Andrew B. Carey

Disturbances and structural development of natural forest ecosystems with silvicultural implications, using Douglas-fir forests as an example

Forest managers need a comprehensive scientific understanding of natural stand development processes when designing silvicultural systems that integrate ecological and economic objectives, including a better appreciation of the nature of disturbance regimes and the biological legacies, such as live trees, snags, and logs, that they leave behind. Most conceptual forest development models do not incorporate current knowledge of the: (1) complexity of structures (including spatial patterns) and developmental processes; (2) duration of development in long-lived forests; (3) complex spatial patterns of stands that develop in later stages of seres; and particularly (4) the role of disturbances in creating structural legacies that become key elements of the post-disturbance stands. We elaborate on existing models for stand structural development using natural stand development of the Douglas-fir—western hemlock sere in the Pacific Northwest as our primary example; most of the principles are broadly applicable while some processes (e.g. role of epicormic branches) are related to specific species. We discuss the use of principles from disturbance ecology and natural stand development to create silvicultural approaches that are more aligned with natural processes. Such approaches provide for a greater abundance of standing dead and down wood and large old trees, perhaps reducing short-term commercial productivity but ultimately enhancing wildlife habitat, biodiversity, and ecosystem function, including soil protection and nutrient retention. # 2002 Elsevier Science B.V. All rights reserved.

Small Mammals in Managed, Naturally Young, and Old-Growth Forests

Forest managers in the Pacific Northwest are faced with new challenges of providing for all wildlife in managed forests. Our objective was to elucidate the factors governing the composition and biomass of forest floor mammal communities that are ame- nable to management. We sampled small mammal communities in forests of various man- agement histories on the Olympic Peninsula and contrasted our results with those of other large studies in the Pacific Northwest. Forest floor mammal communities in forests >35 yr old in the Western Hemlock Zone of Washington and Oregon are composed of 5-8 characteristic species. These include Sorex trowbridgii (numerically the most dominant); one species each of Clethrionomys, the Sorex vagrans complex, and Peromyscus; and Neurotrichus gibbsii. Species composition changes from south to north, and the communities on the Olympic Peninsula contain two or three additional species compared to communities to the south. Communities in naturally re- generated and clearcutting regenerated (managed) young forests are similar in composition to those in old growth; old growth, however, supports 1.5 times more individuals and biomass than managed forest. Community diversity seems related to the south-north mois- ture-temperature gradient that is reflected in increased diversity of canopy conifers, de- velopment of forest floor litter layers, accumulation of coarse woody debris, and abundance of herbs, deciduous shrubs, and shade-tolerant seedlings (as opposed to understories dom- inated by evergreen shrubs). Previous work found few habitat variables that were good predictors of species abundance in natural young and old-growth stands. Naturally regen- erated young stands had higher levels of coarse woody debris than old growth. Managed stands had much lower abundance of coarse woody debris and tall shrubs than old growth. Understory vegetation (herbs and shrubs) and coarse woody debris accounted for a major part of the variation in abundance of six of eight species in managed stands, but only two species in old growth. Management of Western Hemlock Zone forest for conservation of biodiversity and restoration of old-growth conditions should concentrate on providing mul- tispecies canopies, coarse woody debris, and well-developed understories.

