Provided by Elliott Menashe, Greenbelt Consulting (www.greenbeltconsulting.com)Provided by Elliott Menashe, Greenbelt for Consulting (www. greenbeltconsulting.com) for the Coastal Training Program Class PNW the Coastal Training Program Class "Shoreline Pacific Northwest Management“Shoreline Management and Stabilization and Stabilization Using Using Vegetation", Vegetation” 2004. Research Station INSIDE The Man-Made Heritage in Forests ...... 2 Soil Seed Banking on the Olympic Peninsula ...... 3 Bad News for Small Mammals ...... 4 Broom and Doom in the Puget Trough? . . . . .4 Variable-Density Thinning: Deliberate Fragments ...... 4 Reserves Versus True Complexity ...... 5 FINDINGS issue thirty-eight/ october 2001

“Science affects the way we think together.” Lewis Thomas

INVASION OF THE EXOTICS: THE OF WESTERN WASHINGTON

IN SUMMARY

Settlement of the Pacific Northwest by immigrants from the Eastern changed the composition of lowland landscapes from dominance by forests and prairie to dominance by , suburbs, agriculture, and trans- portation infrastructure. Historical disturbance regimes imposed by

English ivy is spreading throughout Holly is becoming widespread throughout nature and by indigenous people were ➢ forests in the Puget Trough, and even ➢ forest understories in the Puget Trough, large, dominant trees within the forest crowding out native, less aggressive disrupted. In the uplands, timber are not immune from their stranglehold. species. management activities replaced natu- ral disturbance regimes, often with Described by some as a form of plant and planted to beautify median strips, simplifying effects on ecosystems. biological pollution, these this well-known shrub now threatens some parts of Washington and Oregon with its People intentionally and unintention- species have been introduced— own pretty form of biological desert. sometimes by accident, but ally imported exotic species of plants It is not alone. Weedy exotics such as often with the best intentions— English ivy, Himalayan blackberry, holly, and animals. into systems where they thrive sweet cherry, and many others are spread- at the expense of native species. ing through forests at rates that are alarm- Simplification of ecosystems and intro- ing forest ecologists. duction of new species are contributing Oregonʼs Living Landscape, 1998 “Initially, none of them appeared to be a to globalization of world flora, endan- big problem, but the trend is certainly he golden blaze of glory that lights alarming,” says Andrew Carey, a research gering indigenous species, and reduc- the freeway in the spring... Admit biologist with the Pacific Northwest it, youʼve admired the showy ing ecosystem function. Some perma- T Research Station in Olympia, Washington. blooming of Scotʼs broom on your journey “Simplification of ecosystems and intro- nent changes have been wrought; along I-5. You might even have caught the duction of new species is helping to glob- smell if you were game to wind down the reversal of other changes and main- alize world flora, endanger indigenous window. species—especially those with narrow taining indigenous flora and fauna Yes, it lights the freeway, but it also blights habitats—and restrict ecosystem func- will require purposeful management. the forest. Introduced as an ornamental tions.” Globalization of flora is the process by which certain aggressive species tend to KEY FINDINGS dominate plant communities throughout the world, particularly where human activ- • Studies of soil seed banks in young, closed-canopy, second-growth forests ities are making conditions more con- revealed that 30 percent of all species were weedy exotics, only 24 percent ducive to invasion than they are naturally, were natives, and no tree species were present. Thinning these stands could he explains. Carey has observed that favor exotic species. where natural resources are managed in a homogeneous way, such as in plantation • Many of the small mammal communities in uniform second-growth stands are forestry or row-cropping, the propagules incomplete and differ in structure from communities in naturally young- or old- of aggressive weedy species become so growth stands. pervasive that they can move even into • Variable-density thinning has the potential to increase species richness within a suboptimal sites. short timeframe, provided it is used in a holistic approach that includes biologi- “Some permanent changes have been cal legacies, long rotations, and tree species diversity. wrought where local environmental condi- tions have favored them,” he says. “It will • Exotics may have altered the fuel environment in white oak forests sufficiently take purposeful management to reverse to pose a threat even to large-diameter oaks. Further, western gray squirrels less permanent changes and maintain have dramatically declined in these ecosystems in the last 10 years. indigenous flora and fauna.” THE MAN-MADE HERITAGE IN FORESTS n both Oregon and Washington, to rapid growth of timber and fiber. Fewer toward various late-successional goals, many low- to mid-elevation forested resources were intentionally directed to including the pivotal one of complexity of I landscapes are dominated by even- maintaining biodiversity.” understory. Many silvicultural tools are aged, young forests of a single species, now available to managers for such After decades of this approach, one of the often Douglas-fir. These landscapes are purposes: various harvest systems, reten- most apparent effects is the invasion by typically clearcut descendants. tion levels and patterns, regeneration exotics, which are attracted, opportunisti- methods, and rotation lengths. Shifts in thinking about past management cally, to areas of low competition and are coinciding with increases in human wide open spaces. They have the ability to Carey is involved with three sets of large- population, decreases in timber harvesting, respond rapidly, invade rapidly, occupy scale experiments examining the develop- and concerns about sustainability of sites for a long time, and survive in poor mental effects of exotic species on ecosys- managed forests, Carey notes. conditions. tem function in western Washington; he emphasizes that the problem is certainly “Past management often simplified forest Natives with small, particular niches not limited to his own state. The three composition and structure,” Carey beware. different studies have involved three explains. “Clearcutting, burning, planting Nonetheless, Carey believes that appropri- different forest types, and have all raised of genetically uniform trees, application of ate management intervention can help similar concerns. herbicides, and precommercial thinning these uniform second-growth forests move have diverted many ecosystem resources Purpose of PNW Science Findings

