Changes in plant collection practices from the 16th to 21st centuries: implications for the use of herbarium specimens in global change research

Abstract

Background and aims Herbaria were recently advertised as reliable sources of information regarding historical changes in plant traits and biotic interactions. To justify the use of herbaria in global change research, we asked whether the characteristics of herbarium specimens have changed during the past centuries and whether these changes were due to shifts in plant collection practices. Methods We measured nine characteristics from 515 herbarium specimens of common European trees and large shrubs collected from 1558‒2016. We asked botanists to rank these specimens by their scientific quality, and asked artists to rank these specimens by their beauty. Key results Eight of eleven assessed characteristics of herbarium specimens changed significantly during the study period. The average number of leaves in plant specimens increased threefold, whereas the quality of specimen preparation decreased. Leaf size negatively correlated with leaf number in specimen in both among-species and within-species analyses. The proportion of herbarium sheets containing plant reproductive structures peaked in the 1850s. The scientific value of herbarium specimens increased until the 1700s, but then did not change, whereas their aesthetic value showed no systematic trends. Conclusions Our findings strongly support the hypothesis that many characteristics of herbarium specimens have changed systematically and substantially from the 16 th to 21 st centuries due to changes in plant collection and preservation practices. These changes may both create patterns which could be erroneously attributed to environmental changes and obscure historical trends in plant traits. The utmost care ought to be taken to guard against the possibility of misinterpretation of data obtained from herbarium specimens. We recommend that directional changes in characters of herbarium specimens which occurred during the past 150‒200 years, primarily in specimen’s size and in the presence of reproductive structures, are accounted for when searching for the effects of past environmental changes on plant traits.

From leaves to labels: Building modular machine learning networks for rapid herbarium specimen analysis with LeafMachine2

“…Even so, we look ahead to when every digitized herbarium specimen has a comprehensive set of measured traits and ask, Will it be enough? We suspect that this fantastic corpus of botanical descriptions will be revolutionary but will also amplify known contemporary sampling and taxonomic biases (Loiselle et al, 2008 ; Willis et al, 2017 ; Daru et al, 2018 ; Kozlov et al, 2021 ; Meineke and Daru, 2021 ; Davis, 2022 ; Heberling, 2022 ) and shift focus toward traits that cannot be captured by two‐dimensional images of preserved tissue (Borges et al, 2020 ). Therefore, let this resurgence in attention paid to herbaria also serve as a catalyst for preserving not only physical specimens, but also digital‐only collections.…”

Leaf morphological variation in Betula medwediewii Regel populations from Türkiye

“…Mature leaves were collected in the middle of the upper crown of the tree. Solely fully developed leaves of trees, without signs of damage from pest, disease or wilting were measured (Kozlov et al 2021). Leaves were subjected to a preservation treatment that included pressing and drying (Tomaszewski and Górzkowska 2016).…”

Small and in‐country herbaria are vital for accurate plant threat assessments: A case study from Peru

“…Consequently, they likely contain younger specimens, which usually contain more locality data and more accurate coordinates, which are key for accurate conservation assessments (Willis et al, 2003). While historical specimens are often key for taxonomy and studies of temporal change, younger specimens may be more representative of species current ranges (Pergl et al, 2012) or characteristics (Kozlov et al, 2021). Rare species are often represented by recent collections that are in local herbaria, reflecting intensified collecting effort by local taxonomists (e.g., Gonzáles et al, 2022).…”