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Aboveground net primary production decline with stand age: potential causes
S T Gower1, R E McMurtrie, D Murty
1Stith Gower is at the Dept of Forestry, University of Wisconsin, Madison, WI 53706, USA.
Trends in Ecology & Evolution
|January 18, 2011
Summary
Forest productivity declines with age due to nutrient scarcity and stomatal limitations, not increased respiration. These factors explain reduced aboveground net primary production in mature cold-environment forests.
Area of Science:
- Forest Ecology
- Ecosystem Science
- Plant Physiology
Background:
- Aboveground net primary production (ANPP) typically peaks in young forests and declines significantly with stand age.
- The underlying mechanisms driving this age-related ANPP decline remain incompletely understood.
- Hypotheses include altered tissue balance, reduced soil nutrients, and stomatal limitations on photosynthesis.
Purpose of the Study:
- To investigate the primary drivers of declining aboveground net primary production (ANPP) in maturing forest stands.
- To differentiate the contributions of various hypothesized mechanisms to age-related productivity decline.
- To clarify the role of respiratory costs versus nutrient and stomatal factors in cold-environment forests.
Main Methods:
- Review of recent empirical and modeling studies on forest ANPP and stand age.
- Analysis of factors including photosynthetic/respiratory tissue balance, soil nutrient availability, and stomatal conductance.
- Focus on forests within cold environmental conditions.
Main Results:
- Decreasing soil nutrient availability significantly contributes to age-related ANPP decline.
- Increasing stomatal limitation, reducing photosynthetic rates, is a key factor in reduced productivity.
- Elevated respiratory costs were found to be relatively unimportant in explaining the observed decline.
Conclusions:
- Soil nutrient availability and stomatal limitations are the principal mechanisms driving the decline in forest ANPP with stand age in cold environments.
- The balance between photosynthetic and respiring tissues, and increased respiratory costs, play a minor role.
- Understanding these mechanisms is crucial for predicting forest ecosystem responses to aging and environmental change.
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