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6.2 Pre-typing of Aerial Photographs

Production of an ecosystem map begins with the pre-typing of aerial photographs. The procedure, which should involve all members of a mapping team, is the first step in helping the team understand the ecosystem/terrain/topography relationships within the study area. Some pre-typing should be completed before field reconnaissance, to clarify relationships between photo and ground features (see sections 6.1.3 and 6.1.4). The remaining aerial photos should be typed before field sampling begins. Where mapping that follows the same standards and scale has been previously completed on adjacent areas, the aerial photos from that project should be obtained and border-matched with the new typing.

6.2.1 Conducting initial ecoregion/biogeoclimatic mapping

Existing ecoregion and biogeoclimatic maps and reports should be consulted during the pre-typing stage, and the latest biogeoclimatic line work should be redrawn at the project map scale, using elevational models and obvious east-west or north-south boundaries. Regional Ecologists should be consulted to ensure that up-to-date information is being used. Because it is often very difficult to accurately delineate ecoregion and biogeoclimatic unit boundaries on aerial photos, the final mapping of most of these boundaries is usually done after field work is complete.

At the pre-typing stage, Alpine Tundra and subalpine parkland boundaries and approximate boundaries for the other biogeoclimatic units are mapped on aerial photos. The Alpine Tundra and subalpine parkland lines should be drawn before ecosystem map units are delineated. This provides an initial boundary from which the other ecosystem map units can then be drawn. Other biogeoclimatic map unit boundaries can be drawn either on the typed or non-typed photos, using a different colour than the ecosystem map units. These boundaries will need to be confirmed in the field and finalized after fieldwork.

Delineating Alpine Tundra zone

By definition, the Alpine Tundra zone has alpine vegetation on zonal sites. The Alpine Tundra zone boundary is usually the upper elevation of discontinuous forest (parkland, including krummholz) or in the case of the Spruce-Willow-Birch (SWB) zone, the upper elevational limit of extensive deciduous scrub (which is considered to be subalpine vegetation). The alpine boundary will have to be generalized at a consistent elevation (varying with aspect), because cliffs, rock outcrops, and avalanche chutes often dissect the alpine/subalpine transition (e.g., shrubby avalanche chutes are common in wetter subalpine forested subzones). Trees in krummholz form (prostrate or low in stature) may occur in the alpine zone, but they are of very low cover. Some larger krummholz patches may occur in sheltered, non-zonal sites. The placement of the Alpine Tundra zone boundary is shown in Figure 6.2. Glaciers are considered to be in the biogeoclimatic zone that is expected at that elevation (e.g., glaciers often extend into the subalpine and lower elevations).

Figure 6.2Delineation of Alpine Tundra and parkland subzone


Delineating subalpine parkland

Where possible, parkland subzones of the Mountain Hemlock and Engelmann Spruce- Subalpine Fir and scrub subzones of the Spruce-Willow-Birch zones should be mapped. They are recognized as a distinct elevational transition from closed or continuous forest to the treeless Alpine Tundra. Parkland is characterized by forest clumps interspersed with open subalpine meadows, shrub thickets, and krummholz (Figure 6.2). However, parkland varies in the proportion of treed patches versus open vegetation. It is often discontinuous and intermixed with rock outcrops, cliffs, or talus. Recognition of a distinct parkland subzone is most obvious in gently rising plateau areas or rounded mountains of relatively gentle relief (e.g., the Quesnel Highlands). As with alpine, the parkland boundary will have to be generalized at a consistent elevation.

In some areas, especially steep-sided coastal valleys, it is difficult to map subalpine parkland subzones as continuous elevational bands. Parkland in these areas is very narrow and discontinuous, and often dominated by sparsely vegetated ecosystems. In these cases, the entire subalpine subzone would be mapped as forested. Parkland-like ecosystems could then be delineated within the forested subzone as ecosystem units. For example, the biogeoclimatic unit could be designated as MHmm1 (implying that it is a forested unit), but much of the area mapped is sparsely vegetated rock, cliffs, and talus interspersed with patches of forest and heath. In such areas, tree growth is limited more by substrate (steep terrain and lack of soil) than by climate.

