TOP LINE: Sitka spruce are the mangrove trees of the northeastern Pacific Ocean shore.
This is the third of three Public Lands Blog posts that focus on Oregon’s coast. Part 1 looked at Oregon’s (and the nation’s) “blue carbon” and a congressional effort to conserve and restore it. Part 2 examined coastal wetland loss, conservation, and restoration. Part 3 describes a now very rare type of coastal wetland: the forested tidal swamp.
Figure 1. A Sitka spruce–dominated tidal swamp at Blind Slough in the Columbia River estuary. Source: Laura Brophy.
When I hear the word swamp, Oregon does not come to mind. I think of Louisiana (the Atchafalaya Basin), Florida (the Everglades), Georgia (the Okefenokee Swamp), Delaware and Maryland (the Great Cypress Swamp), Virginia and North Carolina (the Great Dismal Swamp), and South Carolina (the Congaree Swamp). I think of Ohio’s and Indiana’s Great Black Swamp, which no longer exists. These are/were great swamps.
I generally pride myself on knowing much about Oregon, natural Oregon, Oregon’s forests, and Sitka spruce in Oregon (which thrives where the coastal fog lingers). Still, I’ve never noticed what Laura Brophy calls Sitka spruce–dominated tidal forested wetland (aka tidal swamp—see Part 1). The reason I’ve never noticed one before is that they are nearly all gone. Given the importance to global ecology of tidal swamps in the Pacific Northwest, this is a wrong that needs to be righted.
What the Heck Is a Tideland Spruce?
I was chatting with Oregon author Paul Koberstein—who’s coming out with a new book soon, Canopy of Titans (coauthored with Jessica Applegate); you heard it here first—a few weeks ago and he started going on about “Oregon’s tidal Sitka spruce forests.” What the hell is he talking about? I thought.
Figure 2. A tidal swamp with a Sitka spruce on the right and deciduous hardwoods on the left. Source: Laura Brophy.
While I had long occasionally heard reference to “tideland spruce,” it never made any sense to me. I should have read more closely Natural Vegetation of Oregon and Washington (first published by the Forest Service in 1973 and reprinted by Oregon State University Press), which is a classic and now downloadable. Coauthor Jerry Franklin wrote:
Picea sitchensis is, of course, the characteristic tree species of tideland areas and has been referred to as “tideland spruce” almost since its discovery. Sprawling, open-growth [Sitka spruce] border tidal flats and channels all along the Oregon and Washington coasts.
One likes to learn something every day, but this is at least a week’s worth of learning. Sitka spruce are the mangrove trees of the northeastern Pacific Ocean shore.
In very general terms, the woody vegetation in scrub-shrub tidal swamps is dominated by hardwoods, while forested tidal swamps on the Oregon coast are dominated by conifers (Figure 2). Besides Sitka spruce, other conifer species found in Oregon coast tidal swamps include Douglas-fir, western redcedar, and shore pine. There are also the occasional Oregon ash (Figure 3) and cottonwood (Figure 4) tidal swamps, especially in the Lower Columbia River estuary.
Figure 3. While most forested tidal swamps of the Oregon coast are dominated by Sitka spruce, some are dominated by Oregon ash, like this one in the Lower Columbia River estuary on Sauvie Island. Pictured is Allan Whiting, an expert in large-scale coastal and riverine restoration. Source: Laura Brophy.
Figure 4. Some Oregon tidal swamps are dominated by cottonwood and willow, like this one in the Lower Columbia River estuary in the Julia Butler Hansen Refuge for the Columbian White-Tailed Deer. Source: Fish and Wildlife Service.
Figure 5. A scrub-shrub tidal swamp in winter in the Yaquina Bay estuary. Dominant shrubs include black twinberry, Pacific crabapple, and Hooker’s willow. Source: Laura Brophy.
Loss of Tidal Swamps: Logged Out and Diked Off
The Oregon coast has lost a lot of its tidal wetlands and most of its tidal swamps. As was shown in Table 1 in Part 2:
• The net loss of Oregon’s coastal tidal wetlands is 53.9 percent.
• Historically, 54.4 percent of Oregon’s coastal tidal wetlands were forested, dominated by Sitka spruce.
• Today, forested tidal wetlands are only 9.8 percent of Oregon’s remaining coastal tidal wetlands.
