Scale‐dependent biases in species counts in a grassland

Abstract

Numbers of plant species were recorded in speciesrich meadows in the Bílé Karpaty Mts., SE Czech Republic, with the aim to evaluate the sampling error made by well-trained observers. Five observers recorded vascular plants in seven plots ranging from 9.8 cm 2 to 4 m 2 independently and were not time-limited. In larger plots a discrepancy of 10-20% was found between individual estimates, in smaller plots discrepancy increased to 33%, on average. The gain in observed species richness by combining records of individual observers (in comparison with the mean numbers estimated by single observers) decreased from the smallest plot (27-82% for two to five observers) to the largest one (13-25%). However, after misidentified and suspicious records were eliminated, the gain was much lower and became scale-independent; two observers added 12% species, on average, and the increase by combining species lists made by three or more observers was negligible (3% more on average). It is concluded that most discrepancies between individual observers were caused by misidentification of rare seedlings and young plants. We suggest that in species-rich meadows plants should be recorded by at least three observers together and that they should consult all problematic plant specimens together in the field, to minimize errors.

Diversity of the Western Carpathian flysch grasslands: Do extremely species-rich plant communities coincide with a high diversity of snails?

“…Alternatively, in the nearby Jazevčí National Nature Reserve, we sampled the richest plot of the entire data set, containing 58 species of vascular plants per 1 m 2 . Even this number is far from the record value of 67 vascular plant species per 1 m 2 reported by Klimeš et al (2001) from the Čertoryje National Nature Reserve, located close to two previous sites.…”

Impact of climate change on alpine vegetation of mountain summits in Norway

“…Moreover, rare and small individuals, especially seedlings, are more easily overlooked or misidentified. Thus, cover estimation may be less consistent compared to more abundant species (Klimesˇet al 2001;Vittoz and Guisan 2007), and temporal cover changes should be treated with care for species having a low cover. A constant plot size, their delimitation with measuring tapes and the occasional use of a transparent template showing the area of small cover percentages, were strongly facilitating cover estimation in our study.…”

Biotic homogenization and differentiation in weed vegetation over the last 70 years

“…Therefore, re-visitation of historical sites is the best method for detecting temporal vegetation changes when permanent plots are not available but results must be interpreted with caution [18]. Bias may be introduced if preferential sampling is done or if the locations sampled are not exact [19,20].…”