South with the spring
April 5, 2008
Springtime has fully arrived and all the deciduous trees are opening their buds at once. Or so it seems. But if you look closely at the trees, you will find diversity. Each species of tree opens its buds at a different time, and responds in its own way to the rising temperatures of springtime. What might be the reason for this pattern?
In the eastern deciduous forest, often the earliest native trees to open their buds are silver maples and elms. In Oklahoma, these trees open their inconspicuous flower buds in February, and produce their seeds (each inside of a winged fruit) in March. Next, the cottonwoods, sycamores, and sweetgums open their flower buds. Each species of oak begins to open its buds at a slightly different time in March. The latest buds to open are those of walnuts, pecans, bois-d’arcs, and catalpas, often in early April. The season of budburst may be short in northern climates such as Minnesota, where I used to live, but usually lasts for two months in Oklahoma.
The tree species that open their buds earliest are those that are wind-pollinated. That is, the wind carries pollen from the numerous, small male flowers of one tree to the small female flowers of another tree. This does not, however, explain why some species of trees open their buds earlier than others. The tree species that allow insects to carry their pollen (the trees with showy flowers, such as catalpa) open their buds later, but it is the leaves, not the flowers, that emerge first. And some of the trees that open their buds latest, such as pecans, are wind-pollinated.
In a study I published in the National Center for Science Education Reports in 2003, I reported that there was a statistically significant pattern in which the trees that opened their buds earliest were members of plant families that had evolved in temperate climates of the northern continents (back before the northern continents were separated as much as they are today), and the trees that opened their buds later were often in plant families that had evolved in the tropics. This is why I called the pattern “south with the spring.”
Trees in plant families that evolved in temperate climates (with cold winters) open their buds earlier because these buds are protected from damage caused by moderate frosts. Trees in tropical plant families are not protected from frosts, and they wait until later in the spring when all chance of frost has passed. Trees of temperate origin resist frost, while trees of tropical origin avoid it. Both resistance and avoidance have their own benefits and costs. Opening buds earlier in the spring allows the trees to have a longer season of absorbing sunlight, but they have to pay for it by protecting their buds from frost. Opening buds later in the spring means that the trees have a shorter growing season, but they do not have to protect their buds from frost. Both resistance and avoidance are good methods of survival. But resistance is better in northern climates, where the growing season is short, and avoidance is better in southern climates, where winters are mild. In eastern North America, both resistance and avoidance may work equally well. The fact that some tree species resist frost and others avoid it is a leftover characteristic from their evolutionary past.
There are, of course, exceptions to the pattern. Pecans, the trees whose buds open latest, are in a plant family (Juglandaceae) of temperate, not tropical, origin. But the overall pattern is a phenomenon that cannot be explained without making reference to the evolutionary past. To find evidence for evolution, it is not necessary to resort to DNA or to human evolution, however valid and interesting these evidences are (as I have written in my encyclopedia). To see evidence of evolution, all you have to do is notice the dates on which trees of each species open their buds.
Somebody oughtta invent a machine…
April 27, 2008
There are so many problems in the world! Somebody ought to invent a machine to solve them.
For example, global warming has entered the world’s attention as a major threat to human society. There ought to be a machine that will remove carbon dioxide from the air and rescue us from global warming. It would be nice if this machine could also produce oxygen for us to breathe.
There are also floods and mudslides that wash away whole villages, and soil erosion that washes away the topsoil on which human food production depends. There ought to be a machine that will hold back flood waters and hold down and protect the soil.
There are so many people, and they need food. There ought to be a machine that will meet their needs, for fiber and building materials as well as for food.
We are always in need of new pharmaceuticals. Germs, especially strains of staph aureus, keep evolving into new forms that resist the antibiotics we have used in the past. There ought to be a machine that generates new drugs.
A machine that could do all of this would be huge. Instead, there should be billions of small machines that do these things. And such a large number of machines would take more fossil fuel energy than we have in the whole world. They would produce more carbon emissions than they would remove from the air. Indeed, current plans exist for “carbon sequestration” in which carbon dioxide would be removed from the waste gas of power plants and stored underground—at the cost of almost one-third of the energy that is produced by the fuel itself. Wouldn’t it be nice if these machines could run on solar power? And since it would take all the combined labor in the world to make these machines, wouldn’t it be nice if they could make themselves?
Such machines already exist. They are called plants. They produce oxygen, remove carbon dioxide from the air, hold down and enrich soil, prevent floods, and make all the food in the world. The evolutionary diversity of plants has allowed them to produce an astonishing variety of chemicals that we can use as drugs. Plants do all of these things, using solar power, and they reproduce themselves. They do all of this in complete silence and with heartbreaking beauty. We do not need to pay them or even thank them for the ecosystem services they provide—we just have to let them live.
For more: see the book Green Planet when it is published.
The Quiet Stand of Alders
May 3, 2008
I suppose I should explain why this website has the name that it does.
One of the research projects which I share with collaborators is the study of the seaside alder, Alnus maritima. This is a rare species of small tree (or large shrub) that consists of three rare subspecies. One subspecies grows on the Delmarva Peninsula, on the east side of Chesapeake Bay (so called because it contains Delaware and parts of Maryland and Virginia). This subspecies is found only in a few swamps. These are the seaside alders that are really beside the sea. The other two subspecies live far from the ocean. One of them grows in a single swamp in northwest Georgia. The third subspecies grows only along creeks and rivers in south central Oklahoma—these are the alders on which I concentrate my work. No other tree species in North America consists of three subspecies, each of them rare and each separated from the other by hundreds of miles. Phil Gibson’s work at the University of Oklahoma, and Jim Schrader’s work at Iowa State University, suggests that these three subspecies are remnants of a larger population of alders that grew all over North America several million years ago.
