bluuebunny/crossref_metadata_2025 huggingface dataset:
A nonlethal approach using strontium in scales to distinguish periods of marine and freshwater residency of anadromous species
Authors: Courtemanche David A , Whoriskey, Jr. Frederick G , Bujold Valerie , Curry R Allen
Published: November 2005

Spatiotemporal migration patterns of brook trout (Salvelinus fontinalis) and various other anadromous fish are poorly understood in many rivers of North America. A new, nonlethal approach to investigate these movements using analysis of scale microchemistry was developed that is relatively simple, cost effective, and potentially more accurate than other monitoring techniques. As fish grow, their scales incorporate in the calcified matrix different concentrations of trace elements present in ambient waters. Seawater Sr concentrations are 10100 times higher compared with fresh water; thus, a higher Sr/Ca ratio in circulii corresponding to periods of life in seawater would be predicted. We used a wavelength-dispersive X-ray electron microprobe to assess Sr/Ca ratios along sagittal cross sections of scales, spanning the life history of a fish. We demonstrate that existing wavelength-dispersive X-ray electron microprobe studies using Sr analysis may suffer inaccuracies related to scale surface topography, and using the alternative embedding and cutting technique increases significantly the precision of Sr/Ca readings.
Light intensity, salinity, and host velocity influence presettlement intensity and distribution on hosts by copepodids of sea lice,Lepeophtheirus salmonis
Authors: Genna R L , Mordue W , Pike A W , Mordue (Luntz) A J
Published: November 2005

Intensity and distribution of presettlement by the copepodid of the sea louse, Lepeophtheirus salmonis, on smolts of its host Atlantic salmon, Salmo salar, were quantified for 27 infection regimes under controlled flume conditions. Each infection regime represented a level of interaction between three levels (low, medium, high) of the physical factors of light (10, 300, 800 lx), salinity (20, 27, 35), and host velocity (0.2, 7.0, 15.0 cm·s1). Light, salinity, and host velocity independently and interactively determined the distribution and number of presettled copepodids on hosts. Host surface area also influenced the number of attached preestablished copepodids. The distribution of presettled copepodids on the host body surface closely corresponded to that of settled copepodids and chalimi reported from other studies, with the greatest levels observed on the fins, in particular the dorsal, caudal, and pectoral fins. Copepodid presettlement occurred on the gills under all conditions. Differential presettlement, not selective mortality, probably produces the distribution pattern of settled stages seen in other studies.
Temporal dynamics in foraging behavior of a pelagic predator
Authors: Scheuerell Jennifer M , Schindler Daniel E , Scheuerell Mark D , Fresh Kurt L , Sibley Thomas H , Litt Arni H , Shepherd Judith H
Published: November 2005

A paradox exists between common observations of highly complex food webs in nature and prevailing ecological theory suggesting that complex food webs are unstable. Qualities of food webs, such as dynamic trophic links, that were not previously considered in theoretical models have been suggested to stabilize complex food webs and resolve this paradox. Flexible foraging behavior can result in dynamic trophic linkages between a predator and its prey over short time scales. Using 4 years of data on diets of juvenile sockeye salmon (Oncorhynchus nerka) and the zooplankton community from Lake Washington (Seattle, Washington, USA), we determined that juvenile sockeye show dynamic foraging behavior that depends solely on the density of its preferred prey, Daphnia. Juvenile sockeye consumed only Daphnia when their density was greater than 0.4·L1. Long-term patterns in Daphnia densities demonstrated that for the last 28 years, trophic links between sockeye and the less preferred copepods are eliminated for approximately 6 months of each year when Daphnia is above this switching density threshold. Our data provide a convincing empirical example of the activation and inactivation of trophic links occurring on short time scales as a result of dynamic foraging and help to explain the commonness of high-complexity food webs.
The importance of recruitment for the production dynamics of stream-dwelling brown trout (Salmo trutta)
Authors: Lobón-Cerviá Javier
Published: November 2005

The objective was to highlight the role of recruitment for production dynamics of stream brown trout (Salmo trutta). The analysis of 51 cohorts (hatched in 19861999) at four sites of Rio Chaballos (northwestern Spain) showed sinusoidal growth patterns with more intense growth in spring and summer and reduced growth in winter. Survivor abundance described two-phase trajectories over the lifetime (10001400 days after emergence). A first phase of negligible or no mortality was prolonged for 500650 days. Severe mortality during the second phase differed among cohorts and among sites. Spatiotemporal variations in growth, mortality, density, spawner abundance, biomass, and production underlay variations in recruitment. Increased recruitment affected growth negatively (except at one site) and mortality positively. Cohort production decreased with increased growth at three sites but increased with increased growth at another site. Greater mortality typified the most productive cohorts. However, 90.8% and 83.6% of the variations in density and production, respectively, were explained by variations in recruitment. Thus, cohort size and production appeared to be determined by recruitment in which postrecruitment processes played a minor role. Recruitment reset the cohort's numerical and productive capacity, and increments in recruitment continued to increase cohort size and production over the recruitment magnitudes observed across sites and years.
Does trophic position of the omnivorous signal crayfish (Pacifastacus leniusculus) in a stream food web vary with life history stage or density?
Authors: Bondar Carin A , Bottriell K , Zeron K , Richardson John S
Published: November 2005

