“Target forest types” are reference communities for the forest steward to target in their plant selections.
The “forest type” is based on research by Chappell (1999, 2006) for the Washington Department of Natural Resources. Each forest type is based on an observed community in areas that are as undisturbed as possible. Chappell’s research concentrates on the Puget Trough Ecoregion (the lowland areas surrounding the Puget Sound), the region Seattle occupies. Selecting which forest types specifically applied to Seattle was based on research by Larson (2005) and by using a key based on GSP inventory site data (Denovan 2012). There are currently twenty-three target forest types assigned to Seattle forests and natural areas. Four of these (discussed below) have been assigned to North Beach Park.
The name of the target forest type is derived from the dominant plant species at every canopy layer. The species are listed by their four letter code in the order of constancy with which they occurred in the sampled plots. Dashes separate species at the same canopy layer, slashes separate canopy layers.
For example, “THPL-TSHE/OPHO/POMU” is THuja-PLicata – TSuga HEterophylla / OPlopanax HOrridus / POlystichum MUnitum” (Western red-cedar – Western hemlock/Devil’s club/Sword fern). This means that there was more Western red-cedar than hemlock in the sampled plots, Devil’s club is the dominant species at the shrub layer, and sword fern the dominant species at the groundcover layer.
A long list of forest plant associations can look bewilderingly similar. The diversity comes with the non-dominant species, especially at the herbaceous level.
Why Target Forest Types
Target forest types were selected by Parks Department plant ecologists to promote heterogeneity among the natural areas undergoing restoration in Seattle. They noticed that, over the years at the city scale, plant selections were very similar.
At first, target forest types were promoted as prescriptive; that is, forest stewards had to consider the TFTs for their park a goal, and select their plants accordingly.
This lead to pushback and confusion from forest stewards. Now forest types are grouped into the seven reference ecosystems as a more general planting palette. Of the two reference ecosystems for North Beach Park, “mesic-moist conifer and conifer deciduous mixed forest” has four target forest types; “riparian forest and shrubland” has nine.
All information about the target forest types is taken from the descriptions by Chappell at the website referenced below. The descriptions are attached to this book as Appendix C, “Target Forest Type Descriptions.” The TFTs are discussed in the order of number of HMUs to which they are assigned.
This target forest type is assigned to the following HMUs: North Slope, 91st St. Slope, West Slope, South Slope, South Plateau.
This forest type is dominated by Western hemlock and Douglas-fir at the canopy level, with sword fern and spreading wood fern at the ground cover level. It is found almost everywhere in the Puget Trough except in San Juan County.
This association is found in moist sites with nutrient-rich soils, and more commonly on lower slopes and riparian terraces. This relates well to the reference ecosystem of mesic-moist conifer and conifer-deciduous mixed forest.
Other plants in this community include Berberis nervosa (Dull Oregon-grape) which grows with sword fern in many places in North Beach Park.
Chappell says that Red alder regenerate after disturbance and that alder typically die out after 80-100 years. The alder canopy in North Beach Park is very mature, and is decaying at the rate of one to three trees per year.
This target forest type is assigned to the Central Valley and Headwaters’ Bowl HMUs.
This forest type has Alnus rubra (Red alder) almost exclusively in the canopy layer, with a dense shrub layer formed mostly of Rubus spectabilis (salmonberry). The herbaceous layer is dominated by Tolmiea menziesii (piggyback). We saw this combination pretty continuously through the Central Valley during the belt transect.
In North Beach Park both Carex obnupta (slough sedge) and Lysichiton americanum (skunk cabbage) were growing before restoration, but not together. In general, the herbaceous layer in these HMUs is not as well developed as described for this community.
Chappell describes this community as existing in palustrine scrub-shrub wetlands, which fits with the riparian forest and shrubland reference ecosystem.
