ERA

Journal Articles (Renewable Resources)

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  1. Prescribed fire as a tool to regenerate live and dead serotinous jack pine (Pinus banksiana) stands [Download]

    Title: Prescribed fire as a tool to regenerate live and dead serotinous jack pine (Pinus banksiana) stands
    Creator: Sharpe, Maria
    Description: This study documents cone opening and natural regeneration of jack pine (Pinus banksiana Lamb.) after burning live and dead stands similar to those killed by the mountain pine beetle (Dendroctonus ponderosae). Trees were killed by girdling in May and were burned in late July, 26 months later. Pairs of live and dead plots were simultaneously burned using three types of fire: surface, intermittent crown and continuous crown fires. Each type of fire was replicated three times; the nine pairs of burns were completed in a 4-day period. After fire, more cones were opened on dead trees than live trees. On dead trees, there was cone opening even when fire charred only the lower part of the bole. Three years after burning, dead stands with continuous crown fires had some of the densest regeneration and the highest rates of stocking. Across all burns in this study, seedling regeneration was best in shallow residual duff and in the more intensely burned plots. Without burning, there was virtually no regeneration 5 years after mortality. The results also show that burning, especially under continuous crown fire, could be used to promote regeneration in dead stands.
    Subjects: Mountain Pine Beetle, Serotiny, Precribed Fire, Jack Pine
    Date Created: 2017
  2. Nobody’s perfect: Can irregularities in pit structure influence vulnerability to cavitation? [Download]

    Title: Nobody’s perfect: Can irregularities in pit structure influence vulnerability to cavitation?
    Creator: Plavcová, Lenka
    Description: Recent studies have suggested that species-specific pit properties such as pit membrane thickness, pit membrane porosity, torus-to-aperture diameter ratio and pit chamber depth influence xylem vulnerability to cavitation. Despite the indisputable importance of using mean pit characteristics, considerable variability in pit structure within a single species or even within a single pit field should be acknowledged. According to the rare pit hypothesis, a single pit that is more air-permeable than many neighboring pits is sufficient to allow air-seeding. Therefore, any irregularities or morphological abnormalities in pit structure allowing air-seeding should be associated with increased vulnerability to cavitation. Considering the currently proposed models of air-seeding, pit features such as rare, large pores in the pit membrane, torus extensions, and plasmodesmatal pores in a torus can represent potential glitches. These aberrations in pit structure could either result from inherent developmental flaws, or from damage caused to the pit membrane by chemical and physical agents. This suggests the existence of interesting feedbacks between abiotic and biotic stresses in xylem physiology.
    Subjects: Pit Membrane, Pit Ontogeny, Bordered Pit, Pit Damage, Xylem Vulnerability, Structural Irregularity
    Date Created: 2013
  3. Water transport in vesselless angiosperms: Conducting efficiency and cavitation safety [Download]

    Title: Water transport in vesselless angiosperms: Conducting efficiency and cavitation safety
    Creator: Hacke, Uwe G.
    Description: Two structure‐function hypotheses were tested for vesselless angiosperm wood. First, vesselless angiosperm wood should have much higher flow resistance than conifer wood because angiosperm tracheids lack low‐resistance torus‐margo pits. Second, vesselless wood ought to be exceptionally safe from cavitation if the small cumulative area of pits between tracheids confers safety (the pit area hypothesis). Data were obtained from branch wood of 19 vesselless angiosperms: Amborella trichopoda, Trochodendron aralioides, Tetracentron sinense, and 16 Winteraceae from Tasmannia, Zygogynum, Bubbia, Pseudowintera, and Drimys. Contrary to the first hypothesis, vesselless and conifer species with narrow tracheids (below ca. 18 μm) had similar area‐specific resistivities. The reason was that vesselless angiosperms had an intertracheid pit resistance (mean $16\pm 2$ MPa s m−1) that was nearly as low as that of conifers ($6\pm 1$ MPa s m−1) and much lower than that of eudicot intervessel pits ($336\pm 81$ MPa s m−1). Low pit resistance was associated with greater pit membrane porosity inferred from scanning electron microscopy observations and silicone penetration and may represent incipient pit membrane loss. Pit resistance was often greater in wider angiosperm tracheids and obscured any drop in wood resistivity with tracheid width. In support of the second hypothesis, vesselless woods averaged a cavitation pressure of $-3.4\pm 0.3$ MPa, which is low for their wet habitats. In agreement with the pit area hypothesis, resistance to cavitation increased with decreasing total pit area between conduits. However, vesselless angiosperms were more vulnerable for a given pit area than eudicots, consistent with their more permeable pit membranes. Small total pit area between conduits may allow angiosperm tracheids to have more porous membranes for conducting efficiency without creating a cavitation problem.
    Subjects: Basal Angiosperm Physiology, Cavitation, Ecological Wood Anatomy, Xylem, Vesselless Angiosperms, Vessel Evolution
    Date Created: 2007
  4. Hydraulic consequences of vessel evolution in angiosperms [Download]

