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I.
Habitat Types
Habitats, as defined in a classic ecological
sense, are the places where organisms normally live. Habitat type
refers to the specific vegetation association classified and mapped
in Volume 3 of the Humboldt Bay Wetlands Study and Baylands Analysis.
A habitat may be described in several different
ways. In the case of a plant, habitat is often defined as a specific
set of physical characteristics and, sometimes, associated plants.
In the case of a terrestrial animal, habitat may be defined as a
variety of plant communities (some with similar physical characteristics)
or a variety of physical characteristics (some with similar plant
communities).
A habitat type, on the other hand, is a
plant community or plant association. Occasionally, physical characteristics
may be used to distinguish certain habitat types with similar plant
associations, such as tidal versus non-tidal freshwater wetlands.
In some parts of the study area, habitat types are classified according
to activity (urban) or physical characteristics (water). However,
the plant community is the primary delineation of habitat type used
in this discussion.
In the Humboldt Bay region, nine major habitat
types have been identified and mapped. These include:
· Urban
· Agriculture
· Grassland
· Shrubland
· Forest
· Water
· Wetland
· Dunes
· Jetties
and Reefs
Several
of these habitat types have been divided into sub-types according
to specific characteristics.
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A.
Urban areas are comprised of residential and industrial habitat
types that are usually found in areas of dense human habitation.
These include transportation facilities, port and harbor structures,
mines and gravel pits, and open areas which have been scraped or
filled but are not otherwise being used. Generally, urban areas
support little wildlife since the vegetation is often sparse, exotic
(non-native), and managed for aesthetic rather than wildlife uses.
Exceptions are wooded residential areas, such as parks, where some
urban-tolerant birds and small mammals are found, and port areas,
where water-oriented birds, fish, and shellfish may be found. Urban
habitat types are centered around the cities of Eureka and Arcata
and the railroad/highway corridor that connects them. These habitat
types are also found at Fields Landing and King Salmon, on South
Bay, and Manila, Fairhaven, and Samoa on North Spit.
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B.
Agriculture habitat types are those pasture and croplands that
are or have been used for commercial farming. Within the study area,
grazing of cattle and sheep is the most common farming activity.
Most of the agricultural areas are lowlands that were diked and
drained to take advantage of the rich alluvial soils found in the
floodplain. Prior to diking, these lands were probably at or near
intertidal elevations and were probably wetland habitat types (saline,
brackish, or fresh). Old tidal channels and sloughs are evident
in many of the grazing lands. Often, these channels, when combined
with drainage ditches, assist in draining low agricultural land.
Some agricultural lands have been noted
as wetlands. The soils of these areas are saturated with sufficient
frequency to support wetland vegetation. Bent grass (Agrostis
alba) and salt grass (Distichlis spicata) are common
in these areas. Rush (Juncus spp.), pickleweed (Salicornia
virginica) and sandspurry (Spergularia spp.) are also
found, but not in abundance.
As noted by Monroe (1973), many agricultural
lands are flooded during winter rains. These areas are often referred
to as seasonal wetlands. Due to the physical, rather than botanical
characteristics, of these areas, it has not been possible to map
their distribution. They are often centered around old tidal channels
and other low areas referred to previously.
Extensive agricultural lands are found between
North Bay and Mad River, west of Arcata. There are also agricultural
areas along the east shore of North Bay, extending up Jacoby Creek
and Freshwater Creek. East of Middle Bay, large portions of the
Elk River valley are agriculture habitat types. Adjacent to South
Bay agricultural lands are found in the vicinity of Hookton Slough
and up the Salmon Creek valley.
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C.
Grassland habitat types are found in those areas where annual
and perennial grasses and forbs dominate, and woody species are
not present in significant numbers. Since there are few, if any,
undisturbed uplands within the Humboldt Bay study area, most grasslands
are abandoned agricultural lands, vacant lots, or roadsides. Grasslands
are found in scattered locations throughout the area.
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D.
