Cyclic and Pattern Phenomena as Exhibited by Alchemilla Alpina

Abstract

Watt (1947a) has shown how measures of the performance of Pteridium aquilinum indicate quite clearly a 'marginal zone' and 'hinterland' in an area of invading bracken. This effect is shown to be due to an initial even-aged stand of maximum performance at the margin, leading to a mosaic of phases in the hinterland connected by an age series as well as by their spatial arrangement. Each phase, descriptively termed 'pioneer', 'building', 'mature' and 'degenerate', has a different level of performance and fits into a general scheme of behaviour. Similar examples of 'marginal effects' have been described by Caldwell (1957) and Ovington (1953). Agrostis tenuis also forms well-defined rings devoid of tillers in the hinterland (Watt 1947b), or with isolated tillers apparently uniformly distributed over the whole of the hinterland (Kershaw 1958). In addition a cycle of development has been discovered in Agrostis basically similar to that of bracken (Kershaw 1958), Watt (1947b) has given several examples where more than a single species is concerned, successive species following as a dominant phase as the preceding phase degenerates, a cyclic rotation being maintained both in time and space. It seems reasonable to suppose that, with increasing age of a perennial plant, degeneration will set in, and it is pertinent to inquire what events are set in motion by the onset of this degeneration. Thus it would appear that a cyclic fluctuation involving a single species or alternatively a cycle of phases involving several species may be widespread phenomena and may possibly be present in most plant communities. A knowledge of such cycles is greatly to be desired. Watt (1947b) has given a generalized curve of the total productivity of a cycle divided into an 'upgrade' and 'downgrade' series as exemplified by seven plant.associations (Fig. 8). Since the total productivity of a phase in these examples (with the exception of bracken) is a reflection of the productivity of several individual species it is interesting to speculate on the form of the individual productivity curves representing the total. In many instances the major difficulty in such an investigation is the determination of the age of any given individual when morphological or anatomical methods are often of no assistance. With the above considerations in mind the morphology, anatomy and performance of Alchemilla alpina were investigated. The data presented below were the results in part of the 1958 Imperial College Expedition to Osa, Hardanger, Norway.