Ecological thinning is like when you take away some plants from a garden. It's a way of making sure that the plants that are left in the garden grow healthy and strong. The idea is to make sure that there are enough resources (like sunlight, water and nutrients) for the plants to get what they need to grow big and strong. If there are too many plants, the resources can get scarce and the plants won't be able to get what they need to do well.