Shrubland habitat types are characterized by woody vegetation
less than six meters (20 feet) in height. Blackberries (Rubus
spp.) and coyote brush (Baccharis pilularis) are most common,
but silktassel (Garrya elliptica), bayberry (Myrica californica),
Indian plum (Osmaronia cerasiformis), and cascara (Rhamnus
purshiana) may also be found. The shrub habitat type is not
extensive anywhere it is found, but it is rather widely scattered
throughout the study area. Dense shrub stands are often found on
dikes or in long-abandoned vacant lots or agricultural lands.
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E.
Forested habitat types are found throughout the study area and
are characterized by the dominance of deciduous and/or coniferous
trees. Although much of the area was originally wooded, only isolated
remnants of the pre-settlement forests remain. Many of the wooded
areas around Humboldt Bay are second-growth which has become established
following early timber harvests.
Within the study area, forest habitat type
can be subdivided as follows:
· Deciduous
forest
· Evergreen
forest
· Mixed deciduous/evergreen
forest
· Closed
cone pine forest
Successional patterns in Northwest forests
have been described by Franklin and Dyrness (1973). Immediately
following logging or burning, herbaceous annuals and perennials
dominate the site. These are soon replaced by shrubs such as blackberries,
barberries (Berberis spp.), rhododendron (Rhododendron
macrophyllum), salal (Gaultheria shallon) and salmonberry
(Rubus spectabilis). In time, a deciduous forest, dominated
by alder (Alnus oregana) develops. Introduction of Douglas
fir (Pseudotsuga menziesii) and Sitka spruce (Picea sitchensis)
leads to a mixed deciduous / evergreen forest. Ultimately, the conifers
dominate, particularly redwood (Sequoia sempervirens) and
Douglas fir. It has been suggested that redwood forests are only
a seral stage, albeit a long-lived one, with climax represented
by hemlock (Tsuga heterophylla) and tanbark oak (Lithocarpus
densiflorus).
1. Deciduous forest
is usually dominated by alder with occasional willow (Salix spp.)
or black cottonwood (Populus trichocarpa) intermixed. The
latter two species are most common in riparian situations. The understory
in deciduous forests may vary from salmonberry or blackberries to
sword ferns (Polystichum spp.) and bracken ferns (Pteridium
spp.)
2. Evergreen forest
in the Humboldt region is usually a mixture of redwood and Douglas
fir. Lowland fir (Abies grandis), Sitka spruce, and alder
may also be present. Occasionally, evergreen forest consists of
a stand of Eucalyptus, an ornamental broadleaf evergreen, present
in several locations around the Bay.
3. The mixed deciduous/evergreen
forest does not exhibit a significant dominance of either evergreen
or deciduous species. It is commonly a very diverse assortment of
trees from both the previously described forests. In some areas,
such as the steep slopes of gulches in Eureka, it may represent
a dynamic equilibrium resulting from conditions of light, water,
and steep slopes. Such an equilibrium might be called an "edaphic
climax" (Odum, 19S9), where local conditions of soil development
and water availability control climax communities, rather than regional
climatic conditions.
4. The closed cone
pine forest is found primarily along the coastal strand and is dominated
by beach pine (Pinus contorta). Silktassel, Douglas fir,
and Sitka spruce are also found within the canopy. Evergreen shrubs
such as salal, bearberry (Arctostaphylos uva-ursi) and huckleberry
(Vaccinium ovatum) are common in the understory.
Riparian
forests are those found adjacent to natural watercourses. In the
Humboldt Bay area, this is generally a narrow band of vegetation
along rivers and streams, but it may also be found adjacent to lakes,
ponds, or the Bay itself. Riparian habitat types are characterized
by the influence of the local water table and often by seasonal
flooding. As a result, the overstory may remain similar to the adjacent
forest but the understory may contain a variety of plant species
adapted to moist or wet substrates.