Northern spotted owls: influence of prey base and landscape character

We studied prey populations and the use and composition of home ranges of 47 Northern Spotted Owls (Strix occidentalis caurina) over 12 mo in five landscapes in two forest types in southwestern Oregon. We measured 1-yr home ranges of 23 owl pairs, 2-yr home ranges of 13 pairs, and 3-yr home ranges of 3 pairs. The landscapes differed in the degree to which old forest had been fragmented by wildfire and logging. Prey populations were measured at 47 sites in southwestern Oregon. Further data on prey populations were gathered on 14 sites on the Olympic Peninsula in northern Washington, where owls use larger ranges than in Oregon. Owls in Washington used - 1700 ha of old forest annually and primarily one prey species; available prey biomass was 61 g/ha. Owls in Oregon Douglas-fir (Pseudotsuga menziesai) forests used 813 + 133 ha (X + SE) of old forest annually and concentrated on two prey species that had a combined biomass of 244 g/ha. Owls in Oregon mixed-conifer forest used 454 ? 84 ha of old forest annually and three primary prey whose availability averaged 338 g/ha. The amount of old forest used by owls studied for 2 yr was 40% greater in the 2nd yr than that used in the Ist yr. No increase in use of old forest was seen in the 3rd yr in Douglas-fir forest; 50% more old forest was used in 3 yr than in the 1st yr in mixed-conifer forest. The most common prey in Washington and Oregon was the northern flying squirrel (Glaucomys sabrinus). In areas where the flying squirrel was the primary prey and where predation was intense (as judged by telemetry), flying squirrel populations were depressed. The addition of medium-sized mammal species, especially woodrats (Ne- otoma spp.), to the prey base appeared to reduce markedly the amount of old forest used for foraging. Owls traversed 85% more Douglas-fir forest and 3 times more mixed-conifer forest in the heavily fragmented areas than in the lightly fragmented areas. Overlap among pairs and separation of birds within pairs in space increased with fragmentation. In the most heavily fragmented landscape, social structure appeared to be abnormal, as judged by the proportion of adult-subadult pairs, instances of adult nomadism, and overlap among the home ranges of pairs. The pattern of fragmentation affected the ability of owls to find concentrations of old forest in the landscapes. Even so, almost all the owls consistently selected old forests for foraging and roosting; only one owl selected a younger type as part of its foraging range. Selection of old forest was significant at three levels: landscape, annual home ranges of pairs, and foraging and roosting sites of individuals. The most important prey species, the northern flying squirrel, was twice as abundant in old forest as in young forest in all areas. Landscape indices (dominance, contagion, variance in density of old forest) had less predictive ability than indices based on owl home ranges because owls selected areas of concentrated old forest and because patterning was complex, reflecting four processes, each operating at a different scale: physiography, human land ownership (259-ha scale), history of catastrophic fires, and history of small-scale fires and timber harvesting.

SCIURIDS IN PACIFIC NORTHWEST MANAGED AND OLD-GROWTH FORESTS'

An understanding of the factors governing sciurid abundance in the Pacific Northwest is essential for prescribing forest management practices for second-growth forests where recovery of Spotted Owl (Strix occidentalis) populations and enhancement of biodiversity are objectives. We compared results of companion studies of sciurids in western Washington and Oregon and examined patterns of abundance in relation to habitat elements on the Olympic Peninsula to elucidate governing factors and make recommendations for forest management. Regional contrasts show that Glaucomys sabrinus and Tamias townsendii in Douglas-fir forests in Oregon are 4 times more abundant than in western hemlock forests in Washington, and dietaries of Glaucomys, and the fungal communities that provide its food, are more diverse in Oregon than in Washington. Glaucomys sabrinus in old forests are 2 times more abundant than in young, managed forests without old-forest legacies (large live trees, large snags and large, decaying fallen trees): populations in young forests with old-forest legacies and with understory development may equal those in old Growth. On the Olympic Peninsula. Glaucomys sabrinus abundance can be predicted by density of large snags and abundance of ericaceous shrubs. At least seven large snags/ha and well-distributed patches of dense shrubs (cover within patches >24% and patches covering 40% of the total area) are necessary for high densities of Glaucomys sabrinus. Abundance of Tamias townsendii reflects size of dominant tree and well-developed understories. Abundance of Ta,niasciurus douglasii seems to reflect territoriality in concordance with food supply and was greatest where Glaucomys and Tamias were low in abundance. Patterns of abundance of the sciurids in old- and managed forests suggests that silvicultural manipulation of vegetation and creative snag or den-tree management could be used in a management strategy to accelerate the development of Spotted Owl habitat in areas where old Growth is lacking.

EFFECTS OF NEW FOREST MANAGEMENT STRATEGIESON SQUIRREL POPULATIONS

Two strategies for managing forests for multiple values have achieved prominence in debates in the Pacific Northwest: (1) legacy retention with passive management and long rotations, and (2) intensive management for timber with commercial thinnings and long rotations. Northern flying squirrels (Glaucomys sabrinus), Townsend’s chipmunks (Tamias townsendii), and Douglas’ squirrels (Tamiasciurus douglasii) were studied retrospectively in Douglas-fir (Pseudotsuga menziesii) forests managed under the alternative strategies in the Puget Trough of Washington. Flying squirrels were twice as abundant under legacy retention as under intensive management for timber, almost as abundant as in old-growth western hemlock (Tsuga heterophylla) forests on the Olympic Peninsula of Washington, but <50% as abundant as in old-growth Douglas-fir forests in western Oregon. Chipmunks were four times as abundant under intensive timber management, as under legacy retention, but less abundant than in old-growth forests. Abundance of...

