Competition-density effect in plant populations

The competition-density effect of plant populations is of significance in theory and practice of forest management and has been studied for long time. The differences between the two reciprocal equations of the competition-density effect in nonself-thinning populations and self-thinning populations were analyzed theoretically. This supplies a theoretical basis for analyzing the dynamics of forest populations and evaluating the effect of forest management.

Bayesian inference of biomass growth characteristics for sugi(C.japonica)and hinoki(C.obtusa)forests in self-thinned and managed stands

Background:Forests are an important sink for atmospheric carbon and could release that carbon upon deforestation and degradation.Knowing stand biomass dynamic of evergreen forests has become necessary to improve current biomass production models.The different growth processes of managed forests compared to self-managed forests imply an adaptation of biomass prediction models.Methods:In this paper we model through three models the biomass growth of two tree species(Japanese cedar,Japanese cypress)at stand level whether they are managed or not(self-thinning).One of them is named self-thinned model which uses a specific self-thinning parameterαand adapted to self-managed forests and an other model is named thinned model adapted to managed forests.The latter is compared to a Mitscherlich model.The self-thinned model takes into account the light competition between trees relying on easily observable parameters(e.g.stand density).A Bayesian inference was carried out to determine parameters values according to a large database collected.Results:In managed forest,Bayesian inference results showed obviously a lack of identifiability of Mitscherlich model parameters and a strong evidence for the thinned model in comparison to Mitscherlich model.In self-thinning forest,the results of Bayesian inference are in accordance with the self-thinning 3/2 rule(α=1.4).Structural dependence between stand density and stand yield in self-thinned model allows to qualifying the expression of biological time as a function of physical time and better qualify growth and mortality rate.Relative mortality rate is 2.5 times more important than relative growth rate after about 40 years old.Stand density and stand yield can be expressed as function of biological time,showing that yield is independent of initial density.Conclusions:This paper addressed stand biomass dynamic models of evergreen forests in order to improve biomass growth dynamic assessment at regional scale relying on easily observable parameters.These models can be used to dynamically estimate forest biomass and more generally estimate the carbon balance and could contribute to a better understanding of climate change factors.

Relationship between the Virtual Dynamic Thinning Line and the Self-Thinning Boundary Line in Simulated Plant Populations

The self-thinning rule defines a straight upper boundary line on log-log scales for all possible combinations of mean individual biomass and density in plant populations. Recently, the traditional slope of the upper boundary line, -3/2, has been challenged by -4/3 which is deduced from some new mechanical theories, like the metabolic theory. More experimental or field studies should be carried out to identify the more accurate self-thinning exponent. But it＇s hard to obtain the accurate self-thinning exponent by fitting to data points directly because of the intrinsic problem of subjectivity in data selection. The virtual dynamic thinning line is derived from the competition-density （C-D） effect as the initial density tends to be positive infinity, avoiding the data selection process. The purpose of this study was to study the relationship between the virtual dynamic thinning line and the upper boundary line in simulated plant stands. Our research showed that the upper boundary line and the virtual dynamic thinning line were both straight lines on log-log scales. The slopes were almost the same value with only a very little difference of 0.059, and the intercept of the upper boundary line was a little larger than that of the virtual dynamic thinning line. As initial size and spatial distribution patterns became more uniform, the virtual dynamic thinning line was more similar to the upper boundary line. This implies that, given appropriate parameters, the virtual dynamic thinning line may be used as the upper boundary line in simulated plant stands.