Forest
habitat types are widely distributed throughout the Humboldt Bay
region. Deciduous forests are common in the gulches of Eureka. Evergreen
forest habitat types are scattered through Eureka and on nearby
hillsides. Mixed deciduous / evergreen forests are most common on
the sides and bottoms of gulches and also on Table Bluff. The closed
cone pine forest is common on North Spit and northward on the coastal
strand to approximately Lanphere Road.
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F.
Water habitat types in the study area are associated either
with the tidal bay regime or the rivers and creeks entering into
the Bay. The water habitat type can be divided into the following
categories:
· Deep tidal
channels
· Shallow
tidal channels
· Tidal creeks
and sloughs
· Creeks
and rivers
· Ditches,
ponds, and closed channels
1. Deep tidal channels
are those areas within the Bay that are subject to maintenance dredging
for navigation and commercial purposes. The depth of these channels
varies from 12 to 47 feet below mean lower low water (MLLW) and
is maintained by the Corps of Engineers (NOAA, 1978). There is a
total of 8.6 miles of these channels in the Bay with widths of 300-800
feet.
Deep
tidal channels are generally characterized by a dearth of macroscopic
vegetation. This is due to both the depth, and subsequent lack of
available light, and also the frequent disturbance associated with
maintenance dredging activities. There is, however, considerable
phytoplankton that occupies the water column in these deep channels
(Harding, 1973). The upper limit of deep tidal channels is defined
as -12 feet (MLLW).
2. Shallow tidal
channels are more shoal than deep tidal channels and do not undergo
periodic maintenance dredging. Biese natural channels are distributed
throughout the Bay and act to drain the mudflats as tide ebbs. The
upper limit of shallow tidal channels is defined as MLLW.
The
lack of disturbance and the shallow character of these channels
allow a few plants to thrive. Eelgrass (Zostera marina) can
be found along the edges or sometimes at the bottom of these channels.
Some algal species, such as sea lettuce (Ulva spp.) or filamentous
green algae, may also be present in these shallow channels.
3. Tidal creeks
and sloughs are shallow channels that meander through agricultural
lands and are usually diked to prevent flooding of the adjacent
areas. Often intertidal mudflats will be distributed along these
channels. Tidal creeks are characterized by depressed salinities
as a result of upland runoff or stream flow into the channel. These
areas are defined as tidal channels, thus their upstream limit is
the limit of tidal influence. In this study, the upstream limit
of tidal influence can only be approximated through field examination
and review of existing literature. Thus, the upstream limit of tidal
areas mapped in this study cannot be considered exact.
Vegetation
in tidal creeks and sloughs varies from marine or brackish algae
in the channel bottoms, to salt or brackish marsh vegetation along
the edges and mudflats. Sea lettuce (Ulva spp.), Enteromorpha,
widgeon grass (Ruppia maritima), and pondweed (Potamogeton
spp.) may be found in the channel bottoms. Salt marsh vegetation
near the mouths of these sloughs includes pickleweed and cordgrass
(Spartina foliosa); brackish marsh vegetation includes bulrush
(Scirpus spp.), hairgrass (Deschampsia caespitosa),
and rush.
Hookton
Slough, Mad River Slough, and Fay Slough are tidal sloughs with
very little freshwater runoff. Jacoby Creek, Eureka Slough, and
Elk River Slough are all tidal creeks with a significant amount
of freshwater inflow from creeks and rivers.
4. Creeks and rivers
are flowing freshwater bodies bringing water from adjacent watersheds
into the Bay. Some of these, like Jacoby Creek, Freshwater and Elk
River are free-flowing, with levees to prevent flooding. Others,
such as McDaniels Creek and Rocky Gulch, are separated from the
Bay by levees and tide gates, thus preventing any tidal intrusion.
Swift-flowing
rivers often have no vegetation in their channels. However, slow-moving
rivers and shallow creeks, such as those meandering through floodplains,
often have extensive vegetation along the edges and occasionally
in the main channel. Cattails (Typha spp.), marsh pennywort
(Hydrocotyl spp.), canarygrass (Phalaris arundinacea),
and Angelica (Angelica spp.) may all be found in or adjacent
to creeks.