Small mammals in young forests: implications for management for sustainability

Abstract Small mammals have been proposed as indicators of sustainability in forests in the Pacific Northwest and elsewhere. Mammal community composition and species abundances purportedly result from interactions among species, forest-floor characteristics, large coarse woody debris, understory vegetation, and overstory composition. Coarse woody debris is thought to be particularly important because of its diverse ecological functions; covers from 10 to 15% have been recommended based on retrospective studies of forests and small mammals. Unfortunately, ecological correlations are not necessarily indicative of causal relationships and magnitudes depend on composition of finite, usually non-random, cross-sectional samples. Retrospective studies must be replicated to confirm relationships. We conducted a large-scale, cross-sectional survey of 30- to 70-year-old coniferous forests in western Washington to determine if previously reported relationships would hold with an unrelated, larger sample. Coarse woody debris cover was 8.3±0.6% ( x ± S.E. , n=8 blocks of forest, range 4–13%). Understory cover was too low (18±8% for shrubs) to allow examining interactions between understory and coarse woody debris. Overstory composition covaried with coarse woody debris. One or two of four statistically extracted habitat factors (overstory composition, herbaceous cover, abundance of Acer circinatum, and abundance of Acer macrophyllum) accounted for 18–70% of variance in abundance of 11 mammal species. Our results support hypotheses that: (1) biocomplexity resulting from interactions of decadence, understory development, and overstory composition provides pre-interactive niche diversification with predictable, diverse, small-mammal communities; (2) these communities incorporate numerous species and multiple trophic pathways, and thus, their integrity measures resiliency and sustainability.

Dens of northern flying squirrels in the Pacific Northwest

Silvicultural prescriptions to enhance northern flying squirrel (Glaucomys sabrinus) habitat have been suggested as an aid for recovery of the threatened northern spotted owl (Strix occidentalis caurina). Flying squirrels are hypothesized to be limited by den sites (cavities in trees) and by food (truffles). However, no quantitative information exists on den sites of flying squirrels. Therefore, during 1986-94, we used radiotelemetry to locate 604 different den sites in the southern Coast Range of Oregon, the southern Olympic Peninsula, and the Puget Trough of Washington. Den sites included cavities in live and dead old-growth trees; cavities, stick nests, and moss nests in small (10-50 cm dbh) second-growth trees; dens in cavities in branches of fallen trees; and dens in decayed stumps of old-growth trees and suppressed young trees. Two-thirds of all dens located were in live trees. Most dens were located during a study of second-growth forests in the Puget Trough. Females selected cavities for maternal dens. Squirrels used multiple dens; denning partners varied with den. Dens of males were 211 ± 7 m apart; dens of females were 108 ± 4 m apart. Males used 2.2 ± 0.1 dens per month; females 2.3 ± 0.1 dens per month. Dens, except maternal dens, were often occupied simultaneously by several adult squirrels. Many fragile den sites were used by females. Secure cavities are scarce and may limit reproductive success. Management for cavity trees and dens could prove fruitful in owl recovery and habitat restoration efforts.

Spotted owl home range and habitat use in southern Oregon coast ranges

We radiotracked 9 adult spotted owls (Strix occidentalis) in the southern Oregon Coast Ranges for 6-12 months. Owls selected home ranges that emphasized old growth within the landscape. Minimum convex polygon home ranges of 4 pairs were 1,153-3,945 ha and contained 726-1,062 ha of old growth. The percentages of. the home ranges in old growth were 25-73%. Home-range size expanded significantly (P < 0.05) with decreasing proportions of old growth (r = -0.83). The amount of old growth in the pair home ranges was less variable than was home-range size. Old growth was selected by the owls for foraging and roosting (P < 0.05); clearcuts and other nonforested areas were not used. Early to middle stages of forest development were used either less than or in proportion to their availability within the home ranges, even where old growth was scarce. J. WILDL. MANAGE. 54(1):11-17 _____________________________________________________________________________________________ Spotted owl management in the Pacific Northwest is controversial because it involves a mix of biological, economic, political, and social issues (Heinrichs 1983, Strong 1987). Spotted owls are associated with commercially valuable old-growth, coniferous forests (Carey 1985). Habitat management rests primarily on 3 telemetry studies of habitat use and home-range sizes (Forsman et al. 1984, Gutierrez et al. 1984, Forsman and Meslow 1985) and various unpublished reports (see Marcot and Holthausen 1987). Only 1 study (Forsman et al. 1984 as supplemented by Forsman and Meslow 1985) is reported in detail. Dawson et al. (1987) conclude that precise information on the owls habitat needs will be necessary to resolve the controversy over the preservation of the species. Forsman et al. (1984) and Forsman and Meslow (1985) report habitat use, home-range sizes, and the composition of home ranges of 8 adult owls radiotracked for 9-12 months in the central Oregon Cascade Range and 6 adult owls tracked for 4 months in the central Oregon Coast Ranges. Gutierrez et al. (1984) tracked 8 owls for up to 1 year in the North Coast Range of California; they provide only an overview of their study. Our objectives were to determine the home-range sizes, home-range composition, habitat use, and response to forest fragmentation of spotted owls across a large landscape, the southern Oregon Coast Ranges. We wanted to assess if the results reported by Forsman and Meslow (1985) could be generalized and to determine possible geographic differences in the habitat of spotted owls in the Western Hemlock Zone of Oregon, as described by Franklin and Dyrness (1973). A. Strassler and P. Christgau provided field assistance; P. Carson was especially helpful in mapping owl home ranges. R. Bown, J. Lint, J. Mires, F. Oliver, J. Witt, and numerous other employees of the Roseburg District of the Bureau of Land Management provided invaluable assistance. Funding was provided by the Oregon State Office of the Bureau of Land Management in cooperation with the U.S. Forest Service’s Old Growth Wildlife Habitat Program. This is contribution 97 of the Old Growth Program. E. Forsman, M. Fuller, G. Gould, N. Green, R. Gutierrez, J. Lint, B. Mannan, C. Meslow, G. Miller, N. Tilghman, R. Reynolds, and J. Verner reviewed earlier draft manuscripts.

