39 research outputs found
Seed Invasion Filters and Forest Fire Severity
Forest seed dispersal is altered after fire. Using seed traps, we studied impacts of fire severity on timing of seed dispersal, total seed rain, and seed rain richness in patches of high and low severity fire and unburned Douglas-fir (Pseudotsuga menziesii) forests in the Fischer and Tyee fire complexes in the eastern Washington Cascades. Unburned plots had the lowest average seed production. The high severity fire patches in the Fischer Fire Complex had a higher total seed production than low severity fire patches of the same complex. At the Tyee Fire Complex, the total seed production for each of the two fire severities was similar, but the period of maximum seed dispersal was later for high severity than low severity fire. Seed rain at the Fischer Fire patches (sampled one year after the fire) was predominantly composed of annual species, while that of the Tyee Fire patches (sampled nine years after fire) was predominantly perennial species. Seed rain richness was greater in Tyee high severity patches than paired low severity fire patches. In these paired Tyee patches the average number of new seed species (species not found in the extant plot vegetation) was greater for high severity than low severity fire. Our results suggest that high severity fire plots are more porous to seed rain than low severity plots. Intact forest canopies may filter seed rain and reduce seed influx, while high severity fires are more open to invasion by seed dispersal
Wildfire may increase habitat quality for spring Chinook salmon in the Wenatchee River subbasin, WA, USA
Pacific Northwest salmonids are adapted to natural disturbance regimes that create dynamic habitat patterns over space and through time. However, human land use, particularly long-term fire suppression, has altered the intensity and frequency of wildfire in forested upland and riparian areas. To examine the potential impacts of wildfire on aquatic systems, we developed stream-reach-scale models of freshwater habitat for three life stages (adult, egg/fry, and juvenile) of spring Chinook salmon (Oncorhynchus tshawytscha) in the Wenatchee River subbasin, Washington. We used variables representing pre- and post-fire habitat conditions and employed novel techniques to capture changes in in-stream fine sediment, wood, and water temperature. Watershed-scale comparisons of high-quality habitat for each life stage of spring Chinook salmon habitat suggested that there are smaller quantities of high-quality juvenile overwinter habitat as compared to habitat for other life stages. We found that wildfire has the potential to increase quality of adult and overwintering juvenile habitat through increased delivery of wood, while decreasing the quality of egg and fry habitat due to the introduction of fine sediments. Model results showed the largest effect of fire on habitat quality associated with the juvenile life stage, resulting in increases in high-quality habitat in all watersheds. Due to the limited availability of pre-fire high-quality juvenile habitat, and increased habitat quality for this life stage post-fire, occurrence of characteristic wildfires would likely create a positive effect on spring Chinook salmon habitat in the Wenatchee River subbasin. We also compared pre- and post-fire model results of freshwater habitat for each life stage, and for the geometric mean of habitat quality across all life stages, using current compared to the historic distribution of spring Chinook salmon. We found that spring Chinook salmon are currently distributed in stream channels in which in-stream habitat for most life stages has a consistently positive response to fire. This compares to the historic distribution of spring Chinook, in which in-stream habitat exhibited a variable response to fire, including decreases in habitat quality overall or for specific life stages. This suggests that as the distribution of spring Chinook has decreased, they now occupy those areas with the most positive potential response to fire. Our work shows the potentially positive link between wildfire and aquatic habitat that supports forest managers in setting broader goals for fire management, perhaps leading to less fire suppression in some situations
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Climate change and vulnerability of bull trout (Salvelinus confluentus) in a fire-prone landscape
Linked atmospheric and wildfire changes will complicate future management of native coldwater fishes in fire-prone
landscapes, and new approaches to management that incorporate uncertainty are needed to address this challenge. We used a
Bayesian network (BN) approach to evaluate population vulnerability of bull trout (Salvelinus confluentus) in the Wenatchee River
basin, Washington, USA, under current and future climate and fire scenarios. The BN was based on modeled estimates of
wildfire, water temperature, and physical habitat prior to, and following, simulated fires throughout the basin. We found that
bull trout population vulnerability depended on the extent to which climate effects can be at least partially offset by managing
factors such as habitat connectivity and fire size. Moreover, our analysis showed that local management can significantly reduce
the vulnerability of bull trout to climate change given appropriate management actions. Tools such as our BN that explicitly
integrate the linked nature of climate and wildfire, and incorporate uncertainty in both input data and vulnerability estimates,
will be vital in effective future management to conserve native coldwater fishes
Tamm Review: Management of mixed-severity fire regime forests in Oregon, Washington, and Northern California
Increasingly, objectives for forests with moderate- or mixed-severity fire regimes are to restore successionally diverse landscapes that are resistant and resilient to current and future stressors. Maintaining native species and characteristic processes requires this successional diversity, but methods to achieve it are poorly explained in the literature. In the Inland Pacific US, large, old, early seral trees were a key historical feature of many young and old forest successional patches, especially where fires frequently occurred. Large, old trees are naturally fire-tolerant, but today are often threatened by dense understory cohorts that create fuel ladders that alter likely post-fire successional pathways. Reducing these understories can contribute to resistance by creating conditions where canopy trees will survive disturbances and climatic stressors; these survivors are important seed sources, soil protectors, and critical habitat elements. Historical timber harvesting has skewed tree size and age class distributions, created hard edges, and altered native patch sizes. Manipulating these altered forests to promote development of larger patches of older, larger, and more widely-spaced trees with diverse understories will increase landscape resistance to severe fires, and enhance wildlife habitat for underrepresented conditions.