To provide scientific information to people who make and influence decisions about managing land. PNW Science Findings is published monthly by: Pacific Northwest Research Station USDA Forest Service P.O. Box 3890 Portland, Oregon 97208 (503) 808-2137 Sherri Richardson Dodge, Editor [email protected] Scot’s broom, originally brought in to beautify roadsides, readily invades newly disturbed ➢ areas.

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United States Forest Service http://www.fs.fed.us/pnw Department of Agriculture 2 SOIL SEED BANKING ON THE OLYMPIC PENINSULA n the early stages of stand develop- ment, coniferous forests of the LAND MANAGEMENT IMPLICATIONS I coastal Pacific Northwest commonly pass through a period of dense shade and • Invasion by exotics and globalization of flora is a real and present problem, intense competition. During this phase, the requiring thoughtful landscape-level planning. abundance and diversity of understory plants decline dramatically. • Management of forests that includes a mix of tree densities at the appropriate scales may help maintain indigenous species and the natural heritage of people This closed-canopy stage represents a crit- in the Pacific Northwest. ical juncture in the development of the forest understory. Canopy closure may • Novel management techniques will be needed for restoration of extirpated result in the local extinction of some forest indigenous species to second-growth forest. species and thus shape longer term patterns of understory composition and diversity, Carey explains. DOUGLAS-FIR FOREST IN THE PUGET TROUGH A prevailing theory is that thinning dense young forests will help stimulate the 120

suppressed understory. But the mecha- A nisms by which understory species persist 100 ➢ Total plant cover in or reestablish are poorly understood. A second-growth, Douglas- 80 fir forests in the Puget cooperative study with Carey and Connie Trough: never-thinned Harrington, a research forester at the PNW 60 stands with old-growth Research Station, Charles Halpern, a legacies (Legacy 40 research associate professor at the Controls), legacy stands

