(2) EXCEPTION. A county drainage board may allow the growth of woody vegetation in portions of a district corridor, provided that the woody vegetation does not interfere with effective access to district drains. A county drainage board, when deciding whether to allow the growth of woody vegetation, shall consider how the woody vegetation may affect the cost of maintaining and cleaning district drains. Any portions of a corridor left in woody vegetation shall be maintained under a resource conservation plan developed in cooperation with the county land conservation department or the United States natural resources conservation service. Note: In some parts of a district corridor, woody vegetation may have important value as wildlife habitat, or for controlling soil erosion. Ordinarily, ditches are not subject to local shoreland or wetland zoning ordinances. However, in a small number of situations, where ditches are considered natural navigable streams, local ordinances may limit the cutting of woody vegetation. See s. 281.31(2m), Stats., and chs. NR 115 and 117.