Abstract
The numbers of tetrad records (plus hectads without any tetrad records) in the BSBI Distribution Database collected annually for twenty species of orchids in Scotland increased 5.9-fold between the periods 1950-69 and 2010-2019. Similarly, the total numbers of records for all plant taxa (duplicates removed) also increased, but even more so (13.6-fold between 1950-69 and 2010-19). These increases were progressive and are thought to reflect an increase in the intensity of recording. Support for this suggestion was provided by regressing mean annual numbers of orchid tetrad records for five time periods since 1950 against the corresponding records for all plant taxa. This revealed that the increases in both were highly correlated (R2 = 0.99). To nullify the effect of the increase in recording effort on numbers of orchid tetrad records I used the corresponding total number of records for all plant taxa as a proxy for changes in amounts of recording. When this was done, compared to 1970-86, two-thirds of the orchid species had declined by more than 50% and two by 80% or more. One species had apparently increased.
Highlights
There is a widespread perception that most, or all of British orchid species are declining, but the published data are less clear-cut
1 Between the first and last time periods. To determine whether these increases were correlated, the mean numbers of orchid tetrad records for the five recording periods were regressed against the corresponding total numbers of records for all taxa
Interpretation of the changes over time in the numbers of records for species in the Botanical Society of Britain and Ireland (BSBI) database is bedevilled by changes in the intensity of recording
Summary
There is a widespread perception that most, or all of British orchid species are declining, but the published data are less clear-cut. A major source of data is the New Atlas of the British and Irish Flora (Preston et al, 2002). This provides data on the distribution of all vascular plants in the British Isles collected by the Botanical Society of Britain and Ireland (BSBI). Based on findings in Preston et al (2002), Harrap & Harrap (2009) reported that in the period 1970-86 the distributions of all British orchid species had declined (except for Ophrys fuciflora that is conserved at protected sites). As species could only decline; the possibility of increase was excluded
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