• The net loss of Oregon’s coastal forested tidal wetlands is 91.8 percent.
Most of the loss of forested tidal swamps is due to diking (disconnecting the land from tides). Just over a quarter (26.8 percent) of formerly forested tidal wetlands is still tidal wetland but is now emergent (high or low) tidal marsh.
Figures 6 and 7 depict the Coquille River estuary, most of which was tidal swamp and most of which is diked. It is the most hammered of any major estuary on the Oregon coast.
Figure 6. The Coquille River estuary. The vast majority of the estuary has been diked (red). Source: Institute for Applied Ecology (Brophy 2019).
Figure 7. The Coquille River estuary. The vast majority of the estuary that has been diked (red in Figure 6) was tidal forested swamp (dark blue here). Source: Institute for Applied Ecology (Brophy 2019).
The Brophy Report shows that only 1,705 acres of forested tidal swamp remain along the Oregon coast, compared to the historical total of more than 20,000 acres. Scrub-shrub tidal swamp occupies 1,438 acres, a small increase from the historical area of 1,280 acres, mostly due to conversion from forested to shrub habitat via logging. Accelerating the loss of forested tidal swamp was the demand for Sitka spruce lumber to build airplanes during World War I. The big spruce trees near water were easier to transport to the mill.
In a few cases, tidal wetlands exist in places where they did not at the onset of the European invasion. Brophy found that 4,374 acres of new tidal marsh has formed since initial European settlement, but there has been no gain of forested tidal swamp. Figure 8 shows the Umpqua River estuary where new wetlands have formed. (Sediment from upstream logging and development, plus dredge material disposal, were contributory factors.) Overall, it’s still a great net loss.
Figure 8. The Umpqua River estuary. Areas that have been diked are shown in red; most were forested tidal swamp. New tidal marshes since European settlement are shown in dark blue, but they are emergent marshes, not forested swamps. Source: Institute for Applied Ecology (Brophy 2019).
Why Coastal Wetlands Are So Important
Tidal wetlands of all kinds sequester a lot of carbon. “On a per-acre basis, tidal wetlands store 3–5 times more carbon than tropical forests,” according to the PNW Blue Carbon Working Group. Confirming this, ecologist and Oregon State University professor J. Boone Kauffman says in a March 2020 lecture available on YouTube entitled “Why conservation and restoration of PNW tidal wetlands is of global significance” that “coastal wetlands are considered as high priorities in climate change adaptation and mitigation strategies throughout the world.”
Regarding the difference between climate change mitigation and adaptation, the World Wildlife Federation says:
Climate change mitigation means avoiding and reducing emissions of heat-trapping greenhouse gases into the atmosphere to prevent the planet from warming to more extreme temperatures. Climate change adaptation means altering our behavior, systems, and—in some cases—ways of life to protect our families, our economies, and the environment in which we live from the impacts of climate change. The more we reduce emissions right now, the easier it will be to adapt to the changes we can no longer avoid. [emphasis in original]
It’s not either/or, but both/and.
Kauffman lists five reasons that coastal wetlands are so important in the context of carbon loss to the atmosphere:
1. Wetlands provide a number of ecosystem services that are vital to the sustainability of local communities, livelihoods, and infrastructure.
2. They have exceptionally high carbon stocks—among the highest of any ecosystem on earth.
3. Their rates of land cover change/deforestation are the highest of any ecosystem on earth.
4. Their emissions from land cover change far exceed emissions from land conversion of upland forests.
5. Their potential for [carbon] sequestration following restoration is among the highest on earth.
Figure 9. An old-growth Sitka spruce in a forested tidal swamp. The trees generally grow in the open, which allows them to rapidly add diameter. Source: Doug Firstbrook.
The Special Importance of PNW Tidal Swamps
PNW tidal wetlands have high potential for carbon sequestration for several reasons enumerated by the PNW Blue Carbon Working Group:
Sediment delivery: Due to coastal geomorphology and climate, PNW rivers deliver large quantities of sediment to tidal wetlands and bays. High sediment delivery means higher resilience to climate change, since sediment accretion is an important component of tidal wetland equilibration with sea level rise. (The other major component is belowground organic matter produced and stored by plants, such as roots and buried woody debris.)
