10  Competition effect

In this section, we discuss the effect of competition on the growth, survival, and recruitment vital rates. For all three demographic functions, competition for light increases linearly with the plot density, determined by the \(\beta\) parameter, indicating the density-dependent effect. Assuming that light represents the most limiting resource for trees, we define that the influence of individuals smaller than the focal tree is negligible. Consequently, we used the total basal area of individuals larger than the focal tree to measure competition. Furthermore, we divided the impact of the total basal area into contributions from conspecific and heterospecific individuals larger than the focal individual.

Conspecific and heterospecific effect

Growth

Figure 10.1: Posterior distribution of conspecific and heterospecific density dependence across species (left panel) and species shade tolerance (right panel). Species are classified by their general growth trait following Burns, Honkala, et al. (1990)

Survival

Figure 10.2: Posterior distribution of conspecific and heterospecific density dependence across species (left panel) and species shade tolerance (right panel). Species are classified by their general growth trait following Burns, Honkala, et al. (1990)

Growth vs survival

Figure 10.3: Correlation between growth and survival density dependence parameters.

Total basal area effect on recruitment survival

Figure 10.4: Posterior distribution of the density dependence parameter affecting the annual survival rate of recruitment individuals.

How does CNDD relate to species latitude and abundance patterns?

This is mostly inspired by Hülsmann et al. (2024), where they test many hypotheses around conspecific density dependence (CNDD) around the world. Their main finding is that CNDD is stronger in the tropics compared to temperature species, but only for low or intermediate abundant species.

Figure 10.5: Posterior distribution of the density dependence parameter affecting the annual survival rate of recruitment individuals.

Figure 10.6: Posterior distribution of the density dependence parameter affecting the annual survival rate of recruitment individuals.

Burns, Russell M, Barbara H Honkala, et al. 1990. “Silvics of North America: 1. Conifers; 2. Hardwoods Agriculture Handbook 654.” US Department of Agriculture, Forest Service, Washington, DC.

Hülsmann, Lisa, Ryan A Chisholm, Liza Comita, Marco D Visser, Melina de Souza Leite, Salomon Aguilar, Kristina J Anderson-Teixeira, et al. 2024. “Latitudinal Patterns in Stabilizing Density Dependence of Forest Communities.” Nature, 1–8.