Seattle Urban Nature Project
Habitat Delineation and Descriptions
September 2002
This document contains information about how the data were collected, a description of
the habitat categories, and a glossary of terms. Formal descriptions are provided within
the document for italicized terms.
Data Collection and Habitat Delineation Techniques
These data were collected using vegetation field surveys and aerial photographs in which
landscape features, such as trees and other vegetation, are visible. Areas that contain
similar vegetation (a.k.a. habitat type) were mapped by drawing lines on the photos.
Areas inside these lines are called polygons. Polygon shapes can be simple, as in a
square drawn around a parking lot, or complicated and irregular, as in a winding line
drawn around a grove of trees. Polygon borders were digitized and made into a GIS data
layer of habitat types. Habitat classifications/categories were based on the Seattle
Department of Parks and Recreation’s “Urban Wildlife and Habitat Management Plan”
July, 1994.
Developed Areas:
Features that could be clearly seen on aerial photographs, such as parking lots, were first
delineated. Nearby buildings and impervious surfaces were often included in the
polygons. Other developed areas contained dense paved trail networks, cemeteries, long,
thin areas with a trail or sidewalk in the center, playgrounds, and picnic areas.
Depending on the proportion of impervious surface, the area is designated as a “light,”
“medium,” or “heavy development” habitat type.
Landscaped Areas:
Next, landscaped areas (e.g. areas where shrubs and trees are pruned or mulched, lawns
are mowed, and/or flowerbeds, paved sidewalks, baseball diamonds and playgrounds
exist) were field mapped. Any area with these conditions and with less than 10%
impervious surface qualified as a landscaped area (aesthetic criteria do not apply).
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Natural Areas:
Finally, the more naturally vegetated areas of the parks were surveyed using the aerial
photos. Areas with similar vegetation types (see Habitat Key) were identified. If the
boundaries of these areas were easily identified on the aerial photos, boundaries were
drawn on the photos at tree canopy edges. In many areas, boundaries between habitat
types (e.g. representative of a change in size class of a forest without a change in the type
of trees or wetlands under a tree canopy, etc.) were difficult to delineate on the
photographs. When this occurred, the area was surveyed from a location identifiable on
the photograph and used measuring tapes and compasses to determine the boundaries.
Wetlands:
To determine the presence of a palustrine (freshwater wetland) system, the prevalence of
hydrophytic (“water-loving”) vegetation, surface water present in the late spring and
summer, and/or the existence of deep, mucky soils were identified. These observations
provided very conservative (smaller) estimates of wetlands areas. The criteria required
by local, state, and federal agencies for jurisdictional delineations includes information
about soil types, depth of ground water and the presence of hydrophytic vegetation.
Using these criteria to determine the wetland area would have expanded the number and
sizes of wetlands already identified.
In many areas, the canopy over wetlands includes overhanging branches from trees
rooted in uplands (non-wetland areas). These wetland areas are thought to function in
many ways as “forested wetlands,” although some vegetation classifications require that
the trees be hydrophytic for the area to be considered a “forested wetland.” However,
although a canopy may not include hydrophytic vegetation, the shading, perching and
foraging contributions of the trees in close association with water, wet soil, and wet
plants can create many qualities of a “forested wetland.”
Roads and Trails:
In order to create a reasonably readable map, only the largest and most durable roads and
trails were assigned their own polygons (see Roads and Trails Criteria). In the future, an
independent road and trail data layer would be very useful for depicting the
fragmentation of some habitats.
Mapping Diverse and Transitional Areas:
The intent of this survey was to show major habitat areas. In general, areas of similar
“character” or ecology were grouped. Habitat boundary definitions were often difficult
to draw and subject to interpretation. It is important to recognize that boundary definition
determination is a subjective process; not only will classifications vary between staff
members, but one person may define the same polygon in an alternative fashion on
different days. The polygons are intended to serve as a tool to help study and inventory
an area, not to act as barriers within ecosystems. However, the database design is able
to accept further refinements as they come to light.
