Riparian Plants: White Alder - Alnus rhombifolia
White alder is less common on the floor of the Central Valley than in montane or coastal rivers and streams but they can be found in riparian forest and willow scrub communities. White alder roots must have close access to the water table; roots must be within 1m reach of water. They are not drought tolerant. Though they must have access to permanent water, they are not able to tolerate long floods. White alder requires sufficiently aerated roots and standing water cannot provide enough oxygen. Often, white alder is found growing in boulders and large grained sediments, possibly because this substrate keeps roots well aerated. White alder seeds can establish quickly on freshly deposited point bars if they are adequately moist.
White Alder grows into moderate to large trees, 9-30m tall and 28 cm in diameter. Typically they grow with a single trunk, but they can develop multiple trunks that arise from one clump. White alder commonly provides shaded riverine aquatic habitat because the trees typically grow along river banks. Insects drop from white alder into the river, along with leaves and twigs that support aquatic insects. White alder is therefore an important source of nutrients to aquatic systems. The smooth bark is frequently eaten by beavers. Alder seeds are eaten by birds and mammals, and mammals will eat the twigs and leaves.
For more information about the ecological tolerances and structure of riparian plants, see Gaines 1977, Conard and others 1977, Holstein 1984, Sacchi and Price 1988, Faber and Holland 1996, Cooper and others 1999, Vaghti 2003, Fremier and Talley 2009, and Vaghti and others 2009.
White Alder dimensions
White Alder in winter