Later herbarium samples had lower effective species counts for spatially adjusted pigment trends in three regions in 1941-2017

We audited the species support for time trends in a public floral UV pigment archive. We used 1,228 complete specimens from Australia, Eurasia and North America in 1941-1985 and 1986-2017. Species-specific month and geographic cell controls permit an exact decomposition of the common trend into positive species weights. At a 5-degree cell size, effective species counts fell from 6.68 to 5.67 in Australia, 11.22 to 4.06 in Eurasia and 5.49 to 3.46 in North America. Only five of twelve species in later North America supplied time information. Finer cells reversed the early-to-late direction in Australia. Equal time-information weights changed the early North American slope sign. These are archive and model diagnostics, not population trends or tests of climate causation. Sparse records, broad cells and nonrandom collection limit interpretation. The package gives code, aggregate results, numerical checks, a figure and exact external source hashes.

herbarium · floral pigment · observation bias · climate change · species weights · effective sample size · geographic controls