Choice of Stand Types and Management Units
The Blodgett Forest is broken into stand types that generally represent areas of homogenous overstory species composition and stocking. The stand types were developed from 1:12,000 color aerial photographs, type designations made by field crews along transects spaced 330 feet apart, and extensive field reconnaissance. There are 79 stand types that are represented in the harvest scheduling analysis.
Management units were constructed by engineers on the forest staff who used slope class information built from a 7 meter DEM that was developed from recent and historic aerial photos, existing and proposed road locations, stream information, logging patterns used in previous entries, and field reconnaissance. The boundaries of these units were designed to ensure that solutions from the harvest scheduling simulation could be feasibly logged and are intended to provide a framework for the development of logging plans. There are 103 management units.
The identification of management units led to a classification of areas that have special logging issues associated with them. Forest staff decided that some units could not be thinned in the first entry because of operability issues. The staff also identified units that would be more expensive to log because artificial anchors would be required.
In riparian stands that flank the large perennial streams, prescriptions were developed that emphasized either conifer or hardwood management. Approximately 50% of perennial stream length is planned to be in stands dominated by hardwoods and 50% in stands dominated by conifers with no more than approximately 1000' of stream length in a given type. Stands on opposite sides of a stream may be different types. To accommodate these prescriptions, the riparian stands were divided into smaller units so that each 1000' segment could be represented in the harvest schedule.
The stand types (both the upland and riparian areas) were intersected with the management units to create subunits, so that the stand differences within the management units could be recognized in the yield projections that were developed for the harvest scheduling analysis. This created the base set of 200 harvest scheduling units.
The upland forest, which lies above the break in slope beyond the influence of past floodwaters, occupies about ninety percent of the Blodgett Tract. Eighty-six percent of the upland forest area supports mixed Douglas-fir and hemlock forests that are over 60 years old.
Fifteen percent of the forest greater than 50 years old has been designated as unsuitable for thinning. These stands will be clearcut harvested.
Background on thinning prescriptions
Using knowledge gained from thinning studies in COPE, the silviculture subcommittee
of the forest planning team designed a set of thinning prescriptions to accelerate
the development of the thinnable forest towards the large tree goal. These
prescriptions were modeled in ORGANON using a sample set of stand types that
represented the range of existing site and stocking characteristics. The results
were presented to the planning team and feedback from team members was used
to modify the prescriptions. This process was repeated several times and after
43 prescriptions were modeled we were able to draw the following conclusions:
1. There was a significant amount of variability in the response of different stand types to different treatment regimes, which convinced us that modeling these types of treatments with stand level inventory data was very important.
2. In general, the treatment regimes for existing stands with the lower basal area or RDI thinning targets in the first thinning entry met the large tree goal earlier than other treatment regimes and favored the development of understory conifers which were identified as important habitat features for some wildlife species. These treatment regimes also created the greatest threat for catastrophic windthrow from severe winter and spring storms, and produced the lowest total volume.
3. The treatment regimes that involved no thinning, or relatively light thinnings produced the highest total volume over a 100 year planning period, but took significantly longer to reach the large tree target and did not favor understory growth.
4. It took longer to reach the large tree target when thinning proportionally throughout the diameter classes than it did when thinning from below.
5. Although many different treatment regimes were suggested and modeled, the results for any given stand followed only a few different general trajectories.
Discussions that weighed the benefits of maintaining high levels of growing stock through light thinnings (which produced more volume over time with less windthrow risk) against moving to lower levels using heavy thinnings (which produced big trees faster and potentially more complex understories) led to a classification of the 200 harvest scheduling units into high and low windthrow risk. “High” risk units were those with slopes exposed to the south/ southwesterly winter storm winds and that had never been thinned before, as well as units on more moderate exposures that are adjacent to clearcuts that could channel winds into them.
It was then decided that on the areas with high windthrow risk and stands with existing heavy basal areas, not more than 40% of the basal area will be removed in the first entry, and the residual basal area will always be near or above 150 ft2. The subsequent entry will occur after about 15 years and may go down to a minimum basal area target of 120ft2. Areas with lower windthrow risk will have heavier thinnings in the first entry (down to 110-120 ft2 residual basal area), with an additional entry after 15 years to 120 ft 2.
It was also decided that we would thin from below even though this would create stands that are more structurally uniform because we can meet our big tree goal faster than thinning proportionally through the diameter classes. Understory structure will be provided by the shrub and hemlock seedling layer that develops between thinning entries. (See figure 6 on page 34.)
