Recent Burn Research Articles

Scale, the dynamic stability of forest ecosystems, and the persistence of biodiversity

Even as ecologists documented the importance of disturbance and non-equilibrium in vegetation dynamics, they began to ask whether the dramatic changes at the local, patch scale, would contribute to an equilibrium at larger spatial scales. Heinselman (1973) hypothesized a ‘shifting mosaic’ for the dynamics of boreal forests in which the spatial location of recent burns and stands of various successional ages would shift, but each would continue to be present within the larger landscape at some relatively constant frequency. The ‘mosaic-cycle concept of ecosystems’ (Remmert 1991) also conjectured that an overall dynamic equilibrium would be maintained in spite of local dynamic changes. Recent studies of disturbance focused on functional resilience, biodiversity and landscape equilibrium (e.g. Romme 1982, Turner et al.1993, Peterson et al. 1998, Engelmark et al. 1999, Frehlich and Reich 1999, White et al. 1999, Walker et al. 1999, White and Jentsch 2001). We defi ne function as the product of an ecological unit (e.g. an organism, a successional sere) and an ecological process (e.g. photosynthesis, nitrogen fi xation). Thus, functional stability and Scale, the Dynamic Stability of Forest Ecosystems, and the Persistence of Biodiversity

Impact of fire on leaf nutrients, arthropod fauna and herbivory of native and exotic eucalypts in Kings Park, Perth, Western Australia

AbstractThe vegetation of Kings Park, near the centre of Perth, Western Australia, once had an overstorey of Eucalyptus marginata (jarrah) or Eucalyptus gomphocephala (tuart), and many trees still remain in the bushland parts of the Park. Avenues and roadsides have been planted with eastern Australian species, including Eucalyptus cladocalyx (sugar gum) and Eucalyptus botryoides (southern mahogany), both of which have become invasive. The present study examined the effect of a recent burn on the level of herbivory on these native and exotic eucalypts. Leaf damage, shoot extension and number of new leaves were measured on tagged shoots of saplings of each tree species in unburnt and burnt areas over an 8‐month period. Leaf macronutrient levels were quantified and the number of arthropods on saplings was measured at the end of the recording period by chemical knockdown. Leaf macronutrients were mostly higher in all four species in the burnt area, and this was associated with generally higher numbers of canopy arthropods and greater levels of leaf damage. It is suggested that the pulse of soil nutrients after the fire resulted in more nutrient‐rich foliage, which in turn was more palatable to arthropods. The resulting high levels of herbivory possibly led to reduced shoot extension of E. gomphocephala, E. botryoides and, to a lesser extent, E. cladocalyx. This acts as a negative feedback mechanism that lessens the tendency for lush, post‐fire regrowth to outcompete other species of plants. There was no consistent difference in the levels of the various types of leaf damage or of arthropods on the native and the exotic eucalypts, suggesting that freedom from herbivory is not contributing to the invasiveness of the two exotic species.

Brazilian Páramos. III. Patterns and Rates of Postfire Regeneration in the Campos de Altitude1

Postfire vegetation development was studied at two recent mountaintop burns in the Serra do Caparaó, Espírito Santo/Minas Gerais, and the Serra dos Órgãos, Rio de Janeiro, Brazil. Both fires occurred within the páramo-like “campos de altitude”, a system of orographic grass- and scrublands restricted to the highest peaks of southeast Brazil. Data collected included pre- and postfire heights and densities of shrubs and trees, and cover of all taxa. Slopes of different aspect and altitude were sampled at each site to evaluate the effects of varying physical environment on regeneration. Rapid vegetative regeneration was common among shrubs and bamboo, with most taxa surviving fire. Regeneration and postfire colonization rates varied among species, and appeared to depend both on physical variables associated with different slopes, aspects and altitudes, and biotic variables. Most plant species in the campos de altitude show some form of evolutionary adaptation to fire. The distribution of species and plant populations across the landscapes of the campos de altitude appears to be largely the result of fire and its interactions with the biota, local topography, and climate. Results suggest that fire is an integral part of the ecology in these humid, seasonally dry ecosystems. Successful management of these unique and highly threatened systems requires a detailed understanding of the fire regime and its role in structuring biotic communities.

