Employing individual plant growth models to quantify the impact of neighboring plants in plant communities
Some agricultural systems have been observed to over-yield in mixture (polyculture). That is, the biomass production is greater when different species are grown together than when they are grown alone (monoculture). The simplest mechanism to explain over-yielding is that each species utilizes the resource pool differently or draws from different portions of the resource pool allowing greater community biomass than that expected from a monoculture at the same plant density. One may state the null hypothesis that there will be no over-yielding, with increased species richness holding plant density constant. In addition, one may predict that the more species, the more the resources would be thoroughly depleted resulting in less resources for the community and subsequent lower total biomass than the monoculture of any of the species. Developing an understanding of the mechanisms that govern the interaction among plants sharing the same resource pool could improve our ability as applied scientists to create more efficient agricultural systems.
A model was designed to understand the interaction among individual plants in close proximity and to predict plant population and community productivity. Historically, population and community ecology have centered around descriptive outcomes of individual interactions by using plant density as the primary independent variable. Plant density has historically been assumed to be surrogate for resource use because each plant is a resource using unit. In this study, we used an individual plant approach to try to develop an understanding of population and community response. The interacting factors that are assumed to influence individual plant growth (size) are: the initial size of the plant (seed weight), the emergence time relative to neighboring plants, the distance to neighboring plants, the size of neighboring plants and the identity of the neighboring plants. It is assumed that different species will have different levels of impact on an individual target plant’s growth. The underlying logic is that plants interact through a resource pool and under simplifying assumptions have a constant resource delivery rate over time and space and the resource pool is drawn down depending on the number, size and distance to neighbors within a given neighborhood (distance from target plant). The rate at which different species can draw on the resource pool is variable, i.e. some species are better at acquiring resources than others.