Most of us can appreciate the value of the full complement of plants present in a diverse and varied forest. Those plants reflect both the conditions that were present at the time the plants established and responses to any changing conditions since that time. But what we often overlook is that living seeds of many other plants are present in the soil beneath the forest. The collection of seeds present in soil at any given time is referred to as the soil seedbank.
In addition to variation in the size, color, shape and abundance of seeds produced by different plants, there are many different types of conditions necessary to stimulate a seed to germinate. Some seeds must germinate almost immediately after ripening, and others can either remain viable for many years under very specific conditions or alternatively under a variety of differing conditions. Some seeds, such as those of the sacred lotus (Nelumbo nucifera), can remain viable for hundreds of years.
Seeds are present in all kinds of soil including lake sediments, sandy banks and wetland muck. They are carried along with the currents that are the lifeblood of our watershed. Seeds are also dispersed by gravity, wind, animals and other means. Germination of these seeds may take place spontaneously, or it may depend on one or more specific stimuli including exposure to a specific temperature or moisture level, exposure to sunlight or fire, or abrasion related to erosion, pressure or even the digestive tract of an animal that ate it. Sometimes all of the seeds of a certain species may germinate at once, and at other times only a small percentage will germinate.
This forest community at the CWC Elm Flats Preserve offers but a small glimpse of the many plant species present in the soil below.
For these reasons, the number and composition of seeds that are present in the soil is ever-changing. Seeds are constantly being added to the soil. Some are germinating, and others are simply resting in reserve for the future. The soil seedbank is a fundamental means of plant colonization after disturbance and is often valuable in conserving rare species by assisting in long-term survival during adverse conditions. Unfortunately, the soil seedbank also harbors the seeds of invasive species and can pose a significant obstacle in ridding landscapes of undesirable species.
The thing to remember is that anytime soil is moved, so are all of the seeds present in the soil. So when an area erodes or is excavated, often all of the topsoil where the seeds are most abundant is displaced. For this and other reasons, many municipalities now require that topsoil be stockpiled onsite and replaced after the completion of a construction project. Likewise, when topsoil is brought into an area from offsite, a new community of seeds arrives with it. Those seeds may be desirable, but often they include invasive species. A recent load of topsoil that I purchased for my own yard yielded a more than ample supply of poison ivy. Oh, what a tangled web we weave as we alter this landscape. On your next stroll through the forest, why not take a moment to ponder the plants that you don't see that lie waiting in the soil beneath you? The standing forest is but a glimpse of the full picture.
The Chautauqua Watershed Conservancy is a local nonprofit organization that is dedicated to preserving and enhancing the water quality, scenic beauty and ecological health of the lakes, streams, wetlands and watersheds of the Chautauqua region. For more information, call 664-2166 or visit www.chautauquawatershed.org or www.facebook.com/chautauquawatershed.