Environmental Issues in Pacific Northwest Forest Management (2000) / Chapter Skim
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4 The Status and Functioning of Pacific Northwest Forests
4 The Status and Functioning of Pacific Northwest Forests
Pages 73-107
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From page 73... ...
The chapter ends by considering the long-term effects of the loss of biological diversity on the stability and functioning of ecosystems In general. The findings presented in this chapter provide importantbases for the assessment of forest management practices in Chapters 7 and S
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From page 74... ...
And checkerboard ownerships of public and private lancis hinder effective assessment and management of forest ecosystem patterns and processes. Measurement of key ecological and ecosystem processes is more able Man an inventory to provide sensitive indicators of forest condition.
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However, such measurements from a representative subset of stands could provide critical insight into the {ong-term trends In forest condition that result from alternative management practices. Maintenance of species assemblages and ecosystem processes both are important in measuring forest condition.
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From page 76... ...
Viable populations of indigenous species might be critical for maintenance of ecological processes in Pacific Northwest forests, but few studies have addressed the contributions of particular species or species assemblages to processes. Many examples of the importance of biodiversity in ecosystem functioning are obvious.
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Elton and Odum were referring to the stability of an entire ecosystem, whereas May and Goodman were referring to the stability of a single species within an ecosystem. May, for instance, demonstrated theoretically that the population size of a species is expected to be more stable (i.e., return to equilibrium more rapidly after a perturbation)
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From page 78... ...
In reviewing these studies on the effects of biodiversity on ecosystem productivity and stability, Kareiva (1994) concludecE that the loss of biodiversity leads to "less productive ecosystems, vulnerable to environmental perturbations, and plagued by declining soil fertility." This conclusion was supported by a field study in which the plant diversity of 147 prairie grasslanct plots was manipulatecl and found to affect directly total plant community productivity, nutrient use, and nutrient leaching loss (Tilman et al.
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From page 79... ...
that increased plant diversity helps stabilize primary production in response to climatic change. For instance, in 1977, a severe ctroughtin eastern Europe caused greatly decreased plant growth and crop yields.
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presented data for the Serengeti savanna that demonstrated that areas with greater plant diversity were more resilient to natural grazing pressure, because ungulate grazers fed more selectively in areas with greater plant diversity. Plant species not consumed by grazers were able to increase rapidly in biomass once freed from competition with the species preferred by the grazers.
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Second habitat fragmentation isolates populations and decreases localpopulation size. Smallpopulation size increases the chance of local extinction (May 1973)
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As we wouIct expect, populations maintain themselves as long as recolonization and population growth produce sufficient numbers of dispersing individuals to balance local extinction. Any population can be reduced or fragmented to the point where this balance no longer is maintained.
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From page 83... ...
can be approximated by the simple formula S = cAZ, where c is equivalent to the average number of species encountered in an area of unit size, and z is the fractional increase in species per fractional increase in area. The effect of habitat loss on regional species diversity is a sharply increasing function of Me proportion of the habitat destroyed.
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From page 84... ...
Certainly, no one would argue that habitat fragmentation or Toss have
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From page 85... ...
Pest outbreaks are nor random events that threaten forest resources but rather, at /east in part, are predictab/e responses to changes in forest condition; thus, they are va/uab/e ina/icators of changes in forest condition. Diseases and Pests Pest outbreaks are not random events that threaten forest resources but rather, at least in part, are predictable responses to changes in forest condition; thus, they are valuable indicators of changes in forest condition.
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From page 86... ...
Plant-feed~ng insects and pathogens have a wide range of abilities to colonize host plants, depending on their tolerances or ability to detoxify plant defensive chemicals (Harborne 1994~. Some insects and pathogens respond rapidly to small changes in concentrations of defensive chemicals in milcIly stressed plants, whereas others can reach outbreak levels only if there has been a considerable reduction in plant clefensivechem~cai production (folio 1993~.
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From page 87... ...
This term refers to the ease with which an insect or pathogen can find individuals of a suitable tree species. Insects adapted to feeding on particular plant species often use the defensive chemicals produced by their host plants and carried in the forest vapor stream (especially if plant injury increases chemical release to the airstream)
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From page 88... ...
provide shelter for owls and porcupines. Root rots create patchiness that diversifies plant species composition.
