Fire at Elk Rock Island

Elk Rock Island is a unique natural resource area and in public ownership in Milwaukie, Oregon. Over the last forty years there has been an ongoing effort to conserve the ecological resources on the island. Portland Parks & Recreation and the City of Milwaukie created a joint management plan for both Elk Rock Island and Spring Park, completed in the 1995 https://www.portlandoregon.gov/parks/article/469533 . In 2017 an iNaturalist place https://www.inaturalist.org/places/elk-rock-island was established to inventory the biological resources of the island. Although incomplete this inventory has identified new and uncommon taxa not observed by previous studies.
On 9 September 2020 there was an uncontrolled fire on the island. Images published by KGW show flames above the tree canopy https://www.kgw.com/article/news/local/wildfire/fire-breaks-out-on-elk-rock-island-milwaukie/283-c40ed9d5-16c7-4145-878f-e16624e21437 and https://pamplinmedia.com/lor/48-news/479842-387503-wednesday-night-fire-on-elk-rock-island-contained-officials-say-pwoff. This occurred during a high wind event and fire storm in the Cascades and Willamette Valley.
A quick assessment of the fire area was undertaken on 12 September to determine the area of burn and an understanding of ecological damage. Images of selected fire damage can be seen at https://www.inaturalist.org/observations?user_id=carexobnupta&on=2020-09-12&place_id=any&verifiable=any . From GPS tagged photos the burn area is estimated at approximately 1.3 acres. This area is at the south and SE edge of the island. Three ecological niches were found to be impacted: the upland woodland 0.7 acres, the south and east cliff face and talus deposits 0.4 acres, and the south basalt scab 0.2 acres. The woodland is a mixture of Oregon Oak, Pacific Madrone, Big-leaf Maple, and Douglas-fir. Portland Parks & Recreation conducted an Oregon Oak release removal of the conifers in the burn area to restore and enhance the habitat’s functions and values. The cliff face and upper were vegetated with Himalayan Blackberry, Atlantic Ivy, and some native understory shrubs and the base of the cliff a mixture of rock fall and debris with a Hawthorn clone and Rose hedge. The talus slopes were poorly vegetated but have been developing a grass and forb cover, mostly non-native species over the last 40 years. The basalt scab was largely unvegetated except with a thin cover of non-native grasses and forbs.

Based on the US Forest Service Soil Burn Severity Level criteria, the burn area was found to consist of a range of soil impacts. As the fire was quickly contained and limited in area there was not the complexity of a larger wildland fire, the very low and unburned class are not present or outside the burn footprint. The soil damage ranged from low to high and was largely dependent on the vegetative canopy. The basalt scab with a light cover of grass and forbs can be rated low. The cliff face and upper steep slopes and bottom talus slopes are medium. The woodland area is a mix of medium and severe soil damage. The upland area west of the trail is the location of the most sever soil destruction with soil completely removed of organic matter and oxidized. This area is a Big-leaf Maple woodland structure with both dead standing trees and large wood on the ground.

Some assessment of the vegetation loss was made in a limited manor. The native vegetation at the site is adapted to sustain itself in a high fire environment with features or responses that allow survival. Oregon Oak, Pacific Madrone, and Big-leaf Maple demonstrate a strong ability to re-sprout from roots and crown. Douglas-fir and Oregon Oak both have bark that protects the cambium layer during a fire event. The structural damage to the trees will require both an inspection for immediate public safety and a reassessment after the spring season. There was no attempt to assess the death of the canopy or the structural condition. Nearly complete removal of the ground level grasses and forbs and the low shrubs occurred. The tall shrubs and tree samplings sustained a range of damages. The loss of vegetation is such that mitigation and enhancement are needed. These treatments should be consistent with the high value Oak-Madrone woodland function and values. This beneficial treatment resulted in renewed vigor of both Oregon Oak and Madrone and the associated Oak-Madrone understory. It is recommended that additional Oak release be part of site restoration. This may be an ideal outcome if the damage to the Douglas-fir indicates removal. The area of high intensity soil damage was dominated by Big-leaf Maple both standing dead and living. Dead standing trees can be observed in the 2019 Google Earth image along with an opening in the canopy. This location should be re-vegetated with Oregon Oak and the associated understory vegetation. An effort to mitigate the fire damage with Oregon Oak Canopy would be the most beneficial treatment for responding to the fire damage. The fire also had an impact on the non-native ecologically damaging weeds Hedera hibernica and Rubus bifrons. Mitigation and conservation restoration treatments require further analysis and development. The subareas in the fire area are unique such that each requires a separate treatment plan. The Oak-Madrone community should be designed so that it is consistent with Classification of Oak Vegetation in the Willamette Valley https://inr.oregonstate.edu/biblio/classification-oak-vegetation-willamette-valley.

Posted by carexobnupta carexobnupta, September 14, 2020 03:39

Observations

Photos / Sounds

What

Pacific Madrone (Arbutus menziesii)

Observer

carexobnupta

Date

September 12, 2020 01:05 PM PDT

Photos / Sounds

What

Oregon Oak (Quercus garryana)

Observer

carexobnupta

Date

September 12, 2020 01:05 PM PDT

Photos / Sounds

What

Oregon Oak (Quercus garryana)

Observer

carexobnupta

Date

September 12, 2020 01:09 PM PDT

Photos / Sounds

What

Pacific Madrone (Arbutus menziesii)

Observer

carexobnupta

Date

September 12, 2020 01:10 PM PDT

Photos / Sounds

What

Bigleaf Maple (Acer macrophyllum)

Observer

carexobnupta

Date

September 12, 2020 01:12 PM PDT

Photos / Sounds

What

Common Douglas-Fir (Pseudotsuga menziesii)

Observer

carexobnupta

Date

September 12, 2020 01:16 PM PDT

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