Cottonwood and the River of Time
On Trees, Evolution, and Society
Publication Year: 2009
Published by: University of Washington Press
Title Page, Copyright
Preface and Acknowledgments
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Cottonwood, Cottonwood Creek, Cottonwood Fishing Camp, Cottonwood Motel, the Town of Cottonwood—what is so magic about cottonwoods? What draws people to cottonwoods? Is it the promise of a cool stream, some shade, and shelter? Indeed, water, the mainspring of life, is at the heart...
Part I. The Tree and the River
The setting is a floodplain of a river on the west side of the Cascade Range, the home turf of black cottonwood. It is a fleeting turf, a temporary home in the ever-changing environment of an active river. Periodic flooding, summer drought, bank erosion, shifting sand and gravel, deposition of woody...
1. The Tree
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The old cottonwood has lost its leaves during the last November storms. It stands there like the Statue of Liberty in the midst of the grove, the one remaining part of its crown reaching above the surrounding trees. Two other segments had come down in storms several years ago and are decomposing at its foot amid hazel shrubs and...
2. The River
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Puget Sound dwellers will remember the Thanksgiving weekend of 1990. It had rained for five solid days, and this after some heavy snowfall in the Cascades. Rain-on-snow is a common sequence of weather conditions in the Northwest when a cold Canadian air mass is met with a moist storm front moving in from the Pacific. But this...
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The point bar downriver from the old cottonwood had been essentially bulldozed by the 1990 flood. It was flat as a pool table and showed the typical distribution of substrate, with cobble at the front gradually turning to gravel, sand, and silt at the back in a smooth gradient across the bar. By the subsequent summer, a...
4. Water and Nutrient Relations
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Having followed the characteristic development of a cottonwood stand from its inception to maturity, let’s go back to our point bar and have a closer look at the environment in which these seedlings grow. It is about as forbidding as you can imagine. Squeezed between cobble and gravel, these young plants send their...
5. Perpetuate and Proliferate!
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Cottonwood’s developmental flexibility is also called into action to serve two additional purposes: to perpetuate the individual, and to make more of itself. We have already gained an appreciation of how challenging the fluctuating environment is in which this tree is growing. It seems that in its dependence on water, the tree has...
Part II. Variation and Variability
In part II of this book we will meet the powerful genetic mechanisms that regulate diversity in natural populations. And poplars are ideally suited to illustrate these mechanisms at work. In plants, it is their methods of reproduction that shape the patterns of variation. At one extreme is cloning, or asexual...
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Aspen, Populus tremuloides, is the most widely distributed tree in North America. Its transcontinental range reaches from the A tlantic to the Pacific, and from the edge of the arctic tundra in the north to the Rocky Mountains of New Mexico in the south, in fact extending even to some isolated populations in northern Mexico.1 And...
7. Why Sex?
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As aspen shows, asexual propagation is an eminently successful formula to hang on to life once a tree has gained a foothold in a particular place. And chances are that if this tree and all its suckers made it for a hundred years in that location, this genet has proven its stuff and has every reason to expect a happy existence for...
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Wind pollination, common in forest trees, makes use of a universally available agent that can be counted on almost any time of the year. It is also enormously wasteful. Pollen may be transported great distances where it won’t do any good. Researchers have found major quantities of pine pollen in the Russian...
9. Natural Hybridization
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It was not lost on Mayr and Dobzhansky, both zoologists, that reproductive isolating mechanisms were occasionally leaky, and that this was much more the case in plants than in animals. But it was the botanist Stebbins who pursued the topic in depth and greatly amplified the evidence. Although hybrids can be found among animals...
Part III. From Species to Populations to Genes
Species are composed of populations, populations of individuals, and individuals of organs and genes. It is genes that set the norm for the way an individual reacts to its environment; it is the pool of genes of individuals that define a population and the way it adapts to that environment, and...
10. Common Gardens
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This third part of the book will take us inside the species. This may be troubling for some readers since a crisp species name, especially a Latin binomial, suggests the comfortable certainty of an officially recognized unit of biological organization, a handle to nature’s confusing diversity. Why probe inside? Shouldn’t we be happy...
