77 
plant of slough margins, and probably finds its way into this situation on 
account of the semi-ponded conditions where the lower slope of one terrace 
meets the more or less steep iront of the next oldest one above it. The 
landward side of this association contains saplings of Populus tacamahacca, 
forerunners of the timber. 
Sharply separated from this association by the front of the next land- 
ward terrace is one that may be another willow association or one of trees. 
If the former occurs it is dominated by a tall species of wide distribution 
in these flood-plains, Salix lut?.a, with a ground cover of the goose-grass 
Equisetum pratense. The ground vegetation is scanty except for the close 
stand of Equisetum, but such shrubs as occur in the poplar association or 
at its margin are rather common: Cornus stoloniiera, Rosa acidularis, 
Amelanchier fiorida. The sand-bar willow is still present in small numbers 
along with sapling balsam poplars. 
Transitions from willows to timber on the local flood-plains do not 
differ essentially from those already described in the deltas, and the poplar 
and spruce forests are, of course, the same. Alnus incana , Salix Bebbiana, 
S, arbusculoides , and S. planifolia are involved, and the ground cover of 
Equisetum pratense is gradually replaced by mosses and woodland herbs. 
As seen from the river, therefore, the lowest, grass-green bank of vege- 
tation is of horsetail Equisetum limosum, the next highest is formed of the 
sand-bar willow Salix interior \ ar. pedicellata. The latter is of light yellow- 
green and has a filmy appearance caused by its pendulous, narrow leaves. 
Due to differing stages of growth on terraces of varying age, this willow 
often forms more than one bank, the upper shading off in colour, by way 
of Salix planifolia, to the darker green of the taller Salix lutea. Above the 
yellow willow (so named because of its yellow branchlets) is the bluish 
green of the balsam poplars, nixed with the nearly black spires of the 
spruces. 
Essentially the same succession is to be found on the island at the 
30th base line (Figure 11, D, and Figure 14). The different associa- 
tions are there made even more prominent by being separated by long, 
narrow sloughs or lagoons. The low mud terraces at the Government Hay 
Camp do not have a yellow willow association, and the sand-bar willow, 
with a ground cover composed mainly of Equisetum pratense, immediately 
follows the E. palustre association and adjoins the timber. It stands on a 
low bar having a wet depressior at its landward side in which are a number 
of marsh or wet meadow plants such as Typha latifolia, Beckmannia Syzi- 
gachne, Poa pratensis. Glycerin grandis, Carex trichocarpa var. aristata, 
C. rostrata, Eleocharis calva, Juncus balticus. Ranunculus Cymbalaria, 
Physostegia parvi flora, Plantago major var. asiatica, and Aster junceus . 
A few individuals of Salix arbusculoides come from the margin of the tim- 
ber. The lack of transition stages to the timber appears to be due to some 
comparatively recent shift in the activity of the river along this shore. 
Subsequent to some erosion period in which the river has cut an earlier 
flood-plain back to the terrace that now holds the timber, a new deposit 
has been begun which now bears the earlier stages of the vegetation. This 
change may be a seasonal one, but this is not likely on account of the 
relative permanence of the vegetation on the highest of the new bars. It 
91963—6 