SOIL CARBON, NITROGEN, AND PHOSPHORUS STOCKS AND DYNAMICS UNDER DISTURBED BLACK SPRUCE FORESTS

In the North American boreal forest, black spruce (Picea mariana) forests have historically regenerated after the passage of large-scale wildfires. Over the past 30 years, tree harvesting has replaced wildfire as the predominant agent of disturbance in black spruce–feathermoss communities in the Lac St. Jean–Chibougamau region of Quebec, Canada. This study addressed how natural and anthropogenic disturbances altered soil and fine root carbon (C), nitrogen (N), and phosphorus (P) stocks and dynamics under four disturbance types in central Quebec including: (1) recently burned sites, (2) sites recently harvested using a practice called “cutting with protection of tree regeneration and soils” (CPRS), (3) sites that were burned 75–85 yr ago, and (4) sites that were horse-logged 55 yr ago. Soil N contents in the surface organic layer of the recently burned sites (91 g/m2) were significantly lower than under the old burn sites (146 g/m2). Using equivalent soil masses, total N stores in the mineral soils under the recently harvested stands (76 g/m2) were significantly lower than N stores under the old burn sites (114 g/m2). In field incubations from June to October 1997, net N mineralization rates in the organic horizons ranged from 3.3 kg/ha (recent burn) to 17.1 kg/ha (old harvest). The largest pools of labile inorganic-P (Bray 2 extractable) were in the organic horizons of the old harvest and old burn sites (59.1 and 55.3 mg/kg, respectively), and these pools increased up to 24% from the beginning to the end of the growing season. Pools of dissolved organic nitrogen in surface organic horizons in all of the disturbance types were highest just after snowmelt and declined steadily through the growing season. The older disturbance types had higher N stores in fine roots compared to the recently disturbed sites, and fine root length in the old harvest sites (1623 m/m2) was higher than in the stands burned 75–85 yr ago (917 m/m2).

Soil Carbon, Nitrogen, and Phosphorus Stocks and Dynamics under Disturbed Black Spruce Forests

In the North American boreal forest, black spruce (Picea mariana) forests have historically regenerated after the passage of large-scale wildfires. Over the past 30 years, tree harvesting has replaced wildfire as the predominant agent of disturbance in black spruce–feathermoss communities in the Lac St. Jean–Chibougamau region of Quebec, Canada. This study addressed how natural and anthropogenic disturbances altered soil and fine root carbon (C), nitrogen (N), and phosphorus (P) stocks and dynamics under four disturbance types in central Quebec including: (1) recently burned sites, (2) sites recently harvested using a practice called “cutting with protection of tree regeneration and soils” (CPRS), (3) sites that were burned 75–85 yr ago, and (4) sites that were horse-logged 55 yr ago. Soil N contents in the surface organic layer of the recently burned sites (91 g/m2) were significantly lower than under the old burn sites (146 g/m2). Using equivalent soil masses, total N stores in the mineral soils under the recently harvested stands (76 g/m2) were significantly lower than N stores under the old burn sites (114 g/m2). In field incubations from June to October 1997, net N mineralization rates in the organic horizons ranged from 3.3 kg/ha (recent burn) to 17.1 kg/ha (old harvest). The largest pools of labile inorganic-P (Bray 2 extractable) were in the organic horizons of the old harvest and old burn sites (59.1 and 55.3 mg/kg, respectively), and these pools increased up to 24% from the beginning to the end of the growing season. Pools of dissolved organic nitrogen in surface organic horizons in all of the disturbance types were highest just after snowmelt and declined steadily through the growing season. The older disturbance types had higher N stores in fine roots compared to the recently disturbed sites, and fine root length in the old harvest sites (1623 m/m2) was higher than in the stands burned 75–85 yr ago (917 m/m2).

Comparing bird assemblages in successional black spruce stands originating from fire and logging

Comparisons of the effects of logging and fire as disturbance agents on the composition of bird assemblages in boreal ecosystems are still lacking or are limited to the short-term impacts of clear-cutting. In Quebec, where the boreal forest is largely dominated by black spruce (Picea mariana (Mill.) B.S.P.) stands, we surveyed 140 point-count stations in 3 postlogging and 4 postfire development stages determined according to the height of the regenerating spruce trees. Species richness did not vary among forest development stages, but bird abundance was higher in recent clearcuts. Recently disturbed areas were characterized by open-land bird assemblages dominated by Neotropical migrants, which reached their highest abundance in clearcuts. Moreover, logged stands were distinguished from burned sites by the absence of cavity-nesting birds. Forest-bird assemblages reestablished themselves as soon as young spruces reached the sapling stage. However, the Black-backed Woodpecker (Picoides arcticus), Three-toed Woodpecker (Picoides tridactylus), and Brown Creeper (Certhia americana) were restricted to mature stands or recent burns and are thus likely to be negatively affected by modern forestry, which involves fire suppression and short logging rotations. We suggest that retention of larger areas of continuous mature forest might be essential to maintain these species in managed regions.

