The Fraser Delta is an evolving landform, emerging from the waters of the Straits of Georgia as the sediments from the Fraser River are dumped where the river meets the sea. This area is now covered with houses, shopping centres, industrial land, and farmland, and transport routes dissect the landscape. There is little left of the original, pre-settlement vegetation such as our first land surveyors would have encountered. Many of the plants we find here today are introduced species from Europe and Asia, arriving as a result of agriculture or garden landscaping. Even our remnant natural areas have been altered by deliberate or accidental changes to the environment. So what was the vegetation that grew here before European settlement? An understanding of the development of the Fraser Delta is crucial to our knowledge of the vegetation that grew on it. We have to go back a long way in geological time to start our story.
In the last million years, several major ice advances have occurred. Climate cooling in the past allowed snow to accumulate in excess of annual melting and the mountainous area north of the Delta was covered with ice. There was no vegetation. Vast glaciers flowed slowly southwards, one between the mainland and Vancouver Island. However the ice sheets did not extend much further south than Bellingham, just across the border. The area that we know as the Delta did not exist at this time.
The Delta only began to accumulate after the last, minor ice sheet in the Fraser Valley melted away, about 10,000 years ago (Figure 6.1). We can imagine the mountains bordering the Fraser River being exposed as the ice melted away and the melt-water carrying the loosened rocks from the slopes into the valley. Here the river picked up the sediments and carried them downstream, dropping the heaviest pieces whenever and wherever the energy of the flow diminished, forming bars and islands in the river channel. Finally, losing all its forward flowing energy as it meets the sea, the river deposits its load of sediment. Only the very lightest, finest sizes of rock particles, the clays, and the dissolved chemicals from the weathered minerals are swept right out to sea. This milky "plume" of fine sediment is visible from the air or from a boat sailing in the Straits off the mouth of the Fraser.
Figure 6.1: Evolution of the Fraser Delta
Just as it takes different amounts of energy to pick up and move the different sizesof sediments that make up the river's load, so the loss of energy leads to the differential deposition of sediment. So a delta, anywhere, is made up of coarser top-set, medium sized fore-set and fine bottom-set beds (Figure 6.2). Top-set beds are deposited first, nearest to the land. On the Fraser Delta these beds are mainly medium to fine sand and silt size particles. The fore-set beds are fine sands to silt; the bottom-set beds are primarily clays. These top-set and bottom-set beds are usually deposited horizontally, the fore-set beds are always sloping, following the configuration of the ocean basin, and maintaining an approximately 30 degree angle of repose. The size (or texture) and the slope (or attitude) of these deposits allow us to reconstruct where the front of the delta was at various times in the past. From the analysis of sediment cores taken at various places on the Delta, geologists have been able to reconstruct the evolution of the delta as it emerged from the sea, at the place we now call New Westminster, about 10,000 years ago.
Figure 6.2: Delta deposits: the evolution of the delta
As the river emerges from its constricted valley at New Westminster it breaks into a number of distributary channels, the North, Middle and South (or Main) Arms. In the past there were probably more channels. They shifted across the emerging delta landform as a deposit of sand or silt blocked one channel after another during times of low water flow. Every year the high flow period, after snow melt in the drainage basin of the Fraser, would flood part of the delta surface as the channels were inadequate to carry all the water to the sea. Flood water would deposit sediments in the same sequence of coarse to fine that occurs from the mainland into the sea, but this time the sequence would be from coarsest, deposited closest to the river channel, to finest, at the greatest distance the floodwater flowed from the channel. These variations in texture also produced a minor variation in the height of the land; the riverbanks being higher and coarser in texture. We will see how this microtopography has affected the vegetation.
When the first European settlers arrived in this part of North America they were preceded by the British Army in the form of the Royal Corps of Engineers, under the command of Colonel Moody. Moody established the site of New Westminster and recorded the vegetation of the Fraser Delta in a map, dated 1859. In this, he indicates that the entire surface was covered by marsh. However, in that same year, the first of the Dominion Land Surveyor's were actually walking across the delta, dragging measuring chains and marking the legal boundaries of land for future purchase. These surveyors were given the job of marking the lot boundaries and also recording the presence of water and type of soil and vegetation. Such information was of crucial importance to future settlers who often purchased their land in the Land Survey Office in New Westminster without even seeing it.
It is the Land Surveyors' Notebooks that allow us to "peep into the past" of the Delta. We can follow these men as they laid-out and marked the Township and Ranges and then subdivided each township into 36 sections. Sometimes they made field sketches in their notebooks; often maps were constructed at a later date to show where the vegetation boundaries were. Even without these maps, the point-specific information is sufficiently detailed to allow the construction of a vegetation map for this early period, 1850 - 1880. Certainly there is more detail than is found on Col. Moody's map from the same time period. His "marsh" becomes separated into communities of grass, grass and shrubs, shrubs, trees, bogs, tidal and salt marshes.