The future stands were modeled the same way as the existing stands, except that a pre-commercial thinning from below to an SDI of 110 occurs two years after crown closure (which happens when the stand is about 14 years old).
Recognizing the role of disturbance in riparian forest from studies in COPE, the silviculture subcommittee considered three different kinds of riparian situations. Each will have a different management regime that is based on the characteristics of the stream. The terms large, medium, small, perennial, and intermittent stream are as defined in ODF Forest Practice Rules Chapter 629, Division 640 and maps created by ODF from these regulations.
Figure 5. Stream class map.
1. Large and medium perennial streams (size L and M)
These streams have specific associated riparian stands mapped in the plan.
Approximately 50% of these stands are to be hardwood dominated; approximately
50% of these stands are to be conifer dominated.
2. Small perennial streams and intermittent streams (size
S)
The forests around these streams are managed at the same time as the surrounding
units. Small perennial and intermittent streams can be subdivided into two
categories:
2a. Not prone to land slides and debris flows
that can deliver significant amounts of gravel
and wood to fish-bearing streams.
2b. Prone to land slides and debris flows that
can deliver significant amounts of gravel and
wood to fish-bearing streams.
The following characteristics are considered
indicative of unstable conditions:
•Any
active landslide
•Uniform or planar
slopes steeper than 80%
•Headwalls, concave
or convergent slopes steeper than 70%
•Valley inner
gorges with side-slopes steeper than 60%
•Any marginally
stable site identified as high risk by the ODF geotechnical specialists
Benda and Sias (1998) provide guidance on predicting conditions that will lead to debris flows entering fish-bearing streams.
Large and medium perennial streams
The silvicultural approach used in this riparian type is the same as in the
upland stands. An active approach is taken to regeneration and density management.
Regeneration is by clearcut except for trees left to meet dead wood goals
(see below). Through density management, large trees, which contribute to
structural diversity, will develop earlier.
1. Alder stands will be planted with at least 500 seedlings per acre (see Ahrens et al. 1992). One or two pre-commercial thinnings, depending on stocking level (large amounts of natural regeneration require two thinnings), will be made before age 20 to reduce density to 180 stems per acre. The first thinning should occur between age 8 and 12.
2. Conifers will be managed as in the upland prescription. Hemlock, because of its low resistance to wood rotting fungi and the negative effect it has on understory vegetation, is the least desirable species to plant and maintain. Douglas-fir, western redcedar and Sitka spruce may be planted here.
3. Mixing conifers and hardwoods (from natural regeneration of one group into plantations of the other) has habitat benefits for some organisms and so may be practiced; however, success depends on paying careful attention to the competitive balance among species.
4. As in the upland stands, a riparian stand must attain and maintain a condition where the average diameter of the 20 largest trees per acre is equal to or greater than 30" for conifers and 16” for hardwoods for 20 years before a regeneration harvest can be made.
5. Trees that are leaning over the water or that are within 20 feet of bank-full-width should not be harvested (although these trees will also count toward meeting dead wood goals if left during a regeneration harvest). Thinning should be practiced to maintain rapid diameter growth. In this 20 foot zone, active regeneration should be practiced when stocking levels drop below 15% RDI. For purposes of bank stability, a large alder or cedar component is desirable in this zone in all stands. Logging machines should not enter this zone and logs passing over it must be fully suspended.
6. Six hundred cubic feet of conifer volume per 1000 feet of stream per decade in conifer stands (300 cubic feet of hardwoods in hardwood stands) will be dedicated to in-stream woody debris. This means that at the time of thinning and regeneration harvest, a proportion of the standing volume is allocated to woody debris. In a thinning, this material is felled toward the stream. In a regeneration harvest, this material is left standing until it falls by itself. Selection of leave trees should favor larger but not necessarily better timber quality trees of the more rot-resistant species. The remainder may be removed as logs.
7. To meet these goals, a survey of the stream must be done prior to each operation to determine how much wood has entered the stream and the near-stream (20') surface since the last entry through wind throw or other means. This can be deducted from the leave requirement. Leave requirements should be met as close to the stream as possible. To count in a dead wood survey, a piece of wood must (1) be at least 10 feet long, have a large end diameter of at least 10 inches in small streams and 14 inches in medium and large streams, and either be in the stream or have a major part of its length within 10 feet of the high water mark or (2) be a standing tree previously designated as a leave tree to meet dead wood requirements.
8. At some points in a rotation, the long-term average of 600 cubic feet/1000 feet/decade may not be met because the trees will be too small. Shortages at one point in a rotation will be made up at a later time.
