Limits...
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.

Show MeSH
Annual trajectories of the Gini coefficient for size and size increment since 1950 at each study plot. The solid line represents the Gini coefficient, and the dotted lines are 95 % confidence intervals calculated from 1000 bootstrap samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2710195&req=5

MCM320F2: Annual trajectories of the Gini coefficient for size and size increment since 1950 at each study plot. The solid line represents the Gini coefficient, and the dotted lines are 95 % confidence intervals calculated from 1000 bootstrap samples.

Mentions: From 1950 to 2004, the Gini coefficient for size was nearly always less than 0·5, meaning that tree sizes could be characterized as equal (Fig. 2). During the same time period, the Gini coefficient for size increment was also generally less than 0·5, but there were periods at all sites when it was greater than 0·5, indicating that size increment could often be considered more unequal than equal (Fig. 2). Size inequality generally declined over time. Based upon the 95 % confidence intervals, the nutrient-poor sites had more unequal tree sizes. Size increment was more unequal than size, and its inequality was also more variable from year to year than inequality in size, showing both increasing and decreasing trends from year to year, depending upon the site. Inequality in size increment was not different at rich and poor sites.


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 Gini coefficient for size and size increment since 1950 at each study plot. The solid line represents the Gini 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

MCM320F2: Annual trajectories of the Gini coefficient for size and size increment since 1950 at each study plot. The solid line represents the Gini coefficient, and the dotted lines are 95 % confidence intervals calculated from 1000 bootstrap samples.
Mentions: From 1950 to 2004, the Gini coefficient for size was nearly always less than 0·5, meaning that tree sizes could be characterized as equal (Fig. 2). During the same time period, the Gini coefficient for size increment was also generally less than 0·5, but there were periods at all sites when it was greater than 0·5, indicating that size increment could often be considered more unequal than equal (Fig. 2). Size inequality generally declined over time. Based upon the 95 % confidence intervals, the nutrient-poor sites had more unequal tree sizes. Size increment was more unequal than size, and its inequality was also more variable from year to year than inequality in size, showing both increasing and decreasing trends from year to year, depending upon the site. Inequality in size increment was not different at rich and poor sites.

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