Biomass Density

Maintain high volume and distribution of woody biomass: Above, Below and On the ground
Trees are the best natural mechanism for sequestering atmospheric carbon dioxide. It’s not just the standing live trees that are important carbon stores. As above, so below: large trees require large root networks deep underground to support their continued growth. Standing dead timber and large woody debris lying on the ground fills out the landscape’s optimal biomass potential, providing wildlife habitat, soil conditioning and hydrological buffering.

The biomass density in most forests is well below their carrying capacity. Measured in board feet per acre, we are accustomed to seeing 10,000 to 40,000 bf/acre, whereas the land can (and historically did) support more than double that. In the Pacific coastal rainforest, we can expect more than 100,000 bf/acre if we are intentionally creating old-growth characteristic.

Gargantuan California Redwoods

Gargantuan California Redwoods - maximum biomass density currently on the planet.

Few sites on the planet have a carrying capacity like the North American Pacific coastal rain forest, stretching from northern California to southern Alaska. Quantifying a forest site's carrying capacity allows us to gauge how close we are to optimizing biomass density.

This stand probably exceeds 200,000 bf/acre.

Dense Old Growth Forest in Western WA State.

Pacific NW conifer rainforest - maximum biomass density in western WA State.

Extraordinary combination of large trees at tight spacing, indicating a very high quality site.

This stand probably exceeds 100,000 bf/acre.

Photo by Joe Jeffers circa 1900, Courtesy of Susan Parish Collection of Photography - Jeffers Studio Collection:

Mature Doug fir stand in Columbia River Gorge, OR

Nearly pure stand of mature, 80-plus year-old Douglas Fir above Wahkeena Falls in the Columbia River Gorge, OR.

This is a fully optimized site for both timber quality and quantity - a "perfect" grove of Douglas Fir, appropriately spaced for its mature age class. This is what an industrial monoculture would look like if it was progressively thinned up to this age. Note the fire scars at the base of the tree trunks: the wide tree spacing and a lack of low branches (ladder fuels), allowed this stand to survive a recent wildfire that quickly passed through the understory.

This stand is estimated to be more than 60,000 bf/acre.

Heavy Thinning

A heavily thinned stand, showing trees widely spaced and sunlight reaching the forest floor.

Aggressive thinning will lead to fewer, larger trees in the long-term. The years immediately following a thinning operation, it might look like too much was cut, but soon the canopy will close again as the trees expand their crowns.

This stand may be only 20,000 bf/acre, but could exceed 40,000 bf/acre in a few decades, thanks to the timely thinning.

Mechanical Harvesting

Commercial thinning with a mechanical harvester.

At about 20-25 years old (for a Pacific NW Doug fir forest), a thinning operation that results in some marketable timber will greatly improve the growth rate of the remaining trees.

Needs Thinning

This plantation needs to be thinned, in this critical time frame between 20 and 40 years old.

This is a typical scenario for a re-planted forest that is left un-managed. These trees are not differentiating and will tend to shut down together, creating a "dog-hair" thicket with little potential for old-growth characteristic.

WTF Riparian Zone at 12 years - west end.

12 year-old mixed species plantation in former cow pasture - Oakville, WA.

At 12 years old, this plantation has already closed its canopy and is entering the "stem exclusion" phase. Originally planted at 10 feet on center, or approx. 450 trees per acre, this site should now be thinned to approx. half the original density to optimize the growth of the remaining trees. Indeed, this young forest is already self-thinning: the aggressive red alders are shading out the slower-growing conifers. This is the key to growing big trees quickly: timely thinning in the early years to keep the best trees on a steady growth trajectory.

35 year-old redwood in Willamette Valley, OR.

How fast can it grow? Check out this 35 year-old Coastal Redwood log in the Willamette Valley, OR. You can even count the rings in the photo!

It doesn't have to take forever to grow big trees. Redwoods and Sequoias are famous for explosive growth under the right conditions. Although this is too fast for optimum timber quality, it is exceptionally good for carbon sequestration.

Tree Growth Curve

Tree Growth Curve

Even so-called "shade-tolerant" tree species prefer plenty of sunshine, and none perform well under heavy competition. For maximum biomass growth, we need to thin trees on a periodic basis to keep them within the moderate to no competition zone.

