Smooth alder is a nitrogen-fixing, thicket-forming shrub or small tree with dark, green foliage. It is a U.S. native. It is suitable for streambank stabilization because of its flexible stems and fibrous root system. A mature height of 8-12 feet may be reached in 10 years. Seed is produced in small cones with pollen contributed by birch-like catkins which bloom in mid-to late March. Compared to other alder species, smooth alder is more densely branched and produces more seed. Alders produce nitrogen for themselves by the activity of nitrogen-fixing bacteria located in root nodules. For this reason, it is not recommended for planting in areas where additional nitrogen might add to water quality problems. Smooth alder has about 400,000 seeds per pound.
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