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  • 1
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    A neighborhood analysis of canopy tree competition: effects of shading versus crowding (2004)
    Canadian Science Publishing
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    Publication Date: 2004-04-01
    Description: We have developed extensions of traditional distance-dependent, spatial competition analyses that estimate the magnitude of the competitive effects of neighboring trees on target tree growth as a function of the species, size, and distance to neighboring trees. Our analyses also estimate inter- and intra-specific competition coefficients and explicitly partition the competitive effects of neighbors into the effects of shading versus crowding. We tested the method using data from forests of northern, interior British Columbia dominated by western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata Donn ex D. Don). For both species, the most parsimonious regression models included terms for the effects of tree size, crowding, and shading and separate competitive effects of four different groups of competing species. The models explained 33%59% of the variation in radial growth of the two species. For both species, growth declined more steeply as a function of crowding than shading. There was striking asymmetry in the strength of interspecific competition between hemlock and redcedar, with crowding by hemlock having a strong per capita effect on redcedar, while crowding by redcedar had relatively little effect on the radial growth of hemlock.
    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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  • 2
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    Seed abundance versus substrate limitation of seedling recruitment in northern temperate forests of British Columbia (2000)
    Canadian Science Publishing
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    Publication Date: 2000-03-01
    Description: We examine the influence of (i) the spatial distribution and abundance of parent trees (as seed sources) and (ii) the abundance and favourability of seedbed substrates, on seedling recruitment for the major tree species in northwestern interior cedar-hemlock forests of British Columbia, under four levels of canopy openness (full canopy, partial canopy, large gap, and clearcut). Substrate distribution varied with canopy openness, and substrate favourability was a function of both canopy openness and seedling species. Lack of suitable substrates was the predominant factor limiting seedling density under full canopies. Partial canopy and gap sites provided a broad range of favourable substrates in close proximity to parent trees, resulting in the highest observed seedling densities. There was much higher effective dispersion of seedlings away from parent trees in gaps than in the partially cut stands. Seedling dispersion to clearcut sites was poor with seedlings being tightly restricted to a narrow band along the forest edge. Thus, seedling recruitment in these forests was a reflection of the interaction between the abundance of seed and substrate favourability, and the relative importance of these factors varied significantly with canopy structure.
    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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  • 3
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    Measurement and modeling of spatially explicit variation in light transmission through interior cedar-hemlock forests of British Columbia (1999)
    Canadian Science Publishing
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    Publication Date: 1999-12-01
    Description: We have characterized canopy geometry and light transmission by the nine dominant conifer and broad-leaved tree species of the interior cedar-hemlock (ICH) forests of northern British Columbia. Our field data were used to parameterize a spatially explicit model of light transmission through mixed-species forests. That model, a component of the forest dynamics simulator SORTIE, was developed for eastern deciduous forests, and this paper presents a test of that model in a very different ecosystem. Our results show that individual crowns of the ICH forests intercepted much more light than species of eastern deciduous forests but that the canopy as a whole allowed greater light penetration, largely because of openings between the relatively narrow, conical crowns of the western conifers. Light transmission by individual crowns was correlated with shade tolerance among the conifers (as in eastern deciduous species), but crown depth was not (in contrast with eastern species). Despite the fundamental differences in the nature of light transmission in the two ecosystems, the SORTIE light model developed for eastern deciduous forests was effective at predicting spatial variation in understory light levels in these western coniferous forests. The goodness of fit of such a simple model suggests that the most important factors regulating spatial variation in understory light levels in these forests are simply the sizes and distribution of nearby trees, and the local sky brightness distribution. Discrete canopy gaps represent a special case in which a region of the canopy is not occupied by crowns.
    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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  • 4
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    Regeneration from seed of six tree species in the interior cedar-hemlock forests of British Columbia as affected by substrate and canopy gap position (1998)
    Canadian Science Publishing
    Details
    Publication Date: 1998-09-01
    Description: Canopy gap size can play a major role in determining composition of tree regeneration after disturbance. The effect of different positions within gaps and within the intact forest has received less study. We seeded six tree species onto two substrates (organic and undisturbed moss) in three positions along a north-south gradient within eight replicate 600-m2 canopy gaps and in the intact forest south of each gap (the gap positions), in 1995 and 1996. Emergence of all species was strongly affected by gap position, seedbed substrate, and year, but there was little evidence of partitioning by gap position among the species. Average emergence was higher in the shady southern position in gaps and within the intact forest and significantly higher on organic than undisturbed moss substrates (with the exception of Abies lasiocarpa (Hook.) Nutt., which showed no preference for seedbed). Seedling survival was greatest for all species in the south end of the gap, where soil moisture remained highest and light levels of approximately 20% full sun were adequate for survival. A species trade-off was observed in the understory of the intact forest, where differential survival based on shade-tolerance ranking occurred. To predict regeneration success in these forests, for either silvicultural purposes or to permit a better understanding of community dynamics and succession, it is important to consider the influence of position inside and outside of gaps and the nature of the seedbed substrate.
