Coastal Marten Returns to Six Rivers Forests

For many years, biologists believed this small carnivore had shifted from being scarce to almost legendary. Fresh field research in the Six Rivers region now indicates that the coastal marten has survived and is adapting its relationship with a landscape affected by logging, fire and climate change.

The return of a mammal once presumed lost

Old-growth forests along the Pacific coast of northern California and southern Oregon once regularly supported coastal martens. Trappers heavily pursued the species for its thick, reddish-brown coat. Meanwhile, extensive logging removed the intricate woodland structure needed for hunting, resting and rearing young.

By the end of the 20th century, records of sightings had become extremely rare. Across much of its former range, specialists thought the animal was effectively absent. In 1996, however, one marten was discovered in an isolated forest in northern California. That single animal raised years of uncertainty: were others still present, or was it the final remnant of a disappearing species?

These questions led scientists to develop more organised survey work. The most recent study ran from August to November 2022 in the Six Rivers region, a nearly 400-square-kilometre patchwork of steep ridges, deep ravines and surviving 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” – tools that gather fur without injuring wildlife – as well as 135 motion-activated cameras. Using these non-invasive methods, they could distinguish between animals and estimate the number of martens travelling through the landscape.

Altogether, the team recorded 46 individual martens: 28 males and 18 females. Detecting them was difficult, with an average of only one marten appearing per 3.6 square kilometres. Even so, the data gave statisticians sufficient evidence to produce reliable population models and the first robust density estimates for this coastal forest area.

Where the remaining coastal martens live

After analysing the figures, the researchers estimated that around 111 martens occupy the surveyed landscape. Although that may initially seem substantial, the animals are confined to only a small proportion of the region’s surviving old-growth woodland.

Their territory lies near the Pacific, although the sea offers little protection. Marten density in this coastal area resembles that recorded in mountain regions including the Sierra Nevada and British Columbia. This pattern suggests a common challenge: fragmented habitat.

Six Rivers has rugged ground, formed of ridges, canyons and discontinuous blocks of forest. Roads built for logging and historic clearcuts have divided the woodland into isolated islands. Martens must also share these broken forests with other medium-sized carnivores.

Grey foxes, bobcats and fishers range across the same hillsides, pursuing comparable prey and possibly competing 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 concentrated in one uniform habitat. They appeared throughout the study area, although two locations were particularly prominent:

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

At Red Mountain’s higher ridges, long-lasting snow and tall trees provide protected feeding habitat. Snow persisting into spring can limit some competitors while supporting prey adapted to colder microclimates.

The ravines around Blue Creek offer equally favourable, though very different, conditions. Cool and damp air moves along the creek bottoms. Layers of dense vegetation, including moss-covered logs and mixed shrub thickets, create a complex three-dimensional environment. This gives martens cover from larger predators while supporting plentiful small mammals and birds.

Forest structure: the essential lifeline

Both ridge and ravine sites repeatedly contain the same physical forest characteristics 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 several purposes simultaneously. Large trees and a closed canopy provide shade, consistent temperatures and cavities for nesting. Hollow logs can function as dens. Dense piles of fallen branches and decaying timber shelter rodents, birds and invertebrates that martens prey upon.

Younger forests, especially those that regenerate after broad, even-aged clearcuts, commonly lack such qualities for many decades. They may appear green when viewed from above, but to a marten seeking prey and shelter they are simplified and sparse.

How altitude changes coastal marten habitat

The research highlights an important variation: identical habitat features do not have the same effect at every elevation.

At lower elevations, martens favour gullies where moisture levels and plant diversity are greatest. Ferns, shrubs, saplings and fallen logs accumulate there, forming a maze for predator and prey alike.

At higher elevations, they are more associated with wooded ridges where snow remains longer and historical human pressure has been lower. In these settings, the animals encounter fewer competing predators and benefit from mature conifers mixed with snags and broken branches.

Why old-growth forests remain crucial

This two-part habitat pattern has one underlying theme: martens avoid open and simplified environments. They generally steer clear of extensive clearings, plantations planted in regular rows and very young woodland with little structural variety.

This dependence leaves them especially exposed to industrial forestry geared towards quickly growing, even-aged timber. Longer and hotter fire seasons, harsher droughts and climate-change-related tree disease further reduce the old-growth areas they require, diminishing both their extent and their quality.

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

The scientists found that marten density responds to vegetation and topography together. Steep ground, varied canopy heights and irregular forest floors appear more significant than simply counting the shrubs in the understorey. Structural complexity matters more than uniform green cover.

Shared responsibility in a fragmented landscape

The species’ future cannot be secured by one group alone in a region divided among logging interests, tribal lands, protected sites and private ownership. The study strongly supports collaborative management.

Public land bodies oversee major forest areas and establish rules for timber harvesting and fire management. Indigenous communities possess extensive knowledge of traditional burning and resource practices that shaped these ecosystems long before industrial logging. Private owners manage important foothill forests and corridors linking isolated marten populations.

Collaborative measures could include:

• Keeping large old trees, snags and fallen logs during timber work
• Identifying and protecting known marten hotspots on ridges and in ravines
• Creating fuel treatments that lower fire danger without removing understorey complexity
• Preserving wooded corridors between old-growth patches
• Financing continued camera and hair-sample surveys to monitor population change

Key concepts behind the research

This study relies on several technical ideas. “Habitat fragmentation” refers to continuous forest being divided into smaller islands by roads, clearcuts or development. Species such as the coastal marten must then cross exposed and hazardous gaps to travel between remaining refuges.

“Structural complexity” describes the physical arrangement of a forest, with tall trees, young saplings, vines, snags, fallen trunks and burrows layered together. For a small predator, this maze provides cover as well as feeding opportunities. A woodland of regularly spaced, similarly aged trees with no dead wood may look orderly to people, but it is barren from a marten’s perspective.

What this could mean for future forests

If current patterns persist, climate change is likely to make large fires more frequent across the Pacific coastal region. Without thoughtful management, post-fire logging and rapid replanting in uniform blocks may further remove the forest structures on which martens depend.

One possible response would be “climate-smart” forestry: thinning selected places to reduce fuel loads, using controlled burns where conditions allow, and intentionally retaining dense, mature woodland patches as refuges. Within those refuges, managers could leave dead timber on the forest floor, accept some natural untidiness and prioritise connectivity over the highest possible timber output.

For nearby residents, coastal martens may provide an ecological signal. When this sensitive carnivore still occupies a woodland patch, the forest will usually have retained considerable ecological integrity. Birdwatchers, walkers and local communities can regard the species as an indicator of forest condition, even if they never see one.

The coastal marten’s return to Six Rivers remains uncertain and unfinished. A population of roughly one hundred animals is far from secure. Nevertheless, it demonstrates that a mammal once nearing disappearance can, at least for now, reclaim part of its ancestral range where structural complexity, old-growth refuges and room to adapt remain.