5. Ditches, ponds,
and closed channels may be described as standing water situations,
although under flood conditions there may be some water movement.
Farm ponds, drainage ditches, millponds, and cutoff slough channels
are all examples of this habitat type. Phytoplankton and filamentous
green algae often fill these areas in the summer, giving the water
a turbid appearance. In shallow areas or around the edges, cattails,
bulrushes, pennywort, and Angelica are common.
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G.
A wide variety of Wetlands are present in the Humboldt Bay
area. Salt marsh, brackish marsh, fresh marsh, swamp, intertidal
flat, and eelgrass are the basic groups into which the various wetlands
may be classified. Each group has unique water regime, substrate,
and vegetation characteristics that distinguish it from the others.
For this report, wetlands are defined according
to Corps regulations 33 CFR 323.2. Several other definitions of
wetlands exist. Most notable of these is that of the U.S. Fish and
Wildlife Service (USFWS), which identifies wetlands according to
the presence of hydric soils. Hydric soils are wet, poorly drained
soils, often consisting of large amounts of organic peat and muck.
These soils often support communities of hydrophytic plants.]
Salt marshes are habitat types that are
inundated by marine waters with sufficient frequency that only certain
salt and water tolerant plant species can become established. These
areas are usually found along the fringes of the Bay or tidal sloughs.
There are also a few examples of this habitat type in agricultural
areas where leaking tidegates allow Bay water to enter.
Two vegetation associations have been identified
in salt marshes. The cordgrass association is generally found at
middle and high elevations within the marsh. Cordgrass generally
exhibits a cover of 75% or more in this habitat type. Pickleweed
and saltgrass may also be present in small amounts.
The pickleweed-saltgrass association is characterized by a low mat
of vegetation that may be found from the lowest to the highest elevations
of the salt marsh. At the lowest elevations pickleweed dominates
with saltgrass usually present in measurable amounts. With increased
elevation, the diversity of this association increases. Jaumea (Jaumea
carnosa), orache (Atriplex patula), sea lavender (Limonium
californicum), arrowgrass (Triglochin maritimum), and
gumweed (Grindelia stricta) are all common, but never dominant
in higher elevation pickleweed marshes. Of particular interest in
these higher elevation areas are Humboldt Bay tarweed (Grindelia
stricta spp. Blakei) and Humboldt Bay owl's clover (Orthocarpus
castillejoides Var. humboldtiensis), both considered uncommon
endemic species of Humboldt Bay.
Brackish marsh is a tidal wetland experiencing
inundation by low salinity water. Often this habitat type is found
at the very highest marsh elevation, where runoff may dilute infrequent
tides, or adjacent to rivers and creeks where a constant freshwater
flow results in depressed salinities. Two brackish marsh associations
have been recognized in the Humboldt Bay region.
Hairgrass dominates one brackish marsh type,
although rush (Juncus patens), bentgrass, and silverweed
(Potentilla spp) are also present. Arrowgrass and yarrow
(Achillea millefolium) may be found, but rarely in more than
spotty locations.
The other common brackish marsh habitat
type is dominated by sedge (Carex obnupta). This is usually
a dense monotypic community with no other species present.
Several different fresh marsh habitat types
have been identified. These are most often associated with rivers
or creeks in the area, or alternatively, closed channel habitat
types such as millponds or drainage ditches. In some situations,
they are tidelands originally diked for agricultural purposes which
maintain a wetland character, having changed from salt marsh to
fresh marsh.
A common fresh marsh in the area is dominated
by Angelica, with occasional rush and marsh pennywort. This habitat
type is often inundated with several inches of water and has a soft,
boggy substrate. Another common fresh marsh habitat type is dominated
by rush with some sedge, bulrush (Scirpus fluviatile) or
silverweed scattered throughout. This habitat type is usually found
on a moist, but firm, substrate and is only rarely inundated. Cattails
also make up a major fresh marsh habitat type. They are usually
found in monospecific associations with varying water regimes. Often
cattails are found in drainage ditches or along the shores of slow
moving creeks.