Induced spatial heterogeneity in forest canopies : Responses of small mammals

We hypothesized that creating a mosaic of interspersed patches of different densities of canopy trees in a second-growth Douglas-fir (Pseudotsuga menziesii) forest would accelerate development of biocomplexity (diversity in ecosystem structure, composition, and processes) by promoting spatial heterogeneity in understory, midstory, and canopy, compared to typical managed forests. In turn, increased spatial heterogeneity was expected to promote variety in fine-scale plant associations, foliage height diversity, and abundance of small mammals. Three years following treatment, understory species richness and herb cover were greater with variable-density thinning than without. Midstory and canopy species did not have time to develop significant differences between treatments. Variable-density thinning resulted in larger populations of deer mice (Peromyscus maniculatus), a species associated with understory shrubs; creeping voles (Microtus oregoni), a species associated with herbaceous vegetation, and vagrant shrews (Sorex vagrans), a species usually associated with openings but common in old growth. No forest-floor small-mammal species, including those associated with old-growth forest, declined in abundance following variabie-density thinning. Annual variation in population size was not related to treatment. Variable-density thinning may accelerate the development of biocomplexity in second-growth forest by promoting spatial heterogeneity and compositional diversity in the plant community, increasing diversity and abundance of small mammals, and similarly affecting other vertebrate communities. When combined with long rotations, legacy retention, and management for snags and coarse woody debris, variable-density thinning has broad applicability to enhance biodiversity in managed Douglas-fir forests across the Pacific Northwest.

Experimental manipulation of spatial heterogeneity in Douglas-fir forests: effects on squirrels

Abstract Squirrel communities simultaneously composed of abundant populations of Glaucomys, Tamias, and Tamiasciurus are: (1) a result of high production of seeds and fruiting bodies by forest plants and fungi and complexity of ecosystem structure, composition, and function; (2) indicative of high carrying capacity for vertebrate predators and (3) characteristic of old, natural forests in the Pacific northwest, USA. I hypothesized that silvicultural manipulation of canopies of second-growth forests could result in spatial heterogeneity that would reproduce the biocomplexity and plant-fungal productivity associated with high squirrel populations. I predicted that accelerating biocomplexity would require ≥20 years, but short-term effects of induced heterogeneity would be apparent in 5 years: initial decreases followed by increases in Glaucomys populations, nonlinear increases in Tamias populations, and little change in Tamiasciurus populations. If my predictions proved accurate, confidence in long-term predictions would be enhanced. I chose 16 13-ha stands with two different management histories for a randomized block experiment and began measuring squirrel populations in 1991. Variable-density thinnings were implemented in spring 1993. Fall and spring populations were measured through fall 1998. Populations responded as predicted, except for a treatment–management history interaction. Previous conventional thinnings altered ecosystem function such that low Glaucomys populations failed to respond to treatment. Variable-density thinning, in conjunction with retention of biological legacies and management of decadence, could possibly accelerate biocomplexity in second-growth forest that mimics that in old, natural forests.