The South Downs

Peter Friend is the author of New Naturalists number 108 Southern England. Writing here, for the New Naturalists online, he welcomes the recent decision to preserve the South Downs as a national park:
 
On 31st March 2009, Natural England designated the South Downs as England’s latest National Park. Most of us associate National Parks with Yosemite or the Grand Canyon, or nearer to home, the Lake District or the Cairngorms.  One point about the South Downs Park is different from these:  it is precisely because of its proximity to centres of population that its designation is so important.  The Park extends from Winchester in Hampshire, to the west, to Eastbourne in Sussex, to the east, a distance of some 70 miles.  For much of this distance it is sandwiched between two of the most intensively built-up areas in Europe.  These are the Thames Valley including London, and the south-coast conurbation extending from Portsmouth, through Chichester, Bognor, Worthing and Brighton.
 
The visionaries behind the new Park share a determination with those behind the great Parks of the U.S.A and our own North, to preserve as much as possible of the landscape and its wildlife.  But given the proximity of so much population and its inevitable increase, the challenge for the South Downs will be enormous.  Perhaps the trick will be to put great effort into the education of visitors to help them develop the delight in discovery that is there, somewhere, in all of us.  Days out in the Park must be enlightened as much as possible by learning how to unlock the secrets of its special features.
 
The secrets of the South Downs Park occur at all levels of scale within its landscapes and wildlife. Here I pick out aspects of its landscape that explain why the Park is there and why its scenery is so special.
 
The South Downs are made of Chalk, an extraordinary material made of minute chalky organisms that was deposited across parts of north-western Europe as a result of special environmental conditions that existed in a tropical sea between about 100 and 65 million years ago.  Before and after this episode much more normal muddy and sometimes sandy materials accumulated in this sea and formed the layers below and above the Chalk.
 
Some millions of years later, movements occurred within the Earth in this area, in the same way that unstable other areas of the Earth are affected in our times.  The layers that originally formed in the sea were gently folded to create the pattern of upfolds and downfolds still visible today.  At the same time the sea withdrew from this part of Britain, and streams and rivers to take the rain-water off the newly emergent land eroding material as they flowed and starting to form the major valleys where the Thames and the English Channel now are.  It was this erosion that was resisted more by the Chalk than by the other materials at the surface, so that the rising Chalky areas became the hills creating the Downs that form the central feature of the Park.
 
The South Downs have recently been described as a “wonderful green whale” referring to another of the secrets.  The hills are unlike most others in Britain in their shape and feel. They are smoothly round, but contain steep-sided and steep-ended valleys, often bare of trees and covered with smooth, closely-cropped grass. Many of the valleys are dry and lack the rivers that might break up the smooth shapes. On a good day, the sensual feel of the shapes is remarkable, especially when the open skies above are full of singing larks.  The rounded green hills are classic features of landscape art, contrasting locally with impressive shaded slopes.  The processes that produced these landscape effects are a direct result of the period of cold climates that we have recently emerged from, and the effects of this on the Chalk bed-rock under the ground.  For much of the last two or three million years, Britain has experienced extreme climate fluctuations, on a time-scale of thousands or tens of thousands of years.  Brief periods when the climate was like that of today have alternated with longer periods when the climate has been much colder.  The general term Ice Age is well known but it is important to realise that the South Downs have never actually been covered by ice sheets or glaciers.  Instead the Chalk hills were subjected to long periods when their rocks and soils were repeatedly frozen and thawed, cracked up and moved, many millions of times. The resulting down-slope creeping and collapse of the Chalk is the reason for the smooth roundness and steep slopes of the Downs, and the way that streams soak into the valley floors and vanish.
 
Near Eastbourne, Beachy Head and the Seven Sisters are spectacular features where the Chalk Hills of the South Downs have been cut by the vigorous storm erosion where the rise of sea-level over the last few thousand years has flooded the Valley previously occupied by the English Channel river.

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