Small perennial and intermittent streams
Management is the same as along large perennial streams except that (1) the
50/50 hardwood/conifer rule does not apply and (2) the dead wood goal is to
provide 150 cubic feet per 1000 feet per decade. No logging machines are allowed
in this zone (except during in-stream enhancement projects), and logs passing
over it must be fully suspended. Herbicide application rules will follow ODF
stream regulations.
1. Stable small perennial and intermittent streams
This is a 20 foot zone on either side of the stream. Trees may be harvested
in this zone, but shrub, herb and duff layers on the stream bank within this
zone must be protected during logging. Disturbance is permitted to enhance
tree regeneration. No logging machines are allowed in this zone and logs passing
over it must be fully suspended.
2. Unstable small perennial and intermittent streams that
can deliver significant amounts of gravel and wood to fish-bearing streams
This is a 20 foot zone on either side of a stream and extends from the location
of instability to the fish-bearing stream. The goal in this zone is to maintain
a high stocking level of larger conifer trees (24" plus) so that debris flows,
if they occur, will carry wood as well as sediment into the fish-bearing stream.
Periodic regeneration and thinning will be needed to maintain this stocking
of large trees (hemlock is not desirable). Thus, periodic regeneration harvests
in this zone are necessary. No more
There are no precedents for setting silvicultural goals pertaining to maintenance of dead wood levels in streams. The Blodgett Tract appears to have adequate logs and rootwad structure in the main stream channels. The guidelines in the Blodgett plan are a first approximation of a level of availability and provision for placement in streams to maintain wood at existing levels or higher.
There are several important works from which the following guidelines were derived. Murphy and Koski (1989) observed that 84% of the dead wood falling into Alaska streams came from within 33 feet of the bank. McDade (1987) observed the same relationship in first, second and third-order streams in Oregon, but with 73% coming from within 50 feet. Murphy and Koski (1989) also reported that it was the larger pieces that led to greater longevity in streams and more stable structures. Thus, it appears that the primary source of local dead wood is very close to the stream itself. Obviously, the additional wood from debris avalanches originates further away from the stream, but these events occur infrequently on the Blodgett Tract.
Levels of wood desirable are arguable. Whereas opinions vary as to whether there is ever enough, there are reports of levels found in old growth stands. We postulate that these represent the upper levels of historic conditions. Specifically, in a COPE study by Van Sickle and Gregory (1990) dead wood input was estimated at 1.5-15 pieces per 1000 feet per decade. Wood volume involved ranged from 17 to 235 ft3 per 1000 feet/decade, depending on probability of treefall in that reach of Cascades old-growth. Murphy and Koski (1989) observed a range of 44-137 total pieces of wood per 1000 feet in Alaska, with an average longevity of some 160 years, or 2-10 pieces per decade, about the center of the range reported by Van Sickle and Gregory (1990). Allowing for variation in study conditions, we assume that a reasonable input average from old growth would range around 300 ft3/1000 ft/decade of stream. To compensate for flood losses and inefficiency in placement, we determined that allocation of 600 ft3/1000 ft/decade would more than meet the dead wood needs relative to standards for old growth.
Managed Douglas-fir on site II ground will have a height of some 170 feet in 100 years and diameter of over 33” in stands being managed for mature forest features, with 20 trees/ac being in those size classes for about a fifth of their life spans. A stand with 240 square feet per acre would have the 20 large trees plus a greater number of smaller trees, and support some 14,000 ft3 /ac and average a mean annual increment of about 200 ft3 /ac (adapted from McArdle et al, 1961). Growth of such stands in stream buffers would require intensive management. However, a streamside stand 33 feet wide on each side would grow 3000 ft3 /decade. Dedication of 20 percent of this over a 100 year period for woody debris is therefore our calculation of the type of buffer management that will meet woody debris requirements.
Most of the above trees will fall toward the stream naturally because of the tendency to fall downhill (Hibbs and Sullivan, unpublished data). Thus, it is anticipated that the dead wood levels will be maintained. However, at the time of each entry to these stands for silvicultural treatment, an inventory of the stream protected by these adjacent stands will reveal the degree to which these trees are currently needed to augment supplies.
Hardwoods are a special case. Productivity and ultimate size are less than that of conifers. We set a target for hardwood areas that is 50% of the conifer target to account for this reduced productivity.
Marcia Humes placing stream temperature gauges in Fishhawk Creek.