Lone Star Tick Abundance, Fire, and Bison Grazing in Tallgrass Prairie

Lone star ticks (Amblyomma americanum L.) were collected by drag samples of 1 km transects on 12 watersheds at Konza Prairie Research Natural Area near Manhattan, Kans., during summer 1995-1996. Watersheds were treated to 2 experimental treatments: 3 burn intervals (1-year, 4-year, and 20-year) and 2 grazing treatments (grazed by bison (Bos bison L.) or ungrazed). The objectives were to determine whether fire interval, time since most recent burn, and the presence of large ungulate grazers would cause changes in lone star tick abundance in tallgrass prairie in central Kansas. Watersheds burned at 1-year intervals had fewer larvae and adults than watersheds burned at 4-year or 20-year intervals. Watersheds burned during the year of sampling had fewer ticks than watersheds burned one or more years in the past. For watersheds burned 1 or more years in the past there was no effect from time since burn. The presence of bison did not affect tick abundance. Spring burning is an effective method to reduce tick populations in tallgrass prairie during the year of the burn.

Fire-induced changes in northern Patagonian landscapes

In northern Patagonia, Argentina we quantify changes in fire frequency along a gradient from mesic Nothofagus dombeyi forest to xeric woodlands of Austrocedrus chilensis at the steppe ecotone, and we examine patterns of vegetation change coincident with the changes in fire regimes across a range of spatial scales. At a regional scale changes in land cover types are documented by comparing 1:250 000 scale cover type maps from 1913 and 1985. Changes in landscape structure are analyzed by comparing vegetation patterns on 1:24 000 scale aerial photographs taken in 1940 and 1970. Fire frequency peaked in the late nineteenth-century due to widespread burning and clearing of forests by European settlers late in the century. Subsequently, fire frequency declined dramatically about 1910 due to the cessation of intentional fires and has remained low due to increasingly effective fire exclusion. At a regional scale there has been a dramatic increase during the twentieth century in the proportion of forest cover relative to areas mapped as recent burns or shrublands in 1913. Remnant forest patches that survived the widespread late-nineteenth century burning have coalesced to form more continuous forest covers, and formerly continuous areas of shrublands have become dissected by forest. Under reduced fire frequency there has been a shift in dominance from short-lived resprouting species (mostly shrubs) towards longer-lived species and obligate seed-dispersers such as Austrocedrus chilensis and Nothofagus dombeyi. Due to limited seed dispersal of these tree species, the spatial configuration of remnant forest patches plays a key role in subsequent changes in landscape pattern.

Purpura fulminans localising to a recent burn injury

The development of progressive, severe skin changes (purpura fulminans) is a serious complication of septicaemia, particularly meningococcal septicaemia. Purpura fulminans almost invariably leads to some full thickness skin loss and may lead to limb amputation. The pathophysiology may involve microemboli, endotoxins and direct bacterial damage to the vessels. We describe a case of purpura fulminans, probably as a result of meningococcal septicaemia, localising to a recent, healed burn with complete resolution. We can find no other record of the skin manifestations of meningococcal septicaemia localising to a previous injury.

Use of Forested Habitat by Breeding Birds in the Gulf Coastal Plain

Abstract I compared birds present during the breeding season in four forest types in the Conecuh National Forest located on the Gulf Coastal Plain in Alabama: (1) longleaf pine (Pinus palustris) that had been subject to several recent burns, (2) longleaf pine that had been subject to few or no recent burns, (3) planted slash pine (P. elliottii), and (4) various forested wetland habitats ranging from stream-side riparian habitat to cypress (Taxodium distichum) ponds. I found significantly higher total individuals and significantly higher bird species richness in the two natural forest types—burned longleaf pine and riparian habitats—than either unburned longleaf or slash pine. To maintain greatest diversity and abundance of birds, managers of forests on the Gulf Coastal Plain should (1)preserve wetland habitat, (2) not convert stands of longleaf pine to stands of slash pine, and (3) regularly burn longleaf pine stands. South. J. Appl. For. 22(3):133-137.