Closed-canopy, multi-layered patches that develop in hot, dry summer environments are vulnerable to droughts, and they increase landscape vulnerability to insect outbreaks and severe wildfires. These same patches provide habitat for species such as the northern spotted owl, which has benefited from increased habitat area. Regional and local planning will be critical for gauging risks, evaluating trade-offs, and restoring dynamics that can support these and other species. The goal will be to manage for heterogeneous landscapes that include variably-sized patches of (1) young, middle-aged, and old, closed canopy forests growing in upper montane, northerly aspect, and valley bottom settings, (2) a similar diversity of open-canopy, fire-tolerant patches growing on ridgetops, southerly aspects, and lower montane settings, and (3) significant montane chaparral and grassland areas. Tools to achieve this goal include managed wildfire, prescribed burning, and variable density thinning at small to large scales. Specifics on ‘‘how much and where?” will vary according to physiographic, topographic and historical templates, and regulatory requirements, and be determined by means of a socio-ecological process
Tamm Review: Management of mixed-severity fire regime forests in Oregon, Washington, and Northern California
Increasingly, objectives for forests with moderate- or mixed-severity fire regimes are to restore successionally diverse landscapes that are resistant and resilient to current and future stressors. Maintaining native species and characteristic processes requires this successional diversity, but methods to achieve it are poorly explained in the literature. In the Inland Pacific US, large, old, early seral trees were a key historical feature of many young and old forest successional patches, especially where fires frequently occurred. Large, old trees are naturally fire-tolerant, but today are often threatened by dense understory cohorts that create fuel ladders that alter likely post-fire successional pathways. Reducing these understories can contribute to resistance by creating conditions where canopy trees will survive disturbances and climatic stressors; these survivors are important seed sources, soil protectors, and critical habitat elements. Historical timber harvesting has skewed tree size and age class distributions, created hard edges, and altered native patch sizes. Manipulating these altered forests to promote development of larger patches of older, larger, and more widely-spaced trees with diverse understories will increase landscape resistance to severe fires, and enhance wildlife habitat for underrepresented conditions.
Closed-canopy, multi-layered patches that develop in hot, dry summer environments are vulnerable to droughts, and they increase landscape vulnerability to insect outbreaks and severe wildfires. These same patches provide habitat for species such as the northern spotted owl, which has benefited from increased habitat area. Regional and local planning will be critical for gauging risks, evaluating trade-offs, and restoring dynamics that can support these and other species. The goal will be to manage for heterogeneous landscapes that include variably-sized patches of (1) young, middle-aged, and old, closed canopy forests growing in upper montane, northerly aspect, and valley bottom settings, (2) a similar diversity of open-canopy, fire-tolerant patches growing on ridgetops, southerly aspects, and lower montane settings, and (3) significant montane chaparral and grassland areas. Tools to achieve this goal include managed wildfire, prescribed burning, and variable density thinning at small to large scales. Specifics on ‘‘how much and where?” will vary according to physiographic, topographic and historical templates, and regulatory requirements, and be determined by means of a socio-ecological process
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Pathogenesis and intertree transmission of Verticicladiella wageneri in Douglas-fir (Pseudotsuga menziesii)
Verticicladiella wageneri Kendr. is a vascular wilt pathogen of
Douglas-fir in the Pacific Northwest, The disease is characterized by
black staining of colonized sapwood; crown symptoms are those typical
of a wilting syndrome. Histopathological studies revealed that the
pathogen is limited to the xylem but causes vascular dysfunction in
both the xylem and phloem. In xylem, hyphae grew in lumens of mature
tracheids increasing resistance to the flow of xylem sap; bordered pit
penetration facilitated intertracheal growth. Living host cells were
never invaded by hyphae and evidence for the primary involvement of
translocateabie phytotoxins was lacking. Increased vertical and circumferential extension of the fungus, systematically reduced the capacity of vascular tissue to conduct water. Phloem vascular dysfunction occurred with no evidence of mycelial invasion of phloem tissues. The
appearance of engorged sieve cells and flattened albuminous cells,
adjacent only to regions of heavily ramified xylem, suggested that this xylem colonization indirectly impeded centripetal transport of
photosynthate through rays. Xylem pressure potential and transpiration water uptake were
periodically measured on V. wageneri inoculated and control seedling
groups to indicate the earliest significant consequence of vascular
tissue colonization. Circumferential colonization of inoculated seedling roots consistently exceeded 90% when significant differences in
pressure potential and water uptake were first apparent; radial colonization was proportionally less (35-61%). This pattern, supported by
the histopathological evidence, suggested that foliage wilting was
related to vascular occlusion.
Root infections of dip-inoculated Douglas-fir seedlings were
initiated through artificial wounds and natural openings to exposed
xylem, and living bark and cambial tissues were never directly
penetrated by hyphae,
Root graft transmission of V. wageneri in Douglas-fir was verified from field excavations in natural infection centers. In potted
seedling experiments, healthy seedlings regularly became infected
whether intertree root contact was allowed or completely restricted. In growth chamber experiments, cool soil temperatures favored
infection and establishment of V. wageneri in inoculated Douglas-fir
seedlings; warm temperatures decreased the likelihood of infection.
Vertical growth rate varied predictably with soil temperature fluctuations in the greenhouse; soil temperatures within or above the growth
optimum range favored faster growth of V. wageneri in xylem. Growth
rates in roots of older trees compared favorably with estimates of the
annual rate of radial increase of infection centers
Making Transparent Environmental Management DecisionsApplications of the Ecosystem Management Decision Support System /
XIX, 337 p. 69 illus., 49 illus. in color.online