Glossary of Terms

Basal Area: 

Basal area is the cross-sectional area of trees at breast height (4.5 ft above ground). It is a common way to describe stand density of forests, usually expressed per acre.


Our Board is a collaborative of activists who were traditionally adversaries in the Western Oregon forestry controversies. Our goal is to collect a large network of Friends with a similarly wide range of outlooks who support our principles and our approach, and to develop broadly supported policy on how O&C Lands should be managed in Western Oregon.

The name “Forest Bridges” and our logo are intended to symbolize this coming together to bring to life a shared vision of long-term forest habitat health, for the benefit of all.

Dry, Moist and Transitional forests:

Dry Forests: Dry forests are generally found in Southwestern Oregon, with the exception of the far southwestern corner. In a dry forest, the forest floor tends to dry out completely in the summer, and frequent fires, every 5-15 years were a natural occurrence in precolonial times. These low-intensity ground fires reduce the presence of dry fuels. Without programs like this for fuel reduction, these fuels increase and create the heat that promotes fires that burn hot enough to destroy whole forests, including green live trees and forest soils

Moist Forests: Moist forests are found more in Northwest Oregon (except in the far northwest corner) and along the Oregon Coast Range. In moist forests, the precipitation is higher, understory vegetation is denser, the forest floor is heavily shaded and remains moist or wet in typical summer conditions. Fires in these forests only happen under extremely dry conditions (every 100-300 years) and are much less frequent but more extreme, due to higher fuel loads. Moist forests require metered variable retention harvests to set the forest up for an array of habitat types aligned with the precolonial condition, as well as certain fuel mitigation.

Transitional Forests: 

These forests are intermediate in geographic location, moisture, directions of slope facing (aspect) and other factors between the dry and moist forests. They have a broad range of habitat types in close proximity. They behave like dry forests in severe fire conditions and many areas need thinning and fuel reduction treatments to mimic a less frequent lower severity fire pattern than moist forests, measured in decades rather than years. Stands facing north or east are more likely appropriate for moist forest treatment, while those facing west and south usually require a dry forest treatment approach, based on site specific characteristics, including moisture, lighting patterns, etc. These transitional areas will require special management planning, determined by professional agency personnel who evaluate each site, to mimic historical habitat patterns in the absence of fire.  

Early seral forests and Pre-forests:

Early Seral are the earliest stage forests after a burn or variable retention harvest that contain conifers and other tree seedlings from a combination of natural and planted trees (see paragraph below). Pre-forests are defined here as early seral forests that are generally devoid of conifer or other tree seedlings, often the result of stand replacement fires or areas that did not have trees in recent or past history. Early seral habitats are unique and necessary habitats in all forest types across the O&C Lands, and require regular renewal, as closing canopies of trees suppress the early seral vegetation.

Swanson et al. (2011) describe naturally regenerating early seral and pre-forest communities that are unique in being co-dominated by a wide range of plant forms including broadleaf shrubs and vines, hardwood and coniferous trees, herbs and grasses, and are accompanied by the living and dead woody legacies of the pre-disturbance stand. Source: 

Pre-forest conditions arise from stand replacement fire effects of 90+ percent mortality – absent reforestation – where the forest is devoid of tree species regenerating from seed sources or replanting.

Fire Resistance:

The ability of a forest to withstand a fire entering and survive. A fire-resistant forest has characteristics that make crown fires unlikely and allow the forest to survive surface fire without significant tree mortality in the main canopy. 

Ecological restoration:

Ecological restoration is the process of “assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed” (Gann et al. 2019). It involves uniting scientific inquiry with on-the-ground practice while understanding that landscapes are dynamic and ever-changing. The Society for Ecological Restoration (SER) has developed nine attributes that are helpful for guiding restoration objectives (SER 2004):

  1. Plant assemblages should resemble historical reference conditions.
  2. Species should be mostly or all native within a reasonable period of historical time.
  3. A restored ecosystem should include all main functional groups of plants. 
  4. It should be able to reproduce new cohorts. 
  5. It should be on a historically appropriate trajectory of growth and change. 
  6. It should be integrated into a larger functioning landscape matrix. 
  7. It should be secured from “threats” originating from off site. 
  8. It should be resilient (e.g., able to return to a pre-disturbance state). 
  9. It should be self-sustaining within normal ranges of fluctuation. 

Fire exclusion and canopy closure:

Dry mixed-conifer forests in southwestern Oregon have been altered by 200 years of colonial settlement and fire suppression that have resulted in ahistorical stand densification, including of shade-tolerant species like white fir and grand fir (Sensenig et al. 2013). Outcomes are at least three-fold (Franklin & Johnson 2012): 

  1. Many fewer old, fire-resistant trees are on the landscape. 
  2. Drought conditions are exacerbated with too many trees per acre competing for water.
  3. Forests are now highly susceptible to stand-replacing wildfire and insect epidemics due to elevated fuel levels. 

