December 15th, 2014

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Uplands and Slopes: South Slope


Figure 1: The South Slope

North is to the top. (Source: Green Seattle Partnership Reference Map on

North is to the top. (Source: Green Seattle Partnership Reference Map on

The South Slope is the slope just north of the South Plateau. It connects the main body of the park with the South Plateau. The northern border of the South Slope is the south loop social trail to the west and the Headwaters Bowl to the east. The southern border is a mixture property lines and the South Plateau.

Some trees in the South Slope have received ivy survival rings. There has been some planting at the lower reaches of the east section of the South Slope, along the border to the Headwaters Bowl. Other than that, the South Slope has received little or no attention.

The South Slope is split by a very steep social trail that connects the South Plateau to the rest of the park. During the dry months, this trail is very fragile and breaks into powder. During the rainy months, it is more stable but also more slick. The two sides of the trail also have different water regimes and different levels of invasive species. Because of this, the trail splits the South Slope into two subareas. This is the only HMU subdivision not based on who can do the work.

The lower reaches of Subarea A (Figure 2, below) are accessible to forest stewards. The trailside reaches of Subarea B are accessible to all volunteers. These are very small sections in the South Slope. Because the South Slope has the steepest slopes in the park, the vast majority of it is accessible only to Natural Area Crew.

The South Slope has less than 1% conifer cover and no observed regeneration of any trees. The canopy is mostly Acer macrophyllum, with 75% percent cover.

The target forest type for the South 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.

Water Flow

Subarea A (Figure 2, below) is above a number of seeps in the Headwaters Bowl that feed into the stream. These seeps flow over gleyed soils. Water and soil movement has been observed in these seeps even in high summer. The slopes above the seeps might receive some attention from the Stewardship Grant, but most attention will focus on the Headwaters Bowl and the Central Valley (as discussed in Stewardship Grant).

Subarea B receives the run off from the South Plateau. It is critical that we explore this area during a heavy rain. There is evidence that the run off from the South Plateau is eroding a section of the south loop social trail and affecting the immediately adjacent section of the Central Valley. How the runoff is affecting the slope, underneath the ivy, needs to be examined. Please see Uplands and Slopes: South Plateau and Water Flow: South Plateau Street Runoff for further discussions of water flow issues affecting the South Slope.


To the west side of the trail (left in the figure below), the South Slope is heavily invaded, with mature Alnus Rubra (Red alder) and Acer Macrophyllum (Big leaf maple) standing above a near-monoculture of Hedera helix (ivy). There is some remnant Polystichum munitum (Sword fern) and a stand of Rubus parviflorus (Thimbleberry).

On the east side of the trail, the section bordering the Headwaters Bowl and the Olympic Terrace properties is less invaded. The canopy mixture is the same, with more sword fern. This area has received some planting during restoration work. There is still a low diversity of native plants.

There has been no systematic plant survey in the South Slope HMU. Table 1, below, lists those plants that have been observed growing there through casual observation or have been planted during restoration activities. It also includes plants listed in the target forest type description but not observed or planted.

Table 1: Vegetation in the South Slope

Scientific Name Common Name Inv TFT So. Slope
Abies grandis Grand Fir   1  
Acer circinatum Vine maple   1  
Acer macrophyllum Big Leaf Maple   1 G
Alnus rubra Red Alder   1 G
Athyrium filix-femina Lady Fern   1  
Blechnum spicant Deer Fern   1  
Bromus vulgaris Columbia brome   1  
Carex deweyana Dewey’s sedge   1  
Cicerbita muralis Wall lettuce 1   G
Corylus cornuta Beaked Hazelnut   1  
Daphne laureola Spurge Laurel 1   G
Dryopteris expansa Spiny Wood Fern   1  
Galium triflorum Sweet-scented bedstraw   1  
Gaultheria shallon Salal   1  
Geranium robertianum Herb robert 1   G
Hedera helix English Ivy 1   G
Ilex aquifolium English Holly 1   G
Lapsana communis Nipplewort 1   G
Mahonia nervosa Dull Oregon-grape   1 G
Polystichum munitum Sword Fern   1 G
Pseudotsuga menziesii Douglas-fir   1  
Pteridium aquilinum Bracken Fern   1  
Rubus armeniacus Himalayan Blackberry 1   G
Rubus parviflorus Thimbleberry     G
Rubus spectabilis Salmonberry   1  
Rubus ursinus Trailing blackberry   1 G
Sambucus racemosa ssp. pubens Red Elderberry   1  
Thuja plicata Western red-cedar   1  
Tiarella trifoliata Threeleaf foamflower   1  
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: “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 So. Slope column indicates the plant has been observed growing or has been planted as part of restoration activities.

14 plant species have been observed growing in the South Slope HMU. Of these, seven (50%) are invasive. Of the 26 plants listed in the target forest type, five (19%) have been observed growing in the South Slope HMU.

Invasive Removal and Restoration Plan

Figure 2: The South Slope

Subarea A is to the east; Subarea B is to the west.

Subarea A is to the east; Subarea B is to the west.

Subarea A

Subarea A lies between the property lines of Olympic Terrace and the Headwaters Bowl. This means it will be affected by the work done in Subarea D of the Headwaters Bowl. It also lies above the seeps in the HWB that will receive some of the attention of the Stewardship Grant. Work here will have to be coordinated with these other projects.

The northern reaches of Subarea A have received numerous tree and shrub plantings in the last two years. These appear to have established well. Unfortunately, we did not keep accurate records, so we do not have accurate mortality rates.

In the parts of Subarea A that have been explored, there are few invasive plants. The efforts here will be to control what invasiveness is there and add to diversity, particularly at the shrub and groundcover layers.

Suggested Tasks for Subarea A:

  • Continue exploration and control of existing invasives. This can be done by forest stewards.
  • Monitor plantings for survival and growth. Replenish as necessary. Plant trees for buttressing in the lower sections; above that, plant shrubs for diversity and to maintain view corridors into the park from Olympic Terrace.
  • Coordinate work in Subarea A with the Stewardship Grant from the Washington Native Plant Society (HWB Subarea B) and with the homeowners of Olympic Terrace (HWB Subarea D) as necessary.

Subarea B

Trailside reaches of Subarea B are accessible to forest stewards and volunteers. There is a stand of Rubus parviflorus (Thimbleberry) along the trailside that can be spread through berry spreading and live staking.

Suggested Tasks for Subarea B:

  • Spread the Rubus parviflorus (Thimbleberry) with a mixture of berries and live stakes.
  • Attend to the trailside weeds such as Lapsana communis (nipplewort) and Cicerbita muralis (wall lettuce).
  • Subarea B cannot receive crew attention until water control efforts on the South Plateau have improved.

Mirrored from Nature Intrudes. Please comment over there.