were selected. To reduce variation among fens, only fens containing the sedge Carex davalliana (characteristic of the Caricion davallianae vegetation community), were regarded as potential study sites. These fens were classified according to management (litter meadows or grazed pastures) and one of three levels of altitude (low = 800–1,000 m a.s.l., medium = 1,000–1,200 m, high = 1,200–1,400 m). For each of the six combinations of these categories, four fens were randomly chosen to give a balanced two-way design of 24 fens with management type and altitude as main effects.
Vegetation surveys: In May 1995, each of the fens was visited to identify those that included populations of S.pratensis. Within each fen, a 2 × 2 m quadrat (the 'main quadrat') was placed at random. During July and August 1995, the number of individuals in each of the four stage classes (seedlings, juveniles, vegetative adults, reproductive adults) was counted to estimate absolute and relative population densities at a local scale within the main quadrat. Because the main quadrat was randomly placed only in respect to the S.pratensis population at a fen, but not in respect to the whole area of the fen, density measured in the main quadrat is termed local density. For an assessment of seed-set, eight reproductive adults were randomly chosen (from within the main quadrat if possible) and their flowering stalks marked. Their flower heads were harvested during September and October 1995 and their seeds counted.
To obtain a reliable estimate of the overall S.pratensis density at a fen, six additional 1 × 2 m quadrats, were randomly distributed over each fen. Within these quadrats, only adult S.pratensis plants were counted.
Management: Within both types of management, fens differed in the intensity of the particular mowing or grazing regime in use. For the 12 grazed fens a quantitative assessment of these differences was made from direct observations, these were used to calculate an index of grazing intensity.
High altitude had a positive effect on the density of adult devil's-bit scabious plants only in mown fens, whereas in grazed fens adult density was highest at medium altitude.
Local densities of seedlings and vegetative adults within a fen were higher in mown than in grazed fens, and lower in fens of the lowest altitude level than of the two higher ones. However, there were no differences in the relative proportions of all four phenological stages among main factors except that significantly fewer seedlings occurred in fens of the lowest altitude level.
The intensity, rather than the type of management regime (i.e. mown vs. grazed) appears crucial in shaping devil's-bit scabious populations in eastern Swiss calcareous fens: for grazed fens, there is a negative relationship between intensity of grazing and density of adult scabious plants. The number, the relative proportion of seedlings and the seed-set are all negatively correlated with grazing intensity.
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