Food mixing behavior of omnivorous consumers can be difficult to predict. We undertook an enclosure experiment to explore the effects of ontogenetic stage and density on food choices of the omnivorous signal crayfish, Pacifastacus leniusculus. Juvenile or adult crayfish were placed in in-stream enclosures for 6 weeks at three different densities. Gut and stable isotope analyses were used to determine the food sources utilized by these organisms. In addition, we analyzed the guts of both adult and juvenile crayfish from outside the enclosures to account for experimental effects. We found few differences in the gut contents between juvenile and adult crayfish from either inside or outside the enclosures, as the majority of food consumed by both ontogenetic stages and all densities was allochthonous detritus. Stable isotope results indicate that crayfish of both ontogenetic stages were relying primarily on detrital biofilms for nutrition, despite an additional laboratory experiment showing that growth would be far more rapid on invertebrates. The dietary choices made by P. leniusculus in its native environment seem to be primarily affected by factors other than the nutritional value of food sources, contrary to expectations that food mixing behavior of omnivores should be based on this factor alone.
Osmoregulation and gene expression of Na+/K+ATPase in families of Atlantic salmon (Salmo salar) smolts
Authors: Mackie P , Wright P A , Glebe B D , Ballantyne J S
Published: November 2005

This study reports that families of Atlantic salmon (Salmo salar) smolts vary in their ability to osmo- and iono-regulate following abrupt transfer to cold seawater. Eleven families of Atlantic salmon 0+ smolts were held in fresh water (2.44 °C) or transferred to seawater (1.94 °C) and sampled 0 h, 24 h, 96 h, and 30 days post-transfer. Plasma osmolality was significantly different among the families after 24 h of seawater exposure. The family with the lowest osmolality at 24 h also displayed the lowest plasma Clconcentrations as well as the highest gill Na+/K+ATPase activity. Gill mRNA expression of the Na+/K+ATPase α1b isoform increased following seawater exposure, whereas the α1a isoform decreased, but there was no significant difference among families. Taken together, the interfamily differences in osmoregulatory ability are correlated with gill Na+/K+ATPase activity but not the expression of two salinity-sensitive Na+/K+ATPase isoforms. Furthermore, the data indicate that family differences in gill Na+/K+ATPase activity were only apparent when assayed at the sampling temperature (4 °C) and not at a higher assay temperature (10 °C).
Food web reliance on allochthonous carbon in two high mountain lakes with contrasting catchments: a stable isotope approach
Authors: Pulido-Villena Elvira , Reche Isabel , Morales-Baquero Rafael
Published: November 2005

The carbon isotopic signature (δ13C) of dissolved inorganic carbon and food web components was examined in two high mountain lakes. Río Seco Lake is partially surrounded by alpine meadows and has temporal inlets, whereas La Caldera Lake is located on rocky terrain and does not receive inputs from runoff. We assessed whether these contrasting catchments involve differences in the isotopic signature of the food web components and then in the reliance on terrestrial carbon. The δ13C of dissolved inorganic carbon was not significantly different between lakes and reflected an atmospheric gas exchange origin. Unexpectedly, bulk particulate organic matter showed enriched δ13C values in both lakes, suggesting a terrestrial vegetation influence. Bulk particulate organic matter was exploited mostly by the cladoceran Daphnia pulicaria, whereas the copepod Mixodiaptomus laciniatus was 13C depleted relative to particulate organic matter, indicating a selective feeding on an isotopically lighter source, likely phytoplankton. The results obtained show that, despite contrasting catchments, the food web of both lakes might be partially supported by terrestrial carbon for which utilization is species specific.
Ecophysiological determinants of the variation in 137Cs concentrations between and within lacustrine fish populations
Authors: Sundbom Marcus , Meili Markus
Published: November 2005

One decade after the Chernobyl fallout, the variability of 137Cs activity concentrations among fish within a Swedish lake was >20-fold based on 1361 individuals from seven species collected continually during 19961999. Of the total variability, 64% was due to differences between species but only 7% due to temporal variation, which was 1.3-fold for the whole community and 1.3- to 2-fold for population means. Contamination increased with body size (0.6- to 6-fold) and decreased with body condition in most species (1.3-fold). Body size and time together accounted for about half of the total variation within populations. Fish 137Cs was related to differences in feeding ecology, both between and within populations. Biomagnification factors ranged from 2.4 to 5.8. Contamination was highest in piscivorous populations and individuals, intermediate in herbivores and zooplanktivores, and lowest in fish specialized in benthic invertebrates despite their association with contaminated sediments. The 137Cs variance within populations was not correlated with their niche width but moderately positively correlated with fish trophic position and strongly positively correlated with functional omnivory (diversity in prey 137Cs). We conclude that individual resource specialization is an important source of variation in 137Cs concentrations within fish populations.
Evidence across multiple scales for offshore transport of yellow perch (Perca flavescens) larvae in Lake Michigan
Authors: Dettmers John M , Janssen John , Pientka Bernard , Fulford Richard S , Jude David J
Published: November 2005