    Title: Hydraulic consequences of vessel evolution in angiosperms
    Creator: Sperry, John S.
    Description: We tested two hypotheses for how vessel evolution in angiosperms influenced xylem function. First, the transition to vessels decreased resistance to flow—often considered the driving force for their evolution. Second, the transition to vessels compromised safety from cavitation—a constraint emerging from the “pit area hypothesis” for vulnerability to cavitation. Data were obtained from branch wood of 17 basal taxa with vessels and two eudicots possessing “primitive” perforation plates. Results were compared with previous data from vesselless angiosperms and eudicots with simple perforation plates. Contrary to the first hypothesis, basal taxa did not have significantly lower sapwood‐specific resistivity than vesselless angiosperms, despite vessels being wider than tracheids. Eudicot resistivity was ca. 4.5 times lower. On a vessel‐area basis, resistivity of “primitive” vessels ($435\pm 104$ MPa s m−2) was lower than angiosperm tracheids ($906\pm 89$ MPa s m−2) but still greater than eudicot vessels ($91\pm 9$ MPa s m−2). High resistivity of primitive vessels could be attributed to their being shorter per diameter than eudicots and to high perforation plate resistivity ($57\% \pm 15\% $ of total) in the species with scalariform plates. In support of the second hypothesis, primitive vessels had a cavitation pressure 1.4 MPa more vulnerable than angiosperm tracheids. This “vulnerability bottleneck” may have been even more extreme without a shift in vessels to less porous interconduit pit membranes. Vessel evolution was not driven by lower flow resistance, and it may have been limited to wet habitats by cavitation risk. A subtle, context‐dependent advantage to primitive vessels is consistent with the distribution of the vesselless condition in the angiosperm tree. The results imply that truly efficient and safe vessels evolved much later than vessels per se, perhaps in concordance with larger radiations among core angiosperms.
    Subjects: Ecological Wood Anatomy, Xylem Cavitation, Basal Angiosperm Physiology, Xylem Evolution, Water Transport, Vessel
    Date Created: 2007
  5. Diversity of Carabidae (Insecta, Coleoptera) in Epiphytic Bromeliaceae in Central Veracruz, Mexico [Download]

    Title: Diversity of Carabidae (Insecta, Coleoptera) in Epiphytic Bromeliaceae in Central Veracruz, Mexico
    Creator: de Oca, E.M.
    Description: This paper documents the existence of carabid assemblages associated with bromeliads on the Cofre de Perote, Veracruz, Mexico. Based on bromeliads sampled over three altitudinal ranges, the assemblages included at least 26 species with an arboreal lifestyle and another 11 species that are not strictly arboreal. Seven species are new to science, urging us to pay attention to the arboreal fauna in forest conservation studies. Composition of carabid assemblages associated with bromeliads changes with altitude. In lowlands, it is comprised almost entirely of species of Lebiini, with the Platynini dominating assemblages found in bromeliads >1,000 m above sea level. Our data suggest that carabids use bromeliads to reduce stresses associated with drought periods, the exact timing of which depends on altitude. The unexpected low diversity of the carabid fauna associated with bromeliads at middle altitude is explained in terms of anthropogenic conversion of the original forest to pastureland. Given the importance of arboreal elements, further fragmentation of subtropical and tropical mountain forest significantly threatens overall carabid diversity.
    Subjects: Carabids, Bromeliads, Diversity, Altitude, Mexico
    Date Created: 2007
  6. Boreal forest CO2 exchange and evapotranspiration predicted by nine ecosystem process models: Inter-model comparisons and relationships to field measurements [Download]

