Biosphere Climate Change Daily Earth Science Environment Repost

The Tongass, home to unique and beautiful ecosystems

Ecological balance within the Tongass National Forest resides in the intimate relationships between aquatic and marine ecosystems

The original article on the Tongas (February 24, 2020) has been expanded with additional reference to the geological background of the forest)

Along the southern reaches of Alaska’s coast, nestled between the Pacific Ocean and Canada, lies the Tongass, America’s largest national forest. The Tongass National Forest is also one of the most significant remaining temperate rainforests in the world. This coastal wilderness and its wetlands form a unique ecosystem that sequesters about eight percent of all carbon stored by U.S. forests. But the Tongass is under a threat encompassing more than just the trees in this distinctive ecosystem. The forest influences ecosystems ranging from the high coastal mountains to the marine wetlands and waterways rimming the Pacific Ocean. Changes in land use put pressure on both the terrestrial and aquatic ecosystems of the region.  

Stretching 350 miles northwest from a southern border between Ketchikan, Alaska and Prince Rupert, Canada, the Tongass National Forest encompasses about 17 million acres. The forest takes its name from indigenous people in the area. Its origins as a national treasure lie in a 1902 proclamation by President Theodore Roosevelt, declaring this coastal Alaskan area as the Alexander Archipelago Forest Reserve. Then, five years later, another proclamation created the Tongass National Forest, and in 1909 the two were combined to form the Tongass we know today.

The Mountains

Pacific coastal mountains rim the western edge of Canada and extend along the southern reaches of Alaska. These mountains are remnants of an ancient oceanic volcanic formation named the Wrangellia Large Igneous Province. During the mid-Triassic, about 232 million years ago, eruptions of magma and flood basalts inundated an ancient ocean floor. The resulting Wrangellia flood basalts were over 4000 feet thick, and probably covered an area of over half-a-million square miles in the middle of a long-gone sea. Tectonics and uplift eventually squeezed these volcanic rocks into the mountain belt we see today.

The Wrangellia eruptions occurred over several million years during the Triassic Carnian interval. The volcanic activity was intense, and greenhouse gases emitted from the eruptions warmed the earth by over 4 degrees Celsius. During this period, known as the Carnian Pluvial Episode, heat, humidity, and changing weather patterns took their toll. Coastal marine reefs and ecosystems were wiped out in many regions by heat and increased sedimentation. Today, Triassic rock formations provide a geological record of the event. Rapid climate change stressed life on ancient earth, and species extinction rates climbed. 

Today these volcanic rocks from the Wrangellia eruptions form the backbone of the Tongass National Forest.

Logging runs amuck

The mountains of the Tongass plunge westward beneath the ocean along this stretch of the Alaskan coast and some 15,000 miles of rivers and streams drain directly into the Pacific Ocean. Within this temperate rainforest, the primary species of trees are Sitka spruce, western hemlock, western red cedar, and Alaska cedar. But these trees are commercially valuable and attract unwanted attention from commercial logging operations. 

Small scale logging occurred before 1950, but in 1954 a large pulp mill operation started in Ketchikan. The contract was with the US Forest Service for the delivery of 50 years of timber. Success begets success, and more mills opened. The pace of logging grew until it was unsustainable. When the ongoing damage was finally recognized in the 1990s, contracts were canceled, and mills closed. However, by that time, about 90% of the mature old-growth forests were lost. Notably, today, as environmental protections are rolled back, efforts are underway to authorize a resumption of logging in the Tongass.

Saul Elbein of National geographic wrote the following in a recent article about logging in the Tongass: 

“The clear-cuts also brought a sort of localized climate change distinct from the global one, as the trees that regulated the ecosystem disappeared, and the bare slopes left behind, washed by the constant rain, disgorged sediment into once-clear streams. Bark sloughed off from log rafts settled to the bottom and fermented into toxic methylmercury, killing the seafloor… Once-lucrative salmon streams and their attached fisheries expired as erosion from the bare hills clogged the once-clear pools, or as the loss of the canopy left them unprotected from the sun.”

Tongass carbon stores

The Tongass National Forest plays a significant role in managing greenhouse gas emissions since its climatic and environmental conditions are optimal for massive carbon storage. The good news is the vegetation biomass is vast, but the better news is the soils are even more effective than trees at carbon storage. Within the Tongass Forest, 66 percent of the total carbon resides in the soil, and the remaining 34% is in vegetation biomass. Also, various environmental factors make carbon storage higher in the Tongass than in most forests.

Contributing factors to the high carbon storage capacity of this ecosystem are a cold climate and high rainfall. Ample water stimulates high growth rates, and colder temperatures retard the decomposition rate, so more carbon remains locked in soils and dead plant material. Another added benefit of the wet, cold environment is reduced susceptibility to wildfires. Fewer fires translate into better carbon management. Notably,  U.S. wildfires annually release an equivalent of 25% of the total carbon stored by trees each year. So we take a quarter-step backward for each step forward.

But the real ecological beauty of the Tongass National Forest is the intimate relationship between the aquatic and marine ecosystems along the coast.

Terrestrial and aquatic symbiosis

Places in the Tongass receive up to 200 inches of rain each year. The constant flushing of water from the steep slopes of the Tongass forests into the ocean directly connects the terrestrial and aquatic/marine ecosystems of the region. This interconnectivity means the nutrients delivered by this system create a robust aquatic food web, and also support Alaska’s multi-billion-dollar fishing industry. 

One of the critical foundations for this web of life is the flux of dissolved organic carbon (DOC) from Tongass soils to the ocean. The streams of the Tongass discharge 36 times more DOC per unit area than the world’s average waterway, and three times as much as the Amazon River. Remember, the Amazon drains the largest tropical rainforest in the world. This bit of nutrient-transport magic depends on the short travel distance from the abundant carbon reserves in the forest soils to the ocean. The distance is significant because long river trips provide more chances for carbon interception before reaching the sea.

At the base of the food web, micro-organisms consume carbon, thus creating the bottom trophic level of a valuable and complex marine ecosystem. The source of this carbon is the soils. But when commercial logging removes trees, it also changes the structure and composition of underlying soils. These changes cascade through life-energy pathways between land and ocean. Therefore, understanding the complete carbon pathways in the combined terrestrial-aquatic ecosystem of the Tongass is the only way to know how newly proposed logging will affect life along the southeast Alaskan Coast. It’s about more than just the trees.


Forests as a pathway for terrestrial carbon sequestration (Source: ArcheanWeb) – Also:

Extractive versus sustainable logging (Source: ArcheanWeb) – Also:

When do forests become a carbon liability? (Source: ArcheanWeb) – Also:


Tongass National Forest (USDA – Forest Service) – Also:

11 facts about North America’s temperate rainforests (By JAYMI HEIMBUCH; Mother Nature Network) –

Greenhouse Gas Emissions Versus Forest Sequestration in Temperate Rain Forests— A Synthesis for Southeast Alaska Communities (By David Nicholls and Trista Patterson; USDA) – Also:

From rock to forest: Southeast’s carbon sink (By  MARY CATHARINE MARTIN; Juneau Empire) – Also:

Baseline Estimates of Carbon Stocks in Forests and Harvested Wood Products for National Forest System Units – Alaska Region (USDA Forest Service) –


Alaska Forest Facts – Also:

History of the Tongass National Forest (American Salmon Forests)  – Also:

Feature Image: Tongass Rain forest 08 (By Gillfoto) (Modified) – – This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. –

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.