I do not particularly like swamps. The Oklahoma alders are along beautiful streamsides that are among the most pleasant places in Oklahoma. But when I first visited the other two subspecies in 2002, I had to wade into swamps. In Hudson Pond in Delaware, I was up to my butt in muck. It was not ordinary muck, but anaerobic swamp muck that sucked like glue and smelled like hell (sulfur). It would take me several minutes just to move my leg for a single step. Frequently, if I moved, I settled a little further into the muck, the depth of which I (stupidly) did not know. I was alone and could have become one of those bog people you see in National Geographic. If I reached up to grab something, the alder branches were too high; all I could reach were thorny rose branches or poison ivy.
But it was worth it—to drive a thousand miles and walk in a swamp—to see the alders that I had come to study. These humble trees have much to teach us about genetics, evolution, and ecology. And some of my other research suggests that they may possess compounds that have medical benefits as well. When I saw my first seaside alder in Oklahoma in 1999, I could not have imagined how important a part these trees would become in my professional and personal life.
Saving the Environment—For Whom?
May 20, 2008
I am a nature nut. When I go into a forest, I seek peace and inspiration. Often I am alone. But one day, there were people all around me making as much noise as possible. Kids sang “ninety-nine bottles of beer on the wall” as they hiked along. And it wasn’t just the kids. One man, when he couldn’t think of anything to say, made loud yawning noises. A woman talked loudly on her cell phone. The forest was a mere background to their artificial worlds. In fact, being out in the wild seemed to release them from the normal bounds of politeness. I wanted them out of my forest.
But the forest does not belong just to people like me. Public lands belong to everybody. That’s part of the bargain. There is no way to set aside public land just for people who enter it with respect.
Nature lovers like me want to save the environment for people like ourselves, but we end up saving it for everyone else too. When environmentalists successfully convince local or national governments to keep the air clean, this clean air is breathed not just by environmentalists, but by all citizens, including those who work for or own polluting industries. When citizens preserve the trees on a mountainside, the leaves and roots hold down the soil and allow water to recharge the underground water supply, not just for nature lovers but for everybody.
The natural world does not belong to corporations who wish to exploit it, or to nature lovers who like to hike through it. The natural world does not belong to people at all. Scientists and citizens are beginning to realize that a change in viewpoint—seeing ourselves as one species among many—is necessary to the survival of civilization. This change in viewpoint is a shift back to a very ancient viewpoint. One of the oldest pieces of literature is the Biblical book of Job, revered by three major religions. In the story, God speaks to Job out of a whirlwind, in a chaos of insight rather than a clear, orderly explanation. God tells Job of storms that bring rain to lands without human inhabitants, and of wild donkeys and oxen that proudly refuse to serve humans. These are not problems to be solved: the rain is not wasted just because there are no people to use it for irrigation. It is good that rain, fields, forests, and animals exist to which human needs and desires are irrelevant. The forest is not mine, or anybody else’s.
It is not just loud and unobservant visitors to the forest, but also nature lovers such as me, that may need a lesson in humility.
June 9, 2008
Nothing could seem more peaceful than the quiet stand of alders. The numerous flexible trunks of the trees sway gently in the wind and create a soothing and hypnotic susurrus, along with the babbling of the water. But conditions are not always this peaceful. In some years, floods occur on the rivers and creeks where the seaside alders (Alnus maritima) live, ripping away many of the trunks. This occurred in June 2007 in central Oklahoma. The floods stopped in July. Before the end of summer, however, new branches had begun emerging from the soil, from the persistent underground rootstocks of the alders. These small but vigorous branches will grow into new trunks. In as little as a year, very little evidence will remain that floods ever disrupted these trees. Such vigorous regrowth is why seaside alders have survived for millions of years.
There are other disturbances, however, from which the seaside alders cannot recuperate. In particular, they need lots of water. The streams along which the seaside alders live are fed by the Arbuckle-Simpson Aquifer. If too much water is pumped from this aquifer (which is what happens with most aquifers all over the world), the river and creeks may dry up, which will eventually kill the alders. They have survived millions of years but only in places with reliable water supplies.
The seaside alders also need lots of light. A study published in 2006 by Jim Schrader, Bill Graves, Phil Gibson, and I (in the International Journal of Plant Sciences) showed that seaside alders were less tolerant of shade than the hazel alder (Alnus serrulata). Hazel alders are found along streams and wetlands all across the eastern United States, while seaside alders are found only in three small populations (see essay 6). The reason appears to be that most places that are wet are also shady, because tall trees such as sycamores cast shade on small trees such as alders. Hazel alders can readily survive in the shade, while seaside alders cannot survive as well. Seaside alders were presumably abundant right after the ice ages, their seeds germinating in the wet gravel of land newly released from the grip of the glaciers and bathed in bright sunlight. Sunny, wet places are now rare in eastern North America, except out in the middle of marshes, where alder seeds cannot germinate. For this reason, seaside alders are survivors—but just barely.
Wild plant species are the evolutionary survivors of millions of years of Earth history. Many plant species have become extinct, as conditions have exceeded their capacity to undergo evolutionary adaptation. Seaside alders have nearly become extinct by such a natural process. Extinction is natural. But many thousands of plant species are threatened by extinction from unnatural processes—particularly from humans destroying their habitats. In the next few decades, many plant species will become extinct as global warming causes climatic conditions to become unsuitable for their survival in the places where they now grow. Extinction is natural but humans have escalated extinction to a vastly unnatural extent, and we haven’t seen anything yet.