Nature Watch: Gone to Seed
About the author: Steve Ellis is a naturalist and Land Trust member who enjoys sharing his love of the natural world. His blog series, “Nature Watch,” will appear each month in “Habitchat,” chronicling native plants and wildlife you can expect to see during that particular time of year. We thank Steve for sharing his passion, illustrating the importance of island conservation.
A majority of the local native plant species have already flowered and were pollinated. Now comes the challenge of seed dispersal.
The simplest method is a reliance on gravity. Seeds falling from the parent plant drop onto soil that is favorable for the species. A disadvantage is the inability to get a meaningful distance.
Wind will broadcast some seeds far away. Bigleaf maple seeds are formed as a samara, the basic seed plus a wing. The seed begins to spiral as it falls, slowing the descent and giving more time for wind to push it along. Maple seeds can land several hundred feet from the source branch.
Some willows produce their seeds in fluff, aiding them to become airborne. Should the fluff fall on the surface of a pond, the breezes scoot it across until it reaches the shore.
Moving water is another distribution option. Streams can carry seeds of bittercress and other aquatics to favorable sites, and ocean currents move the seeds of eelgrass.
Some shrubs and trees go to great lengths to ensure dispersal. They produce an attractive package around the seeds in the form of berries and other fruits. Not only are the berries visually appealing, but they also contain tasty sugars that attract birds and mammals which, in turn – although unintentionally, broadcast the seeds via their digestive systems.
Fruit seeds that pass through birds undergo scarification, a process that opens the seed covering and allows for a high rate of germination. Every madrone tree you see was planted by a Varied Thrush, Northern Flicker, or another bird species.
Mammals contribute to seed dispersal in other ways beyond ingestion. Bedstraw species have low-growing, weak stems that break away easily (as any hiker knows). Seeds attached to the stems can be snagged and transported by a passing deer or coyote. The seeds themselves have tiny hooks which catch on animal fur, or your jeans or wool socks, for transportation elsewhere. Grass seeds often hitch rides in this manner as well.
Birds may become temporary hosts to aid plant reproduction when seeds of some aquatic plants attach to the legs and plumage of waterfowl and are transported from pond to pond. The appropriately-named duckweed is a tiny green aquatic plant often eaten by ducks. These can reproduce by seed but most often rely on plants sticking to duck feathers and hitching a ride to another wetland.
Perhaps the most intriguing method of seed dispersal uses fauna much smaller than birds and mammals. Some wildflowers cover their seeds with fleshy structures called elaiosomes, a similar process to shrubs and their berries except elaiosomes are rich in fats instead of sugars. Some ant species are lured by the fats and carry the seeds back to the colony. The elaiosomes are eaten and the seeds themselves are chucked out into the tilled soil surrounding the colony. Examples of native plants enlisting ants are some violets, western trillium and Pacific bleeding heart. Interestingly, the latter is found on Camano but not Whidbey. Apparently either the plants themselves or the appropriate ants weren’t present when Whidbey was an extension of the mainland.
All these delivery systems are iffy at best, with individual plants having very little if any control over their seeds’ final destination. The strategy most follow is to over-produce a seed crop so a few might germinate into new plants. It’s estimated that one in a million bigleaf maple seeds becomes a tree. This might seem wasteful, but the lives of many birds and mammals are dependent on the overabundance. Seeds that aren’t consumed or don’t germinate return tiny bits of nutrients to the soil.
Seed dispersal may not be as visually appealing as the flowering process, but it’s the crowning achievement for the plants’ summer work. A visit to any forest, field or wetland should reveal several of these vital dispersal methods.
Flora: Grand Fir (Abies grandis)
This stately tree can grow to a height of 150 feet or more. The needles are flat and reach a length of 1 to 2.5 inches. They are shiny dark green on top and have two white lines on the underside. Grand fir bark is grayish to light brown and becomes moderately furrowed with age. It will be 2 to 3 inches thick at full maturity.
Like all true firs, the cones are held erect on the top branches and are quite sticky. The seeds average 23,000 per pound and each seed has a small wing. Cones ripen and come apart while they are on the branches; fall winds scatter the seeds far from the tree. Once the seeds have “helicoptered” to the ground, many are eaten by sparrows, juncos, towhees, chipmunks and deer mice. Small mammals also cache some seeds, often allowing them to germinate and grow into new trees.
Grand firs, especially young trees, have thick foliage that provides excellent protection from fall and winter rains. Many bird species shelter there, as do squirrels, chipmunks and deer mice. In summer, these same branches provide shade for the deer.
The wood is fairly soft and often used by woodpeckers for roost and nest holes. Bats roost in the snags, and chickadees and other cavity-nesters will make use of natural and woodpecker-created holes.
Grand fir grows in a wide variety of conditions. Young trees are more tolerant of shade than Douglas-fir but less so than western hemlock. In moist conditions they are shallow-rooted but on arid sites a taproot is sent down.
This is a comparatively short-lived conifer, with a few reaching an age of 250 years. They are sensitive to rot and don’t last long as snags. Change comes relatively quickly in a forest with many grand firs.
This attractive tree can be seen in most of Whidbey and Camano forests. Its beauty is only surpassed by its importance in local ecosystems.
Fauna: Douglas Squirrel (Tamiasciurus douglasii)
(Sometimes called pine squirrel or chickaree)
Douglas squirrels are busy in September, cutting down the cones from the branches of Douglas-fir and Sitka spruce trees. Their agility and quickness can make it seem like the trees are raining cones. This chatterbox is 10 to 14 inches long, with the tail accounting for half of the total length. It is light to dark brown on top and dull orange underneath.
Perhaps no other mammal in our area is so well-adapted to a life in trees. Like all tree squirrels, the paws can be rotated 180 degrees to allow it to travel down a tree trunk as well as up. The long, bushy tail acts as a balance and can be spread over the back and head for use as an umbrella.
Alertness is a key element of Douglas squirrel life and has earned it the name of Sentinel of the Forest. A loud “Pe-you” call is accompanied with rapid tail jerks when a potential predator has been spotted. Reports indicate deer also take note of these warnings. Other calls include a long chatter often described as scolding, which is used as a territorial proclamation.
In spring, females bear four to six young inside a tree cavity. The young are weaned in about three months and may stay with their mothers a bit longer.
They are active year-round, including winter. A roundish nest high in a conifer may be built for summer living, but usually they move into a tree cavity for sleeping and to wait out storms.
Douglas squirrels eat hazelnuts, maple seeds, berries, and mushrooms, but the mainstay of their diet is conifer seeds. Large piles of cone scales are heaped into middens, marking areas where the squirrels have stripped the seeds from the cones. I once timed a Douglas squirrel as it ate the seeds of a Sitka spruce, a job that only took 45 to 80 seconds per cone. Large quantities of cones are cached for future use. Some of these may not be retrieved and germinate into new generations of trees.
You can find Douglas squirrels in any large patch of conifer or mixed woods. The naturalist John Muir was a great admirer, and there can be no better description than his of this lively creature: “He is the squirrel of squirrels, flashing from branch to branch of his favorite evergreens crisp and glossy and undiseased as a sunbeam. Give him wings and he would outfly any bird in the woods.”