University of Washington, and others from Percent Cover 3 years after treatment 20 the university examined the potential with variable-density contribution of the bank of seeds retained 0 thinning (Legacy VDT), Legacy Legacy Thinned Thinned conventionally thinned in the soil. The Olympic Peninsula was Control VDT Control VDT selected for its extreme tree densities and stands (Thinned 120 Control), and thinned light exclusion during early forest regener- B stands 3 years after ation in this wet and productive climate. 100 VDT treatment (Thinned VDT). “Germination of buried viable seeds is 80 likely to be stimulated by the abrupt A = native species increases in light produced by thinning,” 60 B = exotic species Carey says. “To what degree this promotes desirable species—such as shade-tolerant, 40 Percent Cover native herbs, shrubs and trees—or encour- 20 ages the germination of exotic species, depends in part on the composition of the 0 Legacy Legacy Thinned Thinned seed bank.” Control VDT Control VDT The researchers investigated which species were present in the understory seed bank, and in what relative abundances. They also seed banks of 40- to 60-year-old silvicultural thinning will result in limited looked at how the litter layer seeds unthinned, closed-canopy stands, 30 germination of forest species but will often differed from that of the mineral soil and percent of all species were weedy exotics, favor recruitment of exotic species,” Carey how seed bank composition differed only 24 percent were typical understory says. “Moreover, retrospective studies of among different parts of the forest. species, and tree species were absent. understory response to thinning suggest that some of these weedy species may be able to In an area where increasing attention is “It has been hypothesized that the soil seed persist for decades following treatment.” being given to the concept of restoring bank may provide one source of propagules native understory vegetation via the soil for recruitment of forest understory seed bank, the news is not good. In the species, but our results suggest otherwise:

WRITER’S PROFILE Sally Duncan is a science planner and writer specializing in forest resource issues. She lives in Corvallis, Oregon.

3 BAD NEWS FOR SMALL MAMMALS hat’s not all. Carey notes that regulate some invertebrate populations, deer mouse, and the montane and vagrant many of the small mammal and provide prey for terrestrial and bird shrews. communities in 37 second-growth predators. T Unlike natural upland disturbances, such forests studied were incomplete and Not enough attention has been paid to the as wildfire, windthrow, flooding, or the differed in structure from communities in amounts of understory needed to maintain sustainable Native American burning prac- both naturally young stands and old various food pathways for small mammals tices, management of second-growth growth. “Simplification of forest structure because understory development is often forests more often produces simplified and and composition has had negative conse- simply a by-product of management for homogeneous environments. By reducing quences on small mammals and, presum- high-quality timber. But Carey and others food pathways and ecosystem resilience, ably, on numerous ecosystem processes,” have produced some preliminary studies by opening the door to invasion by he says. suggesting that plant species composition exotics, such management may reduce Small mammal communities have poten- and spatial arrangements of plants are small mammal populations, in turn reduc- tial as indicators of healthy forest floor important to small mammal communities. ing their ability to support predator popu- function because they disseminate seeds, lations. Hence, the arrival and spread of exotics, spores, and propagules of shrubs, often to the exclusion of natives, augurs In the white oak forests of the Puget bryophytes, fungi, and lichens, Carey badly for creatures such as Trowbridge’s Trough area, the results for the western explains. They also physically mix the shrew, red-backed and creeping voles, the gray squirrel may be terminal. soil, decomposed organic matter and litter, BROOM AND DOOM IN THE PUGET TROUGH? n the Puget Trough, the combination The past 6 years has seen a rapid decline sive Douglas-fir to reduce competition of annual burning by Native of western gray squirrel numbers on Fort with oak seedlings. Americans, mild climate, and diverse Lewis Reservation, home to one I But exotic plant species are not so easily landforms has led to some unique plant of the largest remaining tracts of oak removed. Already, about 30 percent of associations. These included Oregon white woodlands. Factors potentially responsible species found in oak woodlands are oak savannas, woodlands, and forests—a for the decline include poor acorn crops, exotics. Carey notes that Scot’s broom dynamic, shifting mosaic of diverse plant drought, motor vehicle impacts, competi- may have altered the fuel environment in communities. But then came European tion with the eastern gray squirrel, and oak woodlands sufficiently to pose a threat settlement, grazing animals, particularly reduction in quality and quantity of habi- even to large-diameter oaks, thereby sheep, and human development, complete tat, disease, and predation. suggesting a need for manual broom with transportation networks, agriculture, “Habitat fragmentation is an all-too- control before prescribed burning around , and cities in the lowlands. common problem for threatened species oaks. Travel corridors between oak habitat “Today, the citizens of Washington are in because many exist in isolated populations areas, with improved water sources, may danger of losing a significant part of their that are increasingly vulnerable to random help the western gray squirrel persist in remaining natural heritage—the legacies events like genetic, demographic, and viable numbers. of the Vashon glaciation,” Carey says. environmental uncertainties, and natural “Currently management is not effectively “Scot’s broom has invaded wetlands and catastrophes,” he says. “The occurrence of addressing issues of decreasing land area oak-dominated sites, and Douglas-fir is such unpredictable events can have poten- available for natural communities, mainte- encroaching as well. Most notably at risk tially devastating effects when population nance of landscape processes such as to loss are the Oregon white oak, the west- numbers decrease below a minimum dispersal and colonization by western gray ern gray squirrel, Roy’s pocket gopher, a threshold.” squirrels, landscape dynamics, or general trillium, and a butterfly.” Unless oak habi- Recommendations for enhancing the values of the oak savanna mosaic,” he tat is actively maintained, it will be western gray squirrel’s chances of says. “Such issues transcend any one replaced by a natural Douglas-fir succes- survival? Foresters could remove exces- management group and require both sion, he adds. community and landscape management.”

