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  • 1
    Electronic Resource
    Electronic Resource
    Neutral theory (communication arising) The stability of forest biodiversity (2004)
    [s.l.] : Nature Publishing Group
    Nature 427 (2004), S. 696-697 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Clark and McLachlan reply The neutral model says that the relative abundance of a species is as likely to increase as it is to decrease, because species are ecologically identical. This hypothesis can be rejected if variance does not increase over time. We used a more ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/427696b
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  • 2
    Electronic Resource
    Electronic Resource
    Stability of forest biodiversity (2003)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 423 (2003), S. 635-638 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Two hypotheses to explain potentially high forest biodiversity have different implications for the number and kinds of species that can coexist and the potential loss of biodiversity in the absence of speciation. The first hypothesis involves stabilizing mechanisms, which include tradeoffs ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature01632
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  • 3
    Electronic Resource
    Electronic Resource
    Density-dependent mortality and the latitudinal gradient in species diversity (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 417 (2002), S. 732-735 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ecologists have long postulated that density-dependent mortality maintains high tree diversity in the tropics. If species experience greater mortality when abundant, then more rare species can persist. Agents of density-dependent mortality (such as host-specific predators, and pathogens) may be ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature00809
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  • 4
    Electronic Resource
    Electronic Resource
    Genetic variation in germination, growth, and survivorship of red maple in response to subambient through elevated atmospheric CO2 (2004)
    Oxford, UK : Blackwell Publishing
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Genetic variation in plant response to atmospheric carbon dioxide (CO2) may have influenced paleo-vegetation dynamics and could determine how future elevated CO2 drives plant evolution and ecosystem productivity. We established how levels of relatedness – the maternal family, population, and provenance – affect variation in the CO2 response of a species. This 2-year growth chamber experiment focused on the germination, growth, biomass allocation, and survivorship responses of Acer rubrum to four concentrations of CO2: 180, 270, 360, and 600 μL L−1– representing Pleistocene through potential future conditions. We found that all levels of relatedness interacted with CO2 to contribute to variation in response. Germination responses to CO2 varied among families and populations, growth responses depended on families and regions of origin, and survivorship responses to CO2 were particularly affected by regional identities. Differences among geographic regions accounted for 23% of the variation in biomass response to CO2. If seeds produced under subambient CO2 conditions behave similarly, our results suggest that A. rubrum may have experienced strong selection on seedling survivorship at Pleistocene CO2 levels. Further, this species may evolve in response to globally rising CO2 so as to increase productivity above that experimentally observed today. Species responses to future atmospheric CO2 and the accompanying biotic effects on the global carbon cycle will vary among families, populations, and provenances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2004.00726.x
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  • 5
    Electronic Resource
    Electronic Resource
    Long-term Perspectives on Lagged Ecosystem Responses to Climate Change: Permafrost in Boreal Peatlands and the Grassland/Woodland Boundary (2000)
    Springer
    Ecosystems 3 (2000), S. 534-544 
    Details
    ISSN: 1435-0629
    Keywords: Key words: climate change; permafrost; boreal peatlands; grassland/woodland boundary; northern Great Plains; warming; buffering; lagged responses.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Changes in climate could have far-reaching consequences for ecosystems sensitive to changes in temperature and precipitation, such as boreal permafrost peatlands and grassland/woodland boundaries. The long-term data from our studies in these ecosystems suggest that transient responses of permafrost and vegetation to climate change may be difficult to predict due to lags and positive feedbacks related to vegetation and disturbance. Boreal permafrost peatlands comprise an ecosystem with strong local controls on microclimate that influence the formation and thaw of permafrost. These local controls may preserve permafrost during the transient stages of climate warming, producing lagged responses. The prairie–forest border region of the northern Great Plains has experienced frequent change and has complex dynamics involving transitions in the grassland composition of prairie and in the degree of woodiness in bordering forests. Fire frequency interacts with fuel loading and tree recruitment in ways that affect the timing and direction of change. Lags and thresholds could lead to sudden large responses to future climate change that are not readily apparent from current vegetation. The creation of adequate models to characterize transient ecosystem changes will require an understanding of the linkages among processes operating at the scale of 10s of meters and over long time periods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100210000047
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  • 6
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    Charcoal production, dispersal, and deposition from the Fort Providence experimental fire: interpreting fire regimes from charcoal records in boreal forests (2004)
    Canadian Science Publishing
    Details
    Publication Date: 2004-08-01