Most freshwater fishes have short pelagic early life stages. Lake Michigan presents an interesting scenario for yellow perch (Perca flavescens), a species with a long pelagic larval stage that may not be well adapted to lakes with an expansive pelagic environment and extensive offshore transport. We investigated the possibility that early life stages of yellow perch were transported well offshore from their nearshore spawning grounds and explored whether food resources were more or less favorable offshore. To determine the extent to which pelagic age-0 yellow perch moved offshore, we sampled at multiple scales ranging from local (<2 km) to across the lake (>120 km). Evidence of offshore movement by fish larvae occurred at each scale. Yellow perch larvae were quickly transported offshore from nearshore spawning sites and remained in the offshore pelagia to sizes of at least 30 mm. Zooplankton density was greater offshore than nearshore, suggesting that pelagic age-0 yellow perch find improved food resources offshore compared with their nearshore spawning sites. Currents operating at oceanographic scales likely influenced the offshore movement of pelagic age-0 yellow perch in Lake Michigan. These currents, coupled with prey availability for pelagic age-0 individuals, may influence the recruitment success of this species.
Parasitism, space constraints, and gonad asymmetry in the pollan (Coregonus autumnalis)
Authors: Harrod Chris , Griffiths David
Published: November 2005

Both sexes of Lough Neagh pollan (Coregonus autumnalis) show directional asymmetry in gonad mass, the left being larger than the right in 70% of individuals. The frequency and degree of asymmetry are size independent in males but become progressively more marked in females of >120 g somatic mass. There is little evidence to support the hypothesis that the size of the body cavity constrains gonad size. Pollan are heavily and size-dependently infected by metacercariae of the trematode Ichthyocotylurus erraticus. Total gonad mass in both sexes of pollan is negatively correlated with infection intensity of this parasite. In females, mean egg size shows no trend but fecundity declines and the degree of asymmetry in ovary mass increases with infection intensity up to a threshold, beyond which it remains constant. While directional asymmetry in gonad size is strongly developmentally controlled in many fish species, variation in the degree of gonad asymmetry in pollan provides a potentially sensitive indicator of stress.
The relative influence of breeding competition and habitat quality on female reproductive success in lacustrine brook trout (Salvelinus fontinalis)
Authors: Blanchfield Paul J , Ridgway Mark S
Published: November 2005

Egg losses for female salmonines primarily occur through competition for egg incubation sites (i.e., redds) and the differences in quality among these sites. Through detailed observations and an experiment linking egg survival to groundwater flow, we estimated the relative influence of redd superimposition and habitat quality on female reproductive success for a population of lake-spawning brook trout (Salvelinus fontinalis). Three quarters of all spawning sites were reused by multiple females; however, brood loss was much less (28%38%) because large females spawned earlier and constructed deeper nests. The relationship between groundwater flow rate and egg survival was not linear, with consistent egg survival occurring only at sites with flows over 20 mL·m2·min1. Varying scenarios of redd superimposition and habitat-related egg survival resulted in an estimated 4%-21% of deposited eggs surviving to emergence and greatly reduced the size-related advantages of larger females owing to fecundity. Limited numbers of high-quality spawning sites and overall low survival of eggs resulted in habitat being the dominant route of egg loss. In the absence of female competition, spawning habitat alone accounted for egg losses of 67%91% and points to the importance of physical habitat features in the maintenance of brook trout populations.
Lake level and trophic state variables among a population of shallow Florida lakes and within individual lakes
Authors: Hoyer Mark V , Horsburgh Christine A , Canfield, Jr. Daniel E , Bachmann Roger W
Published: November 2005

Monthly total phosphorus, total nitrogen, and chlorophyll concentrations, Secchi depth, and lake water level data for 84 Florida lakes were used to examine relations between trophic state variables and water level fluctuation. Lake size averaged 566 ha (range 4.0 to 5609 ha), with the period of record for individual lakes averaging 57 months (range 7 to 175 months). Lake level fluctuation for individual lakes averaged 1.3 m (range 0.1 to 3.5 m). The lakes also ranged from oligotrophic to hypereutrophic, with average chlorophyll values for individual lakes ranging from 1 to 97 µg·L1. No overall relation between trophic state variables and lake level fluctuation could be found among the population of lakes. However, individual lakes showed direct, inverse, or no significant relations between lake trophic state variables and water level fluctuation, regardless of the magnitude of water level fluctuation. These data suggest that predicting how water level fluctuations will impact trophic state variables among a population of lakes will be difficult, if not impossible, and that any accurate predictions will have to be made after first examining several mechanisms within individual lake systems.
Heterogeneity and the markrecapture assessment of the Scotian Shelf population of northern bottlenose whales (Hyperoodon ampullatus)
Authors: Whitehead Hal , Wimmer Tonya
Published: November 2005

