The Tongass National Forest in southeast Alaska spans roughly 17 million acres, making it the largest national forest in the United States and one of the largest remaining tracts of largely intact coastal temperate rainforest on Earth.1The Journal of Wildlife Management. Wildlife studies on the Tongass National Forest challenge essential assumptions of its wildlife conservation strategy What makes it ecologically remarkable is not just its size but the density of biological interactions packed into its dripping canopy, glacially carved waterways, and spongy peat soils. The forest stores a staggering share of America’s forest carbon, ferries marine nutrients deep into its interior through spawning salmon, and harbors animal lineages found nowhere else on the planet.
Old-Growth Architecture and the Forces That Shape It
The Tongass is dominated by two conifers: Sitka spruce and western hemlock. In old-growth stands, these trees create a layered, structurally complex forest that looks nothing like a tidy plantation. Detailed mapping of tree positions in old-growth plots has shown that overstory trees tend to be spaced out at short distances (under about five meters) but become either random or clumped at larger scales. Understory trees, by contrast, are typically random or clumped throughout. In stands with heavy canopy cover above 70 percent, the overstory and understory populations actually repel each other spatially, meaning young trees have a harder time establishing directly beneath the biggest canopy giants.2Canadian Journal of Forest Research. Spatial aspects of structural complexity in Sitka spruce – western hemlock forests, including evaluation of a new canopy gap delineation method That kind of spatial sorting matters because it determines where light reaches the forest floor and where the next generation of trees will eventually grow.
Wind is the primary architect of these patterns. Unlike forests shaped mainly by fire, the Tongass is sculpted by storms rolling in off the Gulf of Alaska. Research on wind disturbance in the region has revealed that these effects exist on a continuum: exposed ridgelines and outer coastlines experience recurrent, large-scale blowdown events, while sheltered interior valleys are dominated by small canopy gaps where individual trees snap or topple.3Treesearch. The effects of wind disturbance on temperate rain forest structure and dynamics of southeast Alaska Both scales of disturbance create openings that allow light to penetrate, restart successional cycles, and maintain the mosaic of young, middle-aged, and ancient trees that defines an intact temperate rainforest. The result is a landscape where individual patches are constantly being reset while the broader forest persists as a functioning whole.
A Massive Carbon Reservoir
The Tongass punches well above its weight in the global carbon budget. When researchers combined geographic data with forest inventory measurements to estimate the total carbon stored in the forest’s biomass and soils, the figure came to roughly 2.8 billion metric tons, with an uncertainty of about half a billion tons in either direction. That single forest holds an estimated eight percent of all the carbon stored in forests across the lower 48 states, and about a quarter of a percent of all carbon in the world’s forest vegetation and soils.4Ecosystems. Effects of Management on Carbon Sequestration in Forest Biomass in Southeast Alaska For a forest that covers less than one percent of the U.S. land area, that is a disproportionately large share.
Much of this carbon sits not in the trees but underground. Upland soils in the Tongass region average around 198 metric tons of organic carbon per hectare, and that figure holds across different types of underlying bedrock. Whether the soil formed over slate, metavolcanic rock, or phyllite, the carbon stocks were broadly similar.5Soil Science Society of America Journal. Spodosol development and soil organic carbon distribution along a lithosequence in perhumid coastal temperate rainforest This makes sense in a climate where constant rain and cool temperatures slow decomposition: organic material piles up in the soil faster than microbes can break it down, year after year, for millennia.
Peatlands at the Forest Edge
Scattered among the dense stands of conifers are waterlogged peatlands, and the zones where forest and peatland meet turn out to be surprisingly important. Conifers in these transition areas can grow on deeply organic soils with organic carbon contents reaching 57 kilograms per square meter in the top meter alone, significantly higher than the carbon stored under adjacent forest stands growing on mineral soils. Yet the rate at which these edge soils release carbon dioxide through respiration is dramatically lower: about three times less than the respiration rates measured under fully forested plots. The difference comes down to water. Peatland and forest-edge water tables sit much closer to the surface than forest water tables, and waterlogged conditions suppress microbial activity and slow decomposition to a crawl.6Soil Science Society of America Journal. Structure and Function of Peatland‐Forest Ecotones in Southeastern Alaska
This has a practical consequence for carbon accounting. Peatland edges are carbon-dense and carbon-stable, acting as slow-leaking vaults. Draining or disturbing these areas, whether through road building, logging, or climate-driven changes in hydrology, could unlock large stores of carbon that have been accumulating for thousands of years. As long as the water table stays high, those stores remain relatively secure.
The Carbon Pipeline to the Sea
Not all of the Tongass’s carbon stays put. During rainstorms, dissolved organic matter flushes out of the forest floor and into streams. Research on coastal temperate watersheds in the region measured stormflow exports of dissolved organic carbon ranging from about 2.3 kilograms of carbon per hectare in upland forested catchments to nearly 14 kilograms per hectare in bog-dominated subcatchments.7Journal of Geophysical Research: Biogeosciences. Changes in the concentration, biodegradability, and fluorescent properties of dissolved organic matter during stormflows in coastal temperate watersheds A substantial portion of this exported carbon is biodegradable, meaning that downstream bacteria and aquatic organisms can use it as an energy source.