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From page 89... ...
For example, ArmiZlaria root rot problems are more severe in productive sites than in harsh, iess-productive sites because of more intense logging on productive sites and the resultant increased true fir component (Hagle and Schmitz 1993~. Some insect outbreaks result from changing climatic conditions, such as droughts, and are especially severe on sites where dominance has shifted to tree species susceptible to insects and pests (Mattson and Haack 1987~.
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The resulting shift in tree species composition was dramatic. Eastside commercial forest land dominated by ponderosa pine has shrunk cturing the 20th century 75%-90%, depending on locale.
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The species that have been most immediately and greatly affected by past lance use in the region are those species most closely associated with late successional and old-growth forests. Because most plant species abundances do not vary greatly among younger, mature, and old-growth forests in western Oregon and Washington (Spies 1991)
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From page 92... ...
And although the ESA has focused attention on species such as the northern spotted owl anct the grizzly bear (Ursus arctos horribiZis) , mandates predating the Multiple Use-Sustainect Yield Act of 1960 pertain to national forests and address the need to maintain key ecological processes and bioctiversity.
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(Paulson 1992~. Habitat loss on southern winter range and on breeding range, habitat fragmentation Mat predisposes interior forest species to increased brood parasitismirombrown-headect cowbirds (MoZothrus ater)
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1993~0 Goshawks (Accipitergentilis) require protection of riparian habitat and protection of known active nest sites, which usually are found only in mature forest with canopy closure (Thomas et al.
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On BUM lands in western Oregon, spotted owl nest sites contained more old-growth forest and were in larger old-growth patches than randomly located sites in managed forests (Meyer et al.
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1996~. The main conclusions from these comparisons is that the population dynamics and habitat relationships of spotted owls vary across the owes range, that populations are declining west of the Cascade crest, and that Insufficient habitat is now available on Westside forests to sustain owl populations.
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v ~ ^ it, Flammulated owl, boreal owl, great gray owl (Strix nebulosa) , whiteheaded woodpecker, black-backed woodpecker (Picoidles arcticus)
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This squirrel is also a major prey species for the northern spotted owl. The chipmunk also consumes fungi, as well as seeds anti fruits.
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Although debates over causes for the declines are heated, the status of many stocks is not in dispute. Most of the salmonid stocks of the mainstem Columbia River have been declining in abundance throughout the past century and have decreased sharply since 1970.
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All species of anactromous salmonicts in the Pacific Northwest have undergone stock extinctions within the past century, and pink salmon is the only species in which the majority of stocks are not known to be declining. Causes for the declines of anactromous salmonids are numerous and include habitat loss and conversion of streamsicte forest to agricultural, range, residential, or urban lands.
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For example, many of the herb and shrub species characteristic of early successional communities in Westside forests (e.g., snowbrush (Ceanothus veZutinus) , manzanita (ArctostaphyZos)
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can provide important refuges for many invertebrate species. Late-successional forest thus provides resources critical to survival of many species that, in turn, contribute to productivity of those forests.
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Mycorrhizal fungi are crucial to ecosystem processes because they facilitate and accelerate the rate at which plants are able to reestablish and recover after disturbances (Trappe and Luoma 1992~. in Eastside and Westside forests, the maintenance of the symbiotic associations in forests is correlated closely with the presence of large, coarse, woody debris.
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From page 104... ...
That can refer either to local populations or metapopulations, depending on the circumstances.2 The number of individuals that constitute a viable population is difficult to determine but depends in part on · The population structure, social dynamic, and breeding characteristics of the species in question. · Environmental fluctuations, particularly the possibility of catastrophic events that sharply reduce population size (Shaffer 1981~.
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From page 105... ...
The risk of extinction from demographic variations in population size is particularly high where factors such as infectious disease or largescale natural events (e.g., hurricanes and wildfires) have the potential to reduce population sizes sharply (Hanson and Tuckwell 1981; Lande 1993~.
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From page 106... ...
For most mammals and birds, effective population sizes are no more than 25-50% of actual population size. Animals that live in family groups, such as wolves, typically have only one mating pair per group.
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1999~. Several PVAs have been conducted in recent years, including ones for the marbled murrelet, the northern spotted owl, ant]
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