Westlake Oak Woodland

What we now call Lake Oswego, Oregon is the traditional land of the Tualatin band of the Kalapuyan Tribe, the Atfalati peoples, whose tribal members today are represented by the Confederated Tribes of Grand Ronde, the Confederated Tribes of Siletz Indians, and the Confederated Tribes of Warm Springs. Active management by indigenous peoples has shaped the landscape we see here today.

Westlake Homeowners Association (HOA) manages commonly owned property in the Westlake Neighborhood. In 2017, a partnership was formed between Westlake HOA,  Oswego Lake Watershed Council , the City of Lake Oswego, and Clackamas Soil and Water Conservation District. These organizations have pooled resources to conduct oak woodland enhancement on Westlake HOA's Tract A, a 17 acre property.

An oak woodland is a plant community with a tree canopy dominated by oaks. Oak woodlands have canopoy composition that is less open than oak savanna, and more open than oak forest. Westlake Oak Woodland is primarily composed of Oregon White Oak (Quercus garryana), and contains pockets of Ash dominant wetland. In some sections of the forest, fast-growing Ash trees are interfering with the health of Oak trees.

Oak Woodlands in the Willamette Valley once covered 400,000 acres, but due to habitat loss, fire suppression, and invasive species encroachment, the Willamette Valley only contains 5% of the original intact oak woodland habitat (Oregon Conservation Strategy). These remaining oak woodland systems are primarily in private ownership and are often observed in rural settings but also can sometimes found in urban areas where natural areas have been left intact, as seen on the Westlake HOA property. Oak woodlands are home to a diversity of native plants, animals, and other organisms. habitat. These 20 acres are divided into three tracts: A (17 acres), B (2 acres), and C (1 acre). The largest, tract A, is the focus of this project and has a high density of mature oak trees in the upper canopy layer along with Oregon ash and Douglas fir. The native sub-canopy layer contains additional smaller ash, maple, osoberry, and a variety of native shrubs. In addition, oak associated species are abundant, including sessile trillium and camas, which are noteworthy oak obligate species. This habitat is also conducive to wildlife such as western gray squirrel, white-breasted nuthatch, and red-tailed hawks.

1. Invasive species are outcompeting native plants and threatening forest health
2. Native trees (primarily Ash) are encroaching, leading to suppressed Oak growth and branching
3. Lack of native shrubs and understory in patches throughout the forest
4. Need for long term maintenance and monitoring

Persistent invasives have dominated Westlake Oak Woodland for years. The understory was dominated by invasive tree ivy, ground ivy, blackberry, lesser celandine, clematis, cherry, holly, hawthorn, and laurel. Since 2018 OLWC has been working with contractors and volunteers to remove these invasive species to improve habitat. To date, over 90% of invasive cover has been erradicated from the site. The remaining invasives will mostly be removed in 2021 and early 2022.

Project Goal: Conduct native Oregon white oak (Quercus garryana) release from faster-growing native tree species including Douglas fir (Pseudotsuga menziesii) and Oregon ash (Fraxinus latifolia) throughout a 17-acre natural area located in Lake Oswego, Oregon. Removing the competing trees, in this case primarily Oregon ash, will improve the growing conditions and long-term health of the oaks.

The scope of this Resource Enhancement Project is aimed at the removal of native ash, Douglas fir, and big leaf maple species to achieve a healthy oak woodland overstory. Removal of these native trees will allow the dominant oak overstory to achieve healthy epicormic (lateral) branching and provide more successful annual acorn production and germination, which are currently limited due to native tree competition. OLWC worked with our contractors to develop a methodology for identifying specific trees that are suppressing oaks and to prescribe an appropriate treatment for each tree. Patches of native ash trees will be left in areas that are not suitable for oak regeneration (such as wetland areas) and will not be removed unless competing with oak trees.

OLWC has a Resource Enhancement Plan for this project, and a Verification Permit has been issued by the City of Lake Oswego for 210 tree removals. From January - February 2021 and September-October 2021, contract crews will be on-site treating 210 trees for this Oak release project. Pruning treatments will be conducted in March 2022.

