| Autor: |
Critchley, C. Nigel R., Poulton, Simon M.C. |
| Předmět: |
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| Zdroj: |
Journal of Vegetation Science; Dec1998, Vol. 9 Issue 6, p837-846, 10p |
| Abstrakt: |
. Methods for monitoring and survey of plant species abundance which do not account for variation in scale are often insensitive and imprecise. In monitoring, repeated observations are usually made within a fixed unit. Counts of species' presence must be made in a range of subunit sizes to accommodate the range of scales at which different species occur. A method comprising a rectangular fixed unit containing an 8 × 4 grid of square subunits has been developed and tested. Each subunit comprises a series of nested cells of increasing size, within which species are recorded cumulatively. Using this method, the concept of optimum scale is introduced. The optimum scale for a species is that for which its frequency count is closest to the midpoint. Two characteristics, sensitivity (absolute change detected) and blindness (failure to detect change in a species) were calculated for 24 plots from lowland grazing marsh which had been partially flooded between the time of two surveys. Optimum scale had greater sensitivity and lower blindness than any single scale in the majority of plots. Combining sensitivity and blindness, optimum scale was always superior. For the whole sample, optimum scale was less likely to cause Type I or Type II errors. The method is recommended for monitoring grasslands and allied plant communities in large geographical areas. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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