This creates a direct carbon link between the forest and the nearshore marine environment. What looks like a loss from the terrestrial ecosystem’s perspective is actually a subsidy for estuaries and coastal waters. In a region where heavy rainfall is the norm, storm-driven carbon pulses represent a regular transfer of forest productivity to the sea, fueling microbial food webs and influencing water chemistry along thousands of kilometers of coastline.
Salmon and the Nutrient Loop Running in Reverse
If dissolved carbon flows from forest to ocean during storms, Pacific salmon push nutrients in the opposite direction. Every year, millions of salmon return from the nutrient-rich open ocean to spawn in the small, nutrient-poor freshwater streams that lace through the Tongass. When they die after spawning, their bodies release nitrogen, phosphorus, and other marine-derived nutrients into the stream ecosystem and surrounding riparian forest. Research in the region has documented that salmon positively influence the abundance of stream-bottom organisms by delivering large quantities of these marine nutrients to waters that would otherwise be quite barren.8Ecology. Timber harvest transforms ecological roles of salmon in southeast Alaska rain forest streams
Bears, eagles, and other scavengers carry salmon carcasses into the forest, where the nutrients eventually enter the soil and are taken up by trees and understory plants. The effect is measurable: trees growing near productive salmon streams tend to grow faster and have higher nitrogen concentrations in their foliage than trees farther from streams. The forest and the ocean, in other words, are not separate systems. Salmon are the couriers that bind them together, and any disruption to salmon runs, whether from overfishing, habitat loss, or climate change, ripples through the terrestrial food web.
Wolves, Deer, and the Understory
The Tongass is home to the Alexander Archipelago wolf, a subspecies of gray wolf found only in southeast Alaska. Research has shown that these wolves depend heavily on the population density of Sitka black-tailed deer for their own reproductive success, while road access by hunters represents the dominant factor affecting wolf mortality.9Landscape and Urban Planning. Maintaining wildlife habitat in southeastern Alaska: implications of new knowledge for forest management and research The deer-wolf relationship links directly to forest management, because deer need accessible, nutritious understory vegetation, and the condition of that understory depends on what happened to the forest canopy decades ago.
When old-growth forest was harvested across parts of the Tongass during the twentieth century, the resulting second-growth stands grew into dense, closed-canopy thickets that let almost no light reach the forest floor. Understory plants withered, and deer forage vanished. Recent field work measuring plant communities across thousands of quadrats found that precommercial thinning of these second-growth stands significantly increased understory forage biomass, digestible energy, and digestible protein compared to unthinned controls. Thinning also doubled the probability that deer would browse in a given area. The effect was strongest when thinning happened within 35 years of the stand’s establishment.10PubMed. Thinning restores ungulate foraging habitat in historically logged forests There was a trade-off: slash debris left behind by thinning operations reduced browse probability by about 11 percent on average, though this effect faded as the slash decomposed over time.10PubMed. Thinning restores ungulate foraging habitat in historically logged forests
Deer in the study selected for both quantity and quality of forage, gravitating toward patches with higher digestible energy and protein, while landscape-level composition had no detectable effect on relative browse probability. Fine-scale habitat quality mattered more than what was happening in the surrounding landscape. For forest managers trying to restore wildlife value to logged areas, thinning early and often appears to be one of the most effective tools available.11Treesearch. Sharing the load to develop young-growth silviculture for forage and biodiversity in southeast Alaska
Bald Eagles and Coastal Nesting
Southeast Alaska supports one of the densest populations of bald eagles in North America, and long-term monitoring has offered a window into how stable those populations really are. Annual surveys conducted from 1972 through 1981 along roughly 90 kilometers of coastline in Seymour Canal, a sheltered waterway in the region, found approximately 90 nests. In a typical late-June survey, about 29 percent of nests were productive, containing an average of 1.56 eggs or downy young per nest. Productivity dipped noticeably in 1979 and 1980, dropping to 19 percent, with a slight recovery to 23 percent in 1981. Natural causes accounted for an average of five percent annual nest loss.12The Condor: Ornithological Applications. Bald Eagle Nesting Studies in Seymour Canal, Southeast Alaska
Eagles in this part of Alaska rely on large old-growth trees for nesting, especially Sitka spruce with broad canopy platforms. They also depend on salmon runs and intertidal foraging. The tight link between eagles, old-growth structure, and salmon availability makes them a useful indicator of overall ecosystem health: when eagles do well, it usually means the forest, the streams, and the marine shoreline are all functioning.