    Title: Boreal forest CO2 exchange and evapotranspiration predicted by nine ecosystem process models: Inter-model comparisons and relationships to field measurements
    Creator: Amthor, J.S.
    Description: Nine ecosystem process models were used to predict CO2 and water vapor exchanges by a 150-year-old black spruce forest in central Canada during 1994-1996 to evaluate and improve the models. Three models had hourly time steps, five had daily time steps, and one had monthly time steps. Model input included site ecosystem characteristics and meteorology. Model predictions were compared to eddy covariance (EC) measurements of whole-ecosystem CO2 exchange and evapotranspiration, to chamber measurements of nighttime moss-surface CO2 release, and to ground-based estimates of annual gross primary production, net primary production, net ecosystem production (NEP), plant respiration, and decomposition. Model-model differences were apparent for all variables. Model-measurement agreement was good in some cases but poor in others. Modeled annual NEP ranged from -11 g C m(-2) (weak CO2 source) to 85 g C m(-2) (moderate CO2 sink). The models generally predicted greater annual CO2 sink activity than measured by EC, a discrepancy consistent with the fact that model parameterizations represented the more productive fraction of the EC tower \"footprint.\" At hourly to monthly timescales, predictions bracketed EC measurements so median predictions were similar to measurements, but there were quantitatively important model-measurement discrepancies found for all models at subannual timescales. For these models and input data, hourly time steps (and greater complexity) compared to daily time steps tended to improve model-measurement agreement for daily scale CO2 exchange and evapotranspiration (as judged by root-mean-squared error). Model time step and complexity played only small roles in monthly to annual predictions.
    Subjects: Climate variability, Land-surface scheme, Soil, Net primary production, Photosynthesis model, Black spruce forest, General-model, Jack pine forest, Atmospheric carbon-dioxide, Regional applications
    Date Created: 2001
  7. Scale-dependent controls on the area burned in the boreal forest of Canada, 1980-2005 [Download]

    Title: Scale-dependent controls on the area burned in the boreal forest of Canada, 1980-2005
    Creator: Parisien, M.A.
    Description: In the boreal forest of North America, as in any fire-prone biome, three environmental factors must coincide for a wildfire to occur: an ignition source, flammable vegetation, and weather that is conducive to fire. Despite recent advances, the relative importance of these factors remains the subject of some debate. The aim of this study was to develop models that identify the environmental controls on spatial patterns in area burned for the period 1980-2005 at several spatial scales in the Canadian boreal forest. Boosted regression tree models were built to relate high-resolution data for area burned to an array of explanatory variables describing ignitions, vegetation, and long-term patterns in fire-conducive weather (i.e., fire climate) at four spatial scales (10(2) km(2), 10(3) km(2), 10(4) km(2), and 10(5) km(2)). We evaluated the relative contributions of these controls on area burned, as well as their functional relationships, across spatial scales. We also assessed geographic patterns of the influence of wildfire controls. The results indicated that extreme temperature during the fire season was a top control at all spatial scales, followed closely by a wind-driven index of ease of fire spread. However, the contributions of some variables differed substantially among the spatial scales, as did their relationship to area burned. In fact, for some key variables the polarity of relationships was inverted from the finest to the broadest spatial scale. It was difficult to unequivocally attribute values of relative importance to the variables chosen to represent ignitions, vegetation, and climate, as the interdependence of these factors precluded clear partitioning. Furthermore, the influence of a variable on patterns of area burned often changed enormously across the biome, which supports the idea that fire-environment relationships in the boreal forest are complex and nonstationary.
    Subjects: Area burned, Climate, Canadian boreal forest, Ignitions, Spatial scale, Boosted regression trees, Topography, Vegetation, Wildfire, Regression modeling
    Date Created: 2011
  8. A 15,800-year record of atmospheric lead deposition on the Devon Island Ice Cap, Nunavut, Canada: Natural and anthropogenic enrichments, isotopic composition, and predominant sources [Download]

