The Regression of Cultivated Land. 



Recognition of the fact that the general aspect of the landscape of 

 the modern countryside expresses the modifying effect of human activities 

 on the original flora, continued along closely similar lines of copse, wood- 

 land, pasture, water-meadows, and arable land, for a period of at least 

 several hundred years, leads to the suggestion as to what would happen 

 if cultivation ceased, and the land were allowed to lapse again to a wild 

 state. In how many years, for example, would land go back to the con- 

 dition described as primitive woodland ? The problem may be approached 

 from several standpoints : 



(1) The reversion of wet flood-meadows and fields of the alluvium. 



(2) The regression of dry hill-pastures. 



(3) The regression of fields on clay (Oxford and Kimeridge), or on 



low gravel-terraces. 



(4) The colonization of waste-heaps, including quarry-banks, already 



indicated. 



(5) The complete covering of ruins, and all remaining traces of human 



occupation. 



Examples of all these phenomena are of general occurrence, and from 

 them it is possible to obtain an idea of what would happen if the entire site 

 of Oxford became derelict, and vegetation again asserted itself. 



The first case is afforded by the neglect of hay-pastures and dry fields 

 affording little feed for cattle. The clean grassland of the meadow flood- 

 area, and of hay-fields generally, is maintained by the agency of annual 

 mowing, whereby the shoots or seedlings of woody plants (Elm, Poplar, 

 Thorn) are kept down, as are also the late summer-growths of thistles of 

 the dry season. Flood-meadows are subject to free invasion from the hedges 

 by suckers of Common Elm and Gray Poplar, for a distance of 20-50 yards 

 from the tree, and these as a rule are not touched by grazing cattle. In the 

 same way damp clay pastures produce seedlings of Crataegus, and such 

 thorny shoots are also avoided by cattle, growing 2-3 ft. in the first two 

 years if not mown over. Hawthorn is followed by Rose-briars, by intrusive 

 Sloe from the hedges, locally by Ononis spinosa, and to a much less extent 

 by Rubus which prefers leaf-mould. All these plants are spinous and are 

 rejected by cattle. As the larger forms become shrubby, cattle graze 

 around them, thus rounding off the bushy growths to compact oases of thorn- 

 scrub. Where there is no grazing the thorn-growth may be fairly uniform, 

 soon becoming impenetrable. 



Good examples of the first stages of Thorn-scrub are afforded by poor 

 pastures on Kimeridge Clay (Iffley, Sandford Brake, Cumnor Hurst), and on 

 Oxford Clay (Binsey). The derelict Marconi Station on Cumnor Hill (Coral 

 Rag), gave close thorn-growth to 5 ft. high in 3 years, having been sown from 

 an adjacent hedge by strong winds for a distance of 50 yards. 



The thorns may thus give isolated tall bush-growths, 10-20 ft. high, with 

 little else but Briars and Brambles (Headington Quarry, Magdalen Bridge 

 Scrub) ; soon becoming impenetrable where grazing is wanting (Chawley Hurst 

 Scrub, Sandford Brake Scrub); the ground-flora of grasses and herbaceous 

 plants being comparatively little affected until canopy is complete. 



With the action of cattle in 'rounding off' the patches of scrub, other 

 plants are protected at their margins, afforded free light, and incidentally 

 manured ; Nettles, Thistles, Solatium Dulcamara, rough grasses of the hedge- 

 rows, Bromus asper, and Umbellifers as Anthriscus sylveslris, Heradeum 

 Sphondylium, Torilis Anthriscus, reproduce the flora of the Hedge-associations, 

 and further stages follow the general lines of regressive woodland. Good 



