Ministry of Environment
Environmental Stewardship Division
Coastal bluff ecosystems represented 0.3% of the study area.
They are by nature very small in extent, typically a couple of
hectares or less, and are confined to areas immediately adjacent
to the ocean. Less than 10% of the bluffs mapped were identified
as coastal cliffs—113 ha in 50 polygons—which may
have been partly due to limitations in identifying vertical cliffs
on air photographs.
Coastal bluffs were very sparse in the area north of the Capital Sub-unit (Figure
22). Each of the three northernmost sub-units (Comox, Nanaimo and Cowichan)
supported well under 50 ha of coastal bluff or under 0.1% of their particular
land base. Bluffs were much better represented in the Capital and Islands sub-units
which reflected the geology, as these sub-units have more extensive areas in
which hummocky, undulating bedrock is exposed.
Figure 22: Proportion of sub-units containing
Coastal Bluff ecosystems
The greater proportion of coastal bluffs mapped for the Islands Sub-unit compared to the Capital Sub-unit probably reflected the much greater coast/interior ratio of the Islands. In addition, the dipping Nanaimo Group sandstones underlie many of the Gulf Islands, and give rise to bluffs on their scarp slopes. In the Comox, Nanaimo and Cowichan Sub-units, deep glacial or fluvial deposits in many places have buried the bedrock surface, and topography is more subdued, so bluffs and cliffs were less abundant.
Scattered trees were often noted in the bluffs mapped, including arbutus, Garry oak and Douglas-fir. In a number of cases in the Cowichan, Capital and Islands sub-units, Rocky Mountain juniper was also present. When occurring in complexed polygons (Figure 23), CB was usually found with arbutus or Garry oak woodland, or with young or mature Douglas-fir forests. In the 247 complexed polygons with CB as either the dominant or secondary component, WD occurred in conjunction with 180 (73%) of them. Most of these were in the southern third of the study area, within the main ranges of Garry oak and arbutus.
Figure 23: Occurrence of CB as 'pure'
or 'complexed' polygons
Site degradation was commonly observed, with trails and recreational use most often noted, and broom and other introduced plant species were found to be a problem at a great many sites. Rare plants were recorded on some of the bluffs that were field checked. A few of the offshore bluffs were identified as nesting sites for cormorant colonies. Fifteen percent of the coastal bluffs were field checked; however, many units initially photo-interpreted as Coastal Bluff units were found upon field checking to be unvegetated intertidal rock (many were sandstone), and were deleted from the database.
Sparsely vegetated ecosystems represented less than 0.1% of the study area. They had higher representation in the Islands Sub-unit than on Vancouver Island (Figure 24). As with coastal bluffs, this was likely a reflection of the greater coastline length on the Gulf Islands, together with the presence of Nanaimo Group sandstones, providing more opportunity for cliffs, sand dunes and gravel and sand spits to develop.
Figure 24: Proportion of sub-units containing
Sparsely Vegetated ecosystems
A total of 86 polygons were mapped with SV as the pure or dominant ecosystem component (Figure 25). Most (52) of them comprised inland cliffs with smaller numbers of vegetated spits (26), and even some sand dunes (8) mapped. An additional 24 polygons contained SV as a secondary component.
Pure units mostly represented spit and dune ecosystems although
in a few cases, wetland marsh was sometimes found in complex
with dune ecosystems. Complexed units most often represented
inland cliffs, which commonly occurred in combination with older
second growth forest and rocky terrestrial herbaceous ecosystems.
Eleven SV polygons exceeded 10 ha, with only 2 exceeding 20 ha. The largest
unit mapped was on Sidney Spit where a large sand spit is protected within
Sidney Spit Provincial Park. Another area of less than 23 ha was mapped on
Pender Island (Swanson Channel).
Figure 25: Occurrence of SV as 'pure'
or 'complexed' polygons
Many of the sites were highly disturbed. At the sites field checked (18%), broom and introduced grasses were a common problem, and many sites were disturbed by recreational trails and other human activities.
4.2.4 Terrestrial Herbaceous (HT)
Terrestrial herbaceous ecosystems cover 1% of the study area.
Figure 26 shows that the greatest proportional representation
of HT occurred within the Capital Sub-unit, whereas the highest
areal extent occurred in the Comox Sub-unit (Table 2). The lowest
proportional representation of HT occurred in the Nanaimo Sub-unit.
The majority of HT polygons, in all sub-units, are rock outcrop types (HT:ro).
Polygon size range is very wide, but average size is small (under 4 ha).
Figure 26: Porportion of sub-units containing
Terrestrail Hervaceous ecosystems
Nearly three quarters (71%) of all polygons containing HT occurred in combination with other ecosystem types, i.e., complexed units (Figure 27). Over half of the polygons were complexed with older second growth forest (SG). Some sites had scattered oak or arbutus on them, and in the southern part of the study area, they were commonly complexed with woodlands (WD).
