The Mode of Competition and Spatial Pattern Formation in Plant Communities

The spatial patterns emerging in plant communities are outcomes of differences in growth rates of individuals. The interplay of endogenous and exogenous factors affecting plant growth generates the differences. The endogenous factors in plant populations imply processes of two kinds: i) neighborhood/spatial effects and ii) the mode of competition between individuals [21, 27]. The competition among plants is usually asymmetric, i.e. larger plants capture more resources, because they can pre-empt resources from their smaller neighbors. The higher the degree of competitive asymmetry, the greater the reduction in individual relative growth rate (absolute growth rate per unit biomass) for smaller individuals. Then, variation in growth rates, caused by differences in local neighborhood conditions, leads to individual size differences and spatial patterns [1]. Exogenous factors can cause disturbances in the environment of individual plants, for example, typhoon, abrupt climate change [12, 15, 16, 17, 18, 22, 23]. Falling down of large trees can generate canopy gaps, where there is lower or no canopy. Canopy gaps allow new plants to grow. The gap dynamics and its spatial distribution, therefore, are related to the emergence and maintenance of species diversity in forest ecosystems. As another example of spatial patterns in plant community, the wave-shaped pattern (‘Shimagare’ in Japanese) is well-known. There, we can see stripes of dieback and zones of growing trees appear alternately almost perpendicular to the mountain slope, resulting in a wave-shaped spatial pattern [5, 10].