The Spectrum of Child Abuse Presenting to a University Hospital in Riyadh

Child abuse is prevalent worldwide, although it is often underreported. we describe the pattern of child abuse and neglect presenting to the emergency room of our hospital, the sociocultural changes which brought this about, and suggest ways to deal with this emotionally sensitive issue. Thirteen cases of child abuse and neglect were seen in the emergency room of King Khalid University Hospital over a period of one year from July 1996 to June 1997. There were four cases of non-accidental injury, three of which had serious injury. There were three cases of sexual abuse, four cases of neglect, resulting in the death of one child and severe emaciation in another. There was one suspected case of Munchausen syndrome by proxy, and one case of child labor with neglect. Public awareness of the problem of child abuse has increased, and recent media reports reflect the significance accorded to the issue. As more information is obtained on this subject and policies and guidelines are set in place, efforts at reporting and preventing physical and psychological trauma will gather momentum.

Plasma concentrations of tumour necrosis factor-α and interleukin-6 during burn wound surgery or dressing

Background: Clinical deterioration after burn wound manipulation may be related to the release of cytokines including tumour necrosis factor-α (TNF) and interleukin-6 (IL-6). Methods: The two cytokines were assayed by immunoenzymetric assay in blood samples taken before and during manipulation of the burn wound. An antibiotic, teicoplanin, was administered to half the patients at the start of the procedure in a randomized fashion as part of a separate trial. Findings: Sixty patients with a median burn size of 8% (range 1–56%) were studied during dressing change ( n = 40) or burn excision ( n = 20). There was little change in TNF levels between preoperative and recovery samples but IL-6 concentrations increased three-fold, particularly in those with large recent burns or bacteraemia, and were correlated with poor clinical outcome. The presence of teicoplanin did not significantly affect the levels of either cytokine. Interpretation: The systemic cytokine response to burn wound dressing or debridement is predominantly that of IL-6 and it is not significantly reduced by preventing Gram-positive bacteraemia during the procedure.

Marten selection of postfire seres in the Alaskan taiga

During 1991 – 1994 we tested whether martens (Martes americana) selectively used postfire seres in the Alaskan taiga and whether selection could be explained by differences in marten hunting behaviour, habitat, prey abundance, or demography. Forest seral stages included early-successional tall shrub – sapling (1985 burn), midsuccessional dense tree (1966 burn), and mature coniferous (100–115 years old). Most studies of marten – habitat relationships from lower latitudes suggest that martens require coniferous forest and avoid open areas. We found that martens did not select forest cover types or burn features at the stand scale (within the home range). However, marten abundance was greatest in the 1985 burn, which had the lowest canopy cover but the highest coarse woody debris density, autumn arvicoline biomass, and winter hunting intensity (index to foraging suitability). Martens in the 1985 burn were predominantly juvenile, with few adult (≥2 years old) females present. We hypothesize that our study area of predominantly early – midsuccessional forest was a "sink" for immature and transient martens dispersing from surrounding mature forest. If our hypothesis is correct and applies elsewhere in the taiga, then fur trapping for martens in recent burns could be a productive yet conservative harvest strategy. Future research should focus on habitat requirements of parturient females.

Buffaloberry [Shepherdia Canadensis (L.) Nutt.] Fruit Production in Fire-Successional Bear Feeding Sites

Buffaloberry [Shepherdia canadensis (L.) Nutt.] fruits are the usual late-summer food for bears (Ursus spp.) in the Front Ranges of Banff National Park, but little is known about the effect of fire or other factors on fruit production. I assessed the association between fruit production (fruits m-2 of buffaloberry shrub) and environmental factors at 76 plots in Banff National Park and found a negative association with forest canopy cover. Forest canopy cover accounted for 70% of the variation in fruit production. Fruit production also decreased from NNE- to SSW- facing slopes, but this effect was small compared to the decrease associated with increasing forest canopy cover. Forty plots were re-established at or near the original 76 sites the following year. A strong negative association between fruit production and forest canopy cover again occurred, but there was no significant association between fruit production and slope aspect. Fruit production began 5 years after fire in 2 recent burns. In sites burned 23 and 25 years ago, fruit production was comparable to the recorded in older-aged burns, and already was low at one site in the 25-year-old burn where regenerating lodgepole pine (Pinus contorta Dougl.) canopy cover measured 72%. Many sites in older burns, however, have remained forest-free due to xeric site conditions, chinook wind, avalanching, or other factors. These open sites were associated with abundant fruit. Managers must consider the prolonged effects of fire when assessing relation ships among fire, forest canopy cover, and buffaloberry fruit production.