We can still find a few remnants of the original vegetation in those areas that the Land Surveyors found unsuitable for agricultural settlement. The surveyors often only went to the edge of these areas and thus they were not completely surveyed. (Note the limits of survey on the map (North, Dunn & Teversham 1979). The central parts of the largest delta bog (Burns Bog) were not surveyed. Here the peat is very deep and it has never been used for agriculture and remains covered by bog vegetation. The areas of the two Lulu Island (Richmond) bogs were traversed by the surveyors so we have a record of what plant communities were there. These bogs have been more significantly altered by agriculture use. Only a few areas of the Lulu Island bogs remain, the Study Area is on one such small remnant.
Large areas of the tidal marshes survive seaward of the farmland. They occupy a strip of tidal land at the landward end of the foreshore. In Mud Bay, similar locations are occupied by the salt marshes. The plant species in these two marsh types differ because of the different amount of salinity in the tidal waters. The tidal marshes at the western end of the delta are exposed to vast amounts of fresh water flowing out of the Fraser. This dilutes the salt concentration of the seawater producing brackish water that can be tolerated by the grass-like reeds and rushes. Where there is no such addition of freshwater, the salinity of the seawater prevents the growth of the reeds and rushes, instead the plant community is dominated by low growing, broadleaf, fleshy plants such as perennial saltwort (Salicornia virginica).
Occasional narrow strips of natural vegetation remain clinging to the riverbanks; lines of willow and cottonwoods, or occasionally, spruce and cedar. This riparian forest is more likely to survive on small islands, like Poplar Island, in the North Arm, that are too small for agricultural use. On a few isolated reserves, as in the northwest corner of Sea Island, we can find patches of the former extensive grass and grass and shrub communities, as described by the surveyors in the 1850s. We can use these remnants to help us visualise the past vegetation.
If we were to take a cross section across Lulu Island, (or walk from west to east across what is now Richmond,) with the surveyors in 1850, we would have encountered the following types of vegetation. Growing at the top end of the currently forming fore-set beds, in the area affected by regular tidal action, is a community dominated by sedges and cattails (Scirpus spp and Typha latifolia), this is the tidal marsh. In detail, we can see today that within the tall, grass-like Scirpus community there is a gradation from one species to another following a salinity and exposure gradient. Thus the plant communities dominated by different sedge species are arranged in bands paralleling the coast. Beyond the tidal influence the plant species that dominate are land plants. Vast areas of grass, described by the Surveyors variously as "good grass", "prairie" or "red-top grass" extended over all the lowest areas. These lands were subject to annual floods and no woody plants could survive the long periods of inundation. Land that was either slightly higher, or was further away from both river or sea floods, supported a community of grass and scattered shrubs. The shrubs usually included hardhack (Spiraea douglassii). Willows (Salix spp.), Pacific crabapple (Malus fusca) and rose (Rosa nutkana) were also commonly found scattered through the grass. Dense patches of willows occupied abandoned channels where the finest silts and clays had settled out in stagnant water. Ridges provided higher and drier sites and were often covered with dense shrubs, occupying narrow strips either along the riverbanks, or along the front of the delta on what is presumably an old beach ridge. The higher these ridges and the older they are the more likely that trees have invaded the shrub communities. Thus the riverbanks at the eastern end of the delta supported cottonwoods (Populus trichocarpa), and conifers (Pseudotsuga douglassii) were recorded on the higher beach ridges of Westham Island, and along the banks of the Chilukthan and Crescent Sloughs. Much of Sea Island was covered with an unusual combination of Sitka spruce (Picea sitkensis) and willow. (A modern day remnant of this community exists along Widgeon Slough, on the west side of Pitt River.)
The delta surface was mainly treeless before agricultural settlement. Apart from on the higher and drier sites, trees were found only in the bogs. The only tree species here that can survive the high water table and acid conditions of the bog soil is the Shore pine (Pinus contorta). In the bog it grows very slowly and in contorted shapes.
The Surveyors did not go into the middle of the Burns Bog, realising that it was not a suitable area for settlement. However they traversed the Lulu Island bogs and recorded the presence of pine and cranberry and moss. They also reported the evidence of fire. This leads us to suspect that the vegetation of the bogs may not be "natural" and the bogs might already have been altered for human use by the 1850s. Our knowledge of the long history of fire in the bogs has come from sediment analysis.
