| Popis: |
Mapping of species richness (SR) patterns is pivotal for biogeography and nature conservation. Vegetation plot databases serve as a new source of information, but they are inherently affected by the methodological background of data collection. This background could bias the SR assessment. Here, we compared two different data sources: (1) a vegetation-plot database, the Polish Vegetation Database (PVD), and (2) a species distribution atlas, the Atlas of Distribution of Vascular Plants in Poland (ATPOL). We calculated species richness recorded by the PVD (PVD SR), the ATPOL (ATPOL SR), and the two harmonized databases (total SR). The sampling bias in the PVD (PVD bias) was assessed by calculating the number of species found in the ATPOL, but not recorded by the PVD. Analogically, the ATPOL bias was calculated. We calculated correlation between the PVD bias and both the number of vegetation plots and the number of vegetation classes. Additionally, the completeness of the PVD dataset was assessed using the species accumulation curve approach. The mean slope of the last 1% of plots number was used as a proxy of inventory completeness and correlated with PVD bias. The results show that the SR documented by the PVD is significantly lower than that recorded by the ATPOL, yet it indicates a significantly increased total SR. The PVD SR increased as more plots and vegetation classes were sampled. However, even with the best sampling, the PVD SR was still significantly lower than that in the ATPOL. Further, although the values for the species accumulation curves suggested high sampling completeness in the PVD, the real bias was still substantial, and no correlation was found between PVD bias and species accumulation curve values. In general, the PVD underestimated SR at a landscape level, yet it augmented information stored in the ATPOL. The underestimations could result from limited sampling effort or from focusing on particular vegetation types, as well as the exclusion of transitional vegetation types and/or disturbed patches of vegetation from sampling. |
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