Greater Observer Expertise Leads to Higher Liverwort Species Richness in Bryophyte Surveys
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2025
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Journal Article
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yes
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Abstract
Aims: We aimed to determine whether observer expertise (unexperienced, intermediate, experienced) affects the detection of overall bryophyte species richness and of different taxonomic bryophyte groups (e.g., mosses, liverworts, Sphagnum spp.) in vegetation surveys. We further tested if observers with different levels of expertise differ in their estimates of the species richness of various bryophyte size classes (small, medium, large), protection classes (threatened and nonthreatened), and cover classes (Braun-Blanquet scale). Location: Switzerland. Methods: From 2011 to 2023, we surveyed bryophytes in 10-m2 plots in a long-term monitoring program. Plots were situated in raised bogs and fens of national importance, which were distributed across Switzerland. The plots were surveyed by 20 professional botanists with a profound knowledge of the Swiss flora and experience in conducting vegetation surveys, but different levels of expertise in bryophyte surveys. Using 2950 relevés, we fitted linear mixed-effects models to test if species richness estimates differed among categories of observer expertise. Results: On average, experienced observers detected 76% and 82% more liverwort species per relevé than intermediate and unexperienced observers. In accordance with this, experienced observers detected significantly more small-sized bryophyte species than intermediate and unexperienced observers. However, total species richness and the richness of other taxonomic groups (mosses, Sphagnum spp.) did not differ significantly between expertise levels. This was due to the low relative richness of liverworts and small species compared to the other taxonomic groups and size classes. Conclusions: Our findings demonstrate the importance of ecological and morphological knowledge of bryophytes for bryophyte surveys in monitoring programs. However, as the total species numbers did not differ significantly between observers with different experience levels, it seems that teams composed of differently experienced observers can also collect reliable data. We recommend continuous training to keep observer errors consistently low and to statistically correct for observer differences.
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36 (6)
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Wiley-Blackwell
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Subject
Biodiversity monitoring; Cover; Fen; liverworts; Mosses; Observer bias; Raised bog; Sphagnum; Vegetation survey