Chronoséquence après feu de la diversité de mammifères et d'oiseaux au nord de la forêt boréale québécoise

Diversity of passerine birds and mammals was estimated in well-drained areas located at proximity of the hydroelectric reservoir La Grande-3, where natural fire regime still prevails in the absence of forest exploitation. Forest stands were divided up into four post-fire stages: (i) recent burns (4 years old), (ii) shrubs (25 years old), (iii) young forests (50 years old), and (iv) mature forests (≥71 years old). Richness and species diversity were highest in middle stages, in shrubs and young forests. The degree of opening seems to have affected more the composition of bird communities than stand age. Some bird species, typical of shrub stands, in particular white-crowned sparrow (Zonotrichialeucophrys Forster), Lincoln's sparrow (Melospizalincolnii Audubon), and alder flycatcher (Empidonaxalnorum Brewster), appeared after the falling of dead trees, ≈15 years after fire, and disappeared progressively as forests matured. Deer mice (Peromyscusmaniculatus Wagner), moose (Alcesalces L.), and black bears (Ursusamericanus Pallas) were more common at the beginning of succession, whereas northern red-backed voles (Clethrionomysgapperi Vigors) and caribou (Rangifertarandus L.) were typical of late stages. Mammal presence was mostly associated to their feeding requirements. Fire creates a mosaic of forest stands through periodic killing of trees in the north of the boreal forest, which contributes to maintain regional wildlife diversity; its suppression would reduce biodiversity.

Changes in O horizon mass, thickness and carbon content following fire in northern hardwood forests

This study examines temporal changes in the thickness, mass, and organic carbon content of the O horizon (forest floor) of eight forested plots in northern Michigan, USA. Each plot had experienced a recent burn (prescribed or accidental); burn dates ranged from 1798 to 1980. The climax forest in this region is mixed Pinus-Acer-Betula-Tsuga, whereas the fire successional species are predominantly Populus spp. and Betula papyrifera. O horizon data were fit to logarithmic functions (chronofunctions) that depicted rapid accumulations of mass and thickness in the first years after the fire, followed by decreasing rates of increase after ≈ 100 years. Extension of the chronofunctions to ≈ 5000 years allowed for a theoretical examination of forest floor conditions, e.g., steady state and time to steady state, after long periods without disturbance. The models predicted greater O horizon thicknesses and slightly lower mass for steady state conditions than have been reported for old-growth stands elsewhere. Steady state accumulations of litter in these mixed, temperate forests requires at least 200 and possibly > 1000 years, which is markedly longer than most other estimates. Although frequent disturbance by fire in these forests would likely preclude such values from being attained, these data provide theoretical maximum values for forest floor conditions in these ecosystems.

Metastatic adenocarcinoma in a recent burn scar

Neoplastic lesions arising in recent burn scars are apparently quite rare and we could find no report of such an occurrence in the literature. Nevertheless we recently treated a patient with a metastatic adenocarcinoma from the lung in a 3-month-old burn scar.

The forest resource of Labrador: Landsat Thematic Mapper imagery provides a unique and current perspective

The need for a current, regional perspective of the forest of Labrador was identified. Mapping of forest cover types, peat-lands, recent burns and clearcut disturbances was accomplished through visual interpretation of 1:1,000,000 scale Landsat Thematic mapper colour composite transparencies and the transfer of interpreted polygons to a geographic information system. The mapping and verification process is described in this paper. The end product, a forest resource map, provides the most up-to-date and detailed information on Labrador's forest cover types and disturbances available on a single map. The digital format of the map facilities area summaries, viewing and printing.