Abiotic and biotic disturbances are a part of the Blodgett forest ecosystem. While it is recognized that biotic and abiotic disturbances are important in maintaining ecosystem biodiversity, poor management practices can result in unintended outbreaks and loss beyond an acceptable level. Acknowledging potential disturbances and incorporating them into management strategies and planning is an integral component of maintaining forest health.
The thinning prescriptions and placement across the landscape were designed to develop wind-firmness over time and minimize catastrophic windthrow risks.
The frequency, intensity and distribution of fire varies considerably over the Pacific Northwest. The Blodgett Tract is located in the coastal mountain range of the Tsuga Heterophylla zone. Agee (1983) describes the natural fire regime of this zone as episodic rather than cyclical as specific fire return intervals are difficult to quantify. Fires in this zone are usually high intensity stand replacement fires, characterized by occasional crown fires or severe surface fires. Fire regimes are a function of temperature and moisture patterns, ignition patterns such as lightning and human origin, vegetation characteristics such as fuel loading and adaptations to fire. Catastrophic fires in this region suppress the natural successional pattern which would result in hemlock dominant climax rather than the more common Douglas-fir dominant stands represented in much of this area. Fires in these regimes are associated with drought years and east wind weather conditions in late summer and fall that decrease humidity and are combined with a combustion source. In the Columbia Gorge, where topographic features are lower or absent, there is a much stronger trend for fire spread to the west. These fires may stop only at stand type boundaries or under extreme conditions when fuels are exhausted at barriers such as rock outcroppings or streams. Young stands in this region may be subject to frequent surface fire re-burns until crown closure occurs (Agee 1983,1990). Fire impact will be minimized with an aggressive fire suppression policy.
Biotic disturbances include pathogenic fungi and insects. The major pathogenic fungi include stem rots, root rots and needle diseases. Stem rots are usually associated with wounding and stumps so they will be of particular concern in thinned stands. Care to minimize wounding should be encouraged in all forest operations. This includes the type of equipment used, season of harvest and species selection. Where unacceptable amounts of root rot occurs, non-susceptible species (red alder or western redcedar) should be selected for and/or planted. Needle diseases have the greatest potential to impact future management of Douglas-fir on the Blodgett Tract. Ten miles to the west, management of Douglas-fir is being discouraged by an extensive outbreak of Swiss needle cast (Phaeocryptopus gaeumannii). The impact on Douglas-fir growth is serious enough to stimulate some landowners to switch to management of alternative species including western hemlock, cedar, Sitka spruce and alder. While this disease is not yet widespread on the Blodgett Tract, it is present in the young plantations and should be carefully monitored. Monitoring should include a baseline aerial survey conducted in the spring just prior to budbreak, followed by field surveys on a limited basis. Insects of concern include Sitka spruce tip weevil (Pissodes strobi), Douglas-fir beetle (Dendroctonus pseudotsugae) and hemlock looper (Lambdina fiscellaria lugubrosa). With the exception of Sitka spruce tip weevil, none of these species are currently causing major impacts. In the past, hemlock looper has caused massive defoliation in hemlock stands in neighboring Clatsop County resulting in widespread mortality. In general, the damage was associated with mature stands and is not expected to be as much of a problem in the Blodgett Tract due to the younger age of the forest and the species mix. Douglas-fir beetle is only damaging following major windthrow. The downed trees provide good rearing habitat and allow populations to reach a level where successful attacks are made on standing Douglas-fir. Salvaging downed wood usually controls these outbreaks. Sitka spruce tip weevil is an endemic insect that caused top death on virtually all young spruce trees resulting in a potential loss of competitive vigor and stem deformity. Forest staff should consider planting Sitka spruce weevil resistant stock, if it becomes available.
The list of diseases and insects here is not intended to be an exhaustive review but to encourage recognition, education of forest staff, careful monitoring and adaptation of management strategies. Current and future abiotic and biotic disturbances should be monitored with systematic reporting, record keeping and incorporated in silvicultural prescriptions.
Prescribed burning can be used as a resource management tool when managers evaluate the historical role of fire and are familiar with the ecological responses of vegetation and structure in the system. Controlled use of fire to achieve specific forest management objectives can provide beneficial responses. Such management objectives include control of competing vegetation, creation of seedbeds and planting spots and overall improvement in the efficiency of silvicultural prescriptions by removing impediments to reforestation.
