Archive for category: Articles That Educate

Author: Sally White

Illustrations: Jan Ratcliffe

Date: May 2013

Sparrows don’t quite do it for me: I look at them and I clearly see birds, normal birds, hopping on the ground looking for seed or flying around. But distelfinks are different. Distelfink, literally “thistle finch,” is a handy word still used by the Pennsylvania Dutch for a group of birds that reminded them of the colorful finches of their homeland. It’s both memorable and descriptive, as distelfinks of all species adore thistles—in season, of course. Perhaps you’ve encountered flocks of pine siskins and lesser goldfinches raiding roadside thistle patches in fall, and fluttering wildly away as each car passes. For me, it’s less trouble to say “distelfink” than to list all our yellow finches—pine siskins and American goldfinches and lesser goldfinches—and our pinkish-red finches—purple, house, and Cassin’s finches. Other birds never act like dinosaurs. Distelfinks do, at least at my house.

Scientists who study fossils have, of late, been trying to tell us birds are actually dinosaurs: watching distelfinks makes me a believer. Ounce for ounce, they must be among the most aggressive dinosaurs left alive. This is made apparent by their habit of congregating in mixed flocks for fall and winter feeding. After all, most of us get a little irritable in crowds. Pine siskins are the worst. As they fight for space at the thistle feeder in our yard, they hiss and spit at each other, flashing the yellow under their wings and adopting threatening postures. Sometimes I think firebreathing dragons are the true missing link between birds and other dinosaurs, the extinct ones.

All this aggression is presumably brought about by the survival value of simply getting enough food. Small birds come together in numbers because of the advantages flocking offers: better protection and a warning system for predators. Flocking also means more eyes on the lookout for good food sources, but you still have to get your share while dozens of your fellows try to get theirs. Picture the noon crowd at your local food court.

Fortunately, we have a lot of thistle patches around. Therein arises one of those conundrums of conservation. Plant enthusiasts are trying to eliminate exotic thistles; bird enthusiasts enjoy thistle patches for the many birds they support. Although we have a variety of native thistles, most don’t thrive quite the way foreign invaders like musk and Canada thistle do. Have we improved habitat for distelfinks by allowing alien thistles to spread unchecked these last hundred years? Yes and no. Native birds do have alternatives: pine siskins are aptly named because they pick at pine cones as successfully as at thistles; American goldfinches are equally happy eating sunflower or dandelion seeds. Although their numbers may have increased with new food supplies, I don’t think removing exotic thistles will drive distelfinks toward extinction.

Flocking, or perhaps we’d better call it herding, probably also provided similar advantages to some dinosaur species. Communal dinosaur nesting grounds in Montana remind us of today’s seabird colonies, substituting groups of 25-foot-long duckbills who return to the same place year after year to nest together and care for their young. A herd of these Maiasaura migrating from nesting areas to feeding grounds might foreshadow the long migrations our flying dinosaurs make today.

I imagine the pine siskins as coelurosaurs: scrappy, ostrich-like dinosaurs who may have hunted in groups. Solitary eagles are more reminiscent of lone hunters like Tyrannosaurus rex. A small peregrine falcon may recall Velociraptor; both have a strike that is quick and deadly.

Paleontologists have given us a lot to think about with this bird connection. Just think—now you can study dinosaurs in your own backyard! Much of our understanding of the past must come from our knowledge of the present, because Nature still works much as it did during the Cretaceous Period. Even scientists use their imagination, and often reason from analogy as well as from hard facts. As the famous geologist James Hutton once put it: The present is the key to the past. So if you want to see dinosaurs at home, and speculate on Earth’s older inhabitants, you’re in good company. I should warn you, however, that the bird specialists have not yet fully accepted this new, closer link between dinosaurs and birds.

Because birds are ubiquitous and seem to be a harmless background presence, we don’t consciously notice how thoroughly they’ve occupied “our” world. When you think about it, they’re everywhere. In and amongst our supposedly dominant culture, birds as a group continue to thrive and still live a variety of lifestyles. They are, however, showing the effects of our presence and the pressures we put on them; too many are disappearing. Those earlier dinosaurs, in their heyday, must have similarly dominated their environment, and eventually succumbed, perhaps due to some similar pressure. May the distelfinks last as long.

