. The Canadian field-naturalist. 1998 Begg, Archibold, and Delanoy: Riparian Cottonwoods 691 140- 120- 03 mo I J) C T3 0) 0) 80 CO ^f O <D HO JJ E 40- 20- â North Saskatchewan River â¡ South Saskatchewan River o O) g] 95 CO V o o C\J o CO §. Height class (cm) Figure 8. Height-class distributions for cottonwood seedlings on the North and South Saskatchewan rivers. the time of the survey were at an elevation of m above the water. Numerous sand bars had formed adjacent to the island at site 2b, and seedlings were restricted to the east bank of the island away from the main channel. The ma
. The Canadian field-naturalist. 1998 Begg, Archibold, and Delanoy: Riparian Cottonwoods 691 140- 120- 03 mo I J) C T3 0) 0) 80 CO ^f O <D HO JJ E 40- 20- â North Saskatchewan River â¡ South Saskatchewan River o O) g] 95 CO V o o C\J o CO §. Height class (cm) Figure 8. Height-class distributions for cottonwood seedlings on the North and South Saskatchewan rivers. the time of the survey were at an elevation of m above the water. Numerous sand bars had formed adjacent to the island at site 2b, and seedlings were restricted to the east bank of the island away from the main channel. The mature cottonwoods on the other side of the island were the probable seed source for these young seedlings. Here the zone of seedling establishment was some 30 m from the river's edge at an elevation of m. The seedlings at site 3 had established in a band to m above the water on a fairly steep bank away from the main channel; young saplings were present above this becoming progressively older with distance from the river with stands averaging 20 years in age some 60 m away. Evidence of extensive Beaver (Castor canadensis) activity was noted on the younger trees. At site 4 seedlings had established about m above the water and continued up the bank to about m forming a narrow band about 20 m from the water. The zone of seedling establishment was about 20 m from the older trees which were found on the higher parts of the island about 40 m from the river. Discussion Changes in flood frequency and flood magni- tude, and seasonal alterations in peak discharge patterns have a noticeable impact on the riparian species which inhabit floodplain environments. Cottonwoods are especially sensitive to altered hydrological regimes. Seedling establishment coin- cides with natural flood events at which time mature trees release large numbers of short-lived seeds. Successful establishment is restricted to critical zones on alluvial point bars that are high enough to resist
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Keywords: ., bookauthorottawafi, bookcentury1900, bookdecade1910, bookyear1919
