REGRESSION. 



153 



"progressive" scrub is more frequent than "retrogressive" scrub. It is 

 diflScult to discover the reasons for his change of opinion. The absence of 

 definite evidence of degeneration, and especially of retrogression, due to natural 

 causes, militates strongly against the acceptance of his later view. The 

 question of supposed degeneration is preeminently one in which quantita- 

 tive methods through a number of years are indispensable. Quadrat and 

 transect must be used to determine the precise changes of population and of 

 dominance. Changes of habitat and the degree and direction of reactions 

 must be determined by intensive methods of instrumentation, while the exact 

 developmental sequence can only be ascertained by the minute comparative 

 study of scar-rings and stump-rings, as well as that of soil -layers and relicts. 

 Even the keenest general observations can not take the place of exact methods, 

 which are alone capable of converting opinion into fact. 



Moss considers retrogression of the moor upon pages 166, 188, and 191. 

 The point already made that the Vaccinietum myrtilli is always a stage in the 

 normal progressive development is confirmed by the classification of moorland 

 plant associations. (166) The discussion of retrogressive moors (188-189) 

 adds further emphasis to the fact that retrogression is merely destruction due 

 to denudation. 



"Whilst the peat of the closed association of Eriophorum vaginatum is stiU 

 increasing in tluckness at a comparatively rapid rate, and that of the closed 

 associations of heather and bilberry is also increasing though much more 

 slowly, the peat on the most elevated portions of the moors is gradually being 

 washed away. This process of physical denudation represents a stage through 

 which, it would appear, all peat moors, if left to themselves, must eventually 

 pass. Following Cajander [qf, Nilsson, p. 146], the associations thus formed 

 are termed retrogressive ['regressive'] associations. 



"In the Peak District, the process of retrogression in the cottongrass 

 moors is apparently initiated by the cutting back of streams at their sources. 

 Every storm results in quantities of peat being carried away, in the stream 

 winning its way further back into the peat, and in the channels becoming 

 wider and deeper. Numerous tributary streams are also formed in the course 

 of time, and eventually the network of peaty channels at the head coalesces 

 with a similar system belonging to the stream which flows down the opposite 

 hillside. The peat moor which was formerly the gathering ground of both 

 rivers is divided up into detached masses of peat, locaJHy known as peat hags 

 (plate 45 a); and the final disappearance of even these is merely a matter of 

 time. 



"It is obvious that this process results in a drying up of the peat of the 

 original cottongrass moor; and it is most interesting to trace a series of degra- 

 dation changes of the now decaying peat moor. The first change of impor- 

 tance of the vegetation appears to be the dying out of the more hydrophilous 

 species, such as Eriophorum vaginatum and E. angustifolium, and the increase, 

 on the summits of peaty 'islands' or 'peat-hags,' of plants, such as Vacdnium 

 myrtHlus and Empetrum nigrum, which can tolerate the newer and drier soil 

 conditions. The composition of the upper layers of the peat of these retro- 

 gressive moors has, during the course of the present investigation, been care- 

 fully examined; and it has been found that the peat consists in its upper layers 

 almost wholly of the remains of Eriophorum. The succession of cottongrass 

 moor to the series of retrogressive moors here being described, is established 

 beyond a doubt." 



