Plant Migration Along a Partly Drained Lake 



T. C. Frye 



University of Washington, Seattle 



A few years ago a canal was cut along the southern boundary of the 

 campus of the University of Washington thus connecting Lake Washington 

 with Lake Union. This lowered Lake Washington about 11 feet (3.4 m.). 

 There was thus left a shore largely unoccupied, largely of excellent soil, 

 in certain localities indeed almost wholly of decomposing vegetation. This 

 offered a fine opportunity for the observation of the adjustments of the 

 vegetation to the new water level. 



Three chief lines of observation were followed: (a) What is revealed 

 by the uncovering of the submerged lake margin? (b) What will happen 

 to the plants along the old water level and below it? (c) What gets es- 

 tablished on the unoccupied area, and why ? 



The recession of the water revealed the following plants as the com- 

 moner: Nuphar polysepala (jeWow water \i\y), Brasenia schrebej-i (water 

 shield), Scirpus occidentalis (tule), Elodea canadensis (water weed), 

 Utricular'ui vulgaris (bladderwort). Ceratophyllinn demersum (hornwort), 

 Myriophyllum sp. (water milfoil), Potamogeton rmtans (pondweed). Poly- 

 gonum amphihium (water smartweed), Isoetes echinospora (quillwort). 



Of these the following did not reappear above the new water line: 

 Elodea, Utricularia, Ceratophyllum and Myriophyllum. All are attenu- 

 ated plants which dry easily. Only Ceratophyllum, of the four, was ob- 

 served the first year below the new level. Elodea alone of the four has 

 not been seen since. 



Brasenia and Potamogeton reappeared in the old location, but did not 

 reach maturity. Potamogeton has again appeared below the new level, but 

 Brasenia has not. 



Isoetes was abundant in suitable edapliic situations 8 to 11 feet (S.f) 

 to 4.3 m.) below the old water level at the time of recession. It grew well 

 the first year even where uncovered. But the winds of the next winter 

 caused waves which eroded the new shore, and with it went all the Isoetes. 

 Neither in the old location nor under the new level has it been found since. 

 It might, however, be fairly abundant 8 to 11 feet (2.5 to 4.3 m.) below 

 the new It-vtl without one finding it. 



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