Some of the most diverse and fragile ecosystems in the northwest are those found along the

Skeena River floodplain. Islands of varying size fill the Skeena River all the way to the Pacific Ocean. Our

study area is a medium sized island, Ferry Island Provincial Park, located at the eastern edge of Terrace,

B.C. In the following essay we are going to take a close look at the ecology of this area and those factors

that influence its growth and characteristics. The effect of the local climate, geomorphology, hydrology,

and local wildlife are some of the major variables that we can use in explaining the development and

diversity of plants and animal species found in this location.

Ferry Island is a 150 acre park surrounded by the Skeena River. It is located on the eastern

portion of the Skeena floodplain, an area that is easily accessible to the residents of Terrace and

Thornhill using Highway 16 and bridges that connect the two communities. The floodplains provide a

critical habitat for many of our most important wildlife species, such as bears, ungulates, raptors, and

waterfowl, in addition to amphibians, bats, and other small mammals, songbirds, and many insect

species (Enns et al. 1993). In addition alluvial sites are important both as recreational sites and for

maintaining the hydrological integrity of watersheds (Hicken & Sichingabula 1988; Beaudry et al. 1990).

Ferry Island Satillite Ferry Island Terrain

Site Classification

The study of ecosystems is made more effective when using a standardized system of

classification. The system most widely used is the BEC or Biogeoclimatic Ecological Classification

Program. The following quote provides a brief explanation of the basic concept.

At the regional level, vegetation, soils, and topography are used to infer the regional climate and to identify geographic areas that have relatively uniform climate. These geographic areas are termed biogeoclimatic units.

At the local level, segments of the landscape are classified into site units that have relatively uniform vegetation, soils, and topography. Several site units are distributed within each biogeoclimatic unit, according to differences in topography, soils, and vegetation.

At the chronological level of integration, ecosystems are classified and organized according to site-specific chronosequences. To do this, the vegetation units recognized for a particular site unit are arranged according to site history and successional status (Province of British Columbia).

The system is hierarchical, starting with broad, regional classifications that extend over vast

sections of land. These classifications progressively become more specific and localized. The first

grouping is that of Realm. The Realm delineates major biotic types that reflect gross differences in

water abundance, quality, and source. (MacKenzie & Moran 2004). Realm is then further classified into

Group. The Group describes functionally similar Classes based on a dominant, ecologically relevant

environmental feature(s) (MacKenzie & Moran 2004). The site location of this essay is classified as being

within the Flood Group of the Terrestrial Realm.

The third group of this hierarchical system is that of Site Class. It is composed of three benches,

each with slightly overlapping yet unique differences in hydrology and growing conditions. The Site

Class describes associations with similar basic underlying environmental attributes that support similar

characteristic species guilds at climax (MacKenzie & Moran 2004).

Table 1: Ecosystem Site Classes Source: MacKenzie & Moran 2004

The landforms and ecology of the floodplains are in a constant state of change. Sediment is

deposited at varying frequency in specific locations throughout the season. The resulting changes in the

morphology of the river will then have an effect on the frequency of flooding in a particular area.

Low-Bench Sites:

Low bench ecosystems are usually found beside main river channels and around the edges of

low-lying islands. There are two principal types of Low bench systems found in this area. The first type

consists of coarse gravels and sand (Figure 1.0). The second type (Figure 1.1) is a mixture of sand, silt

and clay, called loam.

Site Realm/Group Site Class Environmental Features

Cover Types Species Groups

Flood Group ofTerrestrialRealm

High Bench Riparian flood zone

Benches above normal water flow

Brief flood periods

Coniferous forested Upland species of seepage sites

Mid Bench Elevated benches flooded most years for < 21 days

Areas of sedimentation

Deciduous trees or forested

Flood-tolerant deciduous trees and shrubs

Low Bench Site directly adjacent to watercourse

Annual flood > 21 days

Significant annual erosion and deposition

Tall deciduous shrub

Flood-tolerant shrubs

Figure 1.0 Figure 1.1

The low bench ecosystem is often flooded during the growing season. The structure,

composition, growth and pattern of alluvial plant communities are largely determined by flooding and

sedimentation. More specifically, the effects on plant communities are a function of flooding frequency,

duration, and seasonality, as well as sediment depth, texture, and mineralogy (McLennan 1993).

This flooding can last for several weeks with profound destructive effects on the soils and

vegetation in the area. When the surface of the soil is submerged in flowing water, it is not possible for

seeds to establish themselves properly. Vegetation that has already been established can also be

disturbed to a great degree. The fast moving water littered with broken trees scours the flooded area.

Large sections of land can be displaced and completely destroyed by heavy erosion. Flooding can make

soils anaerobic, which means they are lacking in oxygen and unable to breathe. This phenomenon

greatly restricts the types of species that normally would occupy such sites.

Vegetation found on low bench sites is limited to grasses, shrubs and flood tolerant tree species.

Plant species must be able to withstand scouring, disturbances to root structure, and short to moderate

periods of inundation.

The dominant tree species of the low bench site are black cottonwood, red-alder m often mixed

with Sitka and Pacific willows. There are also sections covered with herb and moss layers.

