Reproducibility of species lists, visual cover estimates and frequency methods for recording high-mountain vegetation

Vittoz, Pascal; Bayfield, Neil; Brooker, Rob; Elston, David A.; Duff, Elizabeth I.; Theurillat, Jean-Paul; Guisan, Antoine. 2010 Reproducibility of species lists, visual cover estimates and frequency methods for recording high-mountain vegetation. Journal of Vegetation Science, 21 (6). 1035-1047.

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Question: When multiple observers record the same spatial units of alpine vegetation, how much variation is there in the records and what are the consequences of this variation for monitoring schemes to detect changes? Location: One test summit in Switzerland (Alps) and one test summit in Scotland (Cairngorm Mountains). Method: Eight observers used the GLORIA protocols for species composition and visual cover estimates in percentages on large summit sections (>100 m2) and species composition and frequency in nested quadrats (1 m2). Results: The multiple records from the same spatial unit for species composition and species cover showed considerable variation in the two countries. Estimates of pseudo-turnover of composition and coefficients of variation of cover estimates for vascular plant species in 1 m × 1-m quadrats showed less variation than in previously published reports, whereas our results in larger sections were broadly in line with previous reports. In Scotland, estimates for bryophytes and lichens were more variable than for vascular plants. Conclusions: Statistical power calculations indicated that unless large numbers of plots were used, changes in cover or frequency were only likely to be detected for abundant species (exceeding 10% cover) or if relative changes were large (50% or more). Lower variation could be reached with the point method and with larger numbers of small plots. However, as summits often strongly differ from each other, supplementary summits cannot be considered as a way of increasing statistical power without introducing a supplementary component of variance into the analysis and hence into the power calculations.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Topics & Objectives 2009 - 2012 > Biodiversity
UKCEH and CEH Sections/Science Areas: Unaffiliated
ISSN: 1100-9233
Additional Keywords: accuracy, biodiversity monitoring, observer bias, permanent plot, pseudo-turnover, sampling error, statistical power
NORA Subject Terms: Botany
Data and Information
Date made live: 03 Mar 2011 14:54 +0 (UTC)

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