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  • Wiley  (4)
  • 1995-1999  (4)
  • 1
    Online Resource
    Online Resource
    Evaluation of Fine Root Length and Diameter Measurements Obtained Using RHIZO Image Analysis
    Wiley ; 1999
    In:  Agronomy Journal Vol. 91, No. 1 ( 1999-01), p. 142-147
    Details
    In: Agronomy Journal, Wiley, Vol. 91, No. 1 ( 1999-01), p. 142-147
    Abstract: Image analysis systems facilitate rapid measurement of root length and diameter, but their accuracy is not easily determined. The objective of this study was to develop a set of simple experiments for evaluating the accuracy of fine root measurements obtained using image analysis. Using the system RHIZO (trademark of Régent Instruments, Québec), we tested the accuracy of (i) length measurements made over a range of root lengths per unit area, (ii) average diameter measurements and length per diameter distributions in string, wire, and fine root samples of varying diameter, and (iii) diameter measurements on short segments of diagonally oriented objects. Our results suggest that preliminary testing of image analysis systems is absolutely necessary for producing reliable root measurements. Total length was accurately determined for typically encountered length per unit areas of 〈 1.5 cm cm −2 . For samples with higher values, however, the method underestimated total length by 〉 5%. It is therefore recommended that users of image analysis systems determine this maximum length per unit area for accurate delerminations of total root length. In samples that contained different string diameters, the total sample length and average string diameter could accurately be measured. However, the length per diameter class was underestimated by 〉 20% when the string diameter was less than one pixel smaller than the upper limit of the diameter class. Adjustment of diameter intervals and increasing the scanner resolution are required to reduce this underestimation. Both the length and the angle of the short segments analyzed were found to influence diameter measurements. Similar sets of experiments are proposed for a rigorous evaluation of the performance of other image analysis systems on root measurements.
    Type of Medium: Online Resource
    ISSN: 0002-1962 , 1435-0645
    URL: Article
    DOI: 10.2134/agronj1999.00021962009100010022x
    Language: English
    Publisher: Wiley
    Publication Date: 1999
    detail.hit.zdb_id: 1471598-3
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  • 2
    Online Resource
    Online Resource
    Fine‐root production in small experimental gaps in successional mixed boreal forests
    Wiley ; 1998
    In:  Journal of Vegetation Science Vol. 9, No. 4 ( 1998-08), p. 537-542
    Details
    In: Journal of Vegetation Science, Wiley, Vol. 9, No. 4 ( 1998-08), p. 537-542
    Abstract: Abstract. The effects of small 10m × 10m experimental above‐ground gaps on fine‐root production for the first two years were studied in three fire‐initiated stands of the northwestern mixed broad‐leaf‐conifer boreal forest of Québec. The 48‐yr‐old forest is dominated by Populus tremuloides (Trembling aspen), the 122‐yr‐old forest by a mixture of P. tremuloides, Abies balsamea (balsam fir) and Picea glauca (white spruce), and the 232‐yr‐old forest by Thuja occidentalis (eastern white cedar) and A. balsamea , with some P. tremuloides. 40 root‐ingrowth bags were installed in different locations in and around each gap (at gap center, 1 to 2 m either side of gap edge and in adjacent control plots). Half of the ingrowth bags were harvested after one year following gap creation, the other half after two years. Roots were sorted into different species grouping. Fine‐root production was statistically ( P 〈 0.05) larger in the youngest forest compared to the two older ones after one year, but not after two years. The individual species or groups of species increased, decreased or showed no change in fine‐root production in gaps, but overall we did not observe a major shift in species proportion between gap and control plots after two years. Some herbs and also Taxus canadensis seemed to benefit in terms of fine‐root growth from such small openings after two years. No statistical differences ( P 〉 0.10) in total fine‐root production were found among locations within and outside gaps in either year. However, there was a clear tendency for fine‐root production to be smaller in gap center than in the other locations for the two younger successional forests the first year after gap creation. We conclude that small above‐ground gaps (i.e. 〈 100 m 2 ) do not produce a significant and long‐lasting below‐ground gap in terms of total fine‐root production in the successional forests investigated.
