They can only stand in one place. But trees have friends that help them move their seeds to good growing locations. Some seeds are carried by the wind. Cottonwood seeds can blow many miles. Maple seeds twirl like helicopters in the wind.
Some seeds float like little boats.
New trees grow along the shore. Some seeds are carried by birds. Birds plant cherry trees when they eat the fruit and drop the seed. Animal Planters Squirrels plant trees when they forget where they buried their acorns. Furry animals can carry some sticky plant seeds to new places.