Species Versatility in Shore Habitats

Abstract

Materials for the present paper are derived from notes and plant collections made during seven field seasons in the years 1926-30, 1932, and 1935, in the Athabaska-Great Slave Lake region of northwestern Canada.In the course of this work shoreline vegetation was described at approximately 130 places.Seventy-nine of these were on the shores of sloughs, ponds, and small lakes, while the remaining 51 were on the shores of the larger lakes (Athabaska and Great Slave) or on river banks and deltas.The following discussion deals primarily with the vascular flora, though reference is made on occasion to lichens and mosses.A part of the material was published in the author's "Botanical investigations in Wood Buffalo Park" (1935).Itineraries of the seven expeditions will be found in this paper and in others dealing with the vascular flora and its distribution (Raup, 1930b(Raup, , 1936(Raup, , 1941)).A brief account of the vegetation of Shelter Point, Lake Athabaska, was published in 1928, and a paper on the shore vegetation at Fort Reliance, Great Slave Lake, in 1930(a).The most complete sets of supporting plant collections are at the National Herbarium of Canada in Ottawa, and at the Harvard University Herbaria in Cambridge, Massachusetts.Most of the vegetational data for the present study were gathered along transects selected because they showed differences or similarities when compared in the field with other transects.The differences were recorded first in terms of species' presence or absence, and second in terms of primary and secondary species.In common ecological parlance the primary species in an assemblage would be termed "dominants."They are the ones that give a specific form, color, or other characteristic to an assemblage of plants by which the latter is readily distinguished visually from those adjoining it.All other species in the assemblage are regarded as secondary.Usually the primary species are those that predominate in numbers of individuals, but in sparse vegetative cover or in tree or shrub vegetations the populations of primary species may be smaller than those of secondary species.The selection of primary species was done by eye.A general view of the shore floras of the region shows them occupying an extraordinary number of lakes, ponds, and sloughs that dot the landscapes.They are numerous in the great deltas and flood plains of the lower Athabaska, Peace, and Slave rivers, but are especially abundant on the crystalline and metamorphic rocks of the Canadian Shield.Travelers for many years have noted the large numbers of small bodies of water along their routes, but full realization of their extent awaited the advent of aerial photographic mapping.An area of 16 square miles (4 miles square) selected at random in the country north of Lake Athabaska con-1975] RAUP, SPECIES VERSATILITY 127 tains over 100 ponds and lakes large enough to appear on a map scaled at 4 miles to one inch.The number of smaller water bodies can only be conjectured, but a conservative estimate would be another 100.The ponds and small lakes throughout this region are infinitely variable in shape, size, and depth.The large lakes also present a wide variety of shorelines, from almost vertical rock cliffs to wide shelving beaches of sand, mud, or shingle.Further variation is found in the morainic and karst topography west of the Slave River, in flood-plain sloughs and deltas, and in the saline flats that border the Salt and Little Buffalo rivers.However these bodies of water were formed and whatever their subsequent history, their abundance and the large proportion of the total flora they harbor force us to consider their marginal plant life as one of the most important elements in the vegetation of the region.When this study was begun in 1926, major emphasis was placed on the "development of the vegetation."The units of study were to be "com-