The character of a forest seldom changes abruptly. Putting a discrete line between areas
that have a subtle transition or layer transition from one habitat type to another often
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requires a compromise in the boundaries of one of the habitats. For example, when tree
canopies overhang the edges of parking lots, roads, lawns and shrubs, the edges of the
polygons could be drawn at the edge of the pavement or grass or at the edge of the tree
canopy. It was determined that where tree canopies overhang impervious surfaces, the
impervious surface has a greater effect on the habitat of the polygon than the overhanging
trees, so the boundary would be placed at the edge of the impervious surface. However,
when tree canopies overhang other plants, the tree canopy has a greater effect on the
habitat of the polygon, so the boundary was placed at the edge of the tree canopy.
In areas where species or sizes were mixed, questions arose concerning whether or not,
for example, an area with the character of an older forest should encompass only the
groves of large trees or should include groves of smaller trees. Mixed stand polygons
were created when coniferous, deciduous, and broadleaved evergreen trees were found
within the same area. If a patch covered more than 30% of an area a new polygon was
created (see Habitat Key). Features larger than one half acre were mapped, except
wetlands which were mapped in smaller areas. Small groves of one forest type (e.g. a
size class different than the surroundings or patches of conifers or Madrone in a mostly
deciduous forest, etc.) were often grouped for inclusion into the surrounding polygon.
Their presence was recorded in the habitat description or vegetation table on the data
sheet for the polygon.
Describing the Habitat:
Once the perimeter of a polygon was established, it was given a unique identifying code
that indicated where it was located (e.g. discpk1 is the first polygon in Discovery Park).
Cover class was assigned according to the percentage of the polygon that is vegetated,
based on data collected on plants and non-vegetated areas (e.g. “pavement”, “building”,
“sand”, etc.) within polygons. In instances when polygons had multiple layers of
canopies (trees, shrubs, herbaceous groundcovers, etc.), total coverage was often greater
than 100% because each layer was assessed separately. The canopy layer(s) occupied by
each species were indicated. Data on special site features were collected (see
checkboxes) and distinctive characteristics were described (see Habitat Descriptions).
Habitat Descriptions:
Developed Landscapes:
Heavy Development: Buildings, parking lots, etc. (>50% impervious surface).
Medium Development: Housing areas with extensive vegetation, play areas, picnic areas,
dense paved trail networks (30-50% impervious surface).
Light Development: Small yet evident presence of pavement, small structures, etc. (1030% impervious surface).
Landscaped Grassland: Mown grass.
Landscaped Shrubland: Pruned or shaped shrubs (e.g. a rose garden).
Landscaped Tree Savannah: A few trees scattered over mown grass or manicured
shrubs.
Landscaped Forest: More trees over mown grass or manicured shrubs.
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Herbaceous Row Crop: Any food garden, generally restricted to the City P-Patches.
Developed Pasture: Uncommon. Large tracts of land that are grazed by horses (seen) or
other animals (not seen).
Orchards: Restricted to old farm remnants. Uncommon.
Open Canopy:
Beaches and Dunes: Restricted to sandy beachfronts.
Sparsely Vegetated Area: In Seattle, restricted to areas of landslides and formally graded
areas that have not revegetated. Uncommon.
Grassland: Uncut grass, fields.
Shrub Savannah: A few shrubs scattered over uncut grass.
Tree Savannah: A few trees scattered over uncut grass, shrubs or a mixture.
Shrubland: Shrubs dominate the upper canopy..
Wetland Types:
Riverine Consolidated Substrate: Perennial or robustly intermittent streams with an
artificial bed.
Riverine Unconsolidated Substrate: Perennial or robustly intermittent streams with direct
soil connection.
Riverine Tidal: Wetlands along large rivers whose hydrology is linked to tidal cycles.
Forest Types:
Riparian Forests: Contains many size classes and potential many species. Common trees
are Cottonwood (Populus trichocarpa), Willow (Salix spp.), and Red Alder
(Alnus rubra). Western Red Cedar (Thuja plicata) and Spruce (Picea spp.) are
present and much less common. Unlike riverine systems, streams in riparian
forests are well connected to the flood plain and the surrounding hydrology is
impacted by or contributes to the stream’s water table
Deciduous Forests: Primarily comprised of Red Alder, Big-leaf Maple (Acer
macrophyllum) and Cottonwood. Large size classes include pre-settlement
remnants, stands with less valuable timber, areas in recovery, and sites occupied
by rapidly growing species (particularly Cottonwood). Small size designations
include areas recovering from repeated logging, regenerating old farm sites or
developed areas, and stands clinging to sliding hillsides. Wet sites and wetland
margins commonly have a long-term succession of Alder and Cottonwood
species.
