Modeling age-related stand respiration changes in forest stands under the self-thinning law

- Age-related changes in stand respiration after canopy closure were modeled.
- This model revealed that there exists possibility of increasing stand respiration.
- Possibilities of respiration constancy and decrease were regarded to be reasonable.
- Significant contribution is provided to the long-standing discussion on the productivity decline.

There are three different age-related changes in stand respiration (woody + foliage respiration) in an even-aged pure forest stand after canopy closure: (A) monotonous increase (Kira and Shidei, 1967; Odum, 1969), (B) constancy (Oohata and Shidei, 1974; Ogawa et al., 2010), and (C) monotonous decrease (Ryan et al., 1997; Drake et al., 2011). These contrasting views were based on observational data rather than on theoretical arguments. The present study was performed to model age-related changes in stand respiration to elucidate the mechanism of stand respiration dynamics after canopy closure in compliance with three concepts: (i) the self-thinning law, (ii) power scaling between mean individual annual respiration and mean individual mass, and (iii) the logistic function of stand density changes. Simulations showed that although the three hypotheses were tenable theoretically, that proposed by Kira and Shidei is a mathematically special case. Considering these modeling results, age-related stand respiration changes in plantations of hinoki (Chamaecyparis obtusa) (Ogawa et al., 1985) can be regarded as decreasing as well as constant after canopy closure. The present modeling revealed that there exists possibility of increasing stand respiration in Kira and Shidei's hypothesis from the theoretical viewpoints, although no observed data support their hypothetical trend. However, from both of the empirical and theoretical viewpoints, we understood that possibilities of stand respiration constancy and decrease in forest stands were regarded to be reasonable after the canopy closure.