The 91st St. Slope is a long, narrow strip that runs between the main social trail at the lower end and property lines at the upper. It is 23,313 square feet. Because of its steepness, it’s relatively unexplored.
The southeast corner is known as “Knotweed Hill” because it had a thicket of Reynoutria japonica (Japanese knotweed) that was treated in 2012. There is some knotweed resurgence that has been reported and is being monitored. For the full story of Knotweed Hill, please see “Park and Restoration History.”
The majority of the 91st St. Slope has no conifer canopy and less than 1% conifer regeneration. However, at the north end, where the 91st St. Slope abuts the 92nd St. wetlands, there is close to 10% Tsuga heterophylla (Western hemlock).
The target forest type for the 91st St. Slope is Tsuga heterophylla – Pseudotsuga menziesii/Polystichum munitum – Dryopteris expansa (Western hemlock – Douglas fir/Sword fern – Spreading wood fern; TSHE-PSME/POMU-DREX). The reference ecosystem is Mesic-moist conifer and conifer-deciduous mixed forest.
One section of the trail bordering the 91st St. Slope dips below the water table. No other water flow has been observed from the 91st St. Slope.
Trailside, there are canopy gaps along this HMU that encourage the growth of blackberry and even grasses. There are dense laurel thickets, which were treated in the summer of 2014 with stem injection. Most of the rest of the trailside vegetation is Rubus armeniacus (blackberry) with Hedera helix (ivy) and some Rubus ursinus (trailing blackberry).
In October, 2012, three Alnus rubra (Red alder) trees fell from the 91st St. Slope across the main social trail and into a laurel thicket. This enlarged a canopy gap and blocked the trail until February, 2013, when it was cleared by the Natural Area Crew.
Because of the steepness of the rise from the trail, it’s difficult to see what is on the slope. The 91st St. Slope still has some trees that need ivy survival rings, but they are on nearly vertical sections of the slope.
No systematic monitoring has been done for the 91st St. Slope. However, what we have observed growing is listed in Table 1, below. Please see the key below the table for an explanation.
Table 1: Plants observed growing on the 91st St. Slope.
|Scientific Name||Common Name||Inv||TFT||91st Slope|
|Abies grandis||Grand Fir||1||R|
|Acer circinatum||Vine maple||1|
|Acer macrophyllum||Big Leaf Maple||1||G|
|Alnus rubra||Red Alder||1||G|
|Asarum caudatum||Wild ginger||R|
|Athyrium filix-femina||Lady Fern||1|
|Blechnum spicant||Deer Fern||1|
|Bromus vulgaris||Columbia brome||1|
|Carex deweyana||Dewey’s sedge||1|
|Claytonia sibirica var. sibirica||Siberian spring beauty||G|
|Corylus cornuta||Beaked Hazelnut||1|
|Daphne laureola||Spurge Laurel||1||G|
|Dryopteris expansa||Spiny Wood Fern||1|
|Galium triflorum||Sweet-scented bedstraw||1|
|Hedera helix||English Ivy||1||G|
|Hydrophyllum tenuipes||Pacific Waterleaf||G|
|Ilex aquifolium||English Holly||1||G|
|Impatiens glandulifera||Policeman’s helmet||1||G|
|Mahonia nervosa||Dull Oregon-grape||1||G|
|Malus fusca||Pacific Crab Apple||R|
|Oemleria cerasiformis||Osoberry (Indian plum)||G|
|Osmorhiza berteroi||Sweet Cicely||G|
|Polystichum munitum||Sword Fern||1||G|
|Pteridium aquilinum||Bracken Fern||1|
|Ranunculus repens||Creeping buttercup||1||G|
|Reynoutria japonica||Japanese Knotweed||1||G|
|Rosa gymnocarpa||Baldhip rose||R|
|Rosa nutkana||Nootka rose||R|
|Rubus armeniacus||Himalayan Blackberry||1||G|
|Rubus ursinus||Trailing blackberry||1||G|
|Rumex occidentalis||Western dock||G|
|Sambucus racemosa ssp. pubens||Red Elderberry||1||G|
|Taxus brevifolia||Pacific Yew||G|
|Thuja plicata||Western red-cedar||1||G|
|Tiarella trifoliata||Threeleaf foamflower||1|
|Tolmiea menziesii||Piggyback Plant||G|
|Trientalis borealis ssp latifolia||Western starflower||1|
|Trillium ovatum||Western Trillium||1|
|Tsuga heterophylla||Western Hemlock||1|
|Urtica dioica||Stinging Nettle||G|
|Vaccinium parvifolium||Red Huckleberry||1|
|Vancouveria hexandra||Inside-out Flower||1|
Key: Bold plant names indicate plants listed in a target forest type but not observed growing in any HMU. “1” in Inv column indicates the plant is considered invasive. “1” in TFT column indicates the plant is listed in the Target Forest Type description for the 91st St. Slope. “G” or “R” in the 91st St. Slope column indicates the plant has been observed growing or has been planted as part of restoration activities.
Of the 30 plant species observed growing in the 91st St. Slope HMU, seven (23%) are invasive. Of the 26 plants listed in the target forest type for the 91st St. Slope, nine (34.6%) are found growing in the HMU. These numbers would probably change with systematic observation.
Invasive Removal and Restoration Plan
Figure 1: 91st St. Slope
Subarea A measures 9,400 square feet and is accessible to all volunteers. It is separated from a similar volunteer-accessible area in the Central Valley HMU by a narrow social trail.
EarthCorps, in the fall of 2013, did some invasive removal in the Central Valley adjacent to the 91st St. Slope, reaching to about the dogleg in Figure 1, above.
In the winter of 2014, Friends of North Beach Park leap-frogged this restored area and cleared about 800 square feet on both sides of the trail of blackberry brambles.
Our intention was to continue clearing back towards the EarthCorps-cleared area over the summer months. However, in May and June we instead worked on aftercare for plants installed in dryer areas of the park, particularly near the entrance. In August, we did some re-clearing because the area had had a resurgence of invasives, particularly Ranunculus repens (creeping buttercup).
In August, a contract crew from the Parks Department injected a laurel stand with herbicide.
In November, Friends of North Beach Park cleared and planted in the area. Most of the plants were installed on the Central Valley side of the trail.
Suggested tasks for Subarea A:
- Survey the area to be cleared between where the Friends of North Beach Park worked in January 2014 and EarthCorps worked in Fall of 2013.
- Plan a series of public and forest steward workparties to bring the two areas together.
- Work closer to the trail during wet weather, move to the streambank in the summer.
- Use burlap and mulch to cover bare areas.
- Use GSP provided plants to fill in in the fall.
The tasks above were written in the summer of 2014. As of the fall of 2014, work on the 91st St. Slope has been demoted in favor of concentrating on the Headwaters Bowl.
Subarea B is unexplored as of fall 2014. It is lower priority than the South or West Slopes, which have a much higher extent of invasion; consequently, there is no crew time scheduled or predicted for this subarea.
Suggested tasks for Subarea B:
- Explore as much as possible.
- Put survival rings on any trees that need them.
Green Seattle Partnership, 2014. GSP Reference Map on ArcGIS.com. http://www.arcgis.com/home/webmap/viewer.html?webmap=9be9415001144aa383e5b86e481d2c45&extent=-122.5312,47.374,-121.7945,47.7577 Dates of accession various.
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