Seed-scale environments are very heterogeneous. The affect of density on yield, mortality, plant form and reproduction . As plants develop, the biomass is limited by the availability of resources and the yield per unit area becomes independent of density. Self-thinning in populations forms a hierarchy of dominant and stressed subordinate individuals. Limiting resources of the environment .
Plants interfere with neighbors by depleting limited resources available to another.
Resources are exhaustible and contrast with conditions such as temperature that are not exhaustible. Light, water and nitrates are the three resources most commonly involved but it is often impossible to separate the competitive interaction between resource factors. Mechanisms of interaction between species . Plants modify the environment of their neighbors by changing conditions, reducing the level of available resources or by adding toxins to the environment. These effects can be demonstrated in artificial populations, but demonstrating them in the field has not been successful.