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Inequality of size and size increment in Pinus banksiana in relation to stand dynamics and annual growth rate.

Metsaranta JM, Lieffers VJ - Ann. Bot. (2007)

Bottom Line: The inequality of size increment was greater and more variable than the inequality of size.Inequality of size increment was significantly related to annual growth rate at the stand level, and was higher when growth rate was low.A complete understanding of the dynamics of these forests requires further evaluation of the way in which factors that influence variation in annual growth rate also affect the mode of competition and the development of size hierarchies.

View Article: PubMed Central - PubMed

Affiliation: Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2H1 Canada. jmetsara@nrcan.gc.ca

ABSTRACT

Background and aims: Changes in size inequality in tree populations are often attributed to changes in the mode of competition over time. The mode of competition may also fluctuate annually in response to variation in growing conditions. Factors causing growth rate to vary can also influence competition processes, and thus influence how size hierarchies develop.

Methods: Detailed data obtained by tree-ring reconstruction were used to study annual changes in size and size increment inequality in several even-aged, fire-origin jack pine (Pinus banksiana) stands in the boreal shield and boreal plains ecozones in Saskatchewan and Manitoba, Canada, by using the Gini and Lorenz asymmetry coefficients.

Key results: The inequality of size was related to variables reflecting long-term stand dynamics (e.g. stand density, mean tree size and average competition, as quantified using a distance-weighted absolute size index). The inequality of size increment was greater and more variable than the inequality of size. Inequality of size increment was significantly related to annual growth rate at the stand level, and was higher when growth rate was low. Inequality of size increment was usually due primarily to large numbers of trees with low growth rates, except during years with low growth rate when it was often due to small numbers of trees with high growth rates. The amount of competition to which individual trees were subject was not strongly related to the inequality of size increment.

Conclusions: Differences in growth rate among trees during years of poor growth may form the basis for development of size hierarchies on which asymmetric competition can act. A complete understanding of the dynamics of these forests requires further evaluation of the way in which factors that influence variation in annual growth rate also affect the mode of competition and the development of size hierarchies.

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Annual trajectories of the Lorenz asymmetry coefficient for size and size increment since 1950 at each study plot. The solid line indicates the value 1, where the Lorenz curve is symmetric. The dashed line represents the Lorenz asymmetry coefficient, and the dotted lines are 95 % confidence intervals calculated from 1000 bootstrap samples.
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MCM320F3: Annual trajectories of the Lorenz asymmetry coefficient for size and size increment since 1950 at each study plot. The solid line indicates the value 1, where the Lorenz curve is symmetric. The dashed line represents the Lorenz asymmetry coefficient, and the dotted lines are 95 % confidence intervals calculated from 1000 bootstrap samples.

Mentions: The Lorenz asymmetry coefficient for size increment was also more variable from year to year than the Lorenz asymmetry coefficient for size (Fig. 3). For the vast majority of the time, the Lorenz asymmetry coefficient for size was not significantly different from 1, indicating that the observed inequality in tree size was not due to either large or small trees. The Lorenz asymmetry coefficient for size increment, however, had many periods of time when it was significantly less than 1 at all sites, indicating that the observed inequality in size increments was often due to larger numbers of trees with small size increments. There was one clear exception to this trend. At the nutrient-rich site at Candle Lake, the two years (1966 and 1967) with Lorenz asymmetry coefficients greater than 1 correspond to the years with the lowest growth rate at that site, and also to two years during which the historical records of the Canadian Forest Insect and Disease Survey indicate that this area was subject to a jack pine budworm defoliation event. In this specific case, the observed inequality in growth rates at this stand was due to a small number of trees that had high growth rates, most likely because they were not defoliated and continued to grow at a normal rate.


Inequality of size and size increment in Pinus banksiana in relation to stand dynamics and annual growth rate.

Metsaranta JM, Lieffers VJ - Ann. Bot. (2007)

Annual trajectories of the Lorenz asymmetry coefficient for size and size increment since 1950 at each study plot. The solid line indicates the value 1, where the Lorenz curve is symmetric. The dashed line represents the Lorenz asymmetry coefficient, and the dotted lines are 95 % confidence intervals calculated from 1000 bootstrap samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2710195&req=5

MCM320F3: Annual trajectories of the Lorenz asymmetry coefficient for size and size increment since 1950 at each study plot. The solid line indicates the value 1, where the Lorenz curve is symmetric. The dashed line represents the Lorenz asymmetry coefficient, and the dotted lines are 95 % confidence intervals calculated from 1000 bootstrap samples.
Mentions: The Lorenz asymmetry coefficient for size increment was also more variable from year to year than the Lorenz asymmetry coefficient for size (Fig. 3). For the vast majority of the time, the Lorenz asymmetry coefficient for size was not significantly different from 1, indicating that the observed inequality in tree size was not due to either large or small trees. The Lorenz asymmetry coefficient for size increment, however, had many periods of time when it was significantly less than 1 at all sites, indicating that the observed inequality in size increments was often due to larger numbers of trees with small size increments. There was one clear exception to this trend. At the nutrient-rich site at Candle Lake, the two years (1966 and 1967) with Lorenz asymmetry coefficients greater than 1 correspond to the years with the lowest growth rate at that site, and also to two years during which the historical records of the Canadian Forest Insect and Disease Survey indicate that this area was subject to a jack pine budworm defoliation event. In this specific case, the observed inequality in growth rates at this stand was due to a small number of trees that had high growth rates, most likely because they were not defoliated and continued to grow at a normal rate.

Bottom Line: The inequality of size increment was greater and more variable than the inequality of size.Inequality of size increment was significantly related to annual growth rate at the stand level, and was higher when growth rate was low.A complete understanding of the dynamics of these forests requires further evaluation of the way in which factors that influence variation in annual growth rate also affect the mode of competition and the development of size hierarchies.

View Article: PubMed Central - PubMed

Affiliation: Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2H1 Canada. jmetsara@nrcan.gc.ca

ABSTRACT

Background and aims: Changes in size inequality in tree populations are often attributed to changes in the mode of competition over time. The mode of competition may also fluctuate annually in response to variation in growing conditions. Factors causing growth rate to vary can also influence competition processes, and thus influence how size hierarchies develop.

Methods: Detailed data obtained by tree-ring reconstruction were used to study annual changes in size and size increment inequality in several even-aged, fire-origin jack pine (Pinus banksiana) stands in the boreal shield and boreal plains ecozones in Saskatchewan and Manitoba, Canada, by using the Gini and Lorenz asymmetry coefficients.

Key results: The inequality of size was related to variables reflecting long-term stand dynamics (e.g. stand density, mean tree size and average competition, as quantified using a distance-weighted absolute size index). The inequality of size increment was greater and more variable than the inequality of size. Inequality of size increment was significantly related to annual growth rate at the stand level, and was higher when growth rate was low. Inequality of size increment was usually due primarily to large numbers of trees with low growth rates, except during years with low growth rate when it was often due to small numbers of trees with high growth rates. The amount of competition to which individual trees were subject was not strongly related to the inequality of size increment.

Conclusions: Differences in growth rate among trees during years of poor growth may form the basis for development of size hierarchies on which asymmetric competition can act. A complete understanding of the dynamics of these forests requires further evaluation of the way in which factors that influence variation in annual growth rate also affect the mode of competition and the development of size hierarchies.

Show MeSH