CGRG Bibliography of Canadian Geomorphology
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Author : Blundon, D.J.
Date : 1989
Title : Primary succession following retreat of the Robson Glacier, British Columbia
Publication : Unpublished Ph. D dissertation. University of Alberta, Edmonton
Issue :
Page(s) :
Abstract
Primary succession on highly calcareous parent material of the Mount Robson glacial moraines was examined by documenting plant community development as inferred from studying surfaces of different ages, and as observed by redescribing sites previously documented. Vegetation development within moraines was found to be similar to that observed on a chronosequence of moraines. This similarity supports the inferential methods used to study succession at other sites. The vegetation on the Robson moraines was classified into three phases. The pioneer Hedysarum phase occurred on the youngest recessional moraine (8) and was dominated by the herb Hedysarum boreale var. mackenzii. The Dryas transition phase occurred on recessional moraines 7 and 5 and was dominated by D. drummondii and H. boreale. The oldest successional plant community, the Picea phase, was found on recessional moraines 3, 2, and 1, and the terminal moraine. It was dominated by P.engelmannii and Arctostaphylos rubra. Importance-value curves for all the communities were essentially linear, fitting the niche preemption model which is typical of species poor-communities controlled by a single factor. This conclusion is also supported by the predominance of negative interspecific associations, which indicates that competition may play an important role in structuring the communities throughout the chronosequence. The legume Hedysarum boreale was considered the major nitrogen-fixing agent on the moraines, followed by soil microorganisms. The estimated annual N input from biological nitrogen fixation decreased approximately 8-fold over the 200 year forest succession. Hedysarum boreale formed centres of establishment for Salix seedlings, and for S. glauca and Picea engelmannii which become dominant species on the older moraines, thus facilitating succession. During succession, spatial pattern at first intensifies at the scales initially observed, followed by a general reduction in intensity with community development, following the trends suggested by other researchers. However, the number of scales of pattern of each species remained relatively constant and did not decrease on the older moraines. It is concluded that while the 200 year old vegetation on the Robson moraines is physiognomically mature, it has not attained all the characteristics expected of a fully mature community. Future changes on the Robson moraines may include increased abundance of Abies lasiocarpa and feather mosses together with soil maturation until, in the absence of fire, and other disturbances, the old growth Picea-Abies forest of the subalpine zone is attained.
Bibliography of Canadian Geomorphology