October 13th, 2014

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Success Metrics

Tree-iage Grid

At the start of restoration, each HMU in a park is evaluated according to a 9-square “tree-iage” grid, rating from high composition/low threat to high threat/low composition. This helps GSP estimate how much time and effort the restoration will take. See below.

Forterra "Tree-iage" grid. Source: GSP Unpublished document.

Forterra “Tree-iage” grid. Source: GSP Unpublished document.

To place an HMU into the tree-iage grid, the observer follows the flow chart in below. North Beach Park has a native canopy of greater than 50%, but the tree regeneration rate is very low. At the start of restoration, almost the entire park had areas of greater than 5% invasive cover, and many areas had greater than 50% invasive cover. This put most of the park in square 6 of the tree-iage grid. As of summer 2014, some areas (the areas in blue in Figure 4, below) have moved into square 4, and some areas that were in square 6 have moved into square 5.

Source: Green Seattle Partnership

Source: Green Seattle Partnership

Phases 1-3 Mapping and Assessment

Once restoration begins, that area is mapped as a restoration site in the larger HMU zone. Many large parks have HMUs of several acres, and restoration sites within those HMUs as large as the largest HMU in North Beach Park.
Green Seattle Partnership has four phases of restoration, to track and evaluate progress as a site is restored. The phases are listed in Table 1, below, along with their estimated average labor investment. A restoration site always starts out in phase 1. How long a site stays in the first three phases is suggested by its placement in the tree-iage grid. With North Beach Park starting in squares 5 and 6, the table below applies pretty directly.

Phase Tasks Average Labor Investment
1 Invasive removal 400 hours/acre
2 Secondary removal and planting 100 hours/acre
3 Continued invasive removal, watering and mulching 40 hours/acre for up to three years
4 Stewardship and maintenance 5 hours/acre annually

Some acreage in Seattle has been provisionally approved for phase 4, but exactly what thresholds qualify for the transition from Phase 3 to Phase 4 is under discussion. The figure below shows the phases of restoration in North Beach Park.

Beige areas are not yet in active restoration. Phase 1 (invasive removal) is brown. Phase 2 (planting) is green. Phase 3 (establishment) is blue. Phase 4 would be dark green.

Beige areas are not yet in active restoration. Phase 1 (invasive removal) is brown. Phase 2 (planting) is green. Phase 3 (establishment) is blue. Phase 4 would be dark green.

Deciding what phase a restoration site is in is determined by a number of factors:

  • Work logs filled in by the forest steward, contract crew, or Parks staff.
  • Volunteer hours on a site.
  • GSP-protocol forest monitoring reports (discussed above).
  • Visual inspection and transect by a GSP or Parks Department employee.

After a restoration event (which includes both public work parties and any restoration work done in a park), the forest steward enters data into a web form that includes information on volunteer attendance and total hours, square footage of area cleared, invasives removed, plants installed or watered, square footage of area mulched, and amount of maintenance activities.

Visual inspections and transects are currently on an 18-24 month cycle, with preference going to sites in Phase 1 or 2. Sites in Phase 3 might receive inspection at the longer end of the cycle. North Beach Park was last visited for phase evaluation in October and November of 2013.

The inventory protocols are very similar to the forest monitoring protocols discussed above, with the difference being that the monitoring protocols apply to samples within an HMU, and the inventory is done to an entire HMU. The inventory work is done during the same season as forest monitoring, mid-May through mid-October.

Each HMU receives a profile, taken while walking a transect. Depending on the size of the zone, it also receives a number of plots that assess regeneration or tree density. Because all the HMUs in North Beach Park are less than two acres, each HMU would receive one regeneration plot and two tree density plots.

The zone-wide measurements look at slope, aspect, soil conditions, litter depth, coarse woody debris, canopy cover and average tree diameter; and then special features such as trails, camps, wetlands, or dumps. The tree assessment tallies every native and non-native tree within sight of the transect, and giving estimated heights and DBH (diameter at breast height) measurements. The vegetation assessment records species and estimated percent cover for every species intersecting the inventory line.

The tree regeneration plots are 16’ diameter circles, approximately 1/50th of an acre. Within that circle, all trees less than 5” DBH of every species are tallied and a per-species estimate of percent cover is taken.

The tree density plot starts with a tree close to the transect line greater than 5” DBH. This becomes the center of a circle, and the distance to the nearest 5 trees greater than 5” DBH is measured.

The phase-mapping assessment compares field observations of a site in restoration against work logs submitted by the forest steward. For phases 1-3, the observations are fairly basic. The assessment for phase 4 is more rigorous and is discussed below.

Phase 4 Assessment

Phase 4 assessment is a more rigorous, quantitative assessment than Phases 1-3. If a site under consideration fails to meet any of the thresholds below, it is kept in Phase 3. The tables below show the assessment thresholds for the North Beach Park reference ecosystems.

Canopy Threshold for Phase 4 Assessment

Reference Ecosystem Density (TPA) Cover Diversity Regeneration Regen. Diversity
Mesic-Moist Conifer and Conifer Deciduous Mixed Forest 100 80% 4 200 4
Riparian Forest and Shrubland 75 75% 2 125 2

Note: “TPA” is Trees Per Acre. “Diversity” refers to species diversity.

Understory, Woody Debris, and Invasive Regeneration Threshold for Phase 4 Assessment

Reference Ecosystem Cover Diversity Snag CWD Invasive Regen. Max (TPA)
Mesic-Moist Conifer and Conifer Deciduous Mixed Forest 50% 14 30 2,000 10
Riparian Forest and Shrubland 150% 14 20 3,000 10

Note: “CWD” is “coarse woody debris” and the value is linear feet greater than 5″ diameter.

The South Plateau is roughly half an acre. To apply these tables, the TPA, Regeneration, Snag, and CWD numbers would all be halved, but the percentages and diversity thresholds would remain the same.


Green City Partnerships. 2012. “Monitoring Data Collection Methods.” Green City Partnerships, Seattle.

Green Seattle Partnership. 2012. “Forest Steward Field Guide.” Green Seattle Partnership, Seattle.

— 2014. “Inventory Protocols 2014.” Green Seattle Partnership, Seattle.

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