The North Oregon Coast Range Distinct Population Segment of the Red Tree Vole

A red tree vole in the North Oregon Coast Range West of Corvallis. ©Stephen DeStafano.

Permit me to cut to the chase (but first gaze a bit on that petite example of very charismatic megafauna [yes, it’s looking at you {really!}]). The three bottom-lines are:

• The North Oregon Coast Range distinct population segment of the red tree vole is (a) at risk of extinction; (b) important to the survival of the northern spotted owl (c) depends on forest canopy integrity (density and age) and is therefore sensitive to logging.

• All mature and old-growth forests in the same area must be conserved. Most are already in Late Successional Reserves or Riparian Reserves, but some older forest can be found Matrix land.

• All federal young-managed forests (plantations)—not just those in Late Successional Reserves and Riparian Reserves—in the Oregon Coast Range generally north of the Siuslaw River—must be managed on a path to again make them old-growth forests by the use of variable density thinning, rather than any timber volume-driven logging—either traditional industrial clearcutting the clearcutting variant called “ecoforestry” that incorporates variable retention harvest. 

Introduction

The North Oregon Coast Range NOCR) distinct population segment (DPS) of the red tree vole (RTV) (Arborimus logicaudus) has been found by the US Fish and Wildlife Service (USFWS) to be warranted for protection under the Endangered Species Act (ESA) because of the massive loss of older (mature and old-growth) forests on federal public forestlands and state and private timberlands.

This memorandum summarizes the biological and legal status of the NOCR RTV DPS and addresses management issue and then makes recommendations for action. The legal status follows from its biological status. Management of federal public forestlands—most especially in management hundreds of thousands of acres of late-successional (mature and old-growth) forests and plantations in moist forest types allocated to the Matrix land allocation under the Northwest Forest Plan (NWFP)—must shift emphasis to conserve and restore older forest habitat for the RTV. This habitat is generally the same used by the ESA-protected Northern Spotted Owl (NSO) and Marbled Murrelet (MaMu).

For summarizing the biological and legal status of the NOCR RTV, I relied exclusively on the US Fish and Wildlife Service’s (USFWS) 12-month finding on a petition to list the species (in this case a DPS) under the Endangered Species Act.[1]  For readability, I do not provide a specific citation all the biological and legal facts mentioned herein, but such can be is found in that official agency finding. As for the management issues and the legal observations offered herein, they are mine (and I’m not a lawyer), but don’t be surprised if some very competent environmental lawyers concur with my conclusions and recommendations.

Basic Biology and Ecology

Tree voles (there are but two species: the red tree vole and the Sonoma tree vole) live in conifer forests and almost all of their time is spent in the canopy. If you find one on the ground, they are moving between old live trees. If you find one in a hardwood or a conifer snag (dead tree), a live conifer will be very nearby. 

Species Range. Tree voles are endemic (native or restricted to a certain area) to humid coniferous forests in western Oregon and northwestern California. The red tree vole is found exclusively in Western Oregon and a small portion of northwestern California (Map 1) at lower elevations (they don’t much like snow). USFWS found that the RTVs in the NOCR (Map 2) are a DPS, meaning they are an evolutionarily important subpart of the species. The NOCR RTV DPS is about one-quarter of the range of the RTV. It is bounded by the Siuslaw River on the south, the Pacific Ocean on the West, the Willamette Valley on the East and the Columbia River on the North. 

Nests. Males and female adults live apart (though the females do live with their young) in nests made primarily of twigs and resin ducts discarded from feeding, as well as fecal pellets, lichens, dead twigs, and conifer needles. RTV nests can range from the ephemeral and the size of a grapefruit to the size of a bushel basket that completely encircles the trunk of a tree. Female nests are usually larger. They prefer to nest in the larger trees. 

Size. Tree voles are less than 8.2 inches long and weight up to 1.7 ounces (mouse-sized). Fur color ranges from brownish red to bright brownish red to orange red. Some are all black and occasionally cream-colored. 

Diet. The diet of the NOCR RTV DPS is needles, principally Douglas-fir needles. Using specially evolved fore-limbs, they strip away the resin duct full of terpenoid chemicals that makes the needles unpalatable to most species.[2] The discarded resin ducts are a foolproof method of RTV nest identification because no other species dissects needles this way. In the northern-most portion of the range, RTVs will also eat the needles of western hemlock and Sitka spruce. They get their water from the food or from licking moisture off of needles.