The sedimentary record allows us to look further back into the past, beyond the time of written records. Peat cores extracted from the entire thickness of Burns Bog have been used by Richard Hebda (Hebda 1977) to establish both the age of the bog and its complex history. At least 4000 years ago the Burns Bog started to form in shallow ponds on the top of top-set beds of fine sand and silt. Pollen grains and plant fragments in the inorganic sediments directly below the peat showed that the plant assemblages were identical to the tidal marshes of today. But as time advanced, these sediments became covered by organic sediments, made up of dead plants. At first there were aquatic plants, such as water lilies (Nuphar spp.), indicating the open water habitat. As the aquatic plants died they decomposed only slowly and partially in the water, creating increasingly acid water. The presence of these acid conditions is signalled by the appearance of sphagnum moss (Sphagnum spp.) which rapidly comes to dominate the sediments. Shrub species, such as labrador tea (Ledum groenlandicum), bog laurel (Kalmia polifolia) and blueberry (Vaccinium spp.) appear, and eventually trees, specifically pines. Studies of the bogs today show that this successional change is still going on. As the organic accumulation, the peat, builds continually higher, conditions become drier and this change allows pines and eventually other tree species to become established.
The occurrence of fire in the bogs has had the effect of halting changes in the bog by killing the trees and the shrubs (Figure 6.3). The shrubs re-established rapidly but the trees take longer to grow back. The frequency of fire is established from the numerous charcoal layers in the sediment cores and the presence of charred pine stumps at various depths. The First Nations use of the bogs involved the setting of fires to maintain the shrub and moss communities for human and animal use (Cairns). Both cranberries (Oxycoccus spp.) and blueberries (Vaccinium spp.) were harvested and traded. Labrador tea was collected and used for medicinal purposes and as a tea. Sphagnum had many uses because of its sponge-like properties. These useful plants were gathered from the bogs. The open bog communities also supported resident browsing animals such as deer, moose and bear as well as vast flocks of migratory birds that provided sources of meat for the hunters.
Figure 6.3: Fire induced hummock, sequence.
First Nations people were already living in the uplands around the Straits of Georgia before the delta emerged from the sea. They thus were able to observe succession in the bogs, from open moss to shrubs to trees. They used fire as their management tool to prevent the closing over of trees that would have resulted in shading out of the valuable shrub and sphagnum layers. The bog fires seem to have spread beyond the confines of the bogs and are the probable cause of grassland communities in areas where grass and shrubs or even trees might have been expected. Grassland patches are also found in the areas around the permanent settlements of the First Nations. These sites would obviously have been selected above the general floodwaters and should thus have shrubs, if not trees, growing on them.
The result of human alteration of the vegetation is far more obvious today. Natural plant communities have been deliberately replaced with plants of greater economic or aesthetic value. Even in areas that have not had a complete replacement of the early vegetation, the changes brought about by dyking and draining of the farmland has led to changes in the adjacent remnant vegetation. The purpose of the dyking is to prevent floods. The drains that run under and around the fields facilitate the drying out of the soils that tend to be at or near saturation in the winter and spring. Both these changes lead to the drying of soils and hence to faster successional changes. Shrubs that were not recorded as being present by the Surveyors in 1850 now invade the remnant grasslands in the northwest of Sea Island. Today, birch trees (Betula spp.) have invaded the bogs, yet the Surveyors did not record this tree species. Birch is and was a common component of the surrounding upland forests and its prolific wind-born seed would have been readily available. Its absence in the 1850s indicates that no suitable habitat existed on the delta for its successful growth. However, hybridzation in the 20th century with the alien European birch, a water-tolerant species, and the availability of suitable habitat, has allowed for its establishment throughout the delta lowlands.
Management of the bogs has been continuous throughout the past century. Mining of peat for various industrial purposes has occurred at different locations. Conversion of the thinner bog soils started with the first farmers who simply extended their fields into the bogs. Later drainage ditches were extended to dry out the edges. Wholesale conversion to commercial cranberry fields has replaced much of the eastern Lulu Island (Richmond) bog. Commercial blueberry farms have made steady in-roads into all the bog areas. The spread of cultivated blueberry varieties into the remnant bogs, particularly the area of the Richmond Nature Park, has significantly altered the natural habitat. The most extreme form of change to the bogs has been the covering of its surface with landfill. Recovery of the natural bogs might be possible from all the other changes, but this change is too extreme.
The natural vegetation of the delta lands has been significantly altered. There are few small remnant areas left to show us what we have lost. Even these few, it seems, have not escaped the impact of human settlement. However, they do provide some glimpse of what this land was like when those early surveyors traversed Lulu Island.