A Closer Look: Seed Dispersal

Lorna Dielentheis, local naturalist & contributing writer

When you think of fall, you probably think first of the showy change of colors: lush reds, oranges, and yellows– the complete transformation of the landscape. However, when you look past the bright, intermittently falling leaves and the satisfying crunch underfoot, you may notice another widespread change to the visual ecosystem: seeds. 

Eastern Redcedar

The abundance of seeds in the fall is obvious when you think about it; seeds and seed dispersal appear as some of the most recognizable symbols of fall in New England: pumpkin, apple, and squash, to name a few. These examples all use the same seed dispersal technique, encasing their seeds in an edible fruit which attracts animals who then ingest the seeds and deposit them elsewhere. This dispersal method is used widely and numerous examples can be found at Rock Point and beyond. One such species that uses this method is Eastern Redcedar (Juniperus virginiana), found growing on the limestone bluffs at Rock Point. Their berries, known commonly as juniper berries, provide an important food source for birds during the winter, who in turn unwittingly disperse the seeds encased within the scrumptious fruit. 

a squirrel gathers acorns to cache

Oaks (specifically white oaks, whose acorns contain less tannins than those of red oaks and are therefore more palatable) also temp critters with a delicious morsel. However, the seed itself does not remain intact when ingested; instead, squirrels and chipmunks cache these acorns and inevitably forget about some, which then

germinate and grow where they’ve been stashed. 

Other dispersal methods include by wind, by gravity, by water, and by attaching to the outside of animals. You have undoubtedly at some point in your life aided in one or more of these methods, by blowing a dandelion, for example, or hiking through brush and painstakingly picking off burrs or beggarticks afterward. 

a milkweed pod split open

A particularly fascinating form of seed dispersal is called myrmecochory, or dispersal by ants. This partnership between the ant and the plant benefits them both. The plant produces seeds that are attached to a nutrient-rich parcel, called an elaiosome. Ants carry this seed+elaiosome package, called a diaspore, back to their colony and detach the elaiosome, feeding it to larvae. They then discard the seed, often dumping it underground. The seed avoids predation and can safely germinate, while the ants receive an easy source of food. 

Take a closer look next time you walk a trail. Notice that among the falling leaves of the sugar maple are also twirling samaras making their gentle descent towards ground. Touch the silky clumps of milkweed seed as they spill and float from split pods. Delight as a jewelweed pod bursts open, flinging seeds up to five feet away as you brush past it. Whatever the appearance or dispersal method, seeds are all around us. Traveling miles or mere feet, many now begin their perilous journeys, ensuring that, come spring, it all happens once more.