Mountain holly fern (Polystichum scopulinum) COSEWIC assessment and status report: chapter 7
Population Sizes and Trends
The three recorded populations of P. scopulinum in British Columbia occur on a 100 m by 4 km band of ultramafic rock outcrop that extends from Olivine Mountain on the south side of the Tulameen River to Grasshopper Mountain on the north side of the Tulameen River (Figure 3). Population numbers ranged from four to 400 plants (Table 1). It is quite likely that a number of other populations occur on the ultramafic band, but the rugged terrain makes access extremely difficult. The population of P. scopulinum at Britton Creek has remained stable between 1996 and 2002.
| Population (sub-population) | Elevation | Last Observation - Observer | # Plants - area |
|---|---|---|---|
| OlivineMountain | 1768 m | 1996 – Douglas & Norris |
4 -200
m²
|
| Britton Creek | 979 m | 2002 – Douglas & Penny |
400 - 10,000 m²
|
| GrasshopperMountain (north subpopulation) | 1378 m | 1996 – Douglas & Norris |
5 - 200 m²
|
| GrasshopperMountain (south subpopulation) | 1360 m | 1996 – Douglas & Norris |
3 - 500 m²
|
The single Quebec population was examined recently in 2002 when it was recorded as consisting of seven small colonies in close proximity (0.04 km²), with a total of about 100 individuals. A more extensive survey in 2004 reported nine small colonies in an area of 0.08 km², with a total of about 215 individuals. Because of the rugged terrain, it is possible that other individuals could be found in the Vallée du Diable or on the southern flank of Mount Albert. It is suspected that the population is stable. A site index of “A” (the highest value) has been assigned to the Quebec population and its habitat based on the presence of over 200 plants in an area > 200 m² and presence within an area that receives little disturbance (a provincial park). It is possible that the fern may occur on the small outcrop of serpentine on mont du Sud, a few kilometres to the southwest of Mount Albert.
The population size for the Newfoundland location is unknown but is likely highly restricted in occurrence and possibly in size. The locality for the 1950 collection of P. scopulinum is indicated as site 1 in serpentine area A of Figure 5. Several recent collections of Minuartia marcescens, another serpentine species, have been made within the approximate area of locality 1 but no further localities have been found for the fern. Survey effort within the two largest serpentine sites in Newfoundland (areas A and B, Figure 5) is reflected, in part, by about 20 historic and recent collections of M. marcescens in area A and about 10 in area B, with plants in these areas estimated to occur in the millions.
The lack of additional records of the fern from these two major serpentine areas is taken as an indication that P. scopulinum is likely present only in small numbers and may also be highly restricted in area of occupancy. The black areas in Figure 5 represent locations of serpentine outcrops in Newfoundland. These cover an area of about 3% (about 3200 km²) of the total Newfoundland land mass of 106,000 km² (Roberts 1992). It is conceivable that the fern may be present in other serpentine areas, but considering that M. marcescens, a species abundant in two serpentine areas along the west coast is only found in small numbers in one other inland site (Area C, along the North Gander River), P. scopulinum, a seemingly much rarer plant, may be much more restricted in its occurrence. The west coast serpentine areas are in a region of higher precipitation than the inland sites and would therefore be more conducive to spore germination and fern establishment on these substrates that characteristically have thin soils and little vegetation cover.