Stand dynamics of Pinus flexilis‐dominated subalpine forests in the Colorado Front Range

Population age structure and succession were investigated in subalpine forests in the Colorado Front Range dominated by Pinus flexilis (limber pine). Age, size, and spatial data were collected from three recent burns (<100 yr old), six ca. 240 year‐old post‐fire stands, and two old‐growth stands (individuals > 400 yr old). The sequence of colonization of now extant trees on these post‐fire sites appeared to be consistent: first Pinus flexilis, then Picea engelmannii (Engelmann spruce), and later Abies lasiocarpa (subalpine fir) with a delay between the first Pinus flexilis and Abies of as long as 140 yr. The advantage of Pinus flexilis on post‐burn sites can be attributed to avian seed dispersal and the exceptional drought tolerance of its seedlings. The three recent burns were not extensive, and the delay in establishment of Picea and Abies appeared to be limited by harsh site conditions rather than lack of seed dispersal.Spatial analysis indicated a consistent, although sometimes weak, attraction between Pinus flexilis and Picea and Pinus flexilis and Abies at a scale of 1–4 m, suggesting that Pinus flexilis may facilitate establishment of Picea and Abies seedlings by providing shade or protection from wind. On xeric to slightly xeric sites, Pinus flexilis appeared to form broadly even‐aged, non‐regenerating populations that were gradually being replaced by Picea and Abies. Replacement is proceeding at a faster rate on the least xeric sites (north aspects, valley bottoms) compared to the most xeric sites (south aspects). On the most extreme sites, Pinus flexilis formed all‐aged, self‐maintaining populations with no evidence of replacement by Picea and Abies. In these old‐growth forests with occasional trees aged at > 1300 yr, recruitment is continuous or episodic.

Movements and Habitat Use by Transplanted Marten in the Yukon Territory

One hundred and seventy-one marten (Martes americana) were transplanted to the southwest Yukon Territory between February 1984 and January 1987. I studied survival, movements and habitat use of 30 radio-tagged marten (16 M, 14 F). Implied movement data were also collected from carcass recoveries of transplanted marten (4 M, 3 F). Ten mortalities occurred -30 days after release; however, the survival rate after that time was 595.6%. Post-release movements were classed as transient (n = 9), temporary resident (n = 10), or resident (n = 8). Mean final distances moved from release sites were 13.4 km for males and 8.6 km for females. Home range estimates were 6.0 km2 for a resident male, 7.3 km2 for a temporary resident male, and a mean of 1.9 km2 for 3 resident females. Marten typically occupied late seral or climax coniferous forests, although they freely traversed alpine tundra, open forests, a burn, and large rivers. Recommendations for successful marten transplants include the release of large numbers of marten throughout a target area, during October-January, in temperatures > -20 C. J. WILDL. MANAGE. 53(4):991-997 The Yukon Department of Renewable Resources annually monitors the status of furbearer populations by analyses of fur harvest statistics, trapper questionnaire responses, and winter track-count indices. From these data, a region of marten scarcity, extending over 15,000 kmi2, was identified in the southwest Yukon Territory. Historical accounts, dating back to the early 1900's, suggested that marten have never been common here, although since 1982 marten have been increasing in abundance on the eastern edge of the area (B. G. Slough, unpubl. data). A subjective habitat assessment (C. E. Kennedy, Habitat stud., marten relocation proj., Yukon Dep. Ren. Resour., Whitehorse, 26pp., 1984) identified potential marten habitats that were isolated from typical marten habitat by unforested or poorly forested habitats, including recent burns. The rate of colonization of vacant habitat by marten dispersing from a refuge is about 8-16 km/decade (de Vos 1951). Colonization across early successional burns or sparse forests likely would take longer. The region of marten scarcity was thus selected for a management project involving the enhancement and protection of marten populations through transplants and trapping restrictions. The transplant conducted by the Yukon Department of Renewable Resources in 1984-87 provided an opportunity to study post-release survival, movements and home range establishment, and habitat use by marten. My objective is to report information useful to furbearer managers in planning successful marten transplants. This paper is dedicated posthumously to trapper C. D. Geddes, who was so generous in assisting with the live trapping of marten. I also thank P. A. Smith, K. D. Kilpatrick, R. H. Jessup, C. M. M. Smits, A. M. Baer, H. P. Slama, D. R. Drummond, B. N. Tokarek, J. G. Balmer, K. M. Gustafson, K. L. Bowers, and the numerous Yukon trappers who assisted with all aspects of the transplant study. A. S. Harested, D. H. Mossop, and M. H. Hoefs provided guidance with manuscript preparation.