    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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  • 5
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    Growth and crown morphological responses of boreal conifer seedlings and saplings with contrasting shade tolerance to a gradient of light and height (2002)
    Canadian Science Publishing
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    Publication Date: 2002-03-01
    Description: The effects of gradients in light levels and tree height on growth and crown attributes of six conifer species were studied in eastern and western Canada. Three conifers were studied in British Columbia (Abies lasiocarpa (Hook.) Nutt., Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm., and Pinus contorta Dougl. ex Loud. var. latifolia Engelm.), and three in Quebec (Abies balsamea (L.) Mill., Picea glauca, and Pinus banksiana Lamb.). For several growth and morphological parameters, conifers reacted strongly to both an increase in light and tree height. Significant or nearly significant interactions between light classes and height were found for height and diameter growth of most species as well as for many crown attributes for both Abies and Picea. These interactions usually indicated that growth or morphological changes occurred with increasing height from a certain light level. Within a single genus, both eastern and western tree species showed the same overall acclimation to light and height. As generally reported, Pinus species showed less variation in growth and morphological responses to light than Abies and Picea species.
    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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  • 6
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    Growth of planted tree seedlings in response to ambient light levels in northwestern interior cedar-hemlock forests of British Columbia (1999)
    Canadian Science Publishing
    Details
    Publication Date: 1999-09-15
    Description: Insights into field-planted conifer seedling growth were gained by fitting height and diameter growth to relative irradiance over the growing season using Michaelis-Menten functions. There was little difference among tree species (Abies lasiocarpa (Hook.) Nutt., Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr., Pinus contorta Dougl. ex Loud., Thuja plicata Donn ex D. Don, Tsuga heterophylla (Raf.) Sarg.) in response to ambient light. No significant differences in whole-plant compensation points were observed among species but the ranking of species' compensation points was consistent with their shade-tolerance ranking. Five years after planting, total size and recent growth rates varied little among species from low to high light, implying an absence of trade-offs in low- and high-light growth strategies. Thuja plicata had the greatest response to increased light under deep shade (
    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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    Growth of planted lodgepole pine and hybrid spruce following chemical and manual vegetation control on a frost-prone site (1994)
    Canadian Science Publishing
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    Publication Date: 1994-02-01
    Description: The 5-year height and diameter growth response of a frost-tolerant species, (lodgepole pine, Pinuscontorta var. latifolia Dougl. ex Loud.) and a frost-susceptible species (hybrid spruce, Piceaglauca (Moench) Voss × Piceasitchensis (Bong.) Carr.) to different vegetation-control site-preparation treatment and timing combinations was examined using a factorial experiment. The site chosen for the experiment is subject to frequent summer growing season frosts. The vegetation control treatments were: an untreated control, manual cutting, and glyphosate applied at the rates of 1.4 and 2.1 kg active ingredient (a.i.) per hectare. Each vegetation-control treatment was applied at four dates (timing) that covered the active growing season of the vegetation on the study area. Vegetation-control method had a major impact on the growth of the planted seedlings. The influence of timing of control treatments on growth was found to be minor. Fifth-year height and diameter in the manual cutting and control treatments were equally poor. Growth was significantly improved by both levels of chemical vegetation control and after 5 years, no differences were apparent between the two. Pine height and diameter and spruce diameter continually improved as the level of thimbleberry (Rubusparviflorus Nutt.) was reduced. Below 5% thimbleberry cover, this growth increased dramatically, suggesting a response threshold. As vegetation cover was lowered, however, spruce seedlings were damaged by frost, resulting in reduced total height. In this case, better height growth was associated with either very low or moderately high thimbleberry cover than with moderate to low levels.
