76 
The secondary species are of small importance and are commonest at 
the landward side, where the willow from the following association is 
actively colonizing the mud. There is much driftwood on the shore, mostly 
of large dimensions. 
To summarize the herbaceous associations on these shores — they range 
from complete absence on sandy, well-drained bars, to the abundance and 
complete dominance of species of Equisetum on low mud shores. The 
j Equisetum associations vary from pure stands on the higher mud deposits 
of streams in which the currents are active, to associations with a large 
number of secondary marsh species on bars in the lower deltas where more 
nearly ponded conditions prevail. 
SHRUB AND TREE ASSOCIATIONS 
The sand-bar willow Salix interior var. pedicellata is of nearly universal 
occurrence as a pioneer on the local river flood-plains. It is either the first 
vegetation or follows the horsetail directly in the developmental succession, 
and is admirably adapted to the role by its prolific vegetative means of 
reproduction. Its secondary associates appear to be determined largely 
by the major soil differences described above, the sandy soils growing the 
more xerophytic types of plants. The latter condition is best shown at 
Peace point and on the island at the 30th base line. The initial vegetation 
is a pure stand of Salix, but it is followed immediately on slightly higher 
ground by a more complex association. 
Primary spp.: Salix interior var. pedicellata 
Eqxdsetum prealtum 
Secondary spp.: Picea glaum (seedling) 
Agropyron trachycaulum var. typicum 
Agrostis scabra 
Calamagrostis canadensis var. robusla 
Salix lutea 
S. planifolia 
Alnus in can a (young plants) 
Potentilla Anserina 
Frag aria gtauca 
Epilobium angusiijoUum 
Comics stolonifera (seedling) 
Castilleja Raupii 
Achillea Millefolium 
Solid.ago canadensis 
Eager on philadelphicus 
E. acris var. asteroides 
The primary species are abundant, but the secondary ones are much 
scattered, and for many a careful search must, be made. Many of them 
appear elsewhere in more mesophytic associations, and here indicate the 
trend of the succession. On the driest spots, particularly at the outer edge 
of the association, the primary species are almost alone. As indicated on 
the diagram (Figure 11, B), however, the lower, landward slope of the 
terrace shows a notable change in conditions. Salix planifolia is advanced 
to a primary position, whereas Equisetum pratense shares prominence with 
E. prealtum. In wetter places J uncus balticus is abundant, but most of the 
secondary species remain the same. $. planifolia is characteristically a 