The use of fire as a management tool can have many impacts, both beneficial and negative. Negative impacts include visual and health impacts on air quality, site quality, and wildlife habitat. Other impacts include possible soil disturbance and compaction from mechanical piling, effects on soil productivity from intense burns creating hydrophobic soils and risk of soil erosion. Prescribed burning may also entail increased costs under circumstances of escape due to containment costs and liability. Fire may play an important role in both the creation and loss of dead wood, affecting wildlife habitat and nutrient recycling. In addition, higher merchantability standards in recent years leave less logging residue in the harvest unit than in previous decades.
With these objectives in mind, active fire protection will be practiced to protect resources on the forest, as well as addressing liability concerns from adjacent landowners. Protection includes keeping roads and access open and development of detailed wildfire response plans for efficient containment. Prescribed fire will primarily be used to achieve specific management objectives such as creation of planting spots, and overall improvement in the efficiency of silvicultural operations. Slash burning is the preferred method of disposing of logging residues and other woody debris and vegetation that would otherwise impede reforestation methods as well as create fire liability risks.
Mechanical site preparation or broadcast burning decisions will be formed on a unit by unit basis. Burn plans will be developed ensuring consideration and protection for all forest goals stated previously in the plan including down woody debris and snag levels and soil productivity. The burn plan will describe the unit to be treated, objectives to be achieved, pre and post burn monitoring requirements, fuel and weather conditions needed to meet objectives, funding sources and limitations, burning and containment procedures and personnel and equipment needs. In addition, consideration of air quality and visibility standards, and assessments of risk of escape and resulting consequent damage will be addressed. In Oregon, burn plans are required for all prescribed burning on forestlands during fire season.
Populations of exotic species that have become established on the Blodgett Tract should be maintained at low levels because these species can invade and dominate parts of ecosystems changing the way they function for endemic species within these systems. False brome (Brachypodium sylvaticum), English holly (Ilex aquifolium), Scotch broom (Cytisus scoparius), Himalaya blackberry (Rubus discolor), English Ivy (Hedera helix) and other species can displace native plants that other native species depend on.
Exotic vascular plant species should be managed during harvest, site preparation, conifer release and roadside maintenance. If persistent exotic understory species are identified during the preparation work for these operations, they should be controlled. In the case of harvest units, treatment should occur before the unit is logged. Shrubs and perennial herbs should be killed with systemic chemicals. If exotic plants appear in young plantations, their removal should be planned as a part of the regular release program.
In general, invasive exotics (like false brome) should be controlled before they become epidemic. Toward this end, personnel who are working on other projects at the tract, who are appropriately licensed and trained to apply herbicides, should be equipped with hand spraying equipment and instructions to spot spray exotics that they notice where practical.
Exotic fauna should be managed by minimizing their habitat consistent with the other goals of the plan.
The plan assumes that cultural sites and objects, and antiquities of local, regional and national significance will be protected.
To protect these resources:
1. A professionally supervised cultural resource inventory program will be conducted at the tract and project level in compliance with applicable state and federal historic preservation legislation (see www2.cr.nps.gov/laws/36cfr61.utm). The surveys will be conducted according to an inventory plan and research design agreed to by the Research Forest and the State Historic Preservation Office (SHPO). Based on this database, the Research Forests will develop and maintain a tract-wide cultural resource overview based on summaries of the cultural resource information. This overview (especially of the railroads) will make it easier to develop management plans that will eliminate the need to consult with SHPO on a continuing basis.
2. Cultural resource properties located during inventory will be evaluated by a professional archaeologist/historian to determine their eligibility for listing on the National Register of Historic Places.
3. In concert with inventories and site evaluations, the Research Forests will develop management plans for the various classes of prehistoric and historic resources found on the tract.
4. Protection of cultural resources will be coordinated with the SHPO and the Advisory Council on Historic Preservation as required by state and federal historic preservation laws and regulations.
5. Protection of Native American cultural resources will be coordinated with the tribes. This coordination will include (but not necessarily be limited to) notification to tribes of activities and potential impacts in areas of known concerns. Opportunities for tribal involvement in research of sites with known tribal affiliations will be made.
6. Cultural resources may be developed for scientific and educational purposes to the extent that the integrity of the resource is maintained.
The plan currently assumes that the transportation system will:
1. Provide cost effective access for all-season log hauling and administrative traffic.
2. Protect watershed and fishery resource values.
This will involve:
1. Developing road management objectives for all existing and proposed roads.
2. Integrating road management objectives with long-term logging and stand tending needs and with soil and watershed management objectives.