11. Transplanted Trees
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Common-garden experiments had been initiated with forest trees almost two centuries before the work of Turesson, Clausen, and their contemporaries. And from these early studies emerged a prominent line of investigation, provenance research, that began to shed light on geographic variation in several major tree species. Indeed...
12. Getting Closer to the Genes
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For years, the link between genotype and phenotype remained an elusive problem for students of evolution in natural populations. If organic evolution was a change in gene frequencies in populations from one generation to the next, as the Evolutionary Synthesis proclaimed, how could this change be quantified if all you could...
13. Migrant Trees
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The geographical variation in phenotypic traits we now encounter as we sample natural populations carries the footprint of past history, and no other historical episode has left a larger footprint on temperate-zone vegetation than the last ice age. Glacial and interglacial climates have been major forces in shrinking...
14. Adaptation and Its Limits
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It would be tempting to imagine that the postglacial environmental change was one of gradual, systematic warming and to see that process as a slow but steady opening up of temporarily inhospitable territory, allowing the expelled plant communities to again reclaim their original turf. However, in reality it seems to have been more...
Part IV. Trees and Society
Up to this point we have stayed safely in the natural world, where we have tried to find out, through observation and experiments, how trees function as individuals, populations, and species within their constraints. Here in the final part of the book we will be dealing with the real world...
15. Changing Rivers—Changing Landscapes
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Rivers figure prominently in human history. Rivers and the riparian environment have also provided the major venue in which we familiarized ourselves with the dynamic life of cottonwoods. This chapter brings us back to that world—in fact, to a geographic area we visited earlier in our discussion of natural...
16. The Dawn of Agriculture
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The Euphrates River rises in the mountains of eastern Turkey, crosses through the foothills of the Güneydogutaurus Range before heading south into Syria, then makes a major turn east of Aleppo, traverses the wide plains of Syria, and heads in southeasterly direction toward the Persian Gulf. It is at the big bend in its middle...
17. The Farmer’s Trees
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If annual crops allowed early farmers in the Near East to take advantage of nutritious plants with short life cycles, reaping the benefits of culture within months and thereafter adding successive improvements year after year, this was not as easily accomplished with the trees growing in their surroundings. As a consequence the shift from...
18. From Farmers’ Trees to Tree Farms
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On New Year’s Day 2005, the New York Times carried an article on “Techniques That Might Smile upon Mona Lisa.” It described work by a Smithsonian Institution materials expert who had examined the conditions under which typical paintings from the classical period between the thirteenth and sixteenth...
19. Poplar—A Model Tree
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So far, we’ve found that poplars are among the fastest growing trees, that hybrids are even better in putting on height and diameter than their parent species, and that growing these hybrids in large plantations may be an efficient way of producing raw material for shelter, fiber, and energy. Actually, all these elements differ little...
20. Tree Genomics and Beyond
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In a White House ceremony on June 26, 2000, President Clinton announced to the world the completion of the draft sequence of the human genome. A ten-year international effort to sequence the 3.2 billion units of our DNA had reached its culmination. This momentous achievement, compared by some to the successful landing...
21. Between Old Growth and Plantations
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Genetics is not context free. Even if genes—as Richard Dawkins argues—should be viewed simply as replicators having the sole purpose of making more copies of themselves, they are tied to an organism, at least temporarily. And even if DNA is the grand connector of the living world, from microbes to redwoods to...
22. The Essence of Trees
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Most of this book has been devoted to a discussion of trees in the plural, in the aggregate, and in natural populations, forests, and plantations—as a consequence of its genetic and evolutionary bias and the emphasis on underlying processes. But let us not ignore the tree as an individual, with the ingredients...
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We are now back at the old cottonwood, where our journey in the arboreal world began. In the meantime the old tree has lost its one remaining crown segment to a violent December storm. No longer a statue of liberty, it has been reduced to a splintered snag and is on its way to becoming part of the history of the forest community it helped...
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Publication Year: 2009