A different forest ecology book could be written to summarize what we know about the major features of forests: for a very wide variety of questions, what solid answers emerge for each question from the evidence accumulated over the decades and centuries? That approach would provide a strong reference source for describing the general trends for forests, how variable they are, and what factors account for when forests are likely to be above or below the general trends. The focus of this book is somewhat different, though, as it fosters the thinking and understanding that will provide a strong foundation for adding later evidence found in reference books, journals, and other sources.
The future is not yet written for any forest, and that's also true about this book. If revised editions should appear in the future, they would be much improved by feedback provided by readers of this edition. I gratefully invite feedback about typos, mistakes, omissions, and ideas for how the stories could be stronger and warrant more confidence ([email protected]).
The final introductory point is that this book could be rewritten with all of the graphs and all of the examples switched out with different examples from other forests in other locations and other times. For example, sal (Shorea robusta) is a major, important tree in forests across southern Asia (Figure E), but this is the only sentence in the book that mentions sal. Each reader can make use of the book's questions and perspectives by adding local information for other forests types, other places, and other times.
FIGURE E Sal is a major species across southern Asia, just one species of 700 among 16 genera in the Dipterocarp family. Sal wood is valued for lumber, its leaves are used for various purposes (including plates for food), and oil extracted from its seeds are used in food and mechanical applications
(Source: photo by Anand Osuri).
Acknowledgements
It takes a virtual village to write a book, and I want to acknowledge and thank the villagers whose insights shaped this book, and my career. Each of my university advisors contributed new dimensions to thinking about forest ecology. Wally Covington at Northern Arizona University set the stage, and brought out interests in connecting chemistry and ecology. Hamish Kimmins at the University of British Columbia broadened my experiences, and patiently endured my skeptical challenges of so many ideas. Kermit Cromack's curiosity and enthusiasm across a broad range of ecology and science was infectious – and persistent. Ed Packee at MacMillan Bloedel provided the questions, insights, funding and free reign that were so important early in my career. Colleagues and students at Duke University's School of Forestry and Environmental Studies could not have done a better job of sustaining the momentum provided by earlier members of the village. The worldwide community of scientists in forest ecology and forest soils provided collaboration, ideas, and education over the following decades. Some of the most generous villagers were Tom Stohlgren, Mike Ryan, Peter Högberg, Bill Romme, Bob Powers, Dale Johnson, Jose Luiz Stape and Bob Stottlemyer. Most of my career developed at Colorado State University, with world‐class colleagues and students. I cannot conceive of any village that would have been more fun, more supportive, or more productive; this tree acknowledges coauthors across four decades, with font sizes proportional to how many works we wrote together. Thanks to all of you – and to Mason Carter and Jane Higgins for working through and polishing these chapters. There are many ways a forest ecology textbook could be written; this is the one I could write.
CHAPTER 1 The Nature of Forests
To see a World in a Grain of Sand,
And a Heaven in a Wild Flower,
Hold Infinity in the palm of your hand,
And Eternity in an hour.…
William Blake (1757–1827)
William Blake's poetic approach of seeing the general in the specific is a useful approach, two centuries later, for launching into the ecology of forests. The biology of a single tree in a single hour connects outward in time to the course of the tree's development from a seed, back through evolutionary time for the genes comprising the tree's genome. The environmental influences on the tree also connect outward in space, with strong similarities to the forces shaping trees around the world. The value of this literary approach to describing and understanding forests has limits: trees comprise the greatest part of the living matter within a forest, but the vast majority of organisms and species in forests are not trees at all. The biodiversity of forests resides primarily in understory plants, animals, and especially very small organisms such as arthropods, fungi, and bacteria.
The ecology of forests can be explored using Blake's approach of starting very small to begin to understand very large and complex systems. The hourly, daily, and annual story for a single tree can be expanded outward to encompass the other trees in a forest, a landscape, and the forest biome, just as an hour can be expanded to a day, a year, a millennium, and evolutionary timescales.
Forest Ecology Deals with Individual Trees Across Time
A tulip poplar in the Coweeta Basin of eastern North America will be the launching point for developing insights about forests. This particular tree (Figure 1.1) would be over half a meter in diameter (at a height of 1.4 m above the ground, a common point for measuring) and over 30 m tall. Eighty years of biological processes have led to an accumulation of more than 1000 kg of wood, bark, leaves, and roots. The actual living weight of the living tree would be about twice this mass of the biomass, because trees typically contain as much water as dry matter.
The crown carries about 75 000 leaves, with a total mass of about 25 kg (not counting the water). This is enough leaves to provide more than four distinct layers of leaves above the ground area below by the tree crown. The multiple layers of leaves are displayed to capture 90% of the incoming sunlight. A sunny afternoon might have 1000 W of sunlight reaching each m2 of ground area.
Many Processes Occur in a Tree Every Hour
Over the course of an hour, the tree leaves would intercept about 140 MJ of sunlight, and about half of the light arrives at wavelengths that can be used in photosynthesis. Perhaps 10–15% of the light reaching leaves reflects back into the environment, with no effect on the leaves. About one‐third to one‐half is converted to heat, warming the leaves, which then lose heat to the surrounding air (especially if the wind is blowing). Most of the rest of the intercepted energy is consumed as water evaporates from moist leaf interiors into the dry air, also cooling the leaves.