Flooding patterns and variations in the composition and successional trends of riparian vegetation in the upper and lower Red Deer River in southern Alberta, Canada. were studied in order to establish which flood regimes were most important in the regeneration and maintenance of riparian vegetation communities. with a particular focus on riparian poplars. The dominant riparian tree in the upper river is Populus balsamfleru with some Picea gluuca and in the lower river Populics deltoides (the plains cottonwood). Dendrochronological studies of the poplars along the river show that major periods of regeneration correspond with major flood events during the record period. Extensive cottonwood regeneration occurred in the period 19W20. corresponding with a series of floods. some as high as the I in 100-year event. In addition, just

White spruce forests on the most elevated surfaces of the Mackenzie Delta are dying out and are being replaced by open spruce/lichen‐heath or spruce/bog woodlands. Soil profiles indicate that these woodlands have not received flood‐deposited sediments for many years. The active layer is only 20 to 50 cm deep by mid‐summer, and the organic soils are colder and more acidic than soils under white spruce forests flooded during spring ice breakup in 1961, 1972, and 1982. Spruce regeneration is limited to those stands that are flooded periodically, have moderately‐closed canopies, and have a ground cover of herbs rather than feathermosses and lichens. It is proposed that a decrease in flood frequency is primarily responsible for the poor regeneration of white spruce on the most elevated delta surfaces. Spruce woodlands on the delta could succeed to tundra vegetation if present fluvial regimes continue.

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The d i s t r i b u t i o n o f Equisetum f l u v i a t i l e on t h e Mackenzie Delta, N.W.T., Canada was examined between 1981 and 1987. E. f l u v i a t i l e occupied mineral and organic substrates on t h e l o w e r s h o r e l i n e s o f s t a b l e channels and lakes t h a t were f l o o d e d f o r 1 t o 3 months d u r i n g t h e growing season, and r e c e i v e d 1 t o 15 cm annual deposits o f s i l t y alluvium. The d i s t r i b u t i o n o f E. f l u v i a t i l e i n t h e tundra o f t h e o u t e r d e l t a ( n o r t h o f 69 degrees l a t i t i i d e l was patchy and r e s t r i c t e d t o i n f i 1 l i n g i n t e r -l e v e e basins. Sexual r e p r o d u c t i o n was n o t observed d u r i n g t h e study; E. f l u v i a t i l e propagated and c o l o n i z e d new s i t e s by t h e p r o d u c t i o n o f -annual stems from underground rhizomes and d i s p e r s a l o f p l a n t fragments d u r i n g i c e breakup f l o o d i n g and muskrat grazing. N a t u r a l p r o l i f e r a t i o n o f stem fragments was observed, b u t t h e propagules d i d n o t survive.

A technique for coring flocculent limnic sediments, involving the use of a Livingstone piston sampler and dry ice is described. The technique is most useful when detailed stratigraphic analysis of surface sediments is important.