Middle-Bench Sites:

Figure 2.0 Figure 2.1

Middle bench ecosystems cover a significant portion of the Skeena Valley floodplain. Due to the

build-up of sediment, flooding frequency is lower for Middle-Bench Sites. These sites are usually

flooded from between 15 to 25 days during growing season. Soils at this level are quite deep

and range from coarse sands at depth to sandy loams at the surface. Middle-Bench sites are best suited

to deciduous tree species, with conifers limited to elevated areas.

Figure 2.0 is an image taken near the southwest tip of Ferry Island. Low-Bench gravel bars are

visible in the background. Deciduous black cottonwood are visible on the right hand side of the

photograph, located approximately one metre above the gravel bars. A large red alder can be seen in

the left foreground. Grasses are also visible along the edges of the trail in this image.

Figure 2.1 was a photo taken on the east side of Ferry Island. It is approximately 20 meters from

the bank of the Skeena River with an elevation of 1.5 metres above the river surface. The trees seen in

the background are red alder and black cottonwood. The shrub layer consists of Oplopanax horridus

(Devils Club), Cornus stolonifera (Red –Osier Dogwood), and Ribes bracteosum (Stink Currant).

High-Bench Sites:

Figure 3.0 Figure 3.1

As landforms rise, flooding becomes more and more infrequent. High bench ecosystems are

flooded less than 10 days a year with lengthy periods of subsurface flow in the rooting zone. The lack of

flooding allows conifer species, such as the Sitka spruce and red cedar, to establish themselves. The

soils are made up of fairly deep loam with course sands at depth.

Figure 3.0 is an image of an elevated area towards the southern tip of the island. The trail

depicted here, about 2 meters above the current water level, is being destroyed due to erosion caused

by floodwaters. It can be seen that coniferous spruce have been able to grow in this area, although

many trees located on the edge of the island die due to disturbance to their root systems.

Figure 3.1 is proximally close to figure 3.0, but is farther from the water’s edge. Young conifers

can be seen along the edges of the trail, along with black cottonwood and shrubs that have been cut or

trimmed down. Salmonberry and devils club are also quite common to this area. Differences in ground

elevation between these three ecosystems are no more than 1 to 2 meters.

Hydrology

Hydrology of this area is largely affected by a late spring to early summer peak discharge due to

snowmelt. It is the resulting flooding that is the main disturbance type on the floodplain, and the main

factor in the shaping of the landforms contained within it.

There are actually two types of seasonal flooding that occur here. The first type is that which is

mentioned above, flooding that begins in the spring due to massive snowmelt throughout the

watershed. The second type is seen in the fall and winter months when heavy rainfall (combined with

sudden snowmelt due to fluctuating temperatures) is the main contributing factor. These late season

floods are mostly due to localized weather patterns.

The graph displayed below provides data on the daily discharge levels for the Skeena River for

the year of 2006 (shown in red). The station is located at Usk, which is a hamlet found about 20

kilometres north-east of Ferry Island.

Figure 4.0:

Statistics corresponding to 75 years of data recorded from 1928 to 2006.*

Source: Province of British Columbia

Climate

Climate data was taken for the period between November 1st and November 20th of 2008. It was

gathered at station CYXT at the Terrace airport.

Table 2: Climate Information for Station CYXT

November 2008

Temp. (F) Humidity (%) Wind (mph) Gust Speed (mph) Events

High Avg Low High Avg Low High Avg High1 42 40 39 100 98 93 26 9 32 Fog, Rain

2 48 40 41 100 94 81 24 18 33 Fog, Rain

3 46 40 35 100 89 66 22 17 30 Rain

4 41 36 32 100 95 81 7 1 - Fog, Rain

5 39 36 32 100 95 81 10 4 - Rain, Snow

6 37 36 35 100 92 81 18 14 23 Fog, Rain7 41 38 35 100 98 87 25 3 34 Fog, Rain

8 44 42 41 100 94 93 23 19 30 Rain

9 42 38 33 100 90 70 13 4 - Fog, Rain

10 39 36 33 100 91 81 16 9 24 Snow

11 42 38 35 100 98 93 17 8 23 Fog, Rain12 44 40 37 100 96 87 16 9 24 Rain

13 42 37 32 100 88 70 16 9 30 Rain 14 35 34 32 100 98 93 10 5 - Rain, Snow

15 37 35 33 100 99 93 17 4 23 Fog, Rain, Snow16 35 34 32 100 90 75 25 23 36 Snow

17 39 36 32 100 100 93 23 11 29 Snow

18 37 34 32 100 92 87 16 12 21 Fog, Rain, Snow

19 33 32 30 87 74 65 30 21 39 Fog, Rain

20 33 32 32 93 69 60 29 22 38 Snow

Source: Station CYXT at Terrace Airport

Terrace has a sub-maritime climate. The summer months are warm and moist while winter

months are cool and endure heavy precipitation. Between the months of September and December,

there is an observable rise in the discharge level of the Skeena River that corresponds with the increased

precipitation during the fall and early winter months. The spike in maximum discharge seen in figure 4.0

is a direct result of localized weather events that bring heavy precipitation to the area.