    Type of Medium: Online Resource
    ISSN: 1100-9233 , 1654-1103
    URL: Article
    DOI: 10.2307/3237269
    RVK:
    WA 15000
    Language: English
    Publisher: Wiley
    Publication Date: 1998
    detail.hit.zdb_id: 2047714-4
    detail.hit.zdb_id: 1053769-7
    SSG: 12
    SSG: 23
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  • 3
    Online Resource
    Online Resource
    Accuracy and Limitations of Published Algorithms Using the Twelve-Lead Electrocardiogram to Localize Overt Atrioventricular Accessory Pathways
    Wiley ; 1999
    In:  Journal of Cardiovascular Electrophysiology Vol. 10, No. 10 ( 1999-10), p. 1340-1349
    Details
    In: Journal of Cardiovascular Electrophysiology, Wiley, Vol. 10, No. 10 ( 1999-10), p. 1340-1349
    Type of Medium: Online Resource
    ISSN: 1045-3873 , 1540-8167
    URL: Issue
    URL: Article
    DOI: 10.1111/jce.1999.10.issue-10
    DOI: 10.1111/j.1540-8167.1999.tb00189.x
    Language: English
    Publisher: Wiley
    Publication Date: 1999
    detail.hit.zdb_id: 2037519-0
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  • 4
    Online Resource
    Online Resource
    Effects of overstory and understory vegetation on the understory light environment in mixed boreal forests
    Wiley ; 1998
    In:  Journal of Vegetation Science Vol. 9, No. 4 ( 1998-08), p. 511-520
    Details
    In: Journal of Vegetation Science, Wiley, Vol. 9, No. 4 ( 1998-08), p. 511-520
    Abstract: Abstract. The percentage of above‐canopy Photosynthetic Photon Flux Density (%PPFD) was measured at 0, 50 and 100 cm above the forest floor and above the main understory vegetation in stands of (1) pure Betula papyrifera (White birch), (2) pure Populus tremuloides (Trembling aspen), (3) mixed broad‐leaf‐conifer, (4) shade‐tolerant conifer and (5) pure Pinus banksiana (Jack pine) occurring on both clay and till soil types. %PPFD was measured instantaneously under overcast sky conditions (nine locations within each of 29 stands) and continuously for a full day under clear sky conditions (five locations within each of eight stands). The percentage cover of the understory layer was estimated at the same locations as light measurements. Mean %PPFD varied from 2% at the forest floor under Populus forests to 15% above the understory vegetation cover under Betula forests. Percent PPFD above the understory vegetation cover was significantly higher under shade intolerant tree species such as Populus, Betula and Pinus than under shade tolerant conifers. No significant differences were found in %PPFD above the understory vegetation cover under similar tree species between clay and till soil types. The coefficient of variation in %PPFD measured in the nine locations within each stand was significantly lower under deciduous dominated forests (mean of 19%) than under coniferous dominated forests (mean of 40%). %PPFD measured at the forest floor was positively correlated with %PPFD measured above the understory vegetation and negatively correlated with cumulative total percent cover of the understory vegetation ( R 2 = 0.852). The proportion of sunflecks above 250 and 500 mmol m –2 s –1 was much lower and %PPFD in shade much higher under Populus and Betula forests than under the other forests. Differences in the mean, variability and nature of the light environment found among forest and soil types are discussed in relation to their possible influences on tree succession.
    Type of Medium: Online Resource
    ISSN: 1100-9233 , 1654-1103
    URL: Article
    DOI: 10.2307/3237266
    RVK:
    WA 15000
    Language: English
    Publisher: Wiley
    Publication Date: 1998
    detail.hit.zdb_id: 2047714-4
    detail.hit.zdb_id: 1053769-7
    SSG: 12
    SSG: 23
    Location Call Number Limitation Availability
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    Online Resource
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