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SHORTCUTS TO THE COMMUNITIES

Introduction

The primary purpose of this guide is to describe wetland plant communities on the Kenai Lowlands.  Professional managers, and others interested in wetlands, should view this as a guide to understanding how the plants they see indicate wetlands and their functions.  This guide could be used in a “first cut” for a wetland determination, especially when used in conjunction with the ecosystem and map unit descriptions and the Geographic Information System mapping product which integrates these descriptions (ArcView shapefile download).

Plant Communities and Associations, a caveat

A number of terms, that are not always well-defined, are in use to describe groups of plants growing together.  The two primary terms used in this document, community and type, are defined, and their relationship to another widely used term: association, is described.  These terms are useful organizational tools to begin communicating about what is found growing on the landscape.  Ultimately, however they are only simplifying categories, and in a complex environment with limited plant species richness, as is found on the Kenai Lowlands, a more useful procedure might be to learn the autecological preferences of the 20-50 common dominant plants that cover most wetland plant communities found here.

For complete clarity, we define a plant community as any assemblage of plants found growing together (Daubenmire, 1968).  Type is synonymous with community.  Associations have two predominant definitions, broad and narrow.  The broad definition is: communities found repeatedly in similar habitats across a region (Weaver and Clements, 1938; Smith, 1974; Krebs, 1978; Barbour, et. al., 1980).  The narrower definition is: the theoretical 'climax' or 'potential natural vegetation' of a site (Daubenmire, 1968) used by USDA, Forest Service (1991) and Natural Resources Conservation Service, (1997), respectively. 

Formal plant associations are not named here, although these community names should be used in the process of naming associations.  This is a conservative approach, but only time, continued observation and comparison across a broader region can properly test a communities' repeated occurrence and cohesiveness, thus its rank as an association.  The association naming task is left to another worker who may find these community names consistent, and elevation to the rank of association useful. Towards that end, each community description begins with a reference to previously published descriptions of the same or similar communities and/or associations.

Although we name plant communities, and these named communities are useful in summarizing wetland conditions, it is well known that individual plants respond to a complex environment in individually (Gleason, 1926).  Some are more tolerant of a wide range of conditions, like field horsetail, while others are much more specific, like long-leaved sundew, while others have two separate ecological distributions, for example black spruce in dry lichen woodlands and also in saturated peatlands.

The same plant community frequently occurs in the same local environment across a region.  For example, dense bluejoint meadows are often found on higher-elevation south-facing slopes.  In these instances, plant communities are useful constructs. However, in other environments, unique locale-specific combinations of plants occur.  On many peatlands, for example, the mix of plants depends on heterogeneous micro-topographic differences in water table fluctuations during the growing season.  In this heterogeneous environment community names can dissolve into a confusing array of all possible combinations of a short list of common dominants.

We recognize that one community can be much different than another, as the bluejoint grass meadow is different from a peatland with sphagnum moss and tall cottongrass.  But, because micro-topographic heterogeneity is sometimes dominant, communities are found that cannot be easily sorted from others, or that are seemingly unique.  Because individual plant relationships are observable within and between communities, knowledge of individual plant preferences is useful to the field worker.  

This classification relies heavily on observations recorded at places that could be considered as 'type localities'.  These are sites where gradients are gentle and individual plant responses easily observable.  The large strang-flark complex northwest of the Kenai airport is an example.  There, it is possible to observe monotypic stands of nearly every common peatland plant, and to observe each common plant's relationship to its associates. 

For example, monotypic stands of tufted bulrush are common, but fewflower sedge is less common, and frequently present at locales without tufted bulrush.  Which plant occupies a wetter position?  At a few locales in that large complex northwest of the airport, fewflower sedge could be observed growing in slightly higher, drier positions above stands of tufted bulrush.  Reliance on such observations informs the somewhat arbitrary divisions between communities along the continuous mix of plants from open water to forest (see the lakebed cross-section figure).

Although the use of plant communities is a useful starting place, with a little comparative experience and practice a student can learn the preferences of the plants that make them up.  Forty-eight plants make up the names of the 70 Kenai Lowland wetland communities described here; only 22 of them make up most of what covers our wetlands.  Understanding the individual ecological tolerances of 22 plants is not insurmountable, especially since many of these, such as Lutz and black spruce, bluejoint, horsetail and alder are common and familiar to many.  The plants that define community names are, almost by definition, the common and dominant plants on the Kenai, not the rare, unusual ones.

The user should employ the plant community key and descriptions as a step to understanding the common plants that cover most of the wetlands on the Kenai lowlands, not as a rigid book of rules that plants should adhere to.

Kenai Peninsula Lowlands

For the purposes of this classification, the Kenai Lowlands are the lands west of Kenai National Wildlife Refuge, and north of Kachemak Bay (figure 2).  The lowlands are unique in that they are the only area along the coast of North America where a broad forested transition between maritime and continental climates exists.  This forested transition zone occurs over a complex assortment of glacial landforms, at the western limit of tree growth in North America, creating a heterogeneous environment.  

