Dispersal is the method that the seeds are spread from the plant. Some just drop, others are in fruits, and others are carried by animals or the wind. When the environment is full of the right light and water, seeds can easily spread nearby and germinate. However if the area is difficult, such as a desert, the seeds may disperse but there will be limits on population size due to few habitable areas (rocks for example), low carrying capacity of the soil if it is dry, and perhaps the plant blooming during a rainy period but then the seeds are not dispersed until the area dries and the seeds can be carried by the wind. A plant such as the dandelion weed has tiny seeds that are released at peak time at end of summer and carried by the wind to germinate and put lots of pretty yellow weed flowers all over your lawn.
In the Mojave desert, several flowering plants have developed a way to deal with the dispersal problem. When the plants flower and go to seed, there is a lot of water due to rainstorms that hit the desert. Flooding can occur. The seeds may drop into wet soil and not be carried right away. When the soil dries, the plants die and now the wind can easily carry the seeds. If the seeds were to germinate immediately,they would die because the desert is back to its dry spell. Instead, the seeds remain in a prolonged dormant period and are spread all over. The desert soil is full of these seeds. They remain for a very long time, dormant and resistant to the harsh conditions until the rains come again, and the desert blooms for a short time. The population remains intact, but it appears periodically. Examples are the desert sand verbena, the desert paintbrush and the Mojave aster.
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