Island Endemism and Glacial Refugia
The Tongass encompasses the Alexander Archipelago, a chain of over a thousand islands carved out by advancing and retreating glaciers. That history of ice and isolation has produced something unusual: elevated levels of endemism among mammals. A phylogeographic review of the region’s mammals found that this endemism arises from a combination of deep and shallow evolutionary processes, meaning some lineages have been isolated in the archipelago for tens of thousands of years while others arrived only recently as glaciers receded.13The Journal of Wildlife Management. Phylogeography of mammals in Southeast Alaska and implications for management of the Tongass National Forest
Some of these populations trace back to coastal refugia, ice-free pockets along the coast where plants and animals survived while glaciers covered the interior. Genetic analysis of multiple species, including small mammals, has identified ancient lineages that likely originated in these refugia, consistent with similar findings in other species like ermine.14PubMed Central. Living on the edge: Exploring the role of coastal refugia in the Alexander Archipelago of Alaska The archipelago, in this sense, functions as a living museum of evolutionary experimentation. Populations on different islands may look similar to the untrained eye but carry distinct genetic signatures shaped by thousands of years of isolation. This matters for conservation: treating all wolves or all deer in the Tongass as a single interchangeable population would ignore real genetic diversity that has taken millennia to develop.
The Underground Network
Beneath the forest floor, fungi create another layer of connectivity that is invisible but functionally important. Mycorrhizal fungi form symbiotic relationships with tree roots, extending the reach of root systems and facilitating the exchange of nutrients. Research has demonstrated that carbon can transfer between trees through common mycorrhizal networks, a phenomenon first shown in laboratory settings over half a century ago and later confirmed in the field. More recent work has provided evidence that these transfers can be ecologically meaningful, with carbon moving from mature trees to seedlings through fungal connections.15PubMed Central. Belowground carbon transfer across mycorrhizal networks among trees: Facts, not fantasy.
In a forest like the Tongass, where light is scarce on the forest floor and seedlings struggle to photosynthesize enough to survive, mycorrhizal subsidies from established trees could make the difference between a seedling living and dying. The network architecture has been mapped in some forests, revealing that trees are more interconnected belowground than scientists once assumed. How much carbon actually moves and how much it matters to forest regeneration at landscape scales are still active questions, but the basic mechanism is well established. For temperate rainforests with their dense canopies and shade-limited understories, even small carbon subsidies to struggling seedlings could influence which trees make it to maturity and where gaps in the canopy eventually get filled.
Indigenous Fire in a Rainforest
The idea of fire in a dripping-wet rainforest sounds paradoxical, but emerging research is examining whether pre-contact Indigenous peoples in the Pacific Northwest temperate rainforest, including portions of southeast Alaska, used fire as a deliberate land management tool. A recent research framework explored the evidence for Indigenous fire stewardship in these ecosystems, looking at how intentional burning might have shaped vegetation patterns, maintained openings, and supported culturally important plant species before European contact.16Frontiers in Environmental Archaeology. Pre-contact Indigenous fire stewardship: a research framework and application to a Pacific Northwest temperate rainforest Tlingit, Haida, and Tsimshian peoples have occupied this landscape for thousands of years, and their relationship with the forest was not one of passive coexistence.
Detecting the signal of past human-set fires in a rainforest environment is challenging. Charcoal in soil and lake sediments can indicate fire history, but disentangling human ignitions from rare natural fires or lightning strikes requires careful spatial and temporal analysis. The research is still in early stages, but it raises an important point: the “pristine” rainforest that modern visitors see may itself be a product of long human stewardship that ended only a few centuries ago. If Indigenous burning created or maintained meadows, berry patches, or other clearings, then some of the open habitats that deer, bears, and other wildlife depend on today may owe their existence to human management rather than purely natural processes.
When Logging Changes Salmon Streams
The Tongass’s salmon streams do not exist in isolation from what happens on the hillsides above them. When timber harvesting removes streamside forest, it changes water temperature, sediment load, and the supply of marine-derived nutrients from salmon. Research in southeast Alaska’s rain forest streams found that logging transformed the ecological role of salmon in affected waterways.8Ecology. Timber harvest transforms ecological roles of salmon in southeast Alaska rain forest streams In intact streams, salmon carcasses drive a nutrient fertilization effect that supports the entire food web from algae to invertebrates to juvenile fish. When the surrounding forest is logged, stream conditions change enough that the relationship between salmon nutrients and biological communities can shift in unexpected ways.
This connects back to the carbon story. Riparian forests shade streams, drop organic matter into them, and stabilize banks. They also anchor the mycorrhizal networks that help trees along stream edges access soil nutrients, some of which originated from decomposing salmon. Remove the trees, and you lose not just timber but a cascade of ecological functions: stream shading, nutrient cycling, invertebrate habitat, and the carbon filtering that controls how much dissolved organic matter reaches the ocean during storms. The Tongass functions as a single integrated system where forest, soil, water, fish, and wildlife are linked by flows of carbon and nutrients. Disrupting any one of those links produces consequences that ripple through the rest.