Annual weed seeds exposed by tilling and planting germinate and grow to cover the bare soil. Wildflowers such as goldenrods may blow in as seeds on the wind and find an empty spot in the garden. In forested regions, tree seedlings germinate and start the long process of reforestation. Without constant tending, weeds, unplanted wildflowers, and tree saplings would quickly overtake the garden, turning it into a thicket. Even in the natural habitat garden, it is often beneficial for the gardener to guide change by thwarting succession, in this case by substituting for natural agents of disturbance such as fire.
Meadows remain open grasslands because annual mowing keeps trees out.
A meadow would otherwise soon start to become a forest. Prairies are renewed by wildfires that burn off the thatch, clearing the soil and releasing nutrients. Thankfully, most of us do not have wildfires in our gardens. To keep a prairie healthy, however, we must either mow it, or do a careful prescribed burn. We must lend mother nature a helping hand.