One of the most fascinating abilities plants have is their ability to understand what is going on around them. Although we do not completely understand how this apparent wisdom works, we do understand some of it.
Most plants produce pheromones that stop seeds in the soil germinating. If the plants are removed then the seeds may immediately germinate. This has both benefits and detriments. It allows you to induce lost plants to return. It also means that large numbers of weeds will reappear as soon as you remove them.
They also appear to regulate the flowering of plants. Some species of plants appear not to flower generously if they are growing densely but will flower profusely if you substantially reduce their numbers.
Pheromones to plants are similar to hormones to animals. The plants are susceptible to minute quantities. The plant releases these chemicals into the soil and probably the air as well. The other plants react to them.
This way plants understand what is going on around them. In particular they know if they should flower or conserve their energy for other things.
The important thing to understand is that plants can communicate with each other in a way that is beneficial to their survival. They have a substantial genetic wisdom which can truly test you when you try to eliminate them. It can also be of great help if you are trying to re-establish them.