Seed dispersal is one of the most important factors that influences the ability of a species to colonize new areas. For an invasion to occur, seeds must first be dispersed to a potential habitat. Seeds have an entire array of morphological and structural adaptations which allow them to be dispersed by natural processes and human activities. Seeds may be naturally dispersed by wind, water, and animals. For example, Canada thistle and dandelion produce seeds that have a hairy structure called a pappus that allows them to be easily dispersed by wind.
Many seeds are buoyant and can be dispersed by water.
Seeds may also have specialized structures that allow them to cling to animals. Cheatgrass seeds, for example, possess barbs on the caryopses that attach to animal fur. Finally, seeds can remain viable after passing through the digestive tracts of animals. Once eaten, these seeds can be dispersed over potentially large areas by birds, cattle, horses, and other mammals. Humans activities are another important vector for seed dispersal.