The average annual precipitation between 1971 and 2000 for Terrace is 1322 millimeters, and

the annual mean temperature is 6.3° C or 43°F (Environment Canada 2008). During visits to Ferry Island

between November 1st and 20th, there was daily precipitation and the average temperature dropped

from 40°F to 32°F. Due to the temperature drop, most of the deciduous species had already shed their

leaves to conserve moisture and energy. Although there were several days of snowfall, the temperature

had not dropped significantly for there to be any accumulation on the ground surface.

Geomorphology

Islands located on the floodplain are formed by primarily fluvial processes. As water flows over

the channel bed, sediment is carried downstream. The speed at which the water flows downstream

decreases as it approaches the drainage basin, due to a leveling of the river gradient. When the

gradient is steep, the force of gravity will act more strongly and flow velocity will be greater. When the

stream channel has a gentle gradient, the velocity will be slower (Strahler & Strahler 2005). During low

discharge periods, active erosion and deposition of sediment is limited to the river channel itself.

Flooding brings an increase in the area affected by active erosion and deposition. The islands and banks

of the river are often inundated for significant periods, drastically reshaping the geomorphic structure of

both the channel and floodplain. High velocity flows seen during flooding cause scouring of river banks

resulting in a concave bank profile and erosion around root systems.

Figure 4.0 Figure 4.1

Wildlife

Floodplain forests provide an important ecological niche for a number of animal species.

The basic needs of wildlife are food, water, and cover. Elements too low in supply to support breeding

and survival are considered `limiting factors.’ Limiting factors determine the numbers, types, and

locations of wildlife populations. Carry capacity reflects the number of animals a habitat can maintain in

a healthy condition. Limiting factors of food, water, or cover determine this number (Creighton, J. E.

1997).

The study location is made up of primarily deciduous tree and plant species. Deciduous trees

are used by animals for cavity nesting and are home to a great variety of insects. Birds that use the

trees in this area include the bald eagle, pileated woodpecker, and northern flicker. Large black

cottonwood trees that inhabit the banks of the island provide perfect nesting and perching areas for the

larger birds. Small mammals that inhabit the island include the douglas squirrel and myotis bat. These

small mammals feed on the berries and insects that are abundant in the area.

Larger mammals such as the black bear and moose visit the island less frequently, but are

common in the surrounding area. The black bear feeds on berries in the summer and both berries and

salmon during the fall. Moose browse on willows and red-osier dogwood. Due to the effect of nearby

road development and recreational use of the island forest, these animals will usually avoid the park.

Human Activity

There have been a number of modifications to the local environment that have affected the

ecology of Ferry Island. The island was cleared of many of its older coniferous tree’s as logging along the

Skeena River was popular during the first half of the 20th century. This converted the islands forest into

an almost entirely deciduous population, as these species are more able to establish themselves quickly

and flourish in areas often flooded during growing season.

The New Skeena Bridge was constructed in 1975. This bridge spans two channels of the Skeena

River. It extends from Terrace to Ferry Island, with a second portion connecting Ferry Island to the Town

of Thornhill. The bridge has been designed to withstand the heavy flooding that occurs during the late

spring months (Figure 5.1). Its supports are constructed in a manner that runs parallel with river flow.

This minimizes the water resistance encountered with heavy flooding and interferes to a lesser degree

with freshwater fish that are abundant to the area (Figure 5.0). The highway itself is a source of noise

pollution and is also a barrier to larger mammals such as bears and moose.

Figure 5.0 – Bridge Supports & River Flow Figure 5.1 – Bridge Supports & Flooding

Ferry Island Park consists of a campground of 103 sites. There are also two large clearings found

on the island, one is a parking section for the many people who fish on the banks of the Skeena during

the summer and fall. The second is an open area for parking, a small playground, and a building with

public washrooms. The majority of people visiting the park do so beginning in the late spring and leave

in the early fall when the campground is shut down. Due to the large number of campers, most of the

big mammals will not stay for any length of time in the park. If any of these animals were to find

themselves on the island, it would not be long before either dogs or people scare them off.

Another of the recreational areas visited frequently by people are the Ferry Island Nature Trails.

These trails run the perimeter of the island, with a number of deviations running to more inland areas.

The trails are open for use year-round and are utilized by large numbers of people, with the exception of

those periods of extreme weather. The trail itself does not have much of a deleterious impact on the

surrounding ecosystem. However, the people and dogs walking the trail do cause some disturbance

including noise pollution and litter that may be harmful to some of the wildlife.

Conclusion:

In conclusion, it is evident that each of the variables mentioned has its own contribution and

effect on the ecosystems found on Ferry Island. Hydrological and geomorphologic processes such as

seasonal flooding and the flow and deposition of sediment are the most obvious contributors to the

islands physical characteristics. The local sub-maritime climate determines the flooding frequency and

duration, along with the types of vegetation and wildlife that will flourish. Each of the variables

contributes to a unique, biologically diverse selection of ecosystems. All are interdependent and of

equal importance to the development, establishment, and growth that is found at this location.