As stated by Constance A. Harrington and Warren D. Devine in their “A Practical Guide to Oak Release” technical report, “Oregon white oak savannas and woodlands represent a biological and cultural legacy in the Pacific Northwest.” Although somewhat isolated, this 17-acre woodland maintains many biological characteristics of a native oak woodland including large mature trees with scaffold branches forming dense canopies.

Since Oregon white oaks are not shade-tolerant, removing primarily ash will improve conditions for natural oak regeneration and survival. Ash on site are also in many cases growing near the trunks of Oregon white oaks, restricting epicormic branching and negatively impacting oak health. In the general vicinity of this particular forested stand, thousands of Oregon white oak trees were cut down for farming, housing, and other human endeavors, which resulted in isolated, remnant stands of oaks such as this 17-acre area. Without the traditional management activities (primarily fire), the oak woodlands are no longer open nor mostly competition-free. OLWC and contractors spent three days in the field identifying trees that are suppressing oaks, and documenting whether the relationship was intermediate, sub-dominant and/or co-dominant. Each tree for removal or treatment was marked with yellow paint, yellow flagging, and a numbered metal tag. Each tree number was GPS marked and assigned the appropriate proposed treatment. With this data, we created a spreadsheet of all trees proposed to be treated.

On-ground treatments will be:

● Girdle – cutting through the cambium layer around the bole of the tree just under the bark to disrupt the flow of water and nutrients to and from the tree parts above the girdle cut;

● Felling – cutting the tree down to a stump at or close to ground level. All debris will be left as it falls; directional felling will place the bole and associated debris in strategic locations based on lack of woody material or to create on-ground wildlife habitat through piling.

Above-ground treatments will be:

● Girdle – a climber will ascend the tree to a determined height and perform a girdling cut to kill the upper canopy of the tree while leaving the biomass in place to serve as wildlife habitat for cavity dwellers or other nesting opportunities; an on-ground girdle cut might or might not be used depending on whether or not we want to create a live snag or not.

● Fracture – A rope will be set into a location in the canopy that provides ample strength to resist being pulled over; climber will ascend the tree to a determined height and perform a back-cut; after the climber has descended safely out of the tree, the rope will be pulled using mechanical advantage to fracture the top of the tree; this technique mimics natural breakage, which in turn promotes decay and wildlife habitat; an on-ground girdle cut might or might not be used depending on whether or not we want to create a live snag or not. Or, a climber will ascend the tree to a determined height and fell the top of the tree to the ground; a face-cut and back-cut will be used to directionally fall the debris in strategic directions based on lack of woody material or to create on-ground wildlife habitat through piling; The climber will then use his or her chainsaw to make coronet cuts (a series of vertical cuts mimicking a natural failed stem.

Native trees (primarily ash) were individually selected for removal if competing with or suppressing oak growth. There are several patches of healthy ash dominant seasonal wetlands within Tract A.

We will avoid encroachment into the ash forested wetland and riparian areas and only conduct pruning treatments, and we will be mindful of the transition areas to avoid unnecessarily cutting ash trees when those are areas that should have both ash and oak. The forested wetland and riparian areas are undergoing ongoing habitat enhancement through invasive species removal, replanting of native species, and monitoring.

From January - February and September-October 2021, contract crews will be on-site treating 210 trees for this Oak release project. During work periods, crews will be careful to avoid disturbance of your property and landscaping. You can expect to hear chainsaw noise while work is being conducted. Please do not approach crew members while chainsaws are being used!