Map 1: Range of the Red Tree Vole. Source: USFWS

Predators. Weasels are a primary predator of RTVs. Other predators include ringtails, fisher, northern spotted owl, barred owl, northern flying squirrel and a variety of nocturnal and diurnal raptors. (Yes, some of these species are already ESA-protected or should be—it’s an endangered ecosystem, after all.) Fifteen percent of RTVs survive a year. USFWS says, “Other mortality sources include disease, old age, storms, forest fires, and logging…. [F]orest fires and logging are far more important mortality factors than predation in limiting vole abundance.” 

Reproduction. Litter sizes average 2.9 young per litter (with a range of 1 to 4). Most reproduction occurs between February and September. Females can breed immediately after giving birth which can results in two age-classes of young in the same nest at the same time. Young first exit the nest between 30-35 days and do not fully disperse until 47-60 days of age. 

Home Range. The only published data on home range size comes from RTVs, not NOCR RTVs in particular. Of 45 RTVs, 18 had home ranges consisting of their nest tree and a few adjacent trees. The remainder occupied up to six different nests in trees spaced up to 532 feet apart. Mean and median home ranges were 0.43 and 0.19 acres respectively. The longest known dispersal was 1,115 feet over the course of 40 days.

Habitat. The RTV live successfully in “older” (mature and old-growth) conifer forests. (They are also found in conifer-hardwood forests, but the hardwoods don’t seem to be important to the species.) Rather than a specific age, USFWS says their use of the term “older” forests “represent the mixture of old and large trees, multiple canopy layers, snags and other decay elements, understory development and biologically complex structure and composition often found in forests selected by tree voles.” Those characteristics are more pronounced the older the stand and/or tree. RTVs best like larger stands of intact older forest. Due to extensive logging, mature and old-growth forest are at levels far below what occurred prior to the European invasion. RTVs like closed-canopy forests and very large (old) trees. Such are non-existent on private lands, only occasionally existent on state lands (but not for long if they are logged as planned). Older forests are most extensive on federal forestlands—but are far from abundant. RTV are sometimes found in second-growth managed stands, and these populations may persist if the stands are allowed to grow old, but young stands would likely be population “sinks” if they are managed on a rotation basis, because typical cutting rotations (40 years private industrial to 80 years some public) and cutting styles (clearcut and plant) never develop the habitat complexity of older natural forests. 

Geographic Differences Habitat Quantity and Quality. USFWS distinguishes the southern portion of the range of NOCR RTV DPS from the northern portion. The dividing line is U.S. Highway 20 between Corvallis and Newport. The higher fraction of non-federal (state and private) land in the north means less and poorer habitat than in the southern portion of the NOCR. In general, the Oregon Coast Range is the most logged-to-hell ecoregion in Oregon and, in particular, the north end of it is the most logged-to-hell in Oregon.

Distinct Population. The NOCR RTVs population is distinct genetically from other RTV. The Siuslaw River was chosen as the southern boundary because it generally demarks where the vegetation transitions from more moist in the north toward drier to the south, with resulting differences in the frequency of forest fires and forest characteristics). It may have been glaciers ~12,000 years ago that allowed the establishment of subalpine forests in the Oregon Coast Range, with western hemlock and Sitka spruce forests remaining only in isolated areas that served as refugia for what evolved into NOCR RTVs.

Map 2: North Oregon Coast Range Distinct Population Segment of Red Tree Vole. Source: USFWS

Current Abundance. Only 11% of the original range of the RTV in the NOCR is still potentially suitable habitat, most of which is on federal lands centered in two isolated clusters.