High organic content in soils: Evidence is strong that large quantities of carbon accumulate in PNW tidal wetlands. Several studies have shown very high soil carbon content in Oregon’s tidal marsh and tidal swamps and other PNW tidal wetlands. In many of Oregon’s drowned river mouth estuaries, organic soils are very deep, indicating long-term carbon accumulation and storage.
Sheltered settings: Most of the PNW’s tidal wetlands exist in relatively sheltered landscape settings (the “sheltered coast” of bays and river systems, as opposed to the outer coast where wave and storm action is high). The erosion that threatens coastal wetlands in the Gulf of Mexico, for example, is unlikely to threaten our tidal wetlands because of this sheltered setting.
Brackish tidal swamps: The PNW outer coast once supported large areas of brackish forested and shrub tidal wetlands (“tidal swamps”). Brackish wetlands are less likely to release greenhouse gases (such as methane), compared to freshwater wetlands. In addition, tidal swamps generate large quantities of woody debris, which becomes buried and serves as another carbon storage mechanism. There is high potential to recover many of these altered tidal swamps through restoration actions.
Large tide range and strong tidal/fluvial interactions: Compared to many other parts of the US, tide range is large in the Pacific Northwest. Large tide ranges and strong seasonal fluctuation in precipitation and river flow have led to the development of tidal wetland plant communities with broad tolerances for inundation and salinity. These broad tolerances may allow higher resilience to climate change and the associated changes in inundation and salinity.
Land values and land use types: In many agricultural areas of the Pacific Northwest coast, land values are relatively low compared to urban and rural residential landscapes, increasing opportunities for conservation and restoration of tidal wetlands. [emphasis added and citations omitted]
Figure 10. A comparison of carbon stocks of various blue carbon ecosystems. Source: Kauffman et al. 2020, Figure 4.
Figure 10 compares the carbon stocks of various blue carbon ecosystems. It tells us, among other things, that
• Pacific Northwest seagrass beds store much more carbon per acre than the average global seagrass beds,
• Pacific Northwest emergent wetlands (both high and low marsh) store much more carbon per acre than most other coastal marshes,
• Pacific Northwest forested tidal swamps store more carbon per acre than the average subtropical/tropical mangrove swamp,
• most of the carbon in coastal wetlands is belowground in the soil, and
• on a per-acre basis, an Oregon coastal forested tidal swamp holds about as much carbon as an Oregon Coast Range old-growth forest.
Restoration Needs, Keystone Species, and Rising Seas
It is far easier to restore a tidal marsh (low or high) than a tidal swamp (scrub-shrub or forested). Part 2 featured an example of successful marsh restoration in the Bandon Marsh National Wildlife Refuge. Here we examine the restoration of tidal swamps.
The Brophy Report (in its Appendix 11) addresses restoration of tidal swamps. Brophy sums up restoration needs, opportunities, and priorities:
[C]onservation and restoration of tidal swamps are urgent priorities for the Oregon coast, and restoration of tidal swamps requires careful planning. The first step in planning tidal swamp restoration is selection of an appropriate site, which requires landscape analysis and understanding of historical and current site conditions. Monitoring of physical and biological characteristics of tidal swamp reference and restoration sites provides necessary data to guide restoration. Innovative restoration techniques such as nurse logs and topographic mounds may help overcome challenges due to invasive species. Monitoring results and “lessons learned” should be shared with other restoration practitioners, thus contributing to the regional advancement of restoration science and practice. Finally, in addition to guiding restoration, monitoring and research at tidal swamps are urgently needed to understand the structure, functions, services, and future resilience of these once-prevalent, now-rare ecosystems. [emphasis added]
The serious use of heavy equipment will often be necessary to undo damage and create conditions (such as soil mounds) for tidal swamp reestablishment. Planting of native trees in creative ways (for instance, log cribs and placing nurse logs to establish new trees) is also worth doing in some cases. In this case, the term ecological engineering is not an oxymoron.
Bringing back fully functioning tidal swamps also means bringing back the beavers. Beavers are a keystone species—a species that has a “disproportionately large effect on its natural environment relative to its natural abundance.” See my Public Lands Blog posts “Leave It to Beavers: Good for the Climate, Ecosystems, Watersheds, Ratepayers, and Taxpayers, Part 1 and Part 2.
