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COSEWIC assessment and status report on the Butternut in Canada

Habitat

Habitat Requirements

Butternut grows best on rich, moist, well-drained loams often found on stream bank sites but may be found on well-drained gravelly sites, especially those of limestone origin (Rink, 1990). It is seldom found on dry, compact, or infertile soils (Rink, 1990). Common associates include basswood, black cherry, beech, black walnut, elm, hemlock, hickory, oak, red maple, sugar maple, yellow poplar (tulip-tree), white ash and yellow birch (Rink, 1990). Butternut is intolerant of shade (Rink, 1990). There have also been reports of butternut as an indicator/associate with the rare understory plant ginseng, Panax quinquefolius L. (OMNR, 2000).

The climate for butternut varies greatly within its range. Mean annual temperature ranges from a maximum of 16°C to a minimum of 4°C (Rink, 1990). Frost-free periods extend from 105 days in the north to 210 days in the south (Rink, 1990). Butternut is susceptible to late spring frosts (OMNR, 2000).


Trends

Trends in habitat vary across the range of butternut. Forest cover for the area within the Ontario range of butternut varies from less than 10% in most of southwestern Ontario to 35% in eastern Ontario. In southwestern Ontario, the amount of habitat for all forest-dependent species has been severely reduced and potentially resistant butternut trees have been and are being lost through forest conversion to agriculture and development. However, in eastern Ontario total forest area is increasing due to abandonment of marginal farmland. In N.B., ecodistricts that comprise the majority of butternut range within N.B. are Aukpaque and Meductic, which are 62 and 65 % forested respectively. Within the province overall, the area of agricultural land has declined from 367 000 ha in 1921 to 135 000 in 1996 due to abandonment of marginal lands. Aukpaque and Meductic Ecodistricts contain the richest farmland and therefore are assumed to have experienced a lower rate of decline in farmland. However, there is abandoned farmland within both ecodistricts that has been re-colonized with butternut (Sabine, pers. comm. 2003).


Protection/Ownership

Butternut has been reported in Point Pelee and St. Lawrence Islands National Parks in Ontario. Kouchibouguac National Park, N.B. and Cape Breton Highlands, N.S. are outside the current species range, although archaeological evidence at the former park points to possible butternut inhabitance in the past. There are no records of butternut occurrence in the Bruce Peninsula, ON, Georgian Bay Islands, ON, and La Mauricie, Que., national parks; these national parks may be outside the species range. Information regarding population sizes and health status within each park has been requested but not yet received.

To date, St. Lawrence Islands National Park, ON, has reported populations on Grenadier and Hill Islands; field checks to determine size and health status are currently underway. At Point Pelee National Park, ON, small populations have been reported at 2 locations (13 trees in total), with trees ranging between 4 cm and 60 cm diameter at breast height. Younger trees appear healthy, but older trees show signs of crown dieback. The older trees are bearing fruit, and may have been planted, although records from 1905 list butternut as native to the area.

In Ontario, butternut has also been reported in the following provincial parks; Rondeau, Bronte Creek, Short Hills, Pinery, John E. Pearce, Earl Rowe, Mono Cliff, Forks of the Credit, Boyne Valley, Awenda, Fitzroy, Pretty Valley, Restoule, Sibbald, Voyageur, Westmeath, MacGregor and Provincial Nature Reserves; Nottawasaga Lookout, Trillium Woods, Morris Tract and Hockley Valley.

In New Brunswick, butternut occurs in the following protected areas: Grand Lake Meadows Protected Natural Area, Hal Hinds Forest, near Woodstock (N.B. Dept. Nat. Res. and Energy); Meduxnekeag River Preserve; Maquapit Lake; Sugar Island, (St. John River). The latter two are administered by the Nature Trust of New Brunswick (Zelazny, pers. comm. 2002).

The geographic range of butternut within Ontario coincides with the area where 90% of the land is under private ownership. Where butternut does occur on crown land in Ontario, management is controlled by Silvicultural Guidelines that recommend retention of viable populations for uncommon species, retention of healthy trees for pest threatened species and management to provide conditions for the regeneration of species of concern (Anderson and Nielsen, 1998a). A majority of land within the butternut range in N.B. and Quebec is also under private ownership. Although there are no guidelines specific to management of butternut in N.B., watercourse buffer zone guidelines for Crown Land forestry activities, which limit extent and type of forest overstory removal along watercourses on Crown Lands, might be of some benefit to butternut populations occurring on riparian sites. Watercourse Alteration Regulations under the Clean Water Act provide a similar function for areas within 30 m of watercourses on private lands.