Fire Resilience:

The measure of a forest’s ability to regenerate and adapt after a fire passes through. 


Forest Bridges uses the term “historical” to describe forest types, patterns, densities, and disturbance regimes throughout our work. This usually refers to landscape patterns that existed before European colonization (in the 18th century) and widespread fire suppression (in the early 20th century). 

Large legacy trees:

Old-growth trees are the “structural backbone” of forest ecosystems and should be prioritized for protection and restoration wherever they occur–especially in dry forests (Hagmann et al. 2013). This generally applies to trees older than 150 years, but removal of large trees may be considered in the rare circumstances that ecological goals may be better accomplished. For example, large grand firs may be harvested because they could pose a fire risk to adjacent, favored species like ponderosa pine and oak (in addition to being overrepresented in most dry forest stands because of fire suppression). Similarly, overstocked even-aged stands with continuous and large live crowns may need to be thinned to prevent drought stress, fire risk, and bark beetle infestations (North et al. 2009). In this way, thinning decisions are made according to broad, landscape-scale resilience and ecological function rather than imposed by strict diameter limits. 

Multiaged management:

Multiaged management is the maintenance of forest stands in two or more different age classes as an alternative to even-aged silviculture. It represents an effort to emulate more accurately the complexity and heterogeneity found in unmanaged stands while also providing timber products and sustaining thriving wildlife habitats. Multiaged stands also may be an adaptive management strategy for a changing climate and disturbance regimes because resilience is conferred through more complex forest systems. 

Wildfires, Megafires and Gigafires:

Western Oregon forests are overloaded with fuels after more than 100 years of focus on putting fires out and Smokey Bear, who gained notoriety after being rescued from a 1944 wildfire. Wildfires can be small, or they can burn very hot and become very large and damaging, measured in tens of thousands of acres across BLM and private lands together where the typical ownership size in the O&C Lands checkerboard is 640 acres. “Megafires” is a new term applying to fires, or complexes of fires that converge, and the total exceeds 100,000 acres -- much more common today than historically. “Gigafires” is also a new term to describe wildfires that exceed 1 million acres. All of these fires NOT ONLY cause extreme economic damage, but soil is irreparably damaged, habitats are destroyed, excessive carbon is released into the atmosphere, and water quality, lives, and property are placed at risk.

Policy to put all fires out started around 1915 after the great burns of 1910 which burned 3 million acres and 87 lives were lost. Smokey Bear got his start in 1944 after a bear cub was rescued from a wildfire and nursed back to health, amid a lot of publicity.

O&C lands (small “l”): 

This term refers to the Oregon and California Railroad lands. The O&C lands include about 2.6 million acres. These lands are located across the 18 Western Oregon counties. Originally, these lands were deeded as private lands to railroad companies in 1866 to encourage the development of a rail line across Oregon and to encourage settlement. Portions of land were sold to settlers to raise money, the railroads were built, but eventually, the lands were revested to the Federal Government by Congress with the intent to privatize. Under the O&C Act of 1937, the BLM was tasked with managing the lands under what were considered progressive, conservation-oriented, and sustained yield timber harvest practices, with a portion of revenues going to the 18 counties of Western Oregon as O&C County Receipts. 

O&C Lands (With a capital “L”): 

This term, as used by Forest Bridges, refers to approximately 3 million acres of federally managed lands that comprise: the Oregon and California Railroad (O&C) lands, managed by both the BLM and US Forest service, as well as Public Domain and Coos Bay Wagon Road lands managed by the BLM. The O&C lands managed by the US Forest Service are referred to as “controverted lands,” and are governed by somewhat different overlays of regulations. The Public Domain lands are guided by a different funding formula than the O&C Act lands.

O&C Act of 1937: 

This is a Federal Law, also described in the Frequently Asked Questions. The full title of the Act is, “The revested Oregon and California Railroad and reconveyed Coos bay Wagon Road grant lands situated in the State of Oregon.”

Principles of Agreement (PoAs):

The PoA are a compilation of collaboratively supported concepts intended to comprehensively highlight and address a full suite of major issues faced by the managing agencies of the O&C Lands. With comprehensive resolution, issues solved in one respect will be less likely to re-emerge in another.

Relative Density:

Relative density indicates how fully the trees occupy a site. It is a measure of the number and average size of trees growing in a stand compared to the maximum possible that the site could support (a biological limitation).

Sustainability Funds:

(See Frequently asked Question, “Where will funds needed to support Forest Bridges’ new management programs come from?”)

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