Coastal Marten Returns to Six Rivers Forests

For decades, biologists believed this small carnivore had shifted from being rare to almost legendary. Fresh fieldwork in the Six Rivers region now indicates that the coastal marten has not merely survived: it is actively adapting to a landscape affected by logging, fire and climate change.

The return of a mammal thought lost

Old-growth woodland along the Pacific coast of northern California and southern Oregon once regularly supported coastal martens. Trappers heavily pursued them for their thick, reddish-brown fur. Meanwhile, extensive timber harvesting removed the intricate forest habitat the animals require for hunting, resting and rearing their young.

By the end of the 20th century, reports of the species had become exceptionally scarce. Across much of its former range, many specialists regarded it as functionally absent. In 1996, however, one marten was found in an isolated forest in northern California. That single animal raised years of uncertainty: were other martens still out there, or was it the final trace of a species disappearing?

These questions led researchers to develop more structured survey methods. The most recent survey ran from August to November 2022 across the Six Rivers region, an almost 400-square-kilometre mosaic of steep ridges, deep ravines and remaining old-growth forest.

Across 399 square kilometres, scientists identified 46 individual coastal martens, hinting at a small but real population still clinging on.

Researchers deployed 285 “hair snares” - devices that gather fur without injuring animals - as well as 135 motion-triggered cameras. Using these non-invasive methods, they could distinguish individual martens and estimate the number travelling through the landscape.

Altogether, the team recorded 46 separate martens: 28 males and 18 females. Detecting them was difficult, with only one marten appearing on average in every 3.6 square kilometres. Nevertheless, the records gave statisticians enough information to create robust population models and generate the first reliable density estimates for this coastal forest area.

Where the remaining coastal martens live

After analysing the data, scientists calculated that the survey landscape may contain about 111 martens. Although that figure may initially seem substantial, the animals occupy only a small proportion of the old-growth forest that remains in the region.

Their distribution lies near the Pacific, although the ocean offers little protection in itself. Coastal marten densities are comparable with those reported in mountain regions including the Sierra Nevada and British Columbia. This resemblance suggests the same underlying challenge: fragmented habitat.

Six Rivers has rugged terrain, combining ridges, canyons and scattered forest patches. Timber roads and historic clear-felling have divided the woodland into isolated islands. Martens must also share these broken forests with other medium-sized carnivores.

Grey foxes, bobcats and fishers use the same hillsides, pursue similar prey and may compete for denning sites.

Even where forest still stands, the coastal marten is not alone; it shares a crowded carnivore neighbourhood.

Coastal marten hotspots on ridges and ravines

The martens were not confined to a single habitat type. They occurred throughout the study area, although two locations were particularly notable:

• Forested ridges in northern Red Mountain
• Coastal ravines surrounding Blue Creek

At the higher Red Mountain ridges, long-lasting snow and tall trees provide protected feeding areas. Snow that remains into spring can deter certain competitors while supporting prey adapted to colder microclimates.

The Blue Creek ravines offer equally favourable, though very different, conditions. Cool, damp air moves through the creek bottoms. Layers of vegetation - from moss-covered logs to dense mixed shrubs - create a tangled, three-dimensional environment that conceals martens from larger predators and sustains plentiful small mammals and birds.

Forest structure: the essential lifeline

Both ridge and ravine habitats repeatedly share the same physical forest characteristics in areas where marten detections are most frequent.

Dense canopy, large-diameter trunks, hollow stumps and abundant dead wood form the backbone of marten-friendly forest.

These features serve multiple purposes. Large trees and closed canopies provide shade, consistent temperatures and nest cavities, while hollow logs can serve as dens. Dense piles of fallen branches and decaying timber protect rodents, birds and invertebrates that martens prey upon.

In comparison, younger woodland - particularly forest regrowing after extensive, even-aged clear-felling - commonly lacks these qualities for decades. Such forest may appear green when viewed from above, yet it offers little to a marten seeking cover and food.

