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Criterion 3 Indicator 17
Area and Percent of Forest Land with Diminished Biological Components,Indicative of Changes in Fundamental Ecological Process and/or Ecological Continuity
Timber harvesting and other economic uses remove wood and other materials from forests. The wood and other materials are ecosystem building blocks that would otherwise be used by plants and animals in the forest. Many forest species depend on specific structural or biological forest components.
Bunnell, et. al., (1997) identified several stand level components that could be significantly reduced by timber harvesting, including large trees, snags, downed wood, shrubs, hardwoods, and riparian areas. The loss of key components could represent a reduction of the forest ecosystem’s capability to sustain wildlife and other values. A species by species conservation approach, like the Endangered Species Act, concentrates on the few most endangered species, and may not be the most efficient way to maintain high levels of ecological diversity.
In forest ecosystems, trees die from many causes including fire, disease, wind damage, and competition from other trees. Many silvicultural techniques, such as commercial thinning and timber salvage, are designed to maximize timber production by capturing natural forest mortality and converting it into economic return. However, these techniques can reduce the amount of coarse woody debris in a stand. Snags are also removed from the forest because they present a safety hazard for forest workers, can be a source of forest fires if they are struck by lightning, and can spread forest fires like torches.
Other silvicultural techniques, such as site preparation, treeplanting, and chemical release, are designed to get commercial species of trees growing on the site as quickly as possible. These techniques maximize growth rates for the desired trees and reduce the length of time that the stand is open and dominated by shrubs. Since hardwood trees are less valuable commercially than conifers, these silvicultural treatments favor conifers. Timber rotation ages that are the most economically efficient are too short for large trees and old-growth characteristics to develop in the stands.
Downed wood — Coarse woody debris (CWD) is defined as standing dead trees, fallen logs, dead roots, and fallen branches. This woody debris is a very important source of nutrients, and a fundamental building block of forest soils. Large logs decay slowly and may remain on the forest floor for many years, even centuries, providing nutrients to other plants and animals. An old-growth forest can have up to 20 percent of its organic matter in CWD. As large logs decay they act like a sponge absorbing water, and play an important role in moisture stability. During droughts CWD can act as a moisture reservoir, holding and releasing large quantities of water.
Both fungi and bacteria colonize CWD, and these microorganisms in turn provide food and habitat for a variety of insects and animals. Although there is not a proven obligatory relationship between CWD and mycorrhizal fungi, some researchers hypothesize that there is such a relationship, and that CWD plays an even more significant role in tree nutrition and forest food chains than already recognized.
Snags — In most forest types, about 25 percent of all vertebrate species use cavities in dead trees for nesting, foraging, or reproduction (Bunnell, 1991). In Oregon, that number includes 62 eastside species and 54 westside species (Bunnell, 1997). Twenty-two of the species that use snags in Oregon are considered sensitive, threatened, or endangered by the Oregon Department of Fish and Wildlife.
Large trees — Some species, like lichens, are slow to colonize and grow in a stand and are only associated with large trees. Some cavity-nesters require large cavities and therefore large trees. Large trees have other unique characteristics that make them important for wildlife, such as large limbs that support nesting structures and deeply furrowed bark that provides overwintering habitat for insects. Seven species that use large, live trees in Oregon are considered sensitive, threatened, or endangered by the Oregon Department of Fish and Wildlife.
Shrubs — Shrubs are an integral part of the forest ecosystem. Bunnell, et. al., (1997) lists their beneficial roles as including incorporation of micro/macro nutrients, alteration of soil properties, reduction of soil erosion, disruption of insect pathways, protection of seedlings, provision of wildlife browse and habitat, and contribution to riparian systems. Many bird species, especially neotropical migrant birds, nest in shrubs.
Hardwoods — Many species use or prefer deciduous trees for foraging, nesting, denning, or cover. Hardwoods produce large seed crops that are eaten by many wildlife species. The trees generally decay more easily than conifers, providing opportunities for cavity excavators. Hardwoods also shed their leaves each fall, providing habitat for litter dwellers on the forest floor, and thereby increasing the food supply for insect-eating birds and animals. Studies have found a high correlation between hardwoods and species richness. Bunnell, et. al., (1997) lists 41 eastside wildlife species and 51 westside wildlife species that have strong associations with hardwoods.
Riparian areas — Riparian areas, which are the moist areas next to streams, are among the most productive areas for wildlife and are used by many different species for a wide variety of purposes. Bunnell, et. al., (1997) lists 114 eastside species and 119 westside species that use riparian areas at some time. Riparian vegetation also provides a number of important functions for stream development and fish habitat. It provides nutrients to streams from litter fall, root mass for stream bank stability, shade to control water temperature, and large woody debris for stream channel development.

Can This Indicator Be Quantified
Not at this time.
The data needed for this indicator has not been compiled into a usable format. The U.S. Forest Service Pacific Northwest Research Station is analyzing plot-level data collected on about 11,000 field plots from regional forest inventories that span all land ownerships in Oregon and Washington. The data was collected by the U.S. Forest Service, BLM, and Forest Inventory and Analysis project. Data on snags, fallen trees, and large live trees is being summarized by habitat types and successional stages, to describe the current amounts and characteristics of "decadence" in forest ecosystems across the region. The summaries will be included in a chapter, tentatively titled "Legacies of Forest Disturbance Processes," within the Species Habitat Project book. The book is a collaborative effort led by the Oregon and Washington Departments of Fish and Wildlife.

Some studies suggest that the silvicultural methods used to maximize fiber production and economic returns have reduced the number of non-timber biological components such as snags (Ohmann, et. al., 1994). However, data from forest inventories is not yet compiled into a format that can be used to indicate if the numbers of large trees, snags, downed wood, shrubs, and hardwoods are declining. Riparian areas have not been systematically described or inventoried, so changes in their condition would be difficult to examine

Data Source and Availability

Reliability of Data


Recommended Action for Data Collection
The databases from the regional forest inventories are not readily available in a form that can be used to calculate the abundance of hardwoods, snags, down logs, and large trees. The many federal and regional ground-based sampling systems need to be combined into a single database that can be used by many organizations to answer questions about the abundance of fine-scale forest features and habitat types.
Standard protocols need to be developed for classifying shrubs and riparian vegetation before these features can be inventoried.

Riparian area — Riparian area is defined as the ground along a water of the state where the vegetation and micro-climate are influenced by year-round or seasonal water, associated high water tables, and soils that exhibit some wetness characteristics.

Selected References
Bunnell, F. L., and D. K. Daust, L. L. Kremsater, R. McCann. 1991. Managing for biodiversity in forested ecosystems. Report to the Forest Sector of the Old-growth Strategy. Centre for Applied Conservation Biology, University of British Columbia. Vancouver, BC.
Bunnell, Fred, and Laurie Kremsater, Ralph Wells. 1997. Likely consequences of forest management on terrestrial, forest-dwelling vertebrates in Oregon. Report M-7 of the Centre for Applied Conservation Biology, University of British Columbia. Vancouver, BC.
Ohmann, Janet L., and William C. McComb, Abdel Azim Zumrawi. Snag abundance for primary cavity-nesting birds on nonfederal forest lands in Oregon and Washington. Wildlife Society Bulletin 22:607-620.