Research

When the northern spotted owl was listed as a threatened species under the Federal Endangered Species Act in 1990, it brought into sharp focus the potential conflict between timber operations and wildlife protection in the Northwest.

It was originally believed that the spotted owls could survive only in old growth preserves in which there was little or no forest management activity.

Research conducted on Green Diamond Company's timberland in coastal northern California indicated that this theory was untrue. The species not only survived, but also often flourish on commercial timberlands in this region. In fact, Green Diamond's timberland proved to be one of the most populous spotted owl areas in the Northwest. Since our owl research began in 1990, we have identified over 1,700 adult and juvenile spotted owls on our property alone.

This pioneering research, as well as subseqent studies, led the U.S. Fish and Wildlife Service to award our timber operations the first ever Habitat Conservation Plan (HCP) for the spotted owl.

But our work is not over. We continue to evaluate the effectiveness of the HCP in sustaining populations of spotted owls. Every year we look at long-term population trends including survival and reproductive rates, In addition, the U.S. Fish and Wildlife Service reviews our HCP annually.

More information on our groundbreaking spotted owl research may be obtained from the following peer-reviewed scientific publications:

Diller, Lowell V. and Darrin M. Thome. 1999. Population density of northern spotted owls in managed young-growth forests in coastal northern California. The Journal of Raptor Research 33(4):275-286.

Thome, Darrin M., Cynthia J. Zabel and Lowell V. Diller. 1999. Forest stand characteristics and reproduction of northern spotted owls in managed north-coastal California forests. Journal of Wildlife Management 63(1):44-59.

Thome, Darrin M., Cynthia J. Zabel and Lowell V. Diller. 2000. Spotted owl turnover and reproduction in managed forest of north-coastal California. Journal of Field Ornithology 71(1):140-146.

Folliard, Lee B., Kerry P. Reese and Lowell V. Diller. 2000. Landscape characteristics of northern spotted owl nest sites in managed forests of northwestern California. The Journal of Raptor Research 34(2):75-84.

So what does our research show attracts so many owls to our land? Rats. That's right. The creatures that would make most of us pack up and leave a neighborhood are exactly what encourage the owls to move in. And not just any rat - the dusky-footed woodrat.

The prey on which the owls feed proved to be key in understanding the presence and prosperity of the spotted owl in this region.

While spotted owls throughout much of the rest of the Northwest feed mostly on flying squirrels living in mature forests, studies indicated that spotted owls on California's North Coast feed primarily on dusky-footed woodrats living in very young forests.

This discovery prompted a study on the abundance of woodrats in redwood forests throughout our California ownership. This study indicated that woodrats were most abundant in young stands - those that were 10-20 years old.

Preliminary data from an additional, ongoing study through Humboldt State University shows a similar abundance of wood rats in Douglas-fir forests.

These results helped us understand why spotted owls in this region do well in areas that include both young and mature trees.

Wildlife biologist and others at Green Diamond have continued to study woodrats on California timberlands to better understand how different methods of harvesting trees effect woodrat numbers.

These studies, although not yet published, indicate that opening up the forest to allow sunlight to reach the forest floor allows the growth of the shrubs on which woodrats depend for food.

Given the importance of woodrats as the prey of spotted owls, these results would also suggest that spotted owl populations in this area are best supported in forests that are managed using even-age management.

Published studies and other scientific reports on dusky-footed woodrats:

Hamm, Keith A. 1995. Abundance of dusky-footed woodrats in managed forests of north coastal California. M.S. thesis, Humboldt State University, Arcata, CA.

Hamm, Keith A., Lowell V. Diller and David W. Kitchen. In press. Comparison of indexes for estimating abundance of dusky-footed woodrats. Wildlife Society Bulletin.

Hamm, Keith A. and Lowell V. Diller. Effects of forest age and silviculture on the abundance of dusky-footed woodrats in coastal northern California. Will be submitted to the Journal of Wildlife Management.

The Pacific fisher is a medium-sized carnivore and member of the weasel family. Along with the spotted owl, it is one of several species also thought to be primarily associated with old-growth forests. Although Green Diamond's California Operations spotted owl HCP was primarily designed to benefit the owl, it was expected that measures to protect spotted owls would also benefit other species associated with mature forest conditions.

Green Diamond funded a study of fishers through Humboldt State University to determine their occurrence and habitat associations within our ownership. This study indicated that the fisher had similar habitat associations compared to the spotted owl. This led to a telemetry study of fishers by Green Diamond biologists to follow the fishers' movements and to determine the types of trees that were critical to their habitat. Green Diamond's work on this species demonstrated that most of the same conservation measures developed for the owls were also beneficial for fishers. However, the conservation measures developed for spotted owls were modified to give maximum benefit to both species.