3. Developing an annual road maintenance plan in accordance with the road management objectives.
Since we know that the existing transportation system will require investment to provide for all-season log hauling and that more investment is required on some portions of the system to allow timber harvest than others, over the next year (1999/2000) the forest staff will complete road management planning so that these costs can be disaggregated by road segment. In addition, the staff will suggest a new set of logging costs and harvest revenues that reflect the seasonal fluctuations that are known to occur. A transportation component to the scheduling model will then be developed that can incorporate this new information into the systems that the model uses to search for the best timing and combination of harvest units.
Determining Levels of Dead Wood
SRS is a computer model based on data presented by Neitro et al. (1985) that is designed to assess the number of snags needed to provide habitat for a variety of densities of primary cavity-nesting birds (birds that excavate their own cavities for nest sites). The model is based on limited data for some species. In addition, some of the assumptions concerning secondary-cavity users (species that use cavities excavated by other species) and number of snags necessary to meet foraging needs of specific primary cavity-nesting birds are questionable (Hayes and Hagar in press), and thus likely underestimate the number of snags necessary to meet habitat needs for these cavity-users. However, it provides a valuable estimate for assessing wildlife needs for number of snags, as long as it is recognized that estimates are likely to be underestimates.
We used SRS to determine initial management guidelines for snags in the Blodgett Tract. These estimates should be revisited as new information becomes available. For mature forest habitat, management goals were based on a goal of providing habitat for 80% of the maximum potential population levels for primary cavity-nesting birds. For this population level, SRS suggests maintaining 256 snags per 100 acres exceeding 15 inches DBH. Of these, 66 should be greater than 17 inches DBH and 5 of these should be greater than 25 inches DBH. We opted to emphasize large snags in this habitat type, and thus increased the guidelines for largest snags to at least 20 snags greater than 30 inches in diameter per 100 acres. We slightly increased the number of snags greater than 17 inches in diameter to 75 per 100 acres. For the remaining stands in the Blodgett Tract, numbers of snags approximate numbers suggested by SRS to provide habitat for 60% of maximum population levels (192 snags greater than 15 inches DBH, of which 50 exceed 17 inches DBH, of which 4 exceed 25 inches DBH per 100 acres). However, as we are focusing our larger diameter snags on stands providing mature forest habitat, our guidelines are for 200 snags per 100 acres exceeding 15 inches in diameter.
A number of studies (e.g., Hayes and Cross 1987) and a plethora of anecdotal observations and field observations indicate that large downed wood is used more than smaller logs. Although diameter and length are often confounded, long length of material generally appears to be of much less importance than large diameter (although this generality should not be taken to the extreme). Increased size has been shown to result in both quantitative (amount of use by a particular species) and functional (number and type of species using the dead wood and number of functions served by the dead wood) increases in use.
One of the most comprehensive studies examining the response of small mammals to forest characteristics is Carey and Johnson (1995). Carey and Johnson examined small mammal communities in the Olympic Peninsula, southern Washington Cascades, Oregon Cascades, and Oregon Coast Range. The results indicate that forest floor characteristics and understory vegetation strongly influenced small mammal communities, with two factors (dead wood and prevalence of shrub cover) playing primary roles. Carey and Johnson state “our empirical data suggest that 15-20% cover of dead wood on the forest floor, well distributed across the site, would be adequate for most small mammals, whereas 5-10% cover would not allow the mammals to reach their potential abundances.” Carey and Johnson indicate that tall (1-2 m) stumps from large trees, can help provide the dead wood needs of the stand. While contributing to the needs, however, stumps are structurally very different from logs, and can provide only a part of the solution to the dead wood needs of small mammals.
Butts (1997) found a linear relationship between ensatina (a species of amphibian) captures and dead wood volume. In spring, there appears to be a threshold around 90 m3/ha (ca. 1300 ft3/ac), below which this species did not occur. Although a similar relationship was obtained during her fall trapping, no obvious lower threshold existed, though some stands with up to ca. 130 m3/ha (ca. 1850 ft3/ac) dead wood had no ensatina captures, whereas all stands with greater volumes had ensatina captures.
Thompson (1996) found core areas of home ranges of red-backed voles had a mean log volume of ca. 240 m3/ha (ca. 3400 ft3/ac), whereas random sites had a mean log volume of 120 m3/ha (ca. 1700 ft3/ac). Differences between core areas and random were greatest for soft logs, and less pronounced for hard logs. For managing for red-backed voles, Thompson recommended retaining 236 m3/ha of logs in patches on 20% of the area and sufficient logs in intervening areas to provide for cover and movement corridors.
Snags in "Rowley Salvage" harvest unit.
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