Ecological Changes in the British Flora

Abstract

1. In Britain the long tradition of botanical recording at the local (county) scale provides a unique observational record from which to assess floristic change. In this study I utilise historic and contemporary datasets to assess localised extinction at a variety of spatial and temporal scales.

2. One way to quantify floristic change is to calculate county extinction rates: in lowland England this approach revealed a loss of 0.5 species per year since 1900, and not one species a year as previously thought, with northern counties having a lower rate (0.4 species year-1) than those in the south and east (0.6 species year-1).

3. In lowland counties (Bedfordshire and Northamptonshire) the most important predictors of extinction risk were rarity, habitat specialisation and competitive ability, with short species of open, nutrient-poor habitats having declined the most.

4. A resurvey of fixed plots in Bedfordshire first visited in 1949-1951 gave similar results with tall nutrient-demanding species increasing at the expense of small habitat specialists. Losses were greatest in arable, waste and neutral to acid grassland habitats. Woodlands and calcareous grasslands showed little change and, remarkably, conservation designation had no significant effect on the magnitude of change in most habitats.

5. Population changes of the two short grassland specialists, Trifolium ochroleucon and Pulsatilla vulgaris, reinforced these results. Over the last 40 years, half the populations of both have been lost at the county (Trifolium ochroleucon) and national (Pulsatilla vulgaris) scale, initially due to habitat loss but more latterly due to reduced management (cutting and grazing) of isolated nature reserves and linear fragments of grassland.

6. Synthesis and conclusions: These findings, which parallel national trends, indicate that habitat loss and eutrophication have been the primary drivers of localised extinction in lowland regions over the past 350 years. Lack of management now appears to be a more pervasive threat to habitat specialists isolated in otherwise intensively managed lowland landscapes. Good regenerative ability or conservation designation are unlikely to buffer these species from further extinction, unless management or habitat restoration is undertaken to expand existing populations and promote dispersal and gene-flow.