Seeds are primarily dispersed through natural forces such as animals, wind and water. Many seeds are also planted by man, but most plant species survival depends on organic methods.
Seed dispersion by animals is carried out in several ways. Some plants develop hooks, such as burs and thistles, that will catch in the hair of passing animals. They will drop off or be removed during grooming. Other plants produce seed bearing fruit and nuts that animals like to eat. These seeds travel through the animals digestion and are excreted in droppings.
Wind dispersal is responsible for the spread of many plants with tiny seeds. These seeds are specially adapted with “wings” or hair-like appendages that catch the wind. Strong gusts can tear them away from the plant and carry them for many miles before they are dropped to the ground, where they can grow.
Plants growing near water often develop seeds that float well. As they are shed, the water carries these floating seeds to other areas downstream to new areas. While many small seeds will float on the surface tension of the water, even some very large seeds, such as coconuts, are dispersed this way.
Some specialty plants are more purposeful in their seed dispersal, adapting mechanisms that allow seeds to be ejected from the plant, to travel up to several feet from the host plant. This causes a slower spread as each new generation of plant expands a little further.