Regressive Woodland 65 



in which the overwood is allowed to become dominant 1 need not imply a history 

 of more than 100-200 years. 



Admirable minor examples are afforded by the Hinksey ' Ravines '. These 

 represent deep erosions in Corallian strata, three in number, cut in lower parts 

 to the Oxford Clay bottom, to 50-100 ft. deep at the maximum ; the bottom 

 swampy, and the sides too steep to readily plough or mow. All were originally 

 well-wooded from top to bottom. The present state of these ravines (especially 

 that of the Chilswell Stream, or ' Happy Valley ') epitomizes the story of local 

 woodland. The swampy bottoms give yw-association, as water percolates 

 to the clay strata, residual copses are left in isolated patches (Chilswell Copse, 

 Limekiln Copse), but much of the sides has been cleared to be utilized as 

 rough pasture. The slopes show a remarkably clean-cut sky-line, and the 

 ground above (Coral Rag) is arable, and cultivated to the edge. 2 The grassy 

 slopes tend to revert to thorn-scrub, which may regenerate poor coppice in 

 parts, but in others is kept down by bill-hook. In some more level lower 

 portions, small holders are beginning to struggle with the difficulties of the 

 situation. The ' Happy Valley ' is within the range of school-holidays, and 

 is popular on Good Fridays and Bank-holidays. 



(i) The Chilswell Ravine ('Happy Valley') is continued up above the 

 Kimeridge Clay at Chilswell Farm to the Greensand of Pickett's Heath, 3 giving 

 a few distinctive plants in higher parts (Campanula rotundtfolia), and poor 

 coppice on the clay (Birch Copse). 



(z) The Rifle-range Ravine, north of Chilswell, passes up to clay, over 

 which streams exude giving good Hill-swamp of Equiselum Telmaleia, and 

 subaquatics in profusion, with Eupatorium and Orchis maculata ; at a higher 

 level Juncetum, thorn-scrub, and on the Corallian characteristic thistles, as 

 Carduus acaulis and C. eriophorus, following on to the bottom of Hen Wood. 



(3) The Old Rifle-range Ravine, south of Chilswell, is less deeply cut and 

 cleared. It similarly continues on to the Kimeridge and the derelict coppice of 

 Tommy's Heath to the Greensand of Boar's Hill. 



Grassland and the Evolution of Pasture. 



The original formation of grassland, as a special case of Herbaceous 

 plant-growth, follows as a general adaptation to conditions of reduced rain- 

 fall and water-supply, involving an amount available in the year less than 

 will support tree-life in close canopy. It thus presents a remarkable 

 example of adjustment to extreme seasonal change, originally expressed as 

 the alternation of a hot and dry period with a short rainy season in tropical 

 forest. 



The Grass-type implies the total loss of the primary arboreal factors of 

 erected main axis with cambial increase and a deep-sinking primary root- 

 system ; the prototype being seen in Bamboos of High Forest, as a special 

 biological growth-form, running parallel with the liana in its capacity for 

 rapid rise to the top of the forest with minimum stem-material, but by a 

 wholly distinct mechanism. A tropical Bamboo may be rushed up 100 ft. 

 in a month of the wet season. The main axis reduces to a more or less 

 horizontal rhizome, giving off erected laterals seasonally, which show no 



1 e. g., Oak over Hazel and Bracken, but also intrusive Common Elm over Nettles, or alien 

 Sycamore-coppice over Mercurialis. 



Cf. Schlich, Silviculture (1910), p. 265. The stools of ash, maple, birch, and beech are short- 

 lived, lasting frequently not more than two or three rotations. Oak-stools are practically 

 indestructible, and Hazel freely suckers. Hence where there is little planting, Oak- Hazel coppice 

 becomes the end-term of an artificial selection, as a simple matter of survival. 



2 Headington Wick, on the Elsfield side of the valley, is a similar ravine, cultivated to the 

 southern edge, but still predominantly coppiced. 



8 The old hill-track to Wootton rises straight up the Chilswell valley from S. Hinksey, at 200 ft., 

 to Chilswell Farm on clay at 400 ft., over Pickett's Heath (by Matthew Arnold's tree) to Hill-crest 

 (500 ft.) on the top of the Boar's Hill Road. 



E 