Coniferous Forests: Often dominated by Douglas Fir (Pseudotsuga menziesii), Western
Red Cedar (Thuja plicata), and occasionally Western Hemlock (Tsuga spp.).
Grand Fir (Abies grandis) and Spruce (Picea spp.) are less common. Introduced
species (Redwoods and many horticultural varieties of pine, spruce, fir, cypress,
etc.) have grown large and are regenerating in some areas. Significant stands of
these immigrants have been included in the assessment. Sizes of coniferous
stands range from planted areas full of small trees, to small regeneration stands at
the edges of larger stands, and to all forms of second and third growth natural
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regeneration. A few areas of very large trees (termed old-growth relicts) remain
in Schmitz and Seward Parks. Extensive second growth stands carpet the
Llandover area.
Broadleaved Evergreen Forests: The Pacific Madrone (Arbutus menziesii) makes pure
and nearly pure stands along many ridge and bluff tops with good drainage and
sun exposure. Small trees are seen regenerating in these areas and in harsh
environments (riprap along I-5, not-so-recently graded areas). Larger size trees in
remnant stands dot the city. A dramatic association evident in Lincoln Park and
other bluffs is an overstory of Madrone, a midstory of Dogwood (Cornus spp.),
and Snowberry (Symphoricarpos alba) in the shrub layer.
Mixed Forests: Combinations of Deciduous, Coniferous, and Broadleaved Evergreen
Forests.
Other:
Cliffs: Slumping on steep slopes of glacial till can transport entire habitat areas downhill
into Puget Sound or onto underlying structures. What remains are nearly vertical,
unvegetated areas of substrate ranging from sand to clay. The cliff/bench/cliff
formations in Discovery Park are good examples.
Rock and Talus: Generally large erosion and slide control areas. Uncommon.
Sensitive Species:
The exact locations of five plant species have been masked in the database in the interest
of protecting remnant native populations of locally rare herbaceous species. These
species were determined to be sensitive without formal criteria. The following species
(and associated codes) were found on Seattle’s Public Lands but have not been listed at
the individual park or polygon level:
Vanilla Leaf
Pathfinder
Maiden Hair Fern
Wild Ginger
Trillium
ACTR
ADBI
ADPE
ASCA3
TROV
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Annotated Glossary:
Aerial photograph: Aerial photographs were the primary tool used in the field to assign
polygon boundaries. Photos taken in 1995 were provided by Triathlon in
Bellevue, WA (formerly NIES Mapping Group, Inc.). The large scale (1:2400,
1”=200’) digital photos clearly show tree canopies, roads, buildings, grassy areas,
shrubs and other landscape features. The digital prints were corrected to
overcome the “fisheye” distortion effect at the edges of most photos caused when
using a circular lens. With this correction, distances could be accurately
measured from all locations on the print.
Broadleaved evergreen tree: Trees with wide flat leaves (not needles or scales) that lose
leaves and grow new leaves slowly all year. The most common example in
Seattle is the Madrone (Arbutus menziesii). Some Magnolias (Magnolia spp.) and
Live Oaks (Quercus spp.) also fit the definition although they are rare in the
public land holdings.
Canopy: The upper layer of vegetation. In a forest this includes the leaves and branches
of the trees but not the trunk. The canopy provides a protective cover over the
forest floor. Canopies come in many forms. Deciduous forest canopies provide
summer shade and winter sun (when available) and deep mulch in the fall. They
are often wide and round. Coniferous and broadleaved evergreen forest canopies
provide year round shade, a sheltered climate, and a slow trickle of needles,
leaves, bark, and cones (see Mulch). Canopies can be wide and round as in
Madrone, tall and pointy like many conifers, or broken and ragged like a bluff top
stand of Douglas Fir. Animals at different times of year use canopies for nesting,
feeding, resting, hiding, hunting, or shelter. Many individual plant canopies
together can create distinctly different microclimates and soils and attract
alternative wildlife populations. For example, a mowed area with trees has a
different canopy and habitat potential than one with only grass. While providing
habitat for many species, forest canopies will discourage animals that prefer open
meadows. In addition, areas located between distinct habitats (e.g. on the edge of
a forested area), can provide niches for some animals. Niches can be shade or
shelter islands with hunting and hiding perches that provide direct access to open
areas, or encompass a rich collection of woodland-dwelling or sun-loving plants.