    Title: A 15,800-year record of atmospheric lead deposition on the Devon Island Ice Cap, Nunavut, Canada: Natural and anthropogenic enrichments, isotopic composition, and predominant sources
    Creator: Zheng, J.
    Description: Abstract: Using appropriate clean methods for handling and preparation, 57 ice samples from the Devon Island Ice Cap, representing the period 134 to 15,800 years before present (BP), were analyzed for Pb, Sc, and Pb isotopes (Pb-206, Pb-207, Pb-208) using ICP-SMS. The greatest Pb concentrations were found in samples dating from the Younger Dryas. Despite the large range in Pb concentrations (from 2.2 to 181 pg g(-1)), the Pb concentrations were proportional to those of Sc until 3100 BP when the Pb/Sc ratio exceeded by a factor of 2 the natural \"background\" value (Pb/Sc = 6.3 +/- 1.8) for the first time. The uniform ratio of Pb to Sc until 3100 BP is consistent with the hypothesis that soil dust particles derived from physical and chemical weathering dominate the inputs of Pb to the atmosphere, with the magnitude of these sources climate-dependent. Isotopic analyses of Pb further support this paradigm, with the average ratio of Pb-206/Pb-207 (1.230) and Pb-208/Pb-206 (2.059) well within the range given for the Upper Continental Crust (UCC). The shift to higher Pb/Sc ratios and lower Pb-206/Pb-207 values starting at 3100 BP is consistent with historical records and other archival evidence of the onset of atmospheric Pb contamination caused by Pb mining and smelting in the Iberian Peninsula. Since that time, the Devon Island ice core records several other episodes of notable atmospheric Pb contamination, including those dating from Roman and medieval times, as well as the industrial period. The Pb, Sc, and Pb isotope data presented here represent the first chemical and isotopic record of the natural, \"background\" atmospheric inputs to the Canadian Arctic, against which modern values may be compared.
    Subjects: Swedish lake sediments, Antarctic Ice, Trace-element, Northern hemisphere, Heavy-metals, C-14 YR BP, Ellesmere-Island, Central Greenland, Peat bog, Environmental impact
    Date Created: 2007
  9. The soil microbial community and grain micronutrient concentration of historical and modern hard red spring wheat cultivars grown organically and conventionally in the Black soil zone of the Canadian prairies [Download]

    Title: The soil microbial community and grain micronutrient concentration of historical and modern hard red spring wheat cultivars grown organically and conventionally in the Black soil zone of the Canadian prairies
    Creator: Nelson, A. G.
    Description: Abstract: Micronutrient deficiencies in the diet of many people are common and wheat is a staple food crop, providing a carbohydrate and micronutrient source to a large percentage of the world’s population. We conducted a field study to compare five Canadian red spring wheat cultivars (released over the last century) grown under organic and conventional management systems for yield, grain micronutrient concentration, and soil phospholipid fatty acid (PLFA) profile. The organic system had higher grain Zn, Fe, Mg and K levels, but lower Se and Cu levels. There was no trend in the results to suggest that modern western Canadian hard red spring cultivars have lower grain micronutrient content than historical cultivars. Wheat cultivar choice is important for maximizing grain nutrient levels, which was influenced by management system. It is evident that the emphasis on elevated grain quality in the western Canadian hard red spring class has resulted in the retention of micronutrient quality characters. Three fungal PLFAs were indicators for the organic system, and all three of these indicators were positively correlated with grain Cu concentration. In the organic system, percent arbuscular mycorrhizal fungi were negatively correlated with grain Zn and Fe concentrations, and positively correlated with grain Mn, Cu, K concentrations and grain yield. The organic system had higher levels of fungi in the soil, including arbuscular mycorrhizal fungi. Organic management practices appear to result in elevated levels of grain micronutrient concentration. The hard red spring breeding effort in and for the black soil zone of the northern Great Plains also appears to have led to no diminishment of grain micronutrient concentration. It is evident that both the agronomic system and breeding strategies in this region can be exploited for future increases in grain micronutrient concentration.
    Subjects: Micronutrients, Phospholipid fatty acid analysis, Triticum aestivum L., Arbuscular mycorrhizal fungi, Antioxidants, Conventional agriculture, Organic agriculture
    Date Created: 2011
  10. Effects of contemporary winter seismic exploration on low arctic plant communities and permafrost [Download]

    Title: Effects of contemporary winter seismic exploration on low arctic plant communities and permafrost
    Creator: Kemper, J. T.
    Description: Abstract: We studied effects of oil and gas exploration, using the most recent seismic exploration technologies, on tundra plant communities and soils in four vegetation types in the Low Arctic of western Canada, two to three years post-disturbance. For all four vegetation types, seismic lines had less vascular plant cover and more bare ground than adjacent \"reference\" tundra. For the two upland tundra vegetation types, mosses and lichens were less abundant on seismic lines than in reference plots. There were no apparent differences in organic layer thickness between seismic lines and reference areas, but active layer depth (at the time of sampling) was significantly greater on seismic lines for the upland tundra and one of the wed and vegetation types. Diversity and richness were lower, and community composition was different, on seismic lines (as compared to reference plots) in upland tundra vegetation types but not in wetland types. The results suggest that (I) upland vegetation types are less resistant to seismic disturbance, (2) active layer depth increases following seismic disturbance, and (3) impacts from modern seismic techniques in upland tundra are similar to. or somewhat greater than, the initial impacts observed from the earliest phases of winter exploration similar to 30 years ago.
    Subjects: Restoration, Vegetation recovery, Northeastern Alaska, Recolonization, Ecosystems, Tundra disturbance, Resilience, Surface disturbance, Seed bank
    Date Created: 2009