South of Clam Gulch, the forest is dominated by a hybrid between coastal Sitka spruce (Picea sitchensis) and interior white spruce (Picea glauca), named Lutz spruce (Picea X lutzii).  In the north, black spruce (Picea mariana) is more common, and quaking aspen (Populus tremuloides), which is nearly absent in the south, is abundant.  Winter low temperatures in the Sterling area (in the peninsula's northern interior)  frequently dip to -40^o; in Homer, temperatures have never gone below -20^o F.  In nearly all years, precipitation exceeds evapotranspiration.

In this climatic zone, peatlands are the dominant wetland type.  Peatlands are accumulations of organic material.  Organic material accumulates because productivity is greater than decomposition.  Productivity is moderate during the short growing season and decomposition is retarded by saturated soils, and other factors.

Worldwide, peatlands range from nearly un-decomposed, rapidly-expanding sphagnum mats that almost isolate a second water table above the local water table (bogs), through fens, with groundwater rich in nutrients because of recent contact with a mineral soil, to patterned ground above permafrost (soils where only a thin, surface 'active layer' thaws).  Permafrost is absent on the Kenai Lowlands, and precipitation moderate.  The peatlands that occur here function somewhere between the bogs further south and the patterned ground in Interior Alaska.  Most of the peat on the lowlands is partially decomposed and usually less than two meters thick.  Typical Kenai peatlands can be classified as poor fens; peatlands where groundwater has had some contact with a mineral substrate, and are therefore not as acidic as a bog, yet not as rich as a fen.

Wetlands

Wetlands could first be classified into two categories: 1) Jurisdictional wetlands, those wetlands meeting the criteria outlined in the Army Corps Wetland Delineation Manual (Environmental Laboratory, 1987) and are covered under Section 404 of the Clean Water Act, which regulates dredge and fill activities in wetlands; and 2) Non-jurisdictional, wetlands that might perform functions we associate with wetlands, such as groundwater recharge and shorebird habitat, and which may meet Delineation Manual criteria, but are not covered by the Clean Water Act.  Wetlands completely surrounded by uplands meet Delineation Manual criteria, but are no longer covered under the Clean Water Act, unless they are navigable-in-fact, because of a 2001 Supreme Court decision, Solid Waste Agency of Northern Cook County vs. Army Corps of Engineers (SWANCC).

The descriptions presented here can be useful to help decide whether a jurisdictional wetland is present at a site, but should not be used alone.  Those considering a project requiring the dredging and/or filling of a jurisdictional wetland may need to have a professional perform a wetland delineation.

Jurisdictional Wetlands and Delineation Criteria

Not all of wetland plant communities described here indicate that a Clean Water Act Section 404 dredge and fill permit is required.  Each community description ends with a sentence enumerating the sites that would probably qualify as jurisdictional wetlands.

Jurisdictional wetland delineation is beyond the scope of this document.  Wetland delineation is a complex process involving three primary factors: soils, hydrology and vegetation.  Hydrology alone can definitively indicate a jurisdictional wetland.  As a broad rule of thumb, soils need to be saturated within a foot of the surface for a little longer than a week during the growing season (which can be from May 10th to September 30th, or May 15th to September 10th depending on location).

Hydrologic criteria are occasionally addressed in the plant community descriptions using flooding frequency.  Because hydrology criteria are often expensive to assess, and because plant and soil indicators can be useful proxies for hydrology, indicators for these factors have been devised.

Soils

For soils, a summary of three important hydric (wet) indicators follows:

1)     Organic soils (those where the thickness of peat is greater than 40 cm, about 16”) automatically qualify as indicating wetland conditions. An organic horizon 20 cm thick (histic epipedon) can indicate wetland conditions.

2)  Depth to the water table (can be considered a hydrologic criterion). The water table needs to be within 30 cm of the surface to indicate a wetland in most Kenai soils, depending on how permeable the soil is (more permeable soils require shallower water tables to be classified as wetlands); and

3)   Depth to redoximorphic features, indicating that the water table is sometimes at the level of the features (usually in the form of reddish patches or very light colored zones in the soil profile; interpretation of these features can be difficult).  Only modern redox features are reported in the data we use; NRCS soil scientists attempt to avoid including relict features, generated by (pre)historic conditions.

For each state in the US, the Natural Resources Conservation Service has prepared a list of soils that meet hydric criteria.  In Alaska the list is provisional.  Users should remember that soils, along with most other land cover types that have been mapped, are by nature heterogeneous, so that an area mapped as a hydric soil may have upland soil characteristics, and a soil mapped as upland may also contain wetland inclusions. Click on this Kenai Hydric Soils link  for a list of the soils on the provisional Alaska Hydric Soils list that are found in the project area.

The Army Corps of Engineers is in the process of regionalizing the criteria defined in the 1987 Delineation Manual.  The Natural Resources Conservation Service has prepared a draft manual of hydric soils indicators for Alaska.  Once the regional Delineation Manual is complete, the draft hydric soils indicators prepared for Alaska will be incorporated.

