Halfway through the life of the second edition, the human population passed the 6 billion mark. The world's population has more than doubled since I took my first university-level ecology course: an increase of 3.2 billion people. It is expected to increase by another 3 to 5 billion in the time it takes to grow a tree crop in many sustainably managed, multivalue, temperate or northern forests: 60 to 90 years, or approximately the life expectancy of my generation's grandchildren. The good news for the world's forests is that the rate of human population growth has slowed and may stabilize or even start to decline within this century. Human pressure on the world's forests has followed--but lagged somewhat behind--population growth. The increasing replacement of forest exploitation by sustainable forest management and the combined results of forest protection, product substitution, technology, increasing public concern, and the recycling of wood products have slowed the rate of increase inhuman impacts on forests to less than the increase in human numbers. However, as people continue to increase the range of values that they desire from forests, as the slowing of population growth leads to increased wealth, and