Unhealthy Forests Are Harming Salmon, by Heather Fergus
One-third of California’s total land cover is forest, according to the USDA. Home to some of the oldest, largest, and tallest living trees, California has a huge diversity of tree species. While Southern California is covered in chaparral forests consisting of small trees and shrubs, mixed evergreens can be found along the coast, in Northern California, and the Sierra Nevada. Appearing along the northern coastline are also the iconic redwood forests. With its complex geography and vast amount of flora and fauna, it comes as no surprise that California is one of 36 Global Biodiversity Hotspots.
Walking through a path of monumental trees, dense greenery, and the steady flow of a stream nearby. These are familiar images of Californian forests, which are also home to many of the state’s watersheds, such as the Sacramento River. And running through them, it’s possible to spot a commonly known indicator of healthy ecosystems, the Pacific salmon.
There are many species of salmon in California, including the Chinook, Coho, Chum, and Pink salmon, according to California Trout. Historically, the state has had the highest abundance of Chinook and Coho. Seven Chinook species and one Coho species are actually endemic, meaning they can only be found in California, according to The Nature Conservancy. Easily mistaken for salmon is the Steelhead, which is actually a trout but is anadromous like salmon.
Anadromous refers to fish who spend their adult lives in the sea, but migrate up rivers and streams to spawn in freshwater. While the seasonal timing of migration varies by species, the life cycle of most salmon is anadromous. Females lay their eggs in gravel river beds. After hatching, the juvenile fish grow and proceed to migrate towards the ocean. During this time, they begin the physiological process that prepares them to transition from freshwater to saltwater, known as “smoltification”. They then reach estuaries before finally heading into the ocean. Juvenile salmon, such as Chinook, rely on terrestrial insects and small crustaceans as they journey toward saltwater. On their return to freshwater, adults feed on small fish like herring. Their life cycle and role in both freshwater and saltwater habitats are what make Pacific Salmon such a vital keystone species.
Salmon are important food sources for other species, such as black bears, migratory birds, and marine mammals like the killer whale, according to Pacific Wild. The adults who eventually return to freshwater die after spawning, which cycles nutrients back into the river and forest ecosystems. In fact, salmon ‘feed’ forests through nitrogen from their carcasses, according to KQED.
However, many of California’s salmon populations are declining, with the NOAA listing 28 species of West Coast salmon and steelhead as endangered or threatened. For example, the Winter-run Chinook Salmon are now labeled as an endangered species. Historically numbering around 200,000 adults, only 1000s have been recorded returning to spawn over recent years. The Winter-run Chinook moved to spawn in the Sacramento River after the installation of the Keswick dam blocked their previous locations, an example of how human actions affect salmon. Threats to salmon also include climate change and warming water temperatures, overfishing, pollution, land use and the diversion of water for agriculture, and habitat degradation, according to the State of Salmon in Watersheds.
Logging is a threat to salmon that compounds those already present, particularly water pollution, habitat degradation, and climate change. In intensive forms of even-aged logging, such as clearcutting, trees are felled and extracted, the remaining flora is removed and burned, and in its place seedlings are planted to form an even-aged plantation. This is highly destructive to forest ecosystems and therefore the survival of already vulnerable salmon species.
A recent study conducted in British Columbia found that logging contributes to warming water temperatures by removing forest cover near streams. They found that in areas where 35 percent of the riparian forests were harvested, summer stream temperatures were 3.7 degrees Celsius higher than areas with 5 percent of forest harvested. Salmon are adapted to cooler water flows, and warmer temperatures means there is less oxygen, which suffocates salmon eggs and reduces salmon metabolism. Since warmer water impacts small insects and crustaceans, juveniles have to swim further to find food. Another study also found that warming water makes salmon more vulnerable to predation.
Forest mismanagement and logging can also pollute rivers and streams. A 2012 study on California watersheds found that with an increasing rate of forest harvests, water turbidity also increases. They discuss how logging exacerbates the potential of landslides and gully erosion in watersheds, which increases the amount of sediment pushed into the water.
Road-building that facilitates logging can also pollute waters. According to the Sierra Forest Legacy, roads compact and break up existing soil, and direct high amounts of sediment and pollutants into streams, particularly after heavy rainfall. Sedimentation blocks and alters the gravel beds where salmon eggs are laid, which reduces the amount of oxygen available to the eggs, according to the University of British Columbia. It also reduces visibility in water, forcing salmon to use more energy in finding food.
Currently, California’s Park Fire threatens Spring-run Chinook, as it has now spread to the Mill and Deer Creeks, which feed into the Sacramento River. Experts are concerned about the ash, sediment, and chemicals used fighting the fire polluting the creeks these salmon spawn in, according to KQED. Last year, numbers of Spring-run Chinook were found to have sharply declined, putting them in a very vulnerable position. Practices like clearcutting exacerbate wildfire risk, as they create highly flammable forests and allow fires to spread faster. With warming temperatures, intensive logging will make salmon habitats less resilient to wildfires like the Park Fire.
Forest ecosystems and salmon species are inherently reliant upon each other. Clearcutting and intensive logging not only impacts salmon by disrupting forest ecosystems, but leaves a keystone population more vulnerable, impacting forest and aquatic ecosystems in the future.
There are positive conservation efforts already underway to support the adaptive capacity of salmon. In 2019, the NOAA published one of the first comprehensive assessments of West Coast salmon and steelhead’s vulnerability to climate change. Assessments such as these can inform the best ways to support different salmon species, and understand the major threats they face. This is also why addressing the impacts of logging is vital to protecting Pacific salmon populations. In order to conserve and restore future salmon populations, we need to drastically alter California’s forest management practices, including ending all intensive logging and clearcutting.