    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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    DNA-dependent formation of transcription factor pairs alters their binding specificity (2015)
    Nature Publishing Group (NPG)
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    Publication Date: 2015-11-10
    Description: Gene expression is regulated by transcription factors (TFs), proteins that recognize short DNA sequence motifs. Such sequences are very common in the human genome, and an important determinant of the specificity of gene expression is the cooperative binding of multiple TFs to closely located motifs. However, interactions between DNA-bound TFs have not been systematically characterized. To identify TF pairs that bind cooperatively to DNA, and to characterize their spacing and orientation preferences, we have performed consecutive affinity-purification systematic evolution of ligands by exponential enrichment (CAP-SELEX) analysis of 9,400 TF-TF-DNA interactions. This analysis revealed 315 TF-TF interactions recognizing 618 heterodimeric motifs, most of which have not been previously described. The observed cooperativity occurred promiscuously between TFs from diverse structural families. Structural analysis of the TF pairs, including a novel crystal structure of MEIS1 and DLX3 bound to their identified recognition site, revealed that the interactions between the TFs were predominantly mediated by DNA. Most TF pair sites identified involved a large overlap between individual TF recognition motifs, and resulted in recognition of composite sites that were markedly different from the individual TF's motifs. Together, our results indicate that the DNA molecule commonly plays an active role in cooperative interactions that define the gene regulatory lexicon.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jolma, Arttu -- Yin, Yimeng -- Nitta, Kazuhiro R -- Dave, Kashyap -- Popov, Alexander -- Taipale, Minna -- Enge, Martin -- Kivioja, Teemu -- Morgunova, Ekaterina -- Taipale, Jussi -- England -- Nature. 2015 Nov 19;527(7578):384-8. doi: 10.1038/nature15518. Epub 2015 Nov 9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biosciences and Nutrition, Karolinska Institutet, SE 141 83, Sweden. ; European Synchrotron Radiation Facility, 38043 Grenoble, France. ; Genome-Scale Biology Program, University of Helsinki, P.O. Box 63, FI-00014, Finland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26550823" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Base Sequence ; Binding Sites/genetics ; Crystallography, X-Ray ; DNA/*genetics/*metabolism ; Gene Expression Regulation/genetics ; Humans ; Molecular Sequence Data ; Nucleotide Motifs/genetics ; Reproducibility of Results ; *Substrate Specificity/genetics ; Transcription Factors/*metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 9
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    Baryon cycling in the low-redshift circumgalactic medium: a comparison of simulations to the COS-Halos survey (2016)
    Oxford University Press
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    Publication Date: 2016-04-30
    Description: We analyse the low-redshift ( z 0.2) circumgalactic medium (CGM) by comparing absorption-line data from the COS-Halos survey to absorption around a matched galaxy sample from two cosmological hydrodynamic simulations. The models include different prescriptions for galactic outflows, namely hybrid energy/momentum driven wind (ezw), and constant winds (cw). We compare equivalent widths, covering factors, ion ratios, and kinematics. Both wind models show generally 1 agreement with these observations for H  i and certain low-ionization metal lines, but poorer agreement with higher ionization metal lines including Si  iii and O  vi that are well observed by COS-Halos. This suggests that both models predict too much cool, metal-enriched gas and not enough hot gas, and / or that metals are not sufficiently mixed. This may reflect our model assumption of ejecting outflows as cool and unmixing gas. Our ezw simulation includes a heuristic prescription to quench massive galaxies by superheating interstellar medium gas. This produces low-ionization absorption broadly consistent with observations, but substantial O  vi absorption inconsistent with data, suggesting that gas around quenched galaxies in the real Universe does not cool. At impact parameters of 50 kpc, recycling winds dominate the absorption of low ions and even H  i , while O  vi generally arises from metals ejected 1 Gyr ago. The similarity between the wind models is surprising, since they differ substantially in the amount and phase distribution of halo gas. We show that this similarity owes mainly to our comparison at fixed stellar (not halo) mass, suggesting that CGM properties are more closely tied to galaxy's stellar (versus halo) mass.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Species variability in growth response to light across climatic regions in northwestern British Columbia (1998)
    Canadian Science Publishing
    Details
    Publication Date: 1998-06-01
    Description: We characterize variation in radial and height growth of saplings of 11 tree species across a range of light levels in boreal, sub-boreal, subalpine, and temperate forests of northwestern British Columbia. Shade-tolerant species had the greatest response to an increase in light at low-light levels but had low asymptotic growth at high light. Shade-intolerant species had weaker responses to increases at low light but had the highest growth rates at high light. The effects of climate on intraspecific variation in sapling response to light were also related to shade tolerance: across different climatic regions, the most shade-tolerant species varied in their response to low-light but not high light, while shade-intolerant species varied only in their high-light growth. Species with intermediate shade tolerance varied both their amplitude of growth at high light and the slope of the growth response at low light. Despite the interspecific trade-offs between high- and low-light growth, there was a striking degree of overlap in the light response curves for the component species in virtually all of the climatic regions. Successional dynamics in these forests appear to be more strongly governed by interspecific variation in sapling survival than growth.
    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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