Sitka alder / Field horsetail
Alnus viridis ssp. sinuata / Equisetum arvense
IIB(1)b: Closed Tall Alder Shrub
Ecosystem: Discharge Slope

Variable Sitka alder (Alnus viridis ssp. sinuata) types are widespread in Alaska.  Boggs (2000) and DeVelice, et. al. (1999) describe a type similar to the one described here, although with a Barclay's willow (Salix barclayi) component not present on the Kenai Lowlands.  Craighead et. al. (1988) describe this type for extreme northwestern Alaska.

Sitka alder / field horsetail (Equisetum arvense) is found throughout the Kenai Lowlands on foot- and toeslopes, typically at the edges of moderately steep stream valley walls.  It is also below the Homer bluffs, at the edge of a tidal lagoon near Nikiski, and along the west slope of the Caribou Hills along toeslopes of larger terraces.  

Dense patches of field horsetail with scattered ladyfern (Atyrium felix-femina) occur in the understory.  Sometimes thinleaf alder (Alnus incana ssp. tenuifolia) replaces Sitka alder as the overstory dominant.  Other plants are sparse, though red elderberry, (Sambucus racemosa) may be common.  Bluejoint (Calamagrostis canadensis) may be abundant or absent. 

The water table, or evidence of it, is usually around 20 centimeters from the surface. Sometimes a thick organic layer is present (64 cm at one locale).  pH ranges from strongly to moderately acid (5.0-6.1 at the three sites measured).  Nine of ten of the plots sampled qualify as jurisdictional wetlands.

Table 1. Frequency of occurrence and hydric status of soil series named at NRCS holes.  Bold type indicates soils on the NRCS Alaska hydric soils list. 

   Soil Series n Hydric Criteria Number






  Table 2.  Summary of plant frequency and average cover for plants occurring in more than 50% of plots.

        Wetland Indicator Status


f  Average Cover   Alaska National
Alnus viridis ssp. sinuata 0.8 63.4 FAC FAC, FACW*
Equisetum arvense 0.9 42.7 FAC* FAC*, FACW-
Athyrium filix-femina   0.9 4.2 FAC FAC, FAC+
Calamagrostis canadensis   0.6 27.7 FAC FAC, OBL
Impatiens noli-tangere 0.6 24.8 FACW FACW
Urtica dioica  ssp. gracilis 0.6 23.5 FACU FACU, FACW
Heracleum maximum 0.6 1.0 FACU FACU-, OBL
Moss 0.8 15.3       


 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary

Contact: Mike Gracz
Kenai Watershed Forum 
PO Box 15301
Fritz Creek, AK  99603
The Alaska Natural Heritage Program
Environment and Natural Resource Institute
University of Alaska, Anchorage
707 A Street, Suite 101
Anchorage, Alaska  99501

04 May 2007 09:36