Projected Trends in Red Tree Vole Habitat. The future is not bright. While current land management policies are projected to provide a 20% increase in RTV habitat in the NOCR over the next century, it’s not enough. This is due primarily because so much of the habitat within the range has been lost to logging. The most logging has occurred on private timberlands, followed by state lands. While still heavily logged, relatively the most habitat remains on federal public forestlands. The private lands are anticipated to remain as structurally simplified small- and medium-sized conifer stands. The Board of Forestry and Oregon Department of Forestry occasionally make noise about managing some of the state’s timberlands in a longer rotation and allowing for more complex structure, but such efforts are, at best, token. USFWS says: “Although projected future conditions represent a potential improvement in suitable habitat for the red tree vole, the time lag in achieving these conditions and the fragmented nature of public lands in the northern Oregon Coast Range suggests that a potential gain of 20 percent more suitable habitat 100 years from now is likely not sufficient to offset the loss, modification, and fragmentation of habitat and isolation of populations that collectively pose an immediate threat to the red tree vole in the DPS.”[3]

Causes of Population Losses. The NOCR used to be predominantly covered with older forest. Because of infrequent fire, the old-growth stage of forest development lasted for very long times. First came a series of human-caused fires in the 1800s that were associated with European settlements along the coast and in the Willamette Valley. Then came logging and lots of it. USFWS says: “Nearly 90 percent of the DPS is currently in a habitat condition avoided by red tree voles, and only 0.3 percent of the DPS is in a condition for which red tree voles show strong selection for nesting.”

Legal Status

ESA Status. In 2007, Center for Biological Diversity, Oregon Chapter of the Sierra Club, Audubon Society of Portland, Cascadia Wildlands Project and Oregon Wild petitioned the US Fish and Wildlife Service (UWFWS) to find the red tree vole threatened or endangered under the Endangered Species Act (ESA). In 2011, USFWS found the North Oregon Coast Range population of red tree vole to be both a distinct population segment (DPS) and warranted for protection under ESA. It also found that DPS was precluded from listing at that time due to higher priorities for listing.

A Distinct Population Segment. The DPS Policy’s standard for discreteness requires an entity to be adequately defined and described in some way that distinguishes it from other representatives of its species. According to USFWS: 

a population segment of a vertebrate species may be considered discrete if it satisfies either of the following two conditions:

(1) It is markedly separated from other populations of the same taxon as a consequence of physical, physiological, ecological, or behavioral factors (quantitative measures of genetic or morphological discontinuity may provide evidence of this separation); or

(2) It is delimited by international governmental boundaries within which significant differences in control of exploitation, management of habitat, conservation status, or regulatory mechanisms exist.

USFWS says: “The North Oregon Coast portion of the red tree vole range is markedly separated from the rest of the species’ range based on the genetic discontinuities.”

Management Issues

Ecological Restoration Thinning of Managed Young (Planation) Forests on Federal Public Forestlands. USFWS says: “Thinning these younger stands, while designed to develop late-successional habitat characteristics in the long term, has the potential to degrade or remove tree vole habitat characteristics in the short term, especially if thinning design does not account for structural features and the connectivity of those features that are important to red tree voles.” USFWS continues: “Red tree voles are afforded more protection on Federal lands than on State Forest and private lands within the DPS, primarily as a result of the Survey and Manage protections [of the Northwest Forest Plan]. Before commencing timber harvest activities (except for thinning activities in stands under 80 years old), projects must be surveyed for tree voles and high priority sites protected. [emphasis added]. The adverse effects of plantation thinning on RTV might be mitigated by first surveying all suitable habitat and buffering occupied sites. This will maintain existing occupied sites and populations, and minimize inadvertent loss of occupied sites. Second, retaining a multi-scaled mosaic of thinned and unthinned patches in all thinning projects, regardless of known RTV occupancy, especially when thinning plantations that are adjacent to older forests. This will give RTV populations potential options to expand into new territory.

The Role of Fire in Habitat Loss. Wildfire is sometimes a proximate cause of RTV habitat loss. Given the extremely long fire-return intervals in the North Oregon Coast Range, even where fire occurs, the usual case is that the ultimate cause is logging. Yes, parts of what is now the Tillamook State Forest burned four times in less a quarter century, but these moist old-growth forests were in the process of, or had been, logged, which provided huge amounts of flammable slash that dried out due to the removal of the canopy. Forest fires are relatively rare in the range of the NOCR RTV DPS as it is generally all moist forest types.