Copyright © 2013 Sally L. White

Hidden within our soils are a host of organisms engaged in decomposition, that deconstruction project without which life on Earth would long since have disappeared. As with other ecological systems, this one is an iceberg: The part we can’t see is far bigger and more complex than the small fragments that intrude into our everyday lives. Most of the time, then, we are able to remain blissfully unaware of where everyone’s next meal is coming from. We may be able to talk comfortably about the water cycle, despite the probability of eventually drinking “Cleopatra’s bathwater,” but most of us would rather not examine the nutrient cycle too closely. Perhaps the Halloween season is a good time to talk a bit about the fate that awaits us all, humans, mice, and pine trees alike. Though some may say “we’re a long time dead,” the truth is that, sooner or later, reincarnation is a virtual certainty. We’re not immortal, but the chemicals within us are.

Most of the critters that carry out the phases of decomposition spend much of their lives in soil or in the litter layer that often covers it. The first steps, of course, are occasionally carried out by larger organisms, like mice and squirrels and cows, who eat plant materials and then deposit the indigestible portions on the ground. In the global cycle, that’s only an optional side trip for carbon and nitrogen—most of the organic material tied up in plants, even in the hugest redwoods, will be released by much smaller organisms, those we tend to dismiss as insignificant.

Only in size can we easily dismiss them, for soil life is diverse and abundant. In a good season, one prairie acre might harbor two billion microarthropods (such as mites and springtails), as many as five million earthworms, and 200,000 millipedes. A host of insects and macroarthropods, such as fly larvae, termites, pillbugs, and crickets, also participate in decomposition. Outnumbering them all would be the nematodes, or roundworms: At 22 billion per acre, they are among the most abundant organisms on the planet, and are found in pretty much everything and everybody. In the prairie environment, almost half of the nematodes feed on fungi, which are also abundant soil inhabitants, along with the couple of tons of bacteria also present.

A forest ecosystem, of course, is equally dependent on those tiny soil inhabitants, and some forests produce enough organic matter to support even larger populations of such critters. In our dry forests, decomposition is far less obvious than in the moister forests across the great divide. It may go on more slowly, but still it must go on. It may have to hide, literally, from the light of day, but this is one process that works just fine in the dark. Unless we go looking for evidence of decomposition, sifting through leaves and litter or kicking open rotting logs, we will rarely see this process in action.

When conditions are just right, with cool weather and a little moisture, the last participants in the decomposition process begin to “flower,” reminding us of this unsuspected underground world. Suddenly, often overnight, mushrooms appear in our meadows and forests. Their forms are as varied as their cryptic lifestyles, and we often name them for their underworld associations: Destroying Angel, Jack-o’-lantern, Devil’s Snuffbox, Witches’ Butter, Dead Men’s Fingers are all names that remind us Halloween is approaching. And all are the tips of their own respective icebergs, appearing above ground to spread their spores, ensuring that nowhere on Earth will dead things go undecomposed. If one Giant Puffball (Calvatia gigantea) can produce seven trillion spores, few acres will miss receiving their fair complement.

The real decomposition work, however, is being done by the mycelium, a webby mass of underground strands, called hyphae, that makes up the body of the fungus and occasionally produces the “fruit” we see. Some mycelia are annuals that grow from a single spore each year and die after one season. In contrast, other fungi form “fairy rings,” whose fantasy name reflects our attempt to explain their mysterious origin. Whether produced by deadly Amanita or delicate Marasmius, the rings are formed by the outward growth of mycelia that live year after year and form mushrooms only where they are actively growing. Fairy rings have been found in Colorado that may have taken more than 500 years to develop.

Puffballs spread their spores on the wind, as our child-selves know, but some mushrooms depend on animals to consume the tempting fruits and spread the spores; the stinkhorns even attract flies for that purpose. Slugs, mice, turtles, and squirrels, as well as deer and cattle, will eat these seasonal temptations when they can. We humans are also attracted by the culinary qualities of many species of mushrooms, and by the exotic substances (hallucinogenic or merely deadly) produced by others. The economic importance of edible mushrooms and the yeasts who bring us beer and bread is offset a bit by the financial havoc wrought by the many fungi that cause tree and crop diseases. In the end, however, both of these aspects pale in comparison to the service soil fungi provide us by assuring the final chemical breakdown of organic matter into its constituent minerals. Without the help of these fungi and other decomposers, the continual recycling of life from one form to another would end, and the wheels of chemical reincarnation would stop turning forever.

Copyright © 2013 Sally L. White

Year after year, domestic and wild plants give us—and local wildlife—”free food,” as it were. But some years are special. Trees bent under the weight of fruit they carried; now pantry shelves bend under the weight of jams and jellies as we try to cope with overwhelming abundance.