Currently, Green Diamond is funding another study through Humboldt State University in an effort to determine the abundance and density of fishers within Green Diamond's ownership.

Published studies and other scientific reports on Pacific fishers:

Klug, Richard R. 1997. Occurrence of Pacific fisher (Martes pennanti pacifica) in the Redwood Zone of northern California and the habitat attributes associated with their detections. M.S. thesis, Humboldt State University, Arcata, CA.

Hamm, Keith A., Lowell V. Diller, Richard R. Klug and Trent L. McDonald. Spatial independence of fisher detections at track plates in northwestern California. Submitted to: Wildlife Society Bulletin.

Thomson, Joel L. (In progress) Abundance and density of fisher on managed timberlands in north coastal California M.S. thesis Humboldt State University, Arcata, CA.

Red tree voles are small, nocturnal, arboreal (tree-dwelling) mammals. They are unique in that they apparently feed only on conifer needles. As a result of its unusual habit, tree voles are exceedingly difficult to observe or trap.

In spite of little being known of the species, it is suggested that tree voles have a close association with old growth Douglas-fir forests.

Humboldt State University and Green Diamond biologists conducted several studies to determine the occurrence and relative abundance of tree voles in managed forests in coastal northern California.

These studies found that tree voles are patchily distributed in managed Douglas-fir forests that were approximately 20 years old and older.

There is still much to learn about the habitat needs of the species, but it appears that many of the same conservation measures for the spotted owl will also benefit tree voles.

Published report in progress:

Thompson, Joel L. and Lowell V. Diller. 2002. Relative abundance and nest site characteristics, and nest dynamics of Sonoma Tree Voles of red tree voles in managed timberlands in coastal Northwest California. Northwestern Naturalist 83:91-100

In addition to birds and mammals, there are several amphibian species that are thought to be associated with old-growth forests and potentially sensitive to land management activities.

Since 1993, a series of studies has been conducted on Green Diamonds' California timberlands to determine the distribution, habitat and potential sensitivities of these species to timber management activities. In addition, long-term monitoring of these forest residents has been initiated to ensure that management activities do not threaten their continued survival. A brief synopsis of these species follows.

The Del Norte salamander (Plethodon elongatus) is a terrestrial salamander that is closely associated with talus (loose rock). In portions of its range, it has been shown to be sensitive to soil drying out as a result of timber harvesting. Green Diamond's studies in coastal California indicate that the species is generally not sensitive to timber harvesting activities, apparently due to the cool moist coastal climate. In fact, road-building activities associated with timber harvesting may actually create habitat for the species in many areas.

Published studies:

Diller, Lowell V. and Richard L. Wallace. 1994. Distribution and habitat of Plethodon elongatus on managed, young growth forests in north coastal California. Journal of Herpetology 28(3):310-318.

The southern torrent salamander (Rhyacotriton variegatus) is a small stream-breeding salamander that is found in the uppermost headwaters of streams and seeps. It requires cold water with clean gravel to live and breed. Green Diamond's studies have determined that the species is particularly abundant on its ownership in California even though past unregulated timber harvesting affected much of its habitat.

When the species was petitioned for listing in 1994 as a threatened species under the California Endangered Species Act, Green Diamond Company's predecessor, Green Diamond Timber Company, was one of the leaders in developing a program to train foresters and biologists in the proper identification and protection of the species and its habitat.

Partly as a result of Green Diamond's efforts, the species was not listed, but education and training continues to ensure that the species is adequately protected.

Published studies:

Diller, Lowell V. and Richard L. Wallace. 1996. Distribution and habitat of Rhyacotriton variegatus on managed, young growth forests in north coastal California. Journal of Herpetology 30(2):184-191.

The tailed frog (Ascaphus truei) is a small stream-breeding amphibian. It is the only frog in North America to have internal fertilization. Its larvae are equipped with a sucker-like mouth that enables it to cling to rocks and boulders in fast flowing headwater streams.

Similar to the torrent salamander, tailed frogs require streams with cold water and clean gravel and cobble, and have the potential to be effected by timber harvesting activities.

Research and monitoring of the species on our timberland have identified the potential threats associated with timber harvesting and has resulted in steps to ensure that the species is protected.

To date, some of the most robust populations of tailed frogs have been documented on Green Diamonds' ownership.

Published studies:

Wallace, Richard L. and Lowell V. Diller. 1998. Length of the larval Cycle of Ascaphus truei in coastal streams of the Redwood Region, Northern California. Journal of Herpetology 32(3):404-409.

Diller, Lowell V. and Richard L. Wallace. 1999. Distribution and habitat of Ascaphus truei in streams on managed, young growth forests in north coastal California. Journal of Herpetology 33(1): 71-79.