Salix maccalliana Rowlee
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Basis for Listing
In Minnesota, Salix maccalliana is restricted to certain shallow wetlands in the northwestern counties. These are high-quality shrub swamps, shrubby fens, and sedge meadows. Extensive examples of these habitat types have become very scarce, and the downward trend is continuing. Even within the best remaining habitats, S. maccalliana is uncommon or rare. For this reason, it was listed as a special concern species in Minnesota in 1996.
Salix maccalliana is a visually striking shrub; it has multiple upright stems in the range of 2-4 m (6.6-13.1 ft.) tall that have short, ascending branches and shiny, red twigs. The leaves are dark green and shiny, with finely serrated margins. The larger leaves are 4-8 cm (1.6-3.1 in.) long and 0.8-2.5 cm (0.3-1.0 in.) wide. The bark is brownish to gray brown, smooth or somewhat rough with age. The male catkins are 1.5-3 cm (0.6-1.2 in.) long and borne on flowering branchlets typically 0.3-1.3 cm (0.12-0.51 in.) long; the branchlets can reach 2.5 cm (0.98 in.) long in extreme circumstances. The female catkins are 2-6 cm (0.8-2.4 in.) long and borne on flowering branchlets 1-2.8 cm (0.4-1.1 in.) long. The mature capsules are densely hairy and 6-11 mm (0.24-0.43 in.) long. The willow closest in appearance to S. maccalliana is probably S. serissima (autumn willow), but the petioles of S. serissima are completely hairless, while those of S. maccalliana are sparsely hairy. The leaves of S. planifolia (planeleaf willow) are, like S. maccalliana, smooth and shiny, but they have entire margins, not serrate, and a glaucous (blue-gray) lower surface (Smith 2008).
Salix maccalliana is apparently restricted to shallow wetlands in the northwestern counties, particularly shrub swamps, shrubby fens, and sedge meadows. These are basically sedge-dominated wetlands with varying amounts of Salix spp. (willows), Cornus spp. (dogwoods), or Betula pumila (bog birch) shrubs. The habitats are usually calcareous to circumneutral, sedge-derived peat or sometimes wet loam or wet clayey-loam. It seems that the strongly acidic and nutrient-poor conditions found in bogs are beyond the tolerance of this species.
Biology / Life History
Even in the best habitats, S. maccalliana never seems to be abundant; instead, it usually occurs as scattered individuals in a shrub community dominated by the more common and aggressive S. petiolaris (slender-leaved willow) or S. discolor (pussy willow). Although these habitats may be influenced by cyclical droughts and by localized spring flooding, they are basically stable environments with little or no history of human influence. It appears that S. maccalliana rarely, if ever, occurs in abandoned agricultural land, roadsides, or other grossly disturbed habitats. Under ideal conditions, a vigorous, well-established individual can produce dozens of stems that can grow to a height of over 4 m (13 ft.) and live 20 to 25 years. But individual stems rarely achieve such an age or size in Minnesota. They are often browsed heavily by white-tailed deer (Odocoileus virginianus) or moose (Alces alces), and are frequently top-killed by wildfire or more often by prescribed burns intended to improve wildlife habitat. Salix maccalliana responds to this sort of damage by resprouting vigorously and repeatedly, if necessary, from a diffuse root crown and from layered branches (Smith 2008).
Conservation / Management
Large, intact examples of the habitats where S. maccalliana occurs may require little active management; prescribed dormant-season burns on a rotation of perhaps 4-8 years, but little else. This assumes that natural drainage patterns have not been altered and invasive species are not established. On the other hand, smaller habitat remnants or larger tracts that have been degraded by drain tiles, cattle grazing, or other activities may require intensive management to maintain or restore their integrity. At the very least, ecological conditions in these habitats should be thoroughly evaluated and monitored regularly.
Conservation Efforts in Minnesota
Some of the better habitats where S. maccalliana occurs are owned and managed by private conservation organizations and public land management agencies. Most of these habitats are maintained for wildlife habitat or conservation purposes. With that stated objective, they are usually managed, to one degree or another, in ways compatible with the perpetuation of S. maccalliana.
References and Additional Information
Argus, G. W. 1997. Infrageneric classification of Salix (Salicaceae) in the New World. Systematic Botany Monographs 52:1-121.
Smith, W. R. 2008. Trees and shrubs of Minnesota. University of Minnesota Press, Minneapolis. 703 pp.