This forest type has Thuja plicata (Western red-cedar) and Tsuga heterophylla (Western hemlock) dominant in the canopy layer, with Oplopanax horridus (Devil’s club) in the shrub layer and Polystichum munitum (Sword fern) in the ground layer.
Red alder and Big leaf maple are the current dominant trees in the canopy of North Beach Park. The 92nd St. Wetlands, to which this target forest type is assigned, is the only HMU where the coniferous canopy cover is more than 10%.
Although Chappell rates this community as secure at both the global and state level, he says there are “very few good quality stands remaining.”
We attempted to reintroduce Devil’s club into the park from seed but were unsuccessful. We look forward to reintroducing it soon, perhaps as part of the Washington Native Plant Society Stewardship Grant.
This forest type is assigned to the Fletcher’s Slope HMU.
Unlike the rest of the target forest types assigned to North Beach Park, this forest type is based on research by Kunze (1994). In general, Chappell is preferred because he provides constancy across sampled plots and percent cover of all species. Kunze provides percent cover for only indicator species. All information below was taken from a PDF excerpt of her work supplied by Green Seattle Partnership.
In North Beach Park, Fletcher’s Slope has greater than 10% Western hemlock in the community, with some Douglas-fir. Kunze says either TSHE or THPL can dominate this community. Acer macrophyllum (Big leaf maple) is the dominant deciduous tree in the dryer sections of the park. Lysichiton americanum (skunk cabbage) grows throughout the park, but we have not seen Acer circinatum (vine maple) that wasn’t planted during restoration activities.
This once-common community has few undisturbed examples. Kunze describes it as occurring in conditions that are very similar to North Beach Park: on flat ground, in depressions, with small streams and seeps, with the water level at or slightly below the soil surface.
Adapting the TFT concept to specifics of North Beach Park
Examining the target forest types above against the current conditions in North Beach Park indicates that more restoration needs to happen at the herbaceous level. To date, we’ve concentrated mostly on the tree and shrub layers. We plan to increase our reintroduction of under-represented herbaceous plants.
Putting different forest types into the buckets of reference ecosystems both allows for a greater planting selection and strategy, and perhaps even a climate change adaptation.
Research with grasslands shows that productivity increases with biodiversity (Tilman, 2001). Making several TFTs available for every reference ecosystem can help with climate change and prevent biodiversity loss through both component redundancy (increased species and community redundancy) and functional redundancy (introduction of ecologically equivalent species or novel associations) (Dunwiddie 2009).
Chappell, C.B. 1999. Ecological Classification of Low-Elevation Riparian Vegetation on the Olympic Experimental State Forest: A First Approximation. Washington Department of Natural Resources, Natural Heritage Program, Olympia , Wash.
— 2006. Upland plant associations of the Puget Trough ecoregion, Washington. Natural Heritage Rep. 2006-01. Washington Department of Natural Resources, Natural Heritage Program, Olympia , Wash. [http://www1.dnr.wa.gov/nhp/refdesk/communities/ ].
Denovan R., and Salisbury, N. 2012. GSP Target Forest Type Assignment Key Using GSP Site Inventory Data. (unpublished document)
Dunwiddie, P.W., S.A. Hall, M.W. Ingraham, J.D. Bakker, K.S. Nelson, R. Fuller, E. Gray. 2009. “Rethinking Conservation Practice in Light of Climate Change.” Ecological Restoration 27:3 320-329
Kunze, M. 1994. Preliminary Classification of Native, Low Elevation Freshwater Wetland Vegetation in Western Washington. Washington Department of Natural Resources, Natural Heritage Program, Olympia, WA.
Larson, R.J. 2005. The Flora of Seattle in 1850: Major Species and Landscapes Prior to Urban Development. (Unpublished thesis).
Tilman, D., P.B. Reich, J. Knops, D. Wedlin, T. Mielke, C. Lehman. 2001. “Diversity and Productivity in a Long-Term Grassland Experiment.” Science, Vol. 294, 843-845