A chronosequence of soils and vegetation near the Franz Josef Glacier

Abstract

The recent rapid retreat of the Franz Josef Glacier in South Westland has produced extensive tracts of morainic debris, subsequently fashioned into a series of terraces of varying ages by the meandering Waiho River. These bare and boulder-strewn terraces have been colonised by a succession of different plant communities, and examination of the area by botanists led to the recognition of six representative stages in this succession, whose ages could be accurately determined.

A sequence of very youthful soils has developed on the parent material concomitantly with these successive colonisation stages, and is initiated and influenced mainly by the various plant communities following each other. The major feature of soil development is the progressive accumulation of organic matter in the upper few centimetres of mineral material, and on the surface as a deep, fibrous, greasy brown mor, interlaced with actively ramifying roots.

The situation therefore presents a classical opportunity to investigate a 'Chronosequence' of soils (and associated vegetation), because the youthful sequence of soils within this restricted area have developed under uniform climate on level topography from identical parent materials at ‘time zero’. Soil differences are thus due to the lapse of different increments of time since the terraces were formed and plant succession was initiated.

In this juvenile stage of soil development the gradual accumulation of organic matter governs changes in many soil properties. Therefore, the total amounts of organic matter and the proportions of its various constituents are of paramount importance. Accordingly, it was thought profitable to attempt measurement of only some changes in soil properties, lack of time precluding a more extensive investigation. In spite of sampling problems presented by the unusually coarse parent material, it was hoped that the changes in pH, amounts of Carbon, Nitrogen and organic Phosphorus in the mineral soil, the mor layer and in the vegetation would be interesting and would elucidate the initial processes of soil development. Three earlier studies in Alaska and California on similar situations provided some details of the processes concerned, but it was hoped to extend and refine in various ways the methods used by these workers. The investigations at Franz Josef in all their facets are recorded in the following pages, and it is thought that they may represent a useful addition to the state of knowledge in this field.