Swamps are wetlands dominated by trees and
shrubs. Willows are usually the dominant trees, although alder may
also be present. Swamp understory usually includes salmonberry,
sedge, buttercup (Ranunculus spp.), and bulrush. Angelica
may also be present in especially boggy situations.
In the dune areas of North Spit, swamps
have a slightly different character. In addition to the willows,
beach pine and Sitka spruce may also be a part of the overstory.
The shrub understory may contain bayberry, twinberry (Lonicera
involucrata), and huckleberry. Low understory species may include
silverweed (Potentilla Egedii grandis), sedge, bracken fern
(Pteridium aquilinum), and dock (Rumex crassus) (Johnson,
1963).
Broad expanses of Humboldt Bay consist of
intertidal flat habitat types, extending from the shore of the Bay
out to the edges of the shallow and deep tidal channels. For this
study, extreme low water (ELW) has been chosen at the lower limit
of intertidal flats. In general, ELW corresponds to approximately
-3 feet (MLLW). Most of the flats are bare above an elevation of
about +1 MLLW, with only diatoms or occasional patches of algae.
Below the +1 contour, dense stands of eelgrass
dominate most of the mudflats, and extend at least partially into
adjacent channels (Keller, 1963). The lower limit of eelgrass stands
is dependent on light penetration, nutrients, and numerous other
parameters In Humboldt Bay, studies of eelgrass have gone to a depth
of -1.5 (MLLW) but no maximum depth was noted (Harding and Butler,
1979). Phillips (1974) reported eelgrass to -22 feet (MLLW) in Puget
Sound and below -50 feet (MLLW) in La Jolla Canyon. Almost all flats
except those subject to regular oyster harvest are covered (Monroe,
1973). These stands of eelgrass are monotypic, but they may support
a variety of epiphytic algae.
Both North and South Spit exhibit distinct
and unique (for the study area) dune habitat types. The windblown
sand and salt spray create a highly stressed environment which can
be tolerated by a limited number of organisms.
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H.
Bare dunes are unvegetated areas, often characterized by large
amounts of moving sand. Vegetated dunes have been reasonably stabilized
by a variety of grasses, forbs, and shrubs. Bush lupine (Lupine
spp.), seapink (Armeria maritima californica), bluegrass
(Poa spp.), and goldenrod
(Solidago spathulata) are all common on heavily vegetated,
stabilized dunes (Johnson, 1963; Barker. 1976)
Sparsely vegetated dunes are usually less stable than vegetated
dunes and represent a more mobile sand substrate. Most foredunes
on the spit are included in this habitat type. Beachgrass (Ammophila
arenaria), dune grass (Elymus mollis), sea rocket (Cakile
spp.), ice plant (Mesembryanthemum chilense), and beach strawberry
(Fraceria chiloensis) are often found on sparsely vegetated
dunes. The wallflower (Erysimum menziesii), identified as
threatened (Smithsonian, 1975), has been reported from this habitat
type (ERC, 1977).
Dune hollows are low, blown-out areas between
dunes that are closer to the water table, protected from the wind,
and, therefore, a more conducive habitat for vegetation. A variety
of shrubs, such as bearberry (Arctostaphylos uva-ursi), coyote
brush (Baccharis pilularis), blackberry (Rubus ursinus)
and bayberry (Myrica califomica), may be found in these hollows.
Rush (Juncus lesueurii), birdsfoot trefoil (Lotus micranthus),
and sedge (Carex obnupta) are important components of the
understory.
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I.
Jetties and reefs are man-made structures constructed from impermeable
materials. Rocks, concrete, and tires are some construction materials
in the Humboldt Bay area. Although they do not support flowering
plants, a prolific and diverse algal community develops on the intertidal
and subtidal portions of these habitat types. Green, red, and brown
algae thrive over most of the substrate.
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