Rare arable plants
Some species of weeds have never been common in Britain whilst others have declined in relative abundance to a point where they are now extinct (or nearly so) in the natural flora. There are several reasons for the decline:
- Chemical weedkillers have doubtless played a part, particularly in the latter half of the 20th century, but the decline began well before the introduction of modern herbicides.
- The introduction of improved seed cleaning machinery has arguably had an equally large impact. Previously, large weed seeds like those of corncockle were not easily removed by simple winnowing and remained as contaminants of the grain to be drilled again with the crop seed. Unlike many weeds, corncockle does not form a persistent seedbank in soil and, as has been seen, without repeated re-introduction soon disappears.
- Changes in cropping practice like the move from spring to winter cropping affected species like weasel