Altitude alters the pattern

The research highlights an important variation: identical habitat traits do not function in the same manner at every altitude.

Altitude zone	Preferred locations	Main advantages
Low elevation	Moist ravine bottoms	High plant complexity, cooler microclimate, cover from predators
High elevation	Forested ridgelines with lasting snow	Reduced competition, stable snowpack, secure hunting areas

At lower elevations, martens favour gullies with the greatest moisture and plant diversity. Ferns, shrubs, young trees and fallen trunks accumulate there, forming a maze for predators and prey alike.

At greater heights, the animals tend to use forested ridges where snow persists and historical human pressure has been lower. In these places, they encounter fewer competing predators and benefit from mature conifers mixed with snags and broken branches.

Why old-growth forests remain crucial

This two-part approach has one consistent feature: martens avoid exposed, simplified terrain. They generally keep away from broad clearings, plantations planted in uniform rows and very young stands with limited structural variety.

This dependence leaves them especially exposed to industrial forestry that prioritises fast-growing timber of the same age. Combined with longer and hotter fire seasons, more intense drought and climate-change-related tree disease, the old-growth fragments they rely on are diminishing in both area and condition.

For coastal martens, ancient forests are not a luxury habitat; they are the minimum conditions for long-term survival.

The researchers found that marten density responds simultaneously to vegetation and topography. Steep ground, varied canopy heights and an irregular forest floor appear to be more important than simply counting understory shrubs. Structural complexity matters more than uniformly green vegetation.

Shared responsibility in a fragmented landscape

Within a region containing timber interests, tribal land, protected areas and private property, no individual group can secure the species’ future alone. The study strongly supports collaborative action.

Public land agencies oversee extensive forest areas and establish policies for timber extraction and fire management. Indigenous communities possess longstanding knowledge of traditional burning and resource practices that shaped these ecosystems well before industrial logging. Private landowners manage important foothill forests and corridors linking otherwise isolated marten populations.

Potential shared measures include:

• Keeping large old trees, snags and fallen logs during timber operations
• Identifying and safeguarding established marten hotspots on ridges and in ravines
• Planning fuel treatments that lower fire danger without removing complex understory vegetation
• Preserving wooded connections between old-growth fragments
• Supporting continuing camera and hair-sample surveys to monitor population change

Scientific concepts behind the research

Several technical ideas underpin this work. “Habitat fragmentation” refers to the division of continuous forest into smaller islands by roads, clear-felling or development. Species such as the coastal marten must then cross exposed and dangerous gaps to travel between their remaining refuges.

“Structural complexity” describes a forest’s physical arrangement: tall trees, saplings, vines, snags, fallen trunks and burrows layered together. For a small predator, this complexity supplies places to hunt and hide. A neat stand of evenly spaced trees of the same age, with no dead wood, may appear orderly to people but is barren from a marten’s perspective.

What future forests could mean

Should present trends persist, climate change is likely to make large fires more frequent in the Pacific coastal region. Unless planning is careful, logging after fires and rapid replanting in uniform blocks could further reduce the structural elements on which martens depend.

One potential route is “climate-smart” forestry: thinning selected areas to lower fuel loads, using controlled burns where conditions permit, and intentionally retaining dense old-forest patches as refuges. Within those refuges, managers could leave dead wood in place, allow some natural disorder and prioritise connectivity over the highest possible timber output.

For people living close to these forests, coastal martens may provide an ecological signal. When this sensitive carnivore continues to use a woodland patch, the forest has generally retained substantial ecological integrity. Even without spotting one, birdwatchers, walkers and local communities can view the animal as an indicator of forest health.

The coastal marten’s reappearance in Six Rivers remains a fragile and unfinished story. A population of roughly one hundred animals is far from secure. Even so, it demonstrates that a mammal once nearing disappearance can, at least for now, reoccupy part of its ancestral range where there is sufficient structural complexity, surviving old growth and room to adapt.