Ecology is defined as the study of how organisms interact with one another and their physical surroundings. Weed-crop ecology is the study of how weeds interact with a crop, humans, and their physical surroundings.
Weeds typically invade bare, open areas where more desirable plants tend not to grow. Annual grass weeds typically invade first followed. Next annual broadleaf weeds typically invade. Those are typically followed by perennial grass weeds, perennial broadleaf weeds, and brambles and vines. Trees are typically the last species to invade an area.
Growth habits and seeding are characteristics of weeds that most affect their ability to survive and thrive.
Growth Habits of Weeds
Weeds are typically adaptive, resilient species of plants. They can live in a variety of habitats. They adapt to changing environments, thrive under extreme conditions, establish populations in strange places, and succeed in disturbed environments where other plants cannot.
Some weeds have specialized, modified plant parts to help them thrive where cultivated plants cannot. Some have shallow roots to help them grow in compacted soil. Some have prostrate growth patterns to avoid being damaged by mowing. Others that need to survive drought conditions have reduced leaf area and arial parts.
Seeding of Weeds
Like other weed growth habits, the seeding process for weeds has also adapted itself for survival. Weed can produce a lot of seeds in a single growing season. They can produce thousands, sometimes tens of thousands, of seeds during a growing season. Many have evolved such that their seeds can remain buried and dormant for years until conditions are favorable for germination. The seeds for some plants can remain viable for 40, 50, or 70 years. The seeds of many weeds can continue to mature days after the parent plant has been pulled from the ground.
Weed seeds can be disseminated in a variety of ways. Wind, water, and animals such as birds or humans help to spread their seeds. Some weed seeds have tufts of hair or wing-like structures enabling them to be carried by the wind. Other are lightweight and/or have an oily film allowing them to be carried by rainwater runoff. Still others have physical characteristics like burs, hooks, and other physical properties making it easy for them to attach themselves to animals and humans for transport. Weed seeds are often mixed in with crop seeds since they are sometimes hard to see or separate from crop seeds making it important to use weed-free seeds for planting in a garden. Cultivation of the land can also lead to the spread of weeds.