VARIABLE-DENSITY THINNING: DELIBERATE FRAGMENTS n the millions of acres of second- One of the more promising tools for According to Carey, such a mosaic has growth forests in the Pacific achieving the biocomplexity typical of old been hypothesized to promote processes I Northwest, how might we encourage forests that is so notably lacking in multi- associated with natural development of development of an ecosystem that is less ple-rotation forests, is variable-density widely varying plant associations and vulnerable to exotic invasion and more thinning. Thinning to various densities, foliage heights, along with horizontal inviting to the small mammal populations with corresponding differences in canopy vegetation patchiness. Effects on soil and it has historically supported? cover, creates a mosaic of patches. vertebrate communities follow.

4 Carey and others established an experiment complete small mammal communities or and small mammals, rodents, and winter in Douglas-fir forests in the Puget Trough abundant small mammal populations, birds were showing positive responses. to determine the response of small mammal thereby suggesting both types of stands “Our experiment, fully replicated, seems populations to vegetation changes induced were on developmental tracks deleterious to be the first to evaluate the efficacy of by variable-density thinning during the first to indigenous species,” Carey notes. inducing a mix of tree densities to influ- 4 years following experimental treatment. Three years after treatment, mosaics ence positively a carefully chosen array of They treated stands that had been conven- created by variable-density thinning had life forms,” Carey says. “The changes we tionally thinned as well as stands that had significantly greater plant species richness observed in the understory plant commu- been protected from disturbance. and greater herb cover than controls. The nity following variable-density thinning, Stands that had been thinned twice with variable approach initially resulted in as compared to those following conven- conventional commercial thinning had 94 increased importance of 11 exotic species, tional thinning, seem to better mimic natu- species of vascular plants, twice that in decreased importance of 2 native species, ral gap formation and promote variety in unthinned forest. Eighteen exotic species and increased importance of 20 native understory development.” were found in thinned forest, and none in species, including two kinds of trees. Could it be that certain tenets of conserva- unthinned forest. “Neither thinned nor Furthermore, within 3 years, species rich- tion biology need to be revisited and better unthinned second-growth supported ness overall increased by over 150 percent, evaluated? RESERVES VERSUS TRUE COMPLEXITY e have learned through recent effects on spotted owl prey, fail to provide Perhaps the invasion by exotics will draw experiments, Carey believes, for the biotic integrity of small-mammal attention to yet one more aspect of the W that biological reserves are not communities, decrease the abundance of supreme value of complexity in a healthy sufficient to preserve complexity. In fact, amphibians, and lead to homogenization forest, Carey says. Just like the complexity because not every reserve will contain all and globalization of understory flora. he prefers in an argument, biocomplexity the pieces of a working forest, or all the is known to offer a broader variety of But as with every “solution” that’s offered, elements of randomness inherent in a outcomes and a more dependable Carey reminds us, variable-density thin- dynamic system, a reserve is more likely resilience. ning needs a carefully planned context to to become more homogeneous over time