A population of northern bottlenose whales (Hyperoodon ampullatus) inhabits the waters along the edge of the Scotian Shelf. The most important habitat of this population is the Gully, a large submarine canyon, where animals were photographically identified between 1988 and 2003. Open markrecapture models, including mixture models that allow for heterogeneity in identifiability and (or) mortality among individuals, were fitted to identification-history data. Models without heterogeneity in identifiability had poor fit to the data and underestimated population size. The population is estimated to contain about 163 animals (95% confidence interval 119214), with no statistically significant temporal trend. About 12% of the population has a high probability of being identified within the Gully in any year. Many of them are mature males. The remainder is less likely to be identified in the Gully during any year, spend generally shorter periods in the Gully even in years when they are found, and are more likely to be female. This and other work indicate a poorly mixed population inhabiting the canyons and other deeper waters off the Scotian Shelf. Non parametric bootstrap methods were used to validate the estimation procedure and to estimate the efficiency of future fieldwork scenarios.
Evaluation of a US west coast groundfish habitat conservation regulation via analysis of spatial and temporal patterns of trawl fishing effort
Authors: Bellman Marlene A , Heppell Scott A , Goldfinger Chris
Published: November 2005

We examined the extent to which the 2000 Pacific Fishery Management Council footrope restriction shifted and reduced trawl fishing effort on Oregon fishing grounds, related these changes to the seafloor habitat type over which they occurred, and developed methods for enhancing spatial review of fishing effort. Density analysis of trawl start locations demonstrated how fishing efforts increased and decreased in relation to habitat distribution and fishery management actions between 1995 and 2002. Trawl effort patterns exhibited significant interannual variability and were patchy in distribution. Tow end-point locations from 1998 to 2001 were retrieved from manual logbooks for five reference sites located in proximity to rocky habitat. Trawl towlines were mapped and demonstrated a marked enhancement of fine-scale fishing effort resolution. Spatial shifts in fishing intensity (measured as kilometres towed) away from rock habitat were evident at all reference sites after the footrope restriction, with an average reduction of 86%. Some slight shifts into surrounding unconsolidated sediments also occurred. Our results indicate that the footrope restriction, in conjunction with associated landing limits, was effective in protecting rocky habitats from trawl fishing impacts. Continued spatial monitoring of trawl data would assist in fishery management assessment of conservation objectives for depleted groundfish and essential fish habitat protection.
Rule of age and size at maturity of chum salmon (Oncorhynchus keta): implications of recent trends among Oncorhynchus spp.
Authors: Morita Kentaro , Morita Shoko H , Fukuwaka Masa-aki , Matsuda Hiroyuki
Published: November 2005

In the last quarter of the 20th century, the size at maturity of many North Pacific salmon (Oncorhynchus spp.) populations decreased. During this same period, the age at maturity increased, implying that the growth rate of Pacific salmon decreased, probably owing to environmental changes. To elucidate these trends, we identified the rule of age and size at maturity of Japanese chum salmon (Oncorhynchus keta), which was that slow-growing salmon initiated maturation at an older age and smaller size than did fast-growing salmon. We then simulated the potential modification of age and size at maturity in response to changing growth rate using a size-structured model with age- and size-specific maturation rates. This showed that reducing the growth rate without assuming a genetic change was sufficient for realistic modeling of recent changes. In addition, the observed rule of age and size at maturity was consistent with the optimal age and size at maturity in terms of maximizing the fitness. Our results attributed the recent trends in chum salmon's increasing age and decreasing size at maturity to an adaptive phenotypic response to a reduced growth rate.
Body size, not other morphological traits, characterizes cascading effects in fish assemblage composition following commercial netting
Authors: Layman C A , Langerhans R B , Winemiller K O
Published: November 2005

Traits used to group species and generalize predatorprey interactions can aid in constructing models to assess human impacts on food webs, especially in complex, species-rich systems. Commercial netting has reduced populations of large-bodied piscivores in some lagoons of a Venezuelan floodplain river, and cascading effects result in distinct prey fish communities in netted and unnetted lagoons. In 2002 and 2003, we sampled assemblages of prey fishes in netted and unnetted lagoons and tested whether fish size and (or) other morphological characteristics were associated with differences in assemblage composition. In both years, prey fish assemblages in netted lagoons were dominated numerically by larger species. We used geometric morphometric methods to test for a relationship between species morphological characteristics and found that neither overall morphological ordination nor specific morphological traits could be used to distinguish among assemblages. Thus, size was the only variable that was useful in explaining differences in assemblage composition. Even in this species-rich river with a complex food web, size-structured predatorprey interactions apparently influence community-level patterns and can be used to characterize human impacts.
An experimental evaluation of competitive and thermal effects on brown trout (Salmo trutta) and Bonneville cutthroat trout (Oncorhynchus clarkii utah) performance along an altitudinal gradient
Authors: McHugh Peter , Budy Phaedra
Published: November 2005

