First Advisor

Jeff Gerwing

Community Partner

Oregon Metro Parks and Nature

Date of Award

2018

Document Type

Thesis

Degree Name

Professional Science Master in Environmental Science and Management

Department

Environmental Science and Management

Physical Description

1 online resource (x, 69 pages)

Subjects

Oregon oak -- Oregon -- Portland Metropolitan Area, Restoration ecology, Vernal pools, Metro (Or.), Introduced organisms -- Control, Chehalem Ridge Nature Park

DOI

10.15760/mem.41

Abstract

Effective land management and habitat restoration work rely on the collection of baseline information regarding the existing conditions of the planning area. Existing conditions assessments can include such information as hydrologic conditions, botanical species assessment, land use issues, wildlife surveys, habitat distribution/quality assessments, etc. This project provides Oregon Metro’s Parks and Nature department with updated information regarding the existing conditions of a portion of the Chehalem Ridge Nature Park (CRNP) as well as recommendations and supplemental maps to aid in future management planning.

Within the ~61-acre project area exist several habitat types: a developing seasonal wetland, riparian forest, Douglas-fir forest, and Oregon white oak. Previous land use and proximity of residential/agricultural property has altered the area in a variety of ways; most notable impacts include changes to the hydrologic conditions through the installation of roads and culverts that restrict natural water movement through the system and altered community structure due to the suppression of fire combined with introduction of non-native species. Because the Douglas-fir forest is the result of previous agro-forestry, the stands are even aged stands with high stem density and very little understory perpetuated by dense shade after herbicides previously applied by the timber industry. In contrast, the oak woodlands have abundant understory vegetation and conifer encroachment challenges, likely due to the suppression of fire in the region. The seasonal wetland area appears to be developing as a result of restricted hydrologic activity from the installation of SW Poppy Drive, a private asphalt road with culvert that restrict the surface water flow south of the wetland area of the park. Additionally, flooding in the area is influenced by seasonal variations in precipitation with saturated soils and several pools resulting from wet winter months, but only small areas of saturated soils and little to no pooling for most of the drier summer months. The seasonal nature of the wetland is congruent with the seasonal nature of the streams and spring. As a result, the majority of plants found in these areas tolerate a range of soil conditions from well-drained to saturated. During the dry season, both the wetland and riparian forest areas are incorporated into the oak woodland and Douglas-fir forest habitats that surround them.

Detailed management recommendations include suggestions for maintaining and enhancing the patchwork of habitats as well as other considerations such as erosion control and public access. In summary: resource limitations, the abundance/persistence of non-native plant species, and the ecosystem changes due to previous and current land use activities makes diverging from strict historical conditions and applying the novel ecosystem approach the most reasonable management plan for this area at this time. By focusing on community structure and ecosystem resilience, non-native species may be allowed to persist in a dynamically balanced system as long as they are not inhibiting plant diversity to such an extent that the system’s resilience is threatened.

Because Oregon white oaks (Quercus garryana) are a valuable and threatened species in the PNW, they should be prioritized in this system by applying thinning treatments to mimic historical fire disturbance in order to maintain the desired conditions for oak longevity and fecundity. Wetland enhancement may be achieved through the suppression of reed canary grass populations that inhibit plant diversity. Mimicking beaver activity through the installation of small wood dams can restrict water flow and prolong the flooded/saturated periods, thus increasing the amount of wetland habitat. Metro’s current plans and thinning treatments for the Douglas-fir forest within CRNP are intended to accelerate the development of old-growth forest structure. The additional recommendation for this area is to periodically push back the Douglas-fir boundary to maintain/increase the oak habitat by removing all encroaching conifers.

Finally, this area also has strong potential for increased public access. The area could be an excellent social, educational, and cultural resource. With the installation of trails, regular maintenance in the area would be easier and reduction of erosion and habitat damage from off-trail recreation activities in the area may be mitigated. Trails would also enable events such as acorn harvesting in partnership with local tribes which could enhance cultural awareness and social value for oak habitat. Trails could also facilitate partnership projects with educational institutions to take advantage of abundant research and monitoring opportunities.

Description

A project report submitted in partial fulfillment of the requirements for the degree of Professional Science Master in Environmental Science and Management.

Persistent Identifier

https://archives.pdx.edu/ds/psu/26665

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