smooth alder
Alnus serrulata

Hardiness: Zone 4 to 9
Plant type: Tree
Height: 10- 20'
Spread: 8- 15'
Sun: Full sun to part shade
Water: Medium to wet
Bloom time: March, April
Bloom color: male flowers are brownish yellow, female flowers are red      Soil: Sandy, clay, mucky, acidic soils

More information on this plant here.