Temperature-mediated competition (i.e., dominance shifts between species depending on temperature) may explain the segregation of salmonid species along altitudinal stream gradients. We evaluated this hypothesis for exotic brown trout (Salmo trutta) and native Bonneville cutthroat trout (Oncorhynchus clarkii utah) by rearing them in experimental sympatry and allopatry using enclosures constructed at six sites spaced along a 45-km segment of a mountain stream. For both species, we compared condition and growth between allopatric and sympatric treatment groups. We found that brown trout negatively affected cutthroat trout performance, whereas cutthroat trout failed to impart an effect in the reverse direction, regardless of temperature. Thus, we documented asymmetric competition between these species but found little evidence indicating that its outcome was influenced by temperature. Brown trout  cutthroat trout segregation is therefore unlikely to be due to temperature-mediated competition. Instead, brown trout may have displaced cutthroat trout from downstream areas through competition or other mechanisms, while abiotic factors preclude their (brown trout) invasion of upper elevations. Given the magnitude of effect observed in our study, we recommend that brown trout receive greater consideration in cutthroat trout conservation.
Can otolith elemental signatures record the capture site of Patagonian toothfish (Dissostichus eleginoides), a fully marine fish in the Southern Ocean?
Authors: Ashford J R , Jones C M , Hofmann E , Everson I , Moreno C , Duhamel G , Williams R
Published: November 2005

Otolith chemistry has been successfully used to reconstruct the environmental history experienced by estuarine-dependent teleost fish, including movement between estuaries and coastal areas. However, application has been more limited in species exposed exclusively to oceanic waters, where gradients in physical and chemical properties are less extreme. To test whether otolith elemental signatures record spatial information in an oceanic species, we sampled otoliths from Patagonian toothfish (Dissostichus eleginoides) and used an inductively coupled plasma mass spectrometer (ICP-MS) coupled to a laser ablation system to target the outer otolith edges corresponding to the period immediately before capture. Using multivariate analysis of variance and multivariate discriminant analysis, we found that edge signatures discriminated toothfish by geographic region with near complete success: only 5% of fish caught off South America and in the Antarctic were misclassified to sampling areas in the other region. Moreover, edge signatures showed strong differences between sampling areas within each region: fish captured off South America classified to sampling areas therein with 79%84% success, and Antarctic fish classified to sampling areas therein with 50%67% success. These results compare favourably with rates of classification for estuarine-dependent fish, demonstrating that otolith elemental signatures can discriminate the geographic provenance of oceanic and estuarine-dependent fish.
The importance of Colorado River flow to nursery habitats of the Gulf corvina (Cynoscion othonopterus)
Authors: Rowell Kirsten , Flessa Karl W , Dettman David L , Román Martha
Published: November 2005

We test the hypothesis that Colorado River flow is important in providing nursery habitat for the Gulf corvina (Cynoscion othonopterus), a commercially valuable and endemic fish in the upper Gulf of California. We use oxygen isotopes in otoliths to determine when these fish inhabit isotopically different bodies of water (Gulf of California versus the Colorado Estuary). The δ18O values in the natal otoliths of C. othonopterus, significantly more negative than can be predicted by temperature alone, provide evidence that this species uses the brackish habitats created by flow of the Colorado River. A significant log-linear relationship between the natal δ18O values and the cumulative flow of the Colorado River during natal development confirms use of brackish habitat in years that the Colorado River water reached the Gulf. Natal δ18O values indicate that C. othonopterus seek out estuarine habitats with salinities between 26 and 38. Reduction in Colorado River flow since the construction of upstream dams has reduced the size of nursery habitat for C. othonopterus. Our results support the hypothesis that declines in commercial landings can be at least partially attributed to reduced river flow. Increased flow would increase nursery habitat and likely benefit recruitment.
Validation of Sr isotopes in otoliths by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS): opening avenues in fisheries science applications
Authors: Barnett-Johnson Rachel , Ramos Frank C , Grimes Churchill B , MacFarlane R Bruce
Published: November 2005

Advances in probe-based mass spectrometry allow for high spatial resolution of elemental and isotopic signatures in fish otoliths that can be used to address fundamental questions in fisheries ecology. Analyses of Chinook salmon (Oncorhynchus tshawytscha) otoliths from two river populations yield identical 87Sr/86Sr ratios using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) and thermal ionization mass spectrometry (TIMS). Results were obtained from freshwater otoliths with low Sr concentrations (300800 ppm) using high spatial resolution (50 µm) corresponding to temporal histories of ~12 days fish growth. Low natural variation in 87Sr/86Sr among otoliths from the same rivers allows for conservative estimates of external precision of techniques. Thus, we demonstrate that Sr isotope ratios obtained by LA-MC-ICPMS can be accurate and precise, bypassing the time-intensive sample preparation required by microdrilling and TIMS. This technique opens the use of Sr isotopes for broader ecological questions requiring large sample sizes to characterize nursery habitats, metapopulation dynamics, and stock discrimination similar to studies that focus on elemental concentrations, thereby providing a more robust tool for some freshwater and diadromous fishes.
Landscape-scale spatial distribution of spruce budworm defoliation in relation to bioclimatic conditions
Authors: Candau Jean-Noël , Fleming Richard A
Published: November 2005