succeed in multiple-value management. “It with the loss of pioneer species like The spread of exotic species has should be used in a management system Douglas-fir, even if it does persist for 500 emerged in recent years as one that includes retaining biological legacies years, he says. of large, live and dead trees, coarse woody of the most serious threats to “The need to manage forests in their debris, and intact patches of forest; manag- biodiversity, undermining the dynamic entirety across whole landscapes ing decadence; promoting tree species ecological integrity of many is becoming increasingly obvious, and diversity; and rotations longer than 130 native habitats. until we learn how to do management years. Variable-density thinning should not well, set-asides should be seen as useful be standardized for systematic application; Oregon’s Living Landscape, 1998 interim measures, not solutions in them- the approach must be tailored to the site to selves,” he says. Further, he adds, the achieve biocomplexity and biodiversity concept of “matrix” areas as the leftovers goals.” that can be treated badly is a denigrating notion that does not value the whole forest. FOR FURTHER READING “I have a visceral negative reaction to Carey, A.B.; Harrington, C.A. [In press]. Small mammals in second-growth forests: polarized adversarial relations and false implications for management for sustainability. Forest Ecology and Management. dichotomies, such as timber versus Carey, A. B.; Wilson, S. M. [In press]. Induced spatial heterogeneity in forest canopies: wildlife, matrix versus preserve, and jobs responses of small mammals. Journal of Wildlife Management. 65(4). versus owls. It frames arguments in very unproductive ways, and precludes useful Halpern, C.B. [and others] 1999. Soil seed banks in young, closed-canopy forests of the solutions,” says Carey. Olympic Peninsula, Washington: potential contributions to understory reinitiation. Canadian Journal of Botany. 77: 922-935. Carey suggests that the reason variable- density thinning produces better all-round Thysell, D.R; Carey, A.B. 2000. Effects of forest management on understory and overstory responses in forest values is that conven- vegetation: a retrospective study. Gen. Tech. Rep. PNW-GTR-488. Portland, OR: U.S. tional thinnings are specifically designed Department of Agriculture, Forest Service, Pacific Northwest Research Station. 41 p. to meet goals aimed at timber production, Thysell, D.R.; Carey, A.B. 2001. Quercus garryana communities in the Puget Trough, with little thought to biocomplexity. In Washington. Northwest Science. 75:219-235. fact, he notes, it has been found that even spacing of trees might have negative Thysell, D.R.; Carey, A.B. [In press.] Manipulation of density of Pseudotsuga menziesii canopies: effects on understory vegetation. Canadian Journal of Forest Research.

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SCIENTIST PROFILE

ANDREW B. CAREY is chief research Carey can be reached at: biologist and team leader for the Pacific Northwest Research Station/USDA Forest Service Ecological Foundations of Biodiversity Forestry Sciences Laboratory Research Team, Ecosystem Processes 3625 93rd Avenue Research Program, Pacific Northwest Olympia, Washington 98512-9193 Research Station. He received his B.S. Phone: (360) 753-7688 in forestry and wildlife and an M.S. in E-mail: [email protected] wildlife management from the Virginia Polytechnical Institute and State University, and a Ph.D. in zoology and entomology from Colorado State University. Since 1982, he has been leading research teams studying old-growth, naturally young, and managed forests and their wildlife in the Pacific Northwest.

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