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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 average amount of competition to which each tree is subject (solid line) and the coefficient variation (CV %) of competition to which each tree is subject (dashed line) at each study plot. Competition was quantified using a distance-weighted absolute size index (eqn 4), with a variable search radius defined as 3·5 times each tree's crown width.
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MCM320F4: Annual trajectories of the average amount of competition to which each tree is subject (solid line) and the coefficient variation (CV %) of competition to which each tree is subject (dashed line) at each study plot. Competition was quantified using a distance-weighted absolute size index (eqn 4), with a variable search radius defined as 3·5 times each tree's crown width.

Mentions: The average amount of competition (standardized by the maximum average annual competition observed at a given site so that each plot could be compared on the same scale) showed both increasing and decreasing trends over time at each plot (Fig. 4). Initially, average competition increased at each site up to about 1970 (Fig. 4). After that point, it stayed relatively constant at the nutrient-rich sites, while the nutrient-poor sites showed a second increase in average competition that started about 15 years later (about 1985, Fig. 4). Overall, the increase in average competition from its minimum value was higher at nutrient-poor sites (where the minimum value was 0·4–0·6 times the maximum) than at nutrient-rich sites (where the minimum value was 0·7–0·8 times the maximum). The CV % for competition ranged from 20 to 50 % at all sites (Fig. 4), indicating that even though the average amount of competition that trees were subject to changed over time, the amount that each tree was subject to in a given year tended be similar. In addition, although there were periods of time at each site where the CV % for competition had small increasing or decreasing trends, the value of the CV % at any given site ranged only in the order of ±10 % over the whole study period, indicating that the variability in the amount of competition to which trees were subject to did not change substantially over time.


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 average amount of competition to which each tree is subject (solid line) and the coefficient variation (CV %) of competition to which each tree is subject (dashed line) at each study plot. Competition was quantified using a distance-weighted absolute size index (eqn 4), with a variable search radius defined as 3·5 times each tree's crown width.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

MCM320F4: Annual trajectories of the average amount of competition to which each tree is subject (solid line) and the coefficient variation (CV %) of competition to which each tree is subject (dashed line) at each study plot. Competition was quantified using a distance-weighted absolute size index (eqn 4), with a variable search radius defined as 3·5 times each tree's crown width.
Mentions: The average amount of competition (standardized by the maximum average annual competition observed at a given site so that each plot could be compared on the same scale) showed both increasing and decreasing trends over time at each plot (Fig. 4). Initially, average competition increased at each site up to about 1970 (Fig. 4). After that point, it stayed relatively constant at the nutrient-rich sites, while the nutrient-poor sites showed a second increase in average competition that started about 15 years later (about 1985, Fig. 4). Overall, the increase in average competition from its minimum value was higher at nutrient-poor sites (where the minimum value was 0·4–0·6 times the maximum) than at nutrient-rich sites (where the minimum value was 0·7–0·8 times the maximum). The CV % for competition ranged from 20 to 50 % at all sites (Fig. 4), indicating that even though the average amount of competition that trees were subject to changed over time, the amount that each tree was subject to in a given year tended be similar. In addition, although there were periods of time at each site where the CV % for competition had small increasing or decreasing trends, the value of the CV % at any given site ranged only in the order of ±10 % over the whole study period, indicating that the variability in the amount of competition to which trees were subject to did not change substantially over time.

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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