Two empirical statistical models were developed to describe the spatial variation in defoliation by spruce budworm (Choristoneura fumiferana Clem.), as recorded by Ontario's Forest Health Survey from 1967 to 1998. These models revealed a number of relationships between the spatial distributions of aerially detectable spruce budworm defoliation and bioclimatic conditions over the landscape. A classification tree model relates the northern and southern boundaries of defoliation to the relative abundance of different tree species that host spruce budworm. Between these boundaries, the classification tree uses the maximum winter temperature and the minimum temperature in May to describe where detectable defoliation occurred. A regression tree model uses a total of eight variables related to winter temperatures, forest composition, spring temperatures, summer temperatures, and precipitation to estimate the defoliation frequency in areas where defoliation was detected at least once from 1967 to 1998. High defoliation frequencies were associated with dry Junes (precipitation, <86 mm) and cool springs (mean minimum temperature < 2.7 °C). Conversely, low frequencies were associated with cold winters (mean minimum temperature < 23.3 °C; mean maximum temperature > 11.0 °C) in the north and a low abundance of host species (percentage of the basal area occupied by balsam fir, white spruce, and black spruce, <14.3%) in the south. Spatial autocorrelation in the bioclimatic variables had little effect on their relationships with the spatial distribution of the defoliation frequency.
Simulating the response of natural ecosystems and their fire regimes to climatic variability in Alaska
Authors: Bachelet D , Lenihan J , Neilson R , Drapek R , Kittel T
Published: November 2005

The dynamic global vegetation model MC1 was used to examine climate, fire, and ecosystems interactions in Alaska under historical (19221996) and future (19972100) climate conditions. Projections show that by the end of the 21st century, 75%90% of the area simulated as tundra in 1922 is replaced by boreal and temperate forest. From 1922 to 1996, simulation results show a loss of about 9 g C·m2·year1from fire emissions and 360 000 ha burned each year. During the same period 61% of the C gained (1.7 Pg C) is lost to fires (1 Pg C). Under future climate change scenarios, fire emissions increase to 1112 g C·m2·year1and the area burned increases to 411 000  481 000 ha·year1. The carbon gain between 2025 and 2099 is projected at 0.5 Pg C under the warmer CGCM1 climate change scenario and 3.2 Pg C under HADCM2SUL. The loss to fires under CGCM1 is thus greater than the carbon gained in those 75 years, while under HADCM2SUL it represents only about 40% of the carbon gained. Despite increases in fire losses, the model simulates an increase in carbon gains during the 21st century until its last decade, when, under both climate change scenarios, Alaska becomes a net carbon source.
Stand-level effects of soil burn severity on postfire regeneration in a recently burned black spruce forest
Authors: Johnstone Jill F , Kasischke Eric S
Published: November 2005

This study tested whether variations in soil burn severity (soil organic layer consumption) influenced patterns of early postfire plant regeneration in a black spruce (Picea mariana (Mill.) BSP) forest in interior Alaska. Variations in burn severity were related to measurements of postfire tree seedling establishment and cover of plant growth forms observed 78 years after fire. Black spruce and trembling aspen (Populus tremuloides Michx.) showed significant and opposite responses of seedling density to changes in soil burn severity. Positive correlations between burn severity and aspen density and individual seedling biomass led to an increase of over three orders of magnitude in aspen standing biomass (aboveground, g/m2) from the least to most severely burned sites. Variations in aspen productivity and consequent effects on litter production and seedbed quality possibly explain the observed negative response of black spruce density to increasing burn severity. Variations in the cover of several plant growth forms were also strongly correlated with patterns of soil burn severity. Regenerating plant communities in low-severity sites had a greater cover of evergreen shrubs and graminoids, while high-severity sites had increased cover of aspen and acro carp ous mosses. Observations of regeneration patterns in the burn are largely consistent with experimental studies of severity effects and suggest that variations in soil burn severity can have a strong influence on landscape patterns of postfire forest recovery. In this case, increases in burn severity have shifted successional trajectories away from simple conifer self-replacement towards a trajectory of mixed conifer and deciduous dominance.
Soil carbon stabilization along climate and stand productivity gradients in black spruce forests of interior Alaska
Authors: Kane E S , Valentine D W , Schuur E AG , Dutta K
Published: November 2005