Oregon is prone to wildfires, and land managers should always consider fire when conducting large scale forestry work. OLWC has consulted with the Lake Oswego Fire Department, Clackamas SWCD, and Oregon Department of Forestry to assess fire risk and identify strategies to reduce risk:

• Removal of invasive trees and shrubs
• Cut trees will be broken down to increase contact with soil
• Existing brush piles are being disbursed
• Ladder fuels are minimal due to the lack of conifers in the woodland
• Healthy oak woodland habitat is a fire-adapted landscape with a lower risk for extreme fire events than other local habitat compositions

The Oswego Lake Watershed Council and Westlake HOA is replanting the woodland with native species. Plant selection and location are dependent on site characteristics of hydrology, UV penetration, ecology, and soil composition. These plant species will grow less than 30 feet maximum, reducing the probability of competition with Quercus garryana. These species require little to no maintenance, are well suited to local soils/ hydrologic conditions, and do not need long term irrigation. We are installing a minimum of 400 shrubs/small trees, and 400 wetland plants in Winter 2021 and at the end of 2021. Some additional planting has already occurred.

Riparian: 200 total shrubs/small trees. These plants will be installed along Meadows Creek and Centerpoint Tributary to further enhance the riparian buffer. Most of these species are already present along the creeks in Westlake Oak Woodland, and thrive especially in areas recently cleared of invasive species. These riparian shrubs and small trees will further stabilize soil and provide additional habitat and food sources for wildlife. Plants will be bare root stock and/or 1 gallon. Planting Palate (minimum of 200 plants): Cornus sericea v. stolonifera (red osier dogwood) Physocarpos capitatus (ninebark) Amelanchier alnifolia (serviceberry) Rosa nutkana (Nootka rose) Symphoricarpos albus (common snowberry) Spiraea douglasii (hardhack) Sambucus racemosa (red elderberry) Corylus cornuta v. californica (hazel)

Woodland understory: 200 total shrubs/small trees. These plants will enhance the structural diversity of the woodland, resulting in increased habitat benefits, and screening benefits for neighboring residents. Previous removal of invasive trees and shrubs (cherry, hawthorn, holly, laurel) paired with selective ash removal creates opportunities for the planting of native shrubs. These plantings will supplement existing native vegetation. Plants will be bare root stock and/or 1 gallon. Planting Palate (minimum of 200 plants): Acer circinatum (vine maple) Amelanchier alnifolia (serviceberry) Crataegus douglasii (black Hawthorne) Cornus sericea v. stolonifera (red osier dogwood) Corylus cornuta v. californica (hazel) Mahonia aquifolium (Oregon grape) Oemleria cerasiformis (osoberry) Polystichum munitum (sword fern) Rosa gymnocarpa (wood rose) Rosa nutkana (nootka rose) Sambucus racemosa (red elderberry) Symphoricarpos albus (common snowberry)

Wetland: 400 total. There are several patches of healthy ash dominant seasonal wetlands within Tract A. Within these ash dominant forested wetland patches, where conditions are not suitable for Oregon White Oaks, ash trees will not be removed. These areas have been enhanced thus far by ongoing invasive species removal, and contain abundant naturally occurring species such as Camassia quamash (common camas), Veratrum californicum (corn lilly), Carex obnupta (slough sedge), Juncus effusus (soft rush), Juncus balticus (baltic rush). Existing wetland vegetation will be supplemented by the installation of rush and sedge plugs. Planting Palate: Carex opnupta (200) Juncus effusus (100) Juncus balticus (100)

OLWC is using various methods to track key project metrics over time, including:

• Photo point monitoring to track understory vegetation
• Wildlife monitoring using iNaturalist, iBird, and traditional surveys
• Drone monitoring using a UAS to collect high resolution, geo-referenced orthomosaic imagery
• Maintenance activities include mulching and watering plantings, removing regrowth of invasives

Elevation and tree height (Digital Elevation Model)

Thank you to all partners who have contributed to this project. Project partners fund this work, contribute resources, and technical advising. Oswego Lake Watershed Councils partners on this project include Westlake HOA, the City of Lake Oswego, Clackamas Soil and Water Conservation District, and Oregon Conservation and Recreation Fund. Thank you also to ForeSight Drones, SOLVE, IRCO, United Way, Native Ecosystems NW, and Arboriculture International, Wisdom of the Elders, Tualatin River Watershed Council, Portland Community College, and to all of our community volunteers and supporters who mak this work possible.