Even where a parkland subzone is mapped, parkland-like ecosystems may also occur in the forested subzone below, in areas (such as cirque basins) that receive cold air drainage, or in areas that have long snow duration and wet soils. These non-forested meadow and shrub communities, interspersed with forest patches, should be mapped as parkland-like ecosystem units within the forested subzone; the parkland subzone boundary should not be brought down in elevation to include these ecosystems.

6.2.2 Conducting initial ecosystem mapping

Terrestrial ecosystem mapping integrates vegetation, terrain (surficial geology), and soil features, both in terms of delineation criteria and database attributes. This "bioterrain" approach results in map units that portray ecosystem units (site series, site modifiers and structural stages) with their associated terrain attributes (genetic material, surface expression, qualifiers, geomorphological process, soil drainage).

The interpretative value that results from this bioterrain approach to ecosystem mapping is greatly increased over that of a pure vegetation, soils or terrain map. Since many terrain and landscape features correlate well with ecosystem properties, ecosystem polygons are delineated on aerial photos using a combination of recognizable permanent terrain and landscape features, biological characteristics, and inferences related to significant changes in the landscape (Figure 6.3). Refer to Table 6.2 for further explanation of delineation criteria. The resulting ecosystem map units can be developed in various ways, depending on the experience of the mappers, but polygon delineation is most effectively carried out using an interdisciplinary approach.

In order to develop a common understanding of ecosystem/terrain/landscape relationships, it is essential that the mapping team, usually composed of a vegetation ecologist and terrain/soil specialist, work together on representative photographs. Delineation can then be carried out by either specialist, in a consistent manner, as long as feedback occurs throughout the rest of the pre-typing process.

A useful approach to the initial pre-typing of photographs is to mentally divide the study area into broad landscape areas that have similar, repeatable map units and relationships (Figure 6.4). These areas can be determined from the working legend and consideration of ecosystem/site relationships in broad landscapes such as alpine, mountain slopes, valley floors, plateaus and plains. This frames the mapping process before more detailed terrain and vegetation features are considered.

Figure 6.3Integrated delineation criteria for developing Ecosystem Map Unit polygons


Table 6.2 outlines the main criteria that should be used to delineate ecological polygons and assign core ecosystem and terrain attributes for ecosystem map units. Note that individual polygon attributes (e.g., site series, structural stage) are interpreted from one to many physical or biological criteria (e.g., slope position, vegetation composition and structure) that are either directly observable on the photo (e.g., slope position) or inferred from visual photo features or characteristics (e.g., vegetation composition and structure are inferred from tone, texture, colour, shape, pattern). The assessment of any one attribute is thus an integrated process, whereby many criteria are being observed and processed simultaneously in order to predict the attribute. Depending on the survey intensity level, a portion of the polygons will eventually have their attributes confirmed through ground sampling.

An attempt should be made to consider all of the criteria from Table 6.2. As mappers gain greater experience, this will become second nature. Other useful aids to aerial photo interpretation are the Vegetation Resources Inventory Photo Interpretation Procedures Manual (RIC 1997c), Howes and Kenk (1997), and Keser (1982).

Photo criteria can be integrated in many different ways, depending on the experience and background of the mapper. Some ecosystem or terrain boundaries, such as the edge of a floodplain or terrace, may be sharp (or "hard") and clearly defined; other boundaries may be gradational (or "soft"). The latter can be determined by combining attributes of the ecosystems themselves with presumed terrain unit boundary features. The question of whether to lump or split polygons (e.g., to add or omit a boundary) is largely a matter of judgment, scale of mapping, and project objectives. Thus, if two or more experienced mappers were to independently map the same area, some boundary positions would correspond exactly, some would be fairly similar, and some would differ markedly. For example, a mature, coniferous forest on an active floodplain in the SBS biogeoclimatic zone, representing a Spruce-Horsetail site series, would be delineated in likely the same way by different mappers. However, the extent of the same site series occurring on subdued morainal terrain in the SBS might only be detected through a mapper recognizing subtle differences in species composition, crown closure, stand age, structure, and landscape characteristics. Interpretations of these criteria would vary among mappers as would polygon delineations.