The amount of soil organic carbon (SOC) in stable, slow-turnover pools is likely to change in response to climate warming because processes mediating soil C balance (net primary production and decomposition) vary with environmental conditions. This is important to consider in boreal forests, which constitute one of the world's largest stocks of SOC. We investigated changes in soil C stabilization along four replicate gradients of black spruce productivity and soil temperature in interior Alaska to develop empirical relationships between SOC and stand and physiographic features. Total SOC harbored in mineral soil horizons decreased by 4.4 g C·m2 for every degree-day increase in heat sum within the organic soil across all sites. Furthermore, the proportion of relatively labile light-fraction (density <1.6 g·cm3) soil organic matter decreased significantly with increased stand productivity and soil temperature. Mean residence times of SOC (as determined by Δ14C) in dense-fraction (>1.6 g·cm3) mineral soil ranged from 282 to 672 years. The oldest SOC occurred in the coolest sites, which also harbored the most C and had the lowest rates of stand production. These results suggest that temperature sensitivities of organic matter within discrete soil pools, and not just total soil C stocks, need to be examined to project the effects of changing climate and primary production on soil C balance.
Infrared characterization of fine-scale variability in behavior of boreal forest fires
Authors: McRae D J , Jin J -Z , Conard S G , Sukhinin A I , Ivanova G A , Blake T W
Published: November 2005

Spatial and temporal variability in forest fire behavior, caused by differences in microsites, fuel types and condition, topography, and other factors across even relatively small areas, has been poorly characterized in most previous studies. Past characterization of forest fires has often been limited by monitoring techniques that relied on timing systems in coarse-resolution sampling grids. We report documentation and analysis of fire behavior for several experimental fires using a camcorder-sized infrared camera mounted in a helicopter hovering over the target fires. These fires were conducted as part of the Russian FIRE BEAR Project in boreal Pinus sylvestris L. forests of central Siberia. Final results provide quantitative information on fire front location, rates of spread, temperatures, and total radiation energy (kW/m2) observed during the fires at resolutions from 2.5 to 1.0 m across experimental burn plots ranging from 2.3 to 4.0 ha. Further postfire analysis using GIS produced a detailed spatial and temporal quantification of fireline intensity (kW/m) across the plot area. This type of infrared monitoring and analysis helps to support clearer assessment of relationships between fire behavior and ecological impacts. Such data permit accurate fire behavior estimates at various temporal and spatial scales rather than using an overall plot average. This method allows the sample size to be quite large, so that statistical analysis of the fire behavior data can provide an associated level of confidence.
Seasonal development of Scots pine under climatic warming: effects on photosynthetic production
Authors: Hänninen Heikki , Kolari Pasi , Hari Pertti
Published: November 2005

In boreal conditions under climatic warming, photosynthesis will start earlier in the spring than it does in the present climate. As a first approximation this phenomenon would increase the annual photosynthetic production of boreal conifers, as they can use the high amounts of incoming solar radiation prevailing during spring to a greater extent than in the present climate. However, the recovery of photosynthesis is accompanied by a simultaneous dehardening of the needles. Thus, climatic warming may also cause a premature dehardening of the needles during spring. This may result in needle losses caused by frost damage; so climatic warming may also decrease the annual photosynthetic production of boreal conifers. Using computer simulations with ecophysiological models, these counteracting effects of climatic warming on photosynthetic production were studied in Scots pine (Pinus sylvestris L.) trees growing in southern Finland. The results show that because of our insufficient understanding of the environmental regulation of frost hardiness, it is not possible to conclude which one of the two potential effects will dominate under climatic warming. This finding calls for further empirical development and testing of the frost hardiness models.
Stand density in the last millennium at the upper tree-line ecotone in the Polar Ural Mountains
Authors: Mazepa Valeri S
Published: November 2005

Significant spatiotemporal changes in the establishment, mortality, and abundance of trees have taken place in the upper tree-line ecotone in the Polar Ural Mountains over the last millennium. Until now, these forests have developed mainly under the influence of natural factors. A large number of well-preserved tree remains can be found up to 6080 m above the current tree line, some dating to as early as a maximum of 1300 years ago. The research reported here extends the work begun by S.G. Shiyatov, who examined evidence of tree growth dynamics along a transect on the eastern slope of the Polar Ural Mountains in the 1960s. For this study, 769 discs from dead trees and 378 increment cores from living trees were collected along an altitudinal transect 860 m long and 80 m wide. The positions of all living trees, fallen dead trees, and wood remains were mapped. Dimensions of each living tree, including saplings and understory plants, were measured: basal diameter, diameter at breast height, crown diameter, and height of stems. Calendar years of tree germination and death were estimated using dendrochronological techniques. The earliest distinct maximum in stand density occurred in the 11th to 13th centuries, coincident with Medieval climate warming. Climate warming in the 18th century appears to have resulted in a second stand-density maximum. The recent temperature increase observed in the 20th century is reflected in the high number of young trees observed.
Small root exclusion collars provide reasonable estimates of root respiration when measured during the growing season of installation
Authors: Vogel Jason G , Valentine David W
Published: November 2005