Conifers: Trees or shrubs that have needle- or scale-like leaves and often cones. They
lose and grow leaves throughout the year. Puget Sound lowland native species
include: Douglas Fir (Pseudotsuga menziesii), Grand Fir (Abies amabalis), Shore
Pine (a.k.a. Lodge Pole Pine) (Pinus contorta), Sitka Spruce (Picea sitchensis),
Western Hemlock (Tsuga heterophylla), Western Red Cedar (Thuja plicata), and
Western White Pine (Pinus monticola). A related group is the Yews (Taxus spp.),
which have needles and berries instead of cones. There are also many introduced
conifer species growing in the city.
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Cover class: One of eight categories which represents the proportion of ground surface
included in a polygon covered by a particular species (out of 100%). The
categories are: “1” = a trace or single individual of a species, “2” = 0-5%
coverage, “3” = 5-10%, “4” = 10-25%, “5” = 25-50%, “6” = 50-75%, “7” = 7595%, and “8” = 95-100%. For example, a field with 100% grass would be
classified as an “8”, while an area with 1/3 grass, 1/3 blackberry, and 1/3
pavement would receive a cover class of “5” for each species. An important
consideration is the layering of coverages. A grassy area completely shaded by
trees will have high cover classes (“7” or “8”) for both the grass and the trees.
Data Sheet: The form used in the field to describe polygon characteristics. It contains:
park name and code; staff member’s name who described the polygon; date of
survey; codes to identify the aerial photograph print used to designate the
polygon; polygon number; habitat type; habitat description; special features; the
vegetation table; and the wildlife table.
Deciduous: Trees or shrubs that lose most of their leaves in the fall and grow a new set
of leaves in the spring. Native species include: Big-leaf Maple (Acer
macrophyllum), Bitter Cherry (Prunus emarginata), Cottonwood (Populus
trichocarpa), Oregon Ash (Fraxinus latifolia), Red Alder (Alnus rubra), and
Willows (Salix spp.). There are also many introduced varieties growing in the
city.
Digitize: An electronic process by which lines that have been physically drawn onto an
aerial photograph are converted into digital data for use in a computer database.
This is the critical link in the GIS mapping process. By attaching a specific area
on the ground to a data field in the computer, other data on the characteristics of
the area can be coupled to the specific area. Use of the GIS allows the
information to be accessed, displayed, analyzed, and compared to other areas.
Digitizing also creates a spatial database that displays the polygons, as they exist
on the ground, proportional to other features like roads, bodies of water, etc. and
allows polygons to be measured (area, distance between polygons, etc.). This
spatial database is the computerized GIS map.
Dominant: Describes a tree or other plant species that comprises most of the canopy in a
polygon.
Habitat Key: A series of questions about the polygon that have two answer choices for
each question. The chain of decisions leads to determination of habitat type.
These decisions include determining the amount, type and size of forest, grass and
shrub areas, the amount of pavement, buildings and other development; and the
impact of mowing and other maintenance. This type of key is called a
dichotomous key.
Habitat Description: A brief summary of features of the polygon that are not captured by
the special features or the vegetation table. Possible wetlands, horticultural
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varieties, weeding and replanting activity are a few of the many subjects
discussed in this part of the data sheet.