    Description: The relationship between charcoal production from fires and charcoal deposition in lakes is poorly understood, which limits the interpretation of sediment charcoal records. This calibration study assessed charcoal particle production, size, and transport during the International Crown Fire Modelling Experiment (ICFME) and compared fossil charcoal particle accumulation from 16 lakes in boreal forests of North America. Particle accumulation averaged 20.1 mm2·cm2 inside the ICFME fire; accumulation declined sharply outside the fire, with only 1% of the measured particles transported beyond 20 m from the burn edge. Fossil charcoal accumulation during the past 9000 years was much lower than observed deposition in traps located within the ICFME fire but similar to airborne deposition in traps located 1060 m from the burn edge. A higher fraction of large diameter particles (〉1 mm) was present in fossil charcoal accumulation from historical fires and charcoal peaks that exceeded background accumulation by 1.4 times, suggesting large particles are characteristic of nearby fires. On the basis of a charred-particle production of ~2% of the total fuel consumed by the ICFME fire, we estimate a potential long-term carbon sequestration of 58.2 ± 12 g C·m2 as charred particles from this fire stored in soils or lake sediments.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 7
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    Predicting tree mortality from diameter growth: a comparison of maximum likelihood and Bayesian approaches (2000)
    Canadian Science Publishing
    Details
    Publication Date: 2000-02-01
    Description: Ecologists and foresters have long noted a link between tree growth rate and mortality, and recent work suggests that interspecific differences in low growth tolerance is a key force shaping forest structure. Little information is available, however, on the growth-mortality relationship for most species. We present three methods for estimating growth-mortality functions from readily obtainable field data. All use annual mortality rates and the recent growth rates of living and dead individuals. Annual mortality rates are estimated using both survival analysis and a Bayesian approach. Growth rates are obtained from increment cores. Growth-mortality functions are fitted using two parametric approaches and a nonparametric approach. The three methods are compared using bootstrapped confidence intervals and likelihood ratio tests. For two example species, Acer rubrum L. and Cornus florida L., growth-mortality functions indicate a substantial difference in the two species' abilities to withstand slow growth. Both survival analysis and Bayesian estimates of mortality rates lead to similar growth-mortality functions, with the Bayesian approach providing a means to overcome the absence of long-term census data. In fitting growth-mortality functions, the nonparametric approach reveals that inflexibility in parametric methods can lead to errors in estimating mortality risk at low growth. We thus suggest that nonparametric fits be used as a tool for assessing parametric models.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 8
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    A long-term study of tree seedling recruitment in southern Appalachian forests: the effects of canopy gaps and shrub understories (2000)
    Canadian Science Publishing
    Details
    Publication Date: 2000-10-01
    Description: We examined the importance of intermediate-sized gaps and a dense shrub layer on tree seedling recruitment in a southern Appalachian deciduous forest. We created 12 canopy gaps under two contrasting understory conditions: 6 gaps were dominated by the dense, shade-producing shrub, Rhododendron maximum L., while the remaining gaps were relatively open. Density of first-year and 〉first-year seedlings was monitored for 5 years in transects extending from adjacent undisturbed forest through the experimental gaps. We concurrently measured the understory light environment, soil moisture, litter biomass, and seed rain. Neither species diversity nor richness consistently increased following gap formation. Acer rubrum L. responded consistently to canopy gaps with increased seedling densities while most other species, including both shade-tolerant and shade-intolerant species, did not. Seedling densities were especially low and unresponsive to gap formation in areas dominated by R. maximum. Understory light levels were consistently low beneath R. maximum and did not increase with canopy gap formation. Our results suggest that dense shrub cover can neutralize recruitment opportunities in canopy gaps, that seed rain often limits recruitment in gaps, and that canopy gaps that are larger or include understory disturbance are needed to maintain diversity in these forests.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 9
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    Effects of dispersal, shrubs, and density-dependent mortality on seed and seedling distributions in temperate forests (2003)
    Canadian Science Publishing
    Details
    Publication Date: 2003-05-01
    Description: Processes limiting recruitment of trees may have large impacts on forest dynamics. In this paper, we determined the effects of dispersal, shrubs (Rhododendron maximum), and density-dependent mortality on seed and seedling distributions of Southern Appalachian trees. We quantified the spatial distribution of seed rain, seed bank densities, first-year seedlings, and older than first-year seedlings in five vegetation plots. We fit models to these data assuming effects of limited dispersal, R. maximum (an understory shrub), and (or) density-dependent mortality (as well as a null model with none of these effects) and used best-fitting models to indicate which processes affected a particular species. We found that all factors examined limit species distributions, and thus, affect seedling dynamics. Seedling densities are higher near parent trees long after dispersal occurs. This pattern is less frequently observed for animal-dispersed species than for wind-dispersed species, presumably due to secondary dispersal of seeds by animals. Seedling densities of five species are decreased beneath R. maximum. Shade tolerance does not explain which species are affected, suggesting that factors other than low light are responsible for increased seedling mortality under this shrub. Our results suggest that density-dependent mortality affects four species, decreasing seedling densities close to parent trees. Dispersal, density-dependent mortality, and R. maximum all act in ways that may promote or limit diversity, illustrating that multiple factors are likely to control species diversity.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 10
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    Statistical modeling of seedling mortality (2002)
    Springer
    Details
    Publication Date: 2002-03-01
    Print ISSN: 1085-7117
    Electronic ISSN: 1537-2693
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mathematics
    Published by Springer
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