This uncertainty notwithstanding, it’s widely accepted that certain plant communities are particularly vulnerable to climate change. For example, tidal wetland vegetation bordering hard coastal defenses such as dikes, seawalls, and other armoring structures are unlikely to be permitted to migrate inland in response to rising sea level (Scavia et al. 2002, Erwin 2009). Rising air temperatures or changing groundwater hydrology may also reduce the viability of habitats supporting already endangered species such as the Western lily (Lillium occidentale), and may impede their reproductive function (USFWS 2009).
In the future, precipitation in coastal Oregon is expected to remain a predominately wintertime phenomenon (i.e., most precipitation will continue to occur in the winter). However, the extent to which precipitation timing, frequency and intensity on the Oregon coast may change in the future remains uncertain. There is evidence that high-intensity storms are becoming more frequent, and that the frequency of weak to moderate-strength storms is declining.
Sources: Sharp 2012; OCCRI 2010; OSU 2005
Although most research focuses on the anticipated effects of extreme weather events, experts point out that even low energy storms can create flooding events, which can reduce habitat availability (especially if these events correspond with high tides)(USGS n.d.). One important caveat is that these flood events also deliver sediment to marshes, which is an essential process to assure their persistence (Scavia et al. 2002, USGS n.d.).
Changing weather patterns are likely to affect many other important natural processes that influence the productivity and function of marsh habitats, including evapotranspiration, biogeochemical processes, sediment accumulation, fire regime, tidal and storm water inundation regime, and wave energy (Burkett and Kusler 2000, Gornitz 2001, Gornitz et al. 2001, IPCC 1998, Karl et al. 1995, USGCRP 2000, USGS n.d.). The persistence of eelgrass (Zostera marina) beds that are relatively exposed (e.g., in the South Slough Subsystem) may be jeopardized if more frequent and intense storms result in larger storm-generated waves propagating through the lower estuary (Cornu et al. 2012).
Altered weather patterns have been known to effect “phytopathology” (i.e., diseases and infections in plants). Although research on the anticipated effects of climate change on phytopathology is limited, the existing literature generally concludes that climate change is likely to alter plant-pathogen interactions (Coakley et al. 1999, Chakraborty et al. 2000, Garrett et al. 2006). Abiotic stressors resulting directly from climate change (e.g., warmer temperatures and drought) may alter plant susceptibility to pathogens (Garrett et al. 2006).
Climate-related changes may also affect phytopathology indirectly by altering the structure of existing plant communities. For example, research shows that increased plant density tends to create wetter conditions in vegetated areas, thus increasing the likelihood of infection from certain pathogens (e.g., foliar pathogens)(Burdon 1987, Huber and Gillespie 1992).
These anticipated changes may exacerbate phytopathology concerns that already exist in the project area. In particular, prolonged wet weather in spring is very conducive to Swiss needle cast infection (Stone et al. 2008, Zhao et al. 2011), which causes premature needle loss (i.e. “casting” of needles) in Douglas fir trees, resulting in substantially reduced growth and potentially eliminating the ability to compete with neighboring trees (Shaw 2008).
Source: Mysak 1986
Sources: Dijkema 1987, Kolker et al. 2009, Erwin 2009, Reed 1990, USGS n.d., Scavia et al. 2002, Clough and Larson 2010, Buffington et al. 2015
Many of the region’s tidal freshwater marshes and swamps are expected to convert to brackish marshes due to seawater intrusion from rising sea levels (Glick et al. 2007, Scavia et al. 2002). These changes have the potential to reduce the extent of tidal freshwater marshes and swamps if those habitats are prevented (by hardened shorelines like dikes, sea walls, and other structures) from migrating further inland in response to SLR (Glick et al. 2007, Scavia et al. 2002, Erwin 2009, Dalton et al. 2013, Shaughnessy et al. 2012, Hartig et al. 2002). Because inland migration will be possible for tidal wetlands in some systems and the elevation of some wetlands will keep pace with SLR though natural processes (vertical accretion- see sidebar), the changes described above will not necessary result in the loss of wetland area (Reed 1990, Erwin 2009).
While wetland areas may not change dramatically, even small persistent changes in sea level are likely to affect the distribution of species with narrowly defined habitat requirements.
Changes in plant community distribution are particularly important for rare and endangered species. Two rare plant species, silvery phacelia (Phacelia argentea) and wolf’s evening primrose (Oenothera wolfii) occur just south of the project area. If climate change results in favorable conditions for the northward expansion of these species, the project area could represent an important refuge for plant species struggling to survive in nearby ecosystems. However, it should also be noted that climate-related habitat changes could have deleterious effects on rare and endangered plant species that are not well suited to adaptation (e.g., Western lily)(USFWS 2009).
SLR may be intensified by cyclical long term climatic patterns (see sidebar). For example, Barnard et al. (2011) note that El Niño events may increase regional sea level by as much as 30 cm (~12 in) for several months at a time. Historically, these events have been associated with increased coastal erosion and flooding. They’re likely to periodically intensify the effects of SLR in the future (Dalton et al. 2013).
Our local NOAA tide station in Charleston has documented an average rate of sea level rise (SLR) of 0.84 mm (0.03 inches) per year averaged over the past 30 years (0.27 feet in 100 years). The rate of SLR is expected to accelerate over time. For example, the National Research Council (NRC), predicted SLR rates as high as +23 cm (9 inches) by 2030; +48 cm (19 inches) by 2050; and +143 cm (56 inches) by 2100 for the area to the north of California’s Cape Mendocino (the study’s closest site to the Coos estuary).
Sources: NOAA Tides and Currents 2013, NRC 2012
Uncertainty in Predicting Local Effects of Climate Change
There is inherent uncertainty in predicting what the local effects of climate change are likely to be. The uncertainties generally fall into three categories: 1) Natural variability of the earth’s climate; 2) Climate sensitivity (how the earth’s climate system responds to increases in future greenhouse gas levels); and 3) Future greenhouse gas emissions.
To manage for these uncertainties, climate scientists use multiple models (“multi-model ensembles”) that incorporate the estimated range of possible natural variability, climate sensitivity, and future greenhouse gas emission values when investigating climate-related change. The models typically generate a range of values for potential future air temperatures, ocean surface temperatures, sea level rise, etc., which naturally become increasingly variable the longer into the future the model predicts. This approach gives communities a range of projections to consider when developing climate change vulnerability assessments and adaptation plans.
Sources: Sharp 2012; Hawkins and Sutton 2009