COSEWIC assessment and status report on the Butternut in Canada
- Assessment Summary
- Executive Summary
- COSEWIC History, Mandate, Membership and Definitions
- Lists of Figures and Tables
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- First Nations Traditional Knowledge
- Existing Protection or other Status Designations
- Technical Summary
- Acknowledgements and Authorities Consulted
- Literature Cited and Biographical Summary of the Report Writers
Population Sizes and Trends
A Tree Atlas program was initiated in 1996 to survey the distribution and abundance of all tree species in Ontario on a 10 km2 grid system (Figure 2). Based on the number of surveyed grids within each respective abundance class, a very conservative estimate of the population of butternut in Ontario is approximately 13 000 trees. There are also 32 records for butternut in personal databases of Mike Oldham and Wasyl Bakowsky from the Ontario Natural Heritage Information Centre. The NHIC Natural Areas database (NADb) shows 32 areas where butternut has been recorded and 17 records for butternut in the Element Occurrence (EO) database.
There are also 500 records that were submitted to the FGCA by landowners as part of a voluntary survey completed from 1996 to 1998. These records were not added to the population estimate to avoid double counting.
In N.B., butternut is listed as “Common and native in the Saint John River Valley and Upper Southwest Miramichi River valley” (Hinds, 2000). Hinds' map indicates that the species occurs throughout the above-named valleys, as well as within valleys of several of the major tributary rivers of the lower Saint John River. Relative to overall abundance of other tree species in the province, butternut might be better classed as uncommon, although it is locally abundant on some floodplain sites (Dwayne Sabine, pers. comm. 2003).
Butternut occurrence is not specifically tracked by the NB Department of Natural Resources. The species is coded for on DNR Permanent Sample Plot and Forest Development Survey (temporary sample plot) inventories. It has been recorded from 2 and 29 of these inventory plots respectively, representing approximately 2% of the total number of plots established within the primary portion of NB butternut range in each case.
Tree Atlas volunteers recorded abundance by class for each tree species within an assigned 10 X 10 km square during the period 1996 to 2000.
To further elaborate the number of butternut sites and population size in NB, five DNR staff members with extensive field experience within the butternut range, and who were familiar with the species, were interviewed to compile a list and map known sites of occurrence in the province. Because these recorded occurrences were based on memories of recent visits to sites for reasons other than recording butternut occurrence, data on abundance was difficult to obtain. Staff were asked to conservatively estimate numbers of mature trees in exponential categories: 1-10, 11-100, 101-1000, and 1000+. To compute estimated minimum and maximum numbers of mature trees, sites in the 1000+ category were conservatively considered to have both a minimum and maximum of 1000. Occurrence was recorded as discreet sites or forest stands except in areas where butternut was considered widespread and abundant. In the latter cases, presence of butternut was recorded as a broad area of occurrence, and the number of discreet sites or stands of butternut within these areas were conservatively estimated (Table 1).
Interviewed staff were familiar with 50 areas within which butternut occurs, and estimated a total number of discreet sites or stands of ~370 (Table 2). All of the areas with estimated abundance 1000+ were classed as broad areas of occurrence with multiple sites. These included four large floodplain intervals or islands totaling 6512 ha, and two linear stretches of river valley of unknown width totaling 80 km in length (Table 1). Of 10 areas with estimated abundance of 101-1000 mature trees, four were floodplain areas totaling 1753 ha, and four were linear stretches of river valley totaling 160 km in length.
Totaling the minimum and maximum estimates of butternut abundance at these sites indicates a population of between 7 000 and 17 000 mature trees. Because of the exponential nature of the abundance categories, the minimum estimate is probably closer to true abundance at these known sites. However, because sites known to the interviewed staff constitute an unknown subset of the true total number of sites of occurrence in NB, this minimum abundance estimate is conservative.
Subsequent discussions with the botanist with the Atlantic Canada Conservation Data Centre, local naturalists, and other DNR staff, as well as examination of the map in Hinds 2000, indicated that butternut occurs in at least 75 sites in addition to those discussed above. These include sites on the Kennebecasis and Cannan River drainages (tributary to the lower Saint John River) and a few planted sites scattered throughout the province (Sabine, pers. comm. 2003).
Information for the distribution and abundance of butternut in Quebec was derived from forest inventory plots and ecological inventory plots. Figure 3 shows the 378 stands in Quebec with a butternut component, based on forest inventory plots or ecological inventory plots. Figure 4 depicts 39 plots where butternut represents 25% or more of the basal area or canopy cover (Saucier, pers. comm. 2002).
The Quebec natural heritage data centres do not currently track butternut (Labreque, pers. comm. 2002; Sean Blaney, 2002).
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