Hitchin’ A Ride

HITCHIN’  A  RIDE  

October/November, 2008 issue

Now that my Sheltie Terrier is a senior, she is not able to go for the long walks across the fields like we used to in years past.  I am not certain of my fixation for long-haired dogs, other than the enjoyment of burying my face in their hair, for they are a chore to look after and groom. Their hair also has an irresistible attraction to riders from our jaunts – twigs, dead stalks and once, a sprig of prickly ash clinging for some time on the end of her tail. Mostly though, the riders were harmless seeds from the previous year’s crop of alfalfa which rode for a short distance, then fell off. Others, if we chose to explore neighbouring abandoned fields, were the seeds of beggar-ticks which were less cooperative. Sticktight is another name for these double-barbed achenes which require painstaking plucking to remove them all. On the farm we used to call them Devil’s pitchforks.

While the constant combing of persistent seeds from the coats of pets can be annoying, many of these plants could not exist were it not for this unique way of seed dispersal. We have all inadvertently picked up burs on our clothing. If I recall little else about my early life on our farm, I shall always remember trying to milk cows while dodging their swishing tails in the fall of the year, heavy with the burs from burdock and cockleburs. You haven’t lived until you have been swatted in the face with a rock hard cocklebur.

Not all plants, however, disperse their seeds in this fashion. Dandelions are well known for their method. Also goatsbeard, milkweed, cattails, and many others. Some like jewelweed or touch-me-not explosively eject their seeds, allowing the plant to populate areas several feet away. Others, like the seeds of purple loosestrife, succeed by being small and light, floating on the water’s surface to new locations. Also very buoyant are the seeds of dog strangling vine or swallowwort, taking over an area quickly since their light weight makes them disperse easily.  

Some seeds such as those of water lilies lie dormant in tough seed coats that prevents water or oxygen to seep through. Gradual decay of the seed coat or cracking due to freezing and thawing will eventually allow germination to take place, often several hundred metres from their original location. The cones of some conifers, like the jack pine, trap the seed inside the cone, and only intense heat from a fire will open these cones. Forest fires, therefore, become important in ensuring natural regeneration of these trees. The newly released seeds have a head start then and are able to colonize burned-over areas. If we could introduce jack pine to the large cattail marsh in front of our home, we would surely have a forest as it is set ablaze by arsonists at 2:00 a.m. almost every year with monotonous regularity!

Animal transport of fruits is extremely important for trees with large edible fruits such as beeches and walnuts. A single blue jay may transport over 4,000 acorns up to a distance of four kilometres. Squirrels also become important tree planters as they bury nuts and seeds.

Even seeds that are initially dispersed by being ejected may attract animals that will disperse them further. These seeds have thoughtfully developed characteristics which attract animals, and prevent the seeds from being destroyed when they are eaten. Even if seeds contain nothing to excite the taste buds, many thousands are dispersed annually by being inadvertently eaten by farm livestock. Cow pastures are excellent places to see this dispersal taking place. Foreign plants are often seen growing happily where cow dung has fallen, their new home rich with nutrients for some time to come.

It is at this time of the year when conspicuous blue splay starts showing up on cars and patio furniture and windows. Birds are at work consuming the bountiful harvest of buckthorn berries, seeds passing unharmed through the digestive system, and distributed to new areas when the spirit moves them (pardon the pun).

The transportation of seeds by animals is a fascinating method of plant dispersal in the natural world. I haven’t decided yet though whether I should be excited over the prospect of seeing beggar-ticks on my lawn.