Habitat types: Fifty-eight categories that reflect the kinds of environments encountered
in Seattle. They are listed below and described in the habitat description:
Beach and Dune
Broadleaf Evergreen (3 size classes)
Cliff
Conifer Broadleaf Evergreen Mixed (3 size classes)
Conifer Deciduous Mixed (5 size classes)
Conifer Forest (5 size classes)
Deciduous Broadleaf Evergreen Mixed (4 size classes)
Deciduous Forest (5 size classes)
Developed Pasture
Grassland
Heavy Development
Herbaceous Row Crop
Lacustrine
Landscaped Forest
Landscaped Grassland
Landscaped Shrubland
Landscaped Tree Savannah
Light Development
Medium Development
Orchard or Vineyard
Palustrine Aquatic Bed
Palustrine Emergent Wetland
Palustrine Forested Wetland
Palustrine Open Water
Palustrine Scrub/Shrub Wetland
Riparian Forest (4 size classes)
Riverine Consolidated Substrate
Riverine Tidal
Riverine Unconsolidated Substrate
Rock and Talus
Shrub Savannah
Shrubland
Sparsely Vegetated Habitat
Tree Savannah
Invasive species: Numerous plant species that are not native to the Seattle area have been
intentionally or unintentionally introduced and thrive in this region. These
species can be a detriment to the native habitats in the city. Scot’s Broom
(Cytisus scoparius ), Himalayan Blackberry (Rubus discolor), English Ivy
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(Hedera helix), English Holly (Ilex aquifolium), Cherry Laurel (Prunus
laurocerasus), Clematis (Clematis vitalba ), Japanese Knotweed (Polygonum
cuspidatum), Morning Glory (Convolvulus sepia), Reed Canary Grass (Phalaris
arundinacea), Purple Loosestrife (Lythrum salicaria), and Yellow Flag Iris (Iris
pseudacorus) are aggressive plants that are expanding their range in the city.
Control in some areas has been very effective. Many areas are not controlled.
Impervious surface: Ground cover that does not allow water to penetrate to the soil.
Examples include pavement, buildings, plastic sheeting, and very compacted
ground. Turf is partially pervious, because it allows a fraction of the water to
percolate into the soil. An old growth forest is highly pervious, absorbing rain at
multiple canopy layers.
Jurisdictional delineations: The Washington State Department of Ecology and US Army
Corps of Engineers have established criteria for delineating the edges of wetlands
based on the presence of certain soils, vegetation, and water in the soils that
indicate saturation for a portion of the growing season. These edges determine
buffer areas where building and grading is limited. The wetland edges that appear
on the Seattle Urban Nature Project maps and data are not jurisdictional
delineations. They are core areas with distinct wetland properties (lots of
standing water, many plants that require wet conditions, etc.). Delineating the
edges with established criteria would expand the areas of many of these described
wetlands.
Landscaped: An area that has been regularly mowed, manicured, pruned or recently
planted.
Mulch: The buildup of leaves, needles, cones, branches, and fallen trees that creates the
rich forest soils where woodland plants thrive. Insects, fungi, worms and moles
help convert mulch to soil. Each type of tree or animal species gives a different
“flavor” or chemistry to the mulch.
Palustrine: A fresh water wetland ranging from mid-slope seeps and willow thickets to
large open ponds.
Polygon: An area on a map or aerial photograph that shows a single patch of a habitat
type. Polygons are usually irregular in shape. Habitat polygons were drawn onto
aerial photographs in the field and show the boundary of an area with a particular
habitat type. Once digitized, polygons contain all of the information that exists
about that area (plant and animal species, special features, habitat type, habitat
description, etc.).
Riparian: Streamside vegetation that is regularly flooded or influenced by the stream’s
water table.
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Roads and Trails Criteria: There are many types of roads and trails in Seattle. Seattle
Urban Nature Project maps show only the regularly driven roads and paved trails
over five feet wide.
Savannah: Scattered tall woody plants in an area of generally shorter plants (usually
grass). Tall plants are trees or shrubs (creating tree or shrub savannah) and short
plants are shrubs in a tree savannah or grasses and forbs (in either savannah type).
The habitat key and descriptions provide specifics about the canopy cover of trees
and shrubs in savannahs. In Seattle, savannahs usually receive some level of
management to maintain the dominance of grass species.
Size class: One of five tree diameter categories determined by the diameters of the
dominant trees in the polygon (< 5”, 5-15”, 15-20”, 20-30”, and > 30”).
Spatial database: A collection of polygons, points or features that are arranged
according to their position on the ground and in relation to other polygons, roads,
water features.
Special Features: Features recorded in the field on the data sheet about a polygon
including: “snag” (dead tree > 5” in diameter), “down log” (also >5” in
diameter), “large tree” (> 35” in diameter), “seep” (a damp or boggy area), “slide”
(mud or land slide), “gully erosion” (where water is cutting a ravine), and
“refuse” (e.g. garbage, abandoned vehicles, yard waste dumps).
© 2002 Seattle Urban Nature Project.
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