In the nut and seed world, when plants overwhelm the critters waiting to gobble their seeds, we call it a “mast year.” Production becomes so impressive we can’t help noticing. For pinons and perhaps acorns, this seems to be one of those years. Seed-eaters will never be able to keep up, and the trees will have a chance to produce seedlings that survive. Of course, it may take them a few years to recover from the effort. Mast years often recur on a semi-regular basis, with famine years in between, as if the trees were indeed exhausted. In fact, that’s part of the strategy of masting. Populations of mice, birds, and other seed predators can’t depend on the high production; they have to survive those lean years as well. By being undependable, trees improve their chance of reproductive success. The trees may seem to give freely, but feast is sure to be followed by famine.

The unfamiliar word “mast” literally means food. From the Old English and High German, it traditionally referred to the beech nuts and acorns that dramatically littered the forests of Europe some years and provided quantities of food, mostly for hogs. In temperate areas, however, many woody species have mast years, even our own native conifers and oak. What’s dramatic is that trees of a given species often synchronize, so that their mast years coincide, and woe, in the form of increased seed loss, befalls the misfits. Environmental conditions help control the timing of mast years, but not necessarily as we would expect. For ponderosa pine, for example, this fall’s seed crops were determined by prevailing conditions back in 1996.

Each fall, as seeds of all kinds embark on adventures beyond imagining, a vast harvest begins. Although we may see squirrels busily cutting cones, most of the harvest activity will go unnoticed. For some seeds, getting far away from the parent—where they are easy targets for predators—is crucial to survival. But there’s no guarantee life will be any easier after they get away. [In recent decades, ecologists have shown us that what happens to seeds helps determine what our landscapes look like. Once seeds leave the parent tree, they become invisible and we tend to forget about them—at least until we see new plants coming up. But the seeds are everywhere among the fallen needles and in the soil, as the critters that depend on them never forget.]

Although winged seeds have distance potential, most seeds will fall near their parent plant. For heavy seeds like acorns, travel is limited mostly to places the squirrels take them. Acorns don’t always stay where they fall either. If they land near the route of a foraging wild turkey, for example, their days are up; they become part of his daily calories. A Douglas-fir tree can deposit more than 300 seeds per square meter—that’s about 30 per square foot—directly below its canopy. A large Engelmann spruce puts down thousands of seeds per square meter close to home, but some, if they get into the wind, are carried off. There will still be hundreds of spruce seeds per square meter 150 meters out from the parent tree. If the seed crop is reduced 50% by a poor season or by seed-eaters, the number of seeds getting any distance away is also halved. That leaves plenty for colonization, which is what dispersal is for, after all. Once they land, they’re still vulnerable: in one study of Douglas-fir, 69% of the seeds were eaten or otherwise lost, but the remaining seeds still produced 3.7 seedlings per square meter.

Birds and small mammals collect and bury seeds, especially large nutritious tree seeds, after dispersal. The catch is that caching often works better for these predators than it does for the seeds. In a study of 840 pine seeds in 35 caches made by deer mice, the fate of seeds appears grim indeed. Ten caches were dug up and eaten before the end of autumn; nine more were destroyed the following May; and the others were used through the winter. Forty-nine plants developed from only six of the caches, but the mice uprooted and killed seedlings in three of them. At the end of the first growing season, only one cache still had live seedlings. Next time you see clumps of pine and Douglas-fir seedlings germinating from caches during a wet spring, you might want to go back later and see how many survivors you can find.

Does predation matter? Are forests endangered by mice and squirrels? Studies show that when one cause of mortality is eliminated, others often increase to compensate. Imagine all those cachebased seedlings again. In each clump, not all can survive as trees. Many more will die young, even if the mice don’t get them. Despite fears that forests will be decimated, seed predation only becomes relevant when it reduces the number of seeds below the number of seedlings that can survive in the environment.

The good news is that a plant, even a large tree,needs to reproduce successfully only once in its lifetime to replace itself; its odds are good despite massive losses. You might say that plants pay, sometimes dearly, for the dispersal services they receive. Caching may determine which seed, among the millions produced in the lifetime of a tree, will survive to replace its parent. But because predators cache more seeds than they need, most years improve the odds even further, as more caches are left uneaten. Those uneaten seeds are future forests, gifts to future generations of birds, mice, squirrels, and to all of us.

Copyright © 2011 Sally L. White