Ten thousand years ago the ice Age led to Britain being largely scraped clear of its vegetation. As the ice retreated plant species began to return. At that time Britain was not an island but was linked to the continent by a land bridge and plants made their comeback from there. Pollen analysis has enabled us to gain a picture of what grew where.

Seven thousand years ago the English Channel formed and closed off the European route. By that time, some 1500 plant species had taken root and these formed the basis of Britain's native flora. The areas in the south of England benefitted most from this European influx and many of the rare plants are still concentrated there today.

However, the list of plants found in the United Kingdom has not stood still since then. Many plants have been deliberately or accidentally introduced. The Romans brought Alexanders (Smyrnium olusatrum) with them for food and the Sweet Chestnut (Castanea sativa) which was later used for fencing. Some introductions have not benefitted the native wildlife found in the United Kingdom as many associated birds, animals and insects developed along with the plants growing here.

Changes in agriculture brought changes in human communities so that nomads became hunters and gatherers before settling down in one place. This was facilitated by the use of tools which enabled clearings to be made in the woodland. In turn, this led to changes in the plants being grown and harvested.

Changes in the sustainable uses of woods including developing the techniques of pollarding - cutting back trees to head height to prevent browsing by deer and horses - and coppicing - cutting back trees to some eighteeen inches high for use in making clogs, hurdle fences or handles for tools. Neither of these methods killed the tree. They continued to grow up from where they had left off.

As areas of the woodland could be cleared then the increasing light reaching the woodland floor enabled an early spring growth of flowers to develop. Plants such as Wood sorrel (Anemone nemorosa), Primose (Primula vulgaris), Bluebell (Hyacinthoides non-scripta) and Early purple orchid (Orchis mascula) developed to take advantage of lighter conditions before the leaves grew on the trees and blocked off the light.

The planting of a wood at Windsor in 1580 is taken as an indication of when larger scale manipulation of the natural vegetation began. Areas which were wooded then and remain so are referred to as ancient woodland. Acient woodland is land which has had a continuous woodland cover since at least 1600 AD. A number of species are regarded as indicators of a long-established woodland.

These include Lime (Tilia cordata); Oxlip (Primula elatior); and shrubs such as Midland hawthorn (Crataegus laevigata) and Wild Service tree (Sorbus torminalis); and the Hay-scented buckler fern (Dryopteris aemula).

The increasing development of modes of transport and discovery of new lands led to plants being introduced for food and to gardens - the potato from South America and the Rhododendron from the Himalayas. Spices became a favoured method of brightening up the rather dull medieval European diet as well as providing medicinal cures and tonics.