The mapping team must work out how it will approach these less well-defined areas, to ensure a consistent approach to mapping is used. Where possible, the mappers should first delineate the hard terrain boundaries (these, in most cases, will coincide with ecosystem boundaries). Soft terrain boundaries can then be located either where there are subtle changes in the physical conditions that influence ecosystems (such as surface expression, soil drainage, and geomorphological processes) or where there is a vegetation change suggesting a change in ecosystem unit.

During the pre-typing phase, mappers should label map units with initial terrain and soil drainage symbols (using deciles) following Howes and Kenk (1997). They should also indicate ecosystem attributes (e.g., one to three ecosystem units) for a considerable portion of the project area. However, if they are limited by time or a lack of familiarity with the ecosystems in the map area, some mappers may only pre-type polygons with terrain labels. When this approach is taken, it is recommended that some attempt to label ecosystem map units for a portion of the study area be completed before field sampling, so that relationships of ecosystems to terrain attributes can be assessed in the field. The preferred system is to start with field reconnaissance so that initial ecosystem map units can be assigned to most polygons at the pre-typing stage.

Figure 6.4A landscape profile for the ESSFwk1
Table 6.2Criteria for delineating ecosystem map units on aerial photographs1

Criteria

Observable Feature/ Photo Characteristic

Applicable Mapped Attribute

Vegetation
Tree species compositionTone, texture, colour, size, shape, shadow Site series2, structural stage (seral community type)
Understory or non-forested vegetation composition or characteristics Tone, texture, colour,Site series, structural stage (seral community type)
Canopy characteristics (including crown closure) Tone, texture, colour, shape, shadow, size, pattern (open, closed, layered, clumpy) Site series, structural stage (seral community type)
Height of stand (relative productivity) Texture, size, pattern, tone, densitySite series, structural stage (seral community type)
Topography
Landscape position and shapeShape and three dimensional characteristics Site series, site modifier, soil drainage
AspectShape, three dimensional characteristics and direction Site series, site modifier
SlopeShape and three dimensional characteristics Site series, site modifier, soil drainage
Drainage patternShape, pattern and three dimensional characteristics Site series, site modifier, soil drainage
Terrain
Landform/parent material including surface expression, qualifiers, terrain texture (e.g., active processes) Topographic position, observable drainage and terrain patterns, shape, topography, tone, colour (disturbance) Inferred terrain texture, genetic material, surface expression, qualifiers, site series, site modifier, soil drainage
Geomorphological processPatterns Geomorphological process, site series, site modifier
Soils
Soil drainageTone, drainage patterns, topography Soil drainage, site series, site modifier
Soil depthColour, tone, texture, topography Soil drainage, site series, site modifier
Gradients/Patterns
Relationship to other map unitsPattern, juxtaposition, size and edges Various
Adjacent map unitsPattern, juxtaposition, shape and edges Various
Polygon shape and orientationPattern, juxtaposition, shape, edges and direction Various
1Refer to Vegetation Resources Inventory Photo Interpretation Procedures Manual (RIC, 1997c) for more information on interpreting physical and biological attributes from aerial photographs
2Criteria used for site series assessment are by default also used for assessment of soil moisture and nutrient regimes, but these are not core attributes


During pre-typing, structural stages may be interpreted from aerial photographs or taken from other sources such as forest cover (or Vegetation Resource Inventory) maps, or a combination of these two methods. The best approach should be determined by the date that the aerial photographs were taken and by whether major disturbances have occurred since then.

The mapper should use judgment in delineating small polygons and should limit the complexity of polygon symbols, so that the mapping on the photos remains neat and legible. Photo interpretation is a skill that improves only with much practice, particularly in combination with ground truthing to calibrate the eyes. The mapper needs to develop a mental model of how all the pieces of information relate to the ecosystems that actually occur on the ground (Figure 6.3). This model will have to be "recalibrated" for each new study area, as well as for each biogeoclimatic unit within a study area. These relationships are developed throughout all stages of the project, from initial reconnaissance, and pre-typing, through field sampling and on to final typing and labelling.

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