Plants

For plants, a group of experts has met to determine the "wetland indicator status" of nearly all of the plants in each region of the US, using their best professional judgment and available data.  A formula, outlined in the Wetland Delineation Manual (Environmental Laboratory, 1987) has been devised to use each plant's wetland indicator status to determine whether or not a site meets the plant criteria for a jurisdictional wetland.  Individual plant "wetland indicator status" is listed in the table of plant frequency and cover following each description. Wetland plants alone cannot qualify a site as a jurisdictional wetland.  Some upland sites will fit into some of the plant communities described below, see the individual descriptions for an indication of how often that community will qualify as a jurisdictional wetland.  (A list of Alaska plants' wetland indicator status)

Conventions Used in the Plant Community Descriptions

The five line title of each description first contains a common name for the community type, followed by a scientific name, followed by the number of sites visited.  The fourth line explains where this community fits into The Alaska Vegetation Classification (Viereck, et. al.,1992) the standard reference for Alaskan vegetation descriptions (currently under revision by the Alaska Natural Heritage Program).  The final title line indicates the ecosystem(s) (defined by us) where this plant community most commonly occurs.  A dot map shows the locations of the sites we visited for each community.  We expect that the actual range of the community is broader than the dots suggest.

The first paragraph of the description begins with a short discussion concerning previous descriptions of the type, if any.  In addition to The Alaska Vegetation Classification (Viereck et. al., 1992) and the literature cited within that publication, three more recent classifications of nearby areas are used extensively.  These are: Plant Community Types of the Chugach National Forest: Southcentral Alaska (DeVelice, et. al., 1999); Classification of Community Types, Successional Sequences, and Landscapes of the Copper River Delta, Alaska (Boggs, 2000); and Plant Community Ecology and Classification of the Yakutat Foreland, Alaska (Shephard, 1995).

The second paragraph or two describes the geographic and landscape position of the community. The third or fourth paragraph describes the dominant plants and their habits (e.g. tree, shrub; tall, dwarf). 

A summary of the depth of peat, a frequent soils wetland indicator on the Kenai Lowlands, follows.  A layer, or horizon, of organic material is termed histic:

•  if it is greater than 20 cm thick, a histic “epipedon” (“above the soil”) is present

•  if greater than 40 cm thick, an organic soil, or histosol, is present

In each case a jurisdictional wetland is usually indicated.

A description of water table depth follows, as measured during a single site visit.  Often a water table of 30 cm (one foot) or less indicates a jurisdictional wetland.  Average depth to redoximorphic features (seasonal water table indicators, see below) follows, if important, for that type.  If pH was measured at any of the sites examined it is reported.

Two tables follow each community description.  The first is a list of all the soil series found at NRCS data points classified in that community.  The soil series names that appear in boldface type are on the NRCS Alaska hydric soils list. This list is purported not to exist, yet it is available at:

 ftp://ftp-fc.sc.egov.usda.gov/NSSC/Hydric_Soils/Lists/ak.pdf (click here for an abbreviated table, including only those soils found on the Kenai) Two newly proposed series are not on the list, but are certainly hydric soils, Truuli and Tlikakila.  Other proposed series, with currently unknown hydric status, are footnoted in the tables.   

The second table lists the common plants and their average ground cover, frequency of occurrence, and national and Alaska wetland indicator status.  The user of this wetland management tool should use caution when using the plant frequency and cover tables to interpret the wetland status of each community.  Keep in mind that a summary of the average cover of a plant over all the plots we classified into a particular community is not the same as the cover of that plant at an individual plot.  Because nature is quite variable, any category within a classification is a simplification.  Therefore, marginal plots might not contain all of the plants named as dominants in the title of the community.  A certain amount of art factors into classifying individual plots-- are they new communities,  just a little unusual, or are they unique?  

For example, consider an atypical site that seems to fit best in the sweetgale - dwarf birch - water horsetail community.  It might have 5% cover of sweetgale with the uncommon shrub, leatherleaf replacing it as dominant at 50%. The other dominants, dwarf birch and water horsetail are present in average amounts.  So, both the dwarf birch and water horsetail dominants are present, and sweetgale is, too, although at an atypically low percent cover value to be classified in the sweetgale - dwarf birch - water horsetail community.  However, the plot occupies a similar place on the landscape as a typical sweetgale- dwarf birch- water horsetail plot and it is the only plot of its kind, so does not warrant a new community name.  The presence of the other dominants on the same landscape indicates that it is reasonable to classify it into the sweetgale - dwarf birch - water horsetail community, recognizing that a large amount of variability is present in nature.  

Classifying this plot as sweetgale- dwarf birch - water horsetail however, lowers the overall average cover of sweetgale in that community.  At this unusual plot the dominant shrub layer still covers 70%, but sweetgale is largely replaced by atypical leatherleaf.  At most individual sites a dominant (like sweetgale in the example) may cover over 25%, yet it's average over all sites will be less, due to natural variability (replacement by leatherleaf in the example) and the simplification gained through classification (the leatherleaf plot is unique and can't be classified anywhere else).