Seed dispersal is the movement or transport of seeds away from the parent plant. We all realize that plants have limited mobility, and must consequently rely upon many ways to disperse their seeds. The wildflowers and all the other plants populating Presque Isle State Park use many ways to ensure that their species not only survive but also flourish on the park. Most seeds are spread away from the parent plant individually or collectively. They are also dispersed in different areas and at different times of the year.
The scattering of seeds away from the parent plant has many benefits. The first is that a seed’s chance of survival is often higher away from the parent plant. This may result because of seed predators or pathogens that seem to be higher beneath and in the general area of the adult plants.
Basically, there are five main ways seeds can be dispersed: Gravity, wind, ballistic, water and animals. As most people realize, one of the principle methods that matured seeds use to scatter themselves is the wind. Many of the seeds have feathery plumes that allow them to drift large distances from their mother plant. An important constraint on the dispersal of seeds by the wind is the need for a huge seed production to maximize the likelihood of a seed landing in a location suitable for germination. When I think of seed spreading by wind, I instantly think about the lowly dandelion. To help this spread, many of these same seeds are also gathered by birds for nesting material, and thus are spread to entirely new areas.
Another sort of neat way nature uses to spread seeds is to send them home with you on your clothes as you walk the trails and paths of the park. Of course, I am talking about burrs, hooks, spines and/or adhesives that cling to you and cling to the fur of the animals that roam the park. A good example of that is the common burdock. In fact, a Swiss outdoorsman used the hook/burr structure of the burdock as an example of how Velcro might work.
Many plants simply use gravity to achieve seed dispersal. The effect of gravity on heavier fruits causes them to fall from the plant when ripe. Fruits like apples, coconuts, peaches and passion fruit are examples of this method of seed dispersal. Harder shell fruits often roll away from the adult plant, and others are sometimes carried away by animals or water.
There are several ways a plant goes ballistic and flings their seeds out of the seedpod. All of them rely on the effect of evaporation of water in the seedpod. This method of dispersal usually takes place in the sun. Geraniums use the heat of the sun to actually shoot their seeds out of the pods. When the seeds are ripe, the seed covers split apart, and the seed strip rips up the stem, but is stopped because the stem remains attached, and the seeds are catapulted out at a very high speed.
Many aquatic (water) plants spread their seeds through the water. Some plants that grow near water also use it to disperse seeds. Presque Isle’s water lilies are examples of a plant that uses water. When the water lily flower makes a fruit, it will float in the water for a while and then drop to the pond bottom to take root on the floor of the pond. Most common water plants use the water as their way to spread their seeds.
What is interesting about seed dispersal today are the many consequences for the ecology and evolution of plants it might have. Seed dispersal is necessary for species survival and migration. However, in recent times, with the increasing intervention of humans on natural areas, seed dispersal has become an important factor in whether or not a species transported to a new habitat by humans will become an invasive species. Many of the invasive plants on Presque Isle made their way onto the park courtesy of well-meaning visitors. Now that they are part of Presque Isle, they also have their own way of seed dispersal pattern. Unfortunately, invasive plants usually drive out native plants in just a few years.
Over the years, that I have been involved with Presque Isle, many people, including a garden club or two, have volunteered to plant and tend flower gardens all over the park. They all want to keep the park beautiful, which is a noble idea. The park staff, myself and other volunteers have had to explain why that would be a dreadful idea. It all has to do with seed dispersal of non-native ornamental plants. We try to explain that these plants will spread their seeds into areas where they could drive out the native wildflowers and other natural plants.
Mother Nature has a system for seed dispersal and it usually works quite well when it is allowed to do exactly what nature expects it to do. Water lilies grow exactly where nature intended them to grow and this seems to work well for most plants. Come spring, walk on the park and see how, where and why the natural seed dispersal works quite well.
See you on the park!!
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