We now can add the Sitka spruce to the list of keystone species. In reporting on a 2009 study of Oregon’s Siuslaw River estuary, Laura Brophy wrote, “It seems likely that beaver and Sitka spruce interact in the swamps as ‘system engineers,’ profoundly altering site structure.” The Pacific Northwest Blue Carbon Working Group elaborates:
System engineers: In PNW tidal wetlands, system engineers such as beaver and Sitka spruce create conditions highly conducive to organic matter accumulation. Beaver dams in tidal wetlands raise water tables, increasing soil saturation. Sitka spruce root platforms support production of large woody debris which eventually becomes buried in the saturated soils below, adding to carbon stocks. [emphasis added and citations omitted]
The compounding factor of sea level rise in tidal wetland restoration means that as we humans strategically retreat from the rising sea, we need to retreat far enough that we leave room in between for tidal wetlands.
How far might that be? Figure 11 is a terrorizing graph lifted from J. Boone Kauffman’s video on YouTube. The print quality sucks but not anywhere near as much as the forecast. On the left side, the graph shows sea level in the year 2000 at 45°N latitude (which you and I know more precisely as McMenamin’s Lighthouse Brew Pub in Lincoln City). On the right is the range of sea level rise predictions for the year 2100 (fortunately, I’ll be dead), based on information from the Intergovernmental Panel on Climate Change. The oceans will be between a tad under 4 inches (let’s call it the width of a 2x4) and 45+ inches (let’s call it goddamn near 4 feet) higher at that time. If we get the carbon out of our collective asses, we can hold it to the low end. If not . . .
Figure 11. Range of possible sea level rise at 45°N during the twenty-first century. The range goes from a rise of about 4 inches if we work as if our lives, climate, and ecosystems depended on it, to a rise of 45+ inches if we continue our carbon defecating ways—and so do our children and grandchildren. Source: US Global Change Research Program.
It took nearly two centuries to nearly eradicate tidal forest on the Oregon coast. As it will take centuries to fully restore it, we don’t have a moment to waste.
For More Information
• Laura S. Brophy and Michael J/ Ewald, 2017, “Modeling sea level rise impacts to Oregon’s tidal wetlands: Maps and prioritization tools to help plan for habitat conservation into the future,” MidCoast Watersheds Council
• Laura S. Brophy, December 2019, “Comparing historical losses of forested, scrub-shrub, and emergent tidal wetlands on the Oregon coast, USA: A paradigm shift for estuary restoration and conservation,” Estuary Technical Group, Institute for Applied Ecology
• Laura Brophy, December 1, 2020, “Little-known forests of the tidelands: Oregon’s magnificent tidal swamps, past and present,” Block 15 Tap Talk (“craft beer, conversation, community”—I recommend you crack a local cold one when viewing); slide deck
• Laura Brophy photographs: Oregon Tidal Marsh, Oregon Tidal Swamp, and Intertidal Beaver Dams in Oregon
• J. Boone Kauffman, L. Giovanonni, J. Kelly, et al., 2020, “Total ecosystem carbon stocks at the marine-terrestrial interface: Blue carbon of the Pacific Northwest Coast, United States,” Global Change Biology
• J. Boone Kauffman, Why conservation and restoration of PNW tidal wetlands is of global significance, YouTube video, March 23, 2020.
• Lower Nehalem Community Trust, Sitka Wetlands
• Pacific Northwest Blue Carbon Working Group
• US Fish and Wildlife Service, Cottonwood/Willow Swamp, Julia Butler Hansen Refuge
• US Fish and Wildlife Service, Palustrine Tidal Scrub-shrub Swamp, Julia Butler Hansen Refuge
Make a Donation
Never in the field of natural carbon storage has so much been owed by so many to so few tidal wetland acres—especially forested tidal swamps. These astonishing few and productive acres need our help so they can help the climate, salmon, estuaries, and us.
Rock star tidal wetland scientist Laura Brophy is associated with the Institute for Applied Ecology (based in Corvallis), which happens to be a 501(c)(3) charitable organization. You should make a donation (like I did) and earmark it for their Estuary Technical Group, which Laura directs.
Figure 12. The root mass of a Sitka spruce blown down in December 2007 along Coal Creek in the Nehalem River estuary. Laura Brophy (left) and Doug Adams of NOAA National Geodetic Survey. Source: Kevin Jordan, NOAA National Geodetic Survey.
BOTTOM LINE: Never in the field of natural carbon storage has so much been owed by so many to so few tidal wetland acres—especially forested tidal swamps.