Disturbance of terrestrial herbaceous units was frequently observed
and recreational use and grazing was noted at some sites. This
ecosystem type had been severely influenced by introduced grasses
and other herb species. In some cases, polygons were removed
from the database as the vegetation consisted of more than 90%
introduced grasses.
In total, 248 polygons or 22% were visited. Ten polygons exceeded 50 ha. The
largest polygons included one on Mount Braden, a site on the coast north of
Millstream Road and one on Mount McDonald (all in the Capital Sub-unit). Elsewhere,
the larger sites included an area north of Murder Point on Saturna Island,
a site on the north shore of Comox Lake, and an area at Sheepshank Hill in
the Cowichan area.
Figure 27: Occurrence of HT as 'pure'
or 'complexed' units
Wetlands occupied approximately 1.7% of the study area (Table
2). They were unevenly distributed, being more abundant on Vancouver
Island than in the Islands Sub-unit. On Vancouver Island, the
surface expression of the Nanaimo Plain is at its most extensive,
and the very subdued, gently undulating topography lends itself
to wetland development (see Appendix 10 for more information
on geology).
Wetlands peaked in abundance in the Comox Sub-unit (Figure 28) and were also
well represented in Nanaimo and Cowichan Sub-units. In these three northerly
sub-units, concentrations of numerous small wetlands were mapped as well as
some large contiguous wetland complexes. In total, five wetland polygons exceeded
50 ha—four of them were in the Comox Sub-unit, including the large Newman
Creek wetland. In the Capital and Islands sub-units, however, wetlands covered
much less of the land’s surface. This is due to the increased prevalence
of hummocky, bedrock-controlled topography, as well as lower rainfall and greater
seasonal moisture deficits. These wetlands were individually very small and
widely scattered.
Figure 28: Wetland sub-classes by sub-unit
Wetland polygons occurred primarily as pure units (Figure 29). When occurring in complexed units, they were mostly associated with seasonally flooded agricultural fields (many of these fields were former wetlands which had been drained and cultivated over the past century). In a few locations, they occurred in complex with riparian and older second growth forest ecosystems.
Figure 29: Occurrence of WN as 'pure'
or 'complexed' polygons
More than one-quarter of the wetlands mapped were further classified by up to three sub-classes (see Section 2.3.2 for further discussion).
Swamps (WN:sp) were mapped most often (Figure 30). This may have been due in part to the fact that during the air photo interpretation phase of the inventory this sub-class was assigned to polygons when the wetland classification was uncertain1. Swamp wetlands occurred in 1614 polygons (61% of total), representing nearly 3,900 ha; swamps also occurred as secondary or tertiary components in an additional 204 sites. They usually occurred in complex with marsh and shallow water components.
Figure 30: Occurrence of WN as 'pure'
or 'complexed' polygons
Marsh-dominated wetlands (WN:ms) represented 1,806 ha and occurred in 519 polygons (20% of all wetlands mapped); they also occurred in an additional 259 polygons as a secondary component. Swamp and shallow water were the sub-classes most commonly occurring with marsh (more than half of these sites). Fen-dominated wetlands (WN:fn) had the next largest area representation with 540 ha mapped in 171 polygons (6% of total); they occurred in an additional 44 polygons as a secondary component and were commonly complexed with swamp, bog and shallow water wetlands. Shallow water-dominated wetlands (WN:sw) occurred in 187 polygons (7% of total number of wetlands) representing 482 ha; they also occurred as secondary components in an additional 171 polygons and usually occurred in complex with marsh and swamp sub-classes. Wet meadow-dominated wetlands (WN:wm) were only mapped in 87 polygons (3% of total) representing 160 ha; they occurred as a secondary component in 19 additional sites and again the common companion sub-class was swamp. Bog-dominated wetlands (WN:bg) occurred in only 56 locations (2% of total), representing 172 ha.
Wetlands were one of the primary focuses of the SEI project. Field checking in wetland units was therefore higher than for any category except flooded fields with over 42% checking in total. This high sampling figure was also partly because all 286 polygons included in the 1993 CVWI were field checked and subsequently incorporated in the SEI. However, within the WN category some types received very high levels of checking, especially bogs and fens at over 60% each, whereas the wet meadow class was field checked much less often with only 15 polygons, or 17% of the total number visited.
There were very few examples remaining of undisturbed wet meadow, fen, bog and shallow water wetlands in the study area. Wetlands in the Islands Sub-unit were more disturbed than those on Vancouver Island.
1 For further discussion, see Section 2.6
Section 4.1 - 4.2.1 | Section 4.2.6 - 4.2.11
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