A common method to determine in situ root respiration is to insert root exclusions to sever roots and then to measure soil carbon dioxide (CO2) efflux in and outside the exclusion. We report the use of relatively small root exclusions (15.2 cm diameter plastic pipe) (SREs), installed and measured within a growing season. We switched from long-used, large root exclusions (2.5 m × 3 m) (LREs) for three reasons. First, temperature artifacts were apparent in LREs, likely because increased soil moisture altered soil thermal balance. Second, LREs in dense stands required a relatively low tree density, which then impacted snowpack depth and insolation. Third, the LREs were much more time-consuming to install than SREs. Using a powered mechanical trencher (ditch witch®) decreased LRE installation time, but introduced a large edge-effect apparent in soil profile pCO2 that would obviate trenched plots smaller than 1600 cm2. However, when trenches were dug by hand, the distance from the LRE wall had no effect on soil pCO2. In a subsequent experiment, SREs were installed by cleanly cutting the forest floor, and then immediately measured. Within 1-3 weeks the SREs provided similar root respiration estimates to those made with LREs that had been in place for nearly 10 months. SREs placed in and outside LREs provided indistinguishable microbial respiration values from one another and to the LREs. We conclude SREs provide root respiration estimates indistinguishable from other methods, even when installed and measured within the same growing season.
Impacts of drought on forest growth and regeneration following fire in southwestern Yukon, Canada
Authors: Hogg EH (Ted) , Wein Ross W
Published: November 2005

The valleys of southwestern Yukon have a continental climate with average annual precipitation of <300 mm. In 1958, fires burned large areas of mature mixedwood forests dominated by white spruce (Picea glauca (Moench) Voss) in the valleys near Whitehorse. Since then, the burned areas have shown poor regeneration of spruce, but have been colonized by scattered clones of trembling aspen (Populus tremuloides Michx.) interspersed by grassland. The objective of the study was to examine the influence of climatic variation on forest growth and regeneration in the 1958 burn and the adjacent unburned forests. Tree-ring analysis was conducted on 50 aspen and 54 white spruce in 12 mature stands where these species were codominant, and on 147 regenerating aspen in the 1958 Takhini burn. The mature stands were uneven-aged and the patterns of growth variation for the aspen and spruce between 1944 and 2000 were similar. Growth of both species was most strongly related to variation in precipitation. The regenerating aspen had a wide age-class distribution (19592000) and their growth was also positively related to precipitation. The results indicate that these forests have been slow to regenerate after fire, and are vulnerable if the climate becomes drier under future global change.
Distribution and density of moose in relation to landscape characteristics: effects of scale
Authors: Maier Julie AK , Ver Hoef Jay M , McGuire A David , Bowyer R Terry , Saperstein Lisa , Maier Hilmar A
Published: November 2005

We analyzed the relation between early winter distribution and density of female moose (Alces alces L.) and habitat heterogeneity in interior Alaska. We tested for effects of vegetation type, topography, distance to rivers and towns, occurrence and timing of fire, and landscape metrics. A spatial linear model was used to analyze effects of independent variables organized at multiple scales. Because densities of moose vary widely as a result of differences in management and other factors, a spatial response surface of the log of moose density was fit to remove large-scale effects. The analysis revealed that the densest populations of moose occurred closer to towns, at moderate elevations, near rivers, and in areas where fire occurred between 11 and 30 years ago. Furthermore, moose tended to occur in areas with large compact patches of varied habitat and avoided variable terrain and nonvegetated areas. Relationships of most variables with moose density occurred at or below 34 km2, suggesting that moose respond to environmental variables within a few kilometres of their location. The spatial model of density of moose developed in this study represents an important application for effective monitoring and management of moose in the boreal forest.
Growth and yield of all-aged Douglas-fir  western hemlock forest stands: a matrix model with stand diversity effects
Authors: Liang Jingjing , Buongiorno Joseph , Monserud Robert A
Published: November 2005

A density-dependent matrix model was developed for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)  western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest stands in the Pacific Northwest of the United States. The model predicted the number and volume of trees for 4 species groups and 19 diameter classes. The parameters were based on species-dependent equations linking individual tree growth, mortality, and stand recruitment to tree and stand characteristics, including stand diversity in terms of tree species and size. The equations were estimated with individual tree and stand data from 2706 permanent plots in western Washington and Oregon, largely from private and state lands, measured twice at an average interval of 10 years. Other things being equal, diameter growth increased slightly with species diversity and decreased with size diversity. Recruitment increased with species diversity and decreased with size diversity. Mortality was independent of species diversity and tended to increase with size diversity. There was practically no relationship between individual tree volume and species or size diversity. The number of trees predicted by the model over the interval between successive inventories was generally unbiased. Long-term predictions with different initial conditions were consistent with standard yield tables and compared favorably with those of the Forest Vegetation Simulator. The model also implied that, independently of its initial condition, an undisturbed stand would eventually reach a steady state dominated by western hemlock more than 1 m in diameter, with few trees of other species and size.