The Highest and Best Use of 80-120 Year-Old Stands. Senator Ron Wyden, the Chair of the Senate Energy and Natural Resources Committee and Oregon’s senior senator is on record as supporting the conservation of older forests—he defines as 120 years old and greater—which include older mature and all old-growth forests. It does not include younger mature forest. Conserving all mature forests provide for the greatest probability of conserving the ESA-warranted NOCR DPS of RTV and the ESA-protected Northern Spotted Owl (NSO) and Marbled Murrelet, (MaMu), which are other federally recognized imperiled species that inhabit the NOCR. While it’s not a large amount of acreage, it is extremely important habitat, given the status of NSO, MaMu and NOCR RTVs. Merely retaining forests 120 years and older is simply not enough to conserve and recover RTV, NSO, and/or MaMu. Federal forest policy must grow back much of the older forest that was removed during prior liquidation policies.

The Highest and Best Use of Plantations. For BLM plantations in the Matrix land allocation that are not within Northern Spotted Owl Critical Habitat, Franklin and Johnson propose the practice of variable retention harvest on an average 130-year rotation.[4] While such ecoforestry is far less horrible than a traditional industrial clearcut, it is nowhere as ecologically beneficial as either the real forest it would replace or the naturally occurring early successional forest ecosystem that follows a stand-replacing (wind, fire, volcano, et al.) event that it would mimic. In the NOCR, given the status of the RTV, this kind of forestry will not help the imperiled species.

Management of Federal (Forest Service and BLM) Forests. The lack of formal ESA-listing does not excuse the Forest Service and Bureau of Land Management from their obligations to conserve the species. It is prudent to anticipate eventual listing under the Endangered Species Act and take actions now. The USFWS finding that the NOCR population is a DPS and that DPS is warranted for ESA protection is significant new information under the National Environmental Policy Act. The National Forest Management Act is intended to conserve species on the National Forest System at threshold above the ESA. BLM has interpreted the O&C Act—and federal courts have agreed—to be consistent with efforts to conserve wildlife and keep them off the endangered species list in order to minimize future disruptions in timber production.

Management of Non-Federal (State and Private) Forests. USFWS says: “Barring a significant change in the Oregon Forest Practices Rules and Act, loss, modification, and fragmentation of red tree vole habitat is likely to continue on most of the 62 percent of the DPS that is privately owned.”

Recommendations

To conserve the North Oregon Coast Range Distinct Population Segment of the Red Tree Vole and to comply with law:

The Forest Service and the Bureau of Land Management must:

• Conserve all mature (younger and older) and old-growth forests as it is now habitat for the NOCR DPS RTV.

• Conserve all naturally occurring young forest as it is the quickest and best source of new habitat for the NOCR DPS RTV.

• Conduct appropriate amounts and kinds of ecological restoration thinning of simplified managed stands (plantations) of young forests, providing for appropriate RTV nest buffers and to provide species connectivity.

• Not undertake clearcutting or its variant variable retention harvest often called “ecoforestry” in any stands in the NOCR.

The State of Oregon should:

• Revise the Oregon Forest Practices Act and its rules to provide for the needs of the NOCR DPS of RTV. At a minimum this should include requirements to survey and buffer occupied sites and require long rotations in key areas.

• Add the NOCR DPS RTV to the Oregon endangered species list.

Private Timberland Owners might:

• Encourage federal forestlands and state timberlands in the NOCR to be managed for the benefit of RTV, so as to minimize their own conservation obligations.

All landowners and conservation organizations could:

• Establish and/or support the enrollment of state and private timberlands into atmospheric- carbon offset programs that upgrade the conservation status of those lands enough to benefit the RTV in the NOCR.

Acknowledgements

I am indebted to Doug Heiken of Oregon Wild for his always wise counsel and in particular contributions made in reviewing a draft of this paper. Of course, any errors are none but mine.

Notes

[1] US Fish and Wildlife Service. 12-Month Finding on a Petition to list a Distinct Population Segment of the Red Tree Vole as Endangered or Threatened; Proposed Rule. Federal Register Vol. 76, No 198, October 13, 2011. 63720-63762.

[2] Though Clear Creek Distillery does produce an Eaus de Vie (“water of life”) Douglas Fir (no hyphen, which is inserted by taxonomists to remind themselves that Pseudotsuga menziesiiis is not a “true” fir and which drives English majors bonkers). 

[3] See what is happening to NOCR RTV habitat on non-federal lands.

[4] Johnson, K. Norman and Jerry F. Franklin. 2013 (revised). Recommendations for the Future Implementation of Ecological Forestry Projects of BLM Western Oregon Forests.