The flora of the British Isles consists of about 1300 native species and 150 ‘archaeophytes’ introduced by people before 1500 AD, considered here, plus ‘neophytes’, introduced after 1500, considered in Chapter 5. General trends in our flora since 1945 have included a gradual retreat of northern plants from their southernmost localities and an advance of southern plants. This is likely to be a result of habitat change, especially eutrophication (nutrient enrichment), rather than climate change, though mild Januaries and summer drought may have contributed.

The habitats that have changed most are agricultural, the predominant habitats of the lowlands. Mechanisation and high inputs of fertiliser and pesticide have led to declines in species diversity, including much local extinction. Arable weeds and species-rich hay meadows have suffered the most. Much calcareous grassland, lowland heath and acid grassland has disappeared to agriculture, housing, industry or forestry. Some of the rest has seen species diversity decline through a decline in, or complete cessation of, grazing, along with some eutrophication. A similar story is seen in freshwater habitats. Some woodlands have been destroyed, but extant woods, though seeing great changes in use and an increase in shade and grazing, appear to have kept most of their flora, albeit sometimes in reduced quantity. In the uplands, heather moorland and our internationally important boglands have declined with over-grazing, frequent fires or plantation forestry. Upland grassland has increased. The coasts have remained largely unchanged, with a few losses around the edges, often, again, because of inappropriate grazing. […]