Graph courtesy of Science Findings publication #147: USDA Pacific NW Research Station - Portland OR. PDF here


As above, so below: large trees require a large network of roots underground to support continued growth.

The living biomass of tree roots closely parallels what appears above the ground. Competition above limits available sunlight, while competition below limits available nutrients and water. Dead woody biomass deep in the soil increases soil tilth, microbial and fungal activity, nutrient stores and water retention. Optimizing the live biomass underground, by growing big trees above ground, ensures an endless supply of dead material over time.

Old Growth Western Red Cedar Stump at Clearwater Creek - Naselle, WA

Old-growth Western Red Cedar stump at Clearwater Creek - Naselle, WA.

Example of a "short snag" or a "high stump" that provides long-lasting woody debris in the landscape. This cedar tree may have been cut more than a century ago. Old stumps are a good indicator of the tree size potential for the site - what a wild forest manager should be aiming for.

"">Massive large woody debris on the forest floor next to

Massive woody debris on the forest floor next to the "Kalaloch Cedar" in Olympic National Park.

In an un-managed old-growth forest, the accumulation of large, downed trees creates a network of wooden "topography" several feet thick. Once this layer decomposes or is burned in an intensively managed forest, it will take many centuries to re-attain this volume and density of on-ground biomass, but only if the trees are allowed to grow large and remain where they fall. This is one Wild Forestry attribute that cannot be maintained on production-oriented landscapes.

Clearwater Creek SE corner with LWD and big snag

Big stumps and snags at Clearwater Creek - Naselle, WA.

A site rich with complexity. Live biomass consists of mature forest in the background and six year-old natural regeneration in the foreground. Dead biomass includes numerous second-growth stumps and big, gnarly snags.

Big timber on the Eastern Hill at Clearwater Creek

Large woody debris on the trail at Clearwater Creek - Naselle, WA.

Trees are constantly falling down in this wind-dominated coastal site (Willapa Bay). Generally they cannot be recovered economically outside of a normal harvest cycle, so they become the "large woody debris" essential for optimum ecosystem function. In this case, the trees fell across the trail, so they were chain-sawed into chunks and rolled out of the way.

Big logs on the ground in South Side Unit #4

Logging and storm debris on the forest floor at Clearwater Creek - Naselle, WA.

Excessive amount of large woody debris due to un-treated logging slash coincident with sustained, hurricane-force wind event, 6 years prior. Not a good scenario for commercial timber production or for arid, fire-prone sites, but this higher-than-normal on-ground biomass is a big plus for Wild Forest Management: nutrient and water buffering, wildlife habitat, seedling protection (from browsing elk), etc.

Remnant forest in South Side unit #4, between first two road junctions, showing

Small woody debris at Clearwater Creek - Naselle, WA.

This site was selectively harvested at the same time that a hurricane force wind event ravaged the forest, resulting in exceptional "biomass loading" - a lot of wood on the ground. Six years after the event, this stand was "cleaned up", and the resulting carpet of short-term woody debris will nourish and protect the soil for decades. Many of the stems in this photo are missing their tops (blown off in the storm), but they were retained as standing dead timber for wildlife.

Gargantuan California Redwoods thumbnail
Dense Old Growth Forest in Western WA State. thumbnail
Mature Doug fir stand in Columbia River Gorge, OR thumbnail
Heavy Thinning thumbnail
Mechanical Harvesting thumbnail
Needs Thinning thumbnail
WTF Riparian Zone at 12 years - west end. thumbnail
35 year-old redwood in Willamette Valley, OR. thumbnail
Tree Growth Curve thumbnail
tree_with_roots thumbnail
Old Growth Western Red Cedar Stump at Clearwater Creek - Naselle, WA thumbnail
Massive large woody debris on the forest floor next to
Clearwater Creek SE corner with LWD and big snag thumbnail
Big timber on the Eastern Hill at Clearwater Creek thumbnail
Big logs on the ground in South Side Unit #4 thumbnail
Remnant forest in South Side unit #4, between first two road junctions, showing