Reference Ecosystems

Madrones in the shade

An important principle of restoration is the identification of a reference ecological community to serve as a guide for planning projects and a benchmark for evaluating success. For each of our restoration zones, we have identified two levels to reference based on classifications from efforts to characterize plant communities in the Puget Trough Ecoregion.

A zone’s Target System is a broad classification of the plant community we would like to see in the future. We have identified seven target systems for natural areas in Seattle parks, correspond to NatureServe Ecological Systems and Washington State Natural Heritage Ecological Systems.  We measure restoration progress, in part, by comparing data from our ecological inventory to target benchmarks derived from reference characteristics. The seven big elements we look at are: native tree canopy cover, invasive weed cover, a certain number of stems and diversity of new seedlings in the understory, native understory cover and diversity, and invasive tree presence. Below is a table of our target metrics:

Target Ecosystem Name Regeneration
(trees per acre)
Regeneration Diversity
(# of species)
Understory Cover
Understory Diversity
(# of species)
Invasive Regeneration (trees per acre)
Conifer Broadleaf Evergreen Mixed Forest 125 3 110% 10 10
Dry-Mesic Conifer and Conifer Deciduous Forest 125 3 70% 10 10
Mesic-Moist Conifer and Conifer Deciduous Mixed Forest 200 4 50% 14 10
Oak Woodland 50 3 60% 12 10
Riparian Forest and Shrubland 125 2 150% 14 10
Scrub Shrub Wetland 25 2 120% 11 10
Bog & Fen 50 2 125% 13 10

Within a Target System, there are a number of possible plant associations that may occur.  We have termed these Target Forest Types (or TFT – and we recognize that not all of them may be forests).  A zone’s TFT helps us to select specific species that we may want to include in the planting palette.  While it is often the most likely or desirable association we hope to see within a zone, the TFT is relatively flexible, and project managers and Forest Stewards should feel free to experiment with species from a number of TFTs within their Target System.  It is not uncommon for a range of different plant associations to occur within a zone.

The TFTs we use are based on associations documented by ecologists in nearby places with similar conditions to Seattle.  These associations are named by dominant and diagnostic plant species (The dashes in the names separate species in the same canopy layer; slashes separate species in different canopy layers).

Find your Target Forest Type and Target EcosystemThe GSP reference map showing the target fores type.

To find the target system and TFT for your site, use the GSP Reference Map to pan to the zone that you work in.  Left-click on that zone and a window should pop up that lists both the target system and TFT.

The table below shows the target systems and TFTs selected for all GSP restoration zones and the corresponding number of citywide acres.

Target Systems  Target Forest Types (TFT) # of acres
Bog and Fen PICO/LEGR/SP  shore pine / Labrador tea / sphagnum spp 6.2
Conifer Broadleaf Evergreen Mixed Forest PSME-ARME/GASH  Douglas-fir- Pacific madrone /salal 71.7
PSME-ARME/HODI/LOHI  Douglas-fir- Pacific madrone / oceaspray / honeysuckle 101.8
PSME-ARME/VAOV  Douglas-fir- Pacific madrone / evergreen huckleberry 34.2
Dry-Mesic Conifer and Conifer Deciduous Mixed Forest PSME/GASH/POMU  Douglas-fir / salal / sword fern 391.1
PSME-TSHE/GASH/POMU  Douglas-fir- western hemlock / salal / sword fern 570.3
PSME-TSHE/GASH-MANE  Douglas-fir- western hemlock / salal- dwarf Oregon grape 204.5
Mesic-Moist Conifer and Conifer Deciduous Mixed Forest ACMA-ALRU/POMU-TEGR  big leaf maple- red alder/ sword fern – fringecup 33.7
PSME-TSHE/MANE-POMU  Douglas-fir- western hemlock/ dwarf Oregon grape/ sword fern 647.7
THPL-TSHE/OPHO/POMU  western red cedar- western hemlock/ devils club/ sword fern 106.5
TSHE-PSME/POMU-DREX  western hemlock – Douglas-fir / sword fern – spreading woodfern 103.7
Oak Woodland QUGA-PSME/SYAL/POMU  Oregon white oak- Douglas-fir / common snowberry/ sword fern 24.9
Riparian Forest and Shrubland ACMA-PSME/ACCI/POMU  big leaf maple – Douglas-fir / vine maple / sword fern 15.2
ACMA-PSME/COCO/HYTE  big leaf maple – Douglas-fir / beaked hazelnut / Pacific waterleaf 30.5
ACMA-THPL/OECE  big leaf maple – western red cedar / Indian plum 122.0
ALRU/RUSP/CAOB-LYAM  red alder / salmonberry / slough sedge – skunk cabbage 136.6
FRLA-POBA/RUSP  Oregon ash – black cottonwood / salmonberry 6.3
POBA/COSE  black cottonwood / red-twig dogwood 14.8
POBA/SYAL  black cottonwood / snowberry 13.8
POBA-ALRU/RUSP  black cottonwood – red alder / salmonberry 22.0
TSHE-THPL-ACMA/ACCI/LYAM  western hemlock – western red cedar – big leaf maple / vine maple / skunk cabbage 43.7
Scrub Shrub Wetland SA/SPDO-COSE-LOIN  willow / Douglas spirea – red-twig dogwood – black twinberry 24.2
SASI/SPDO  Sitka willow / Douglas spirea 27.8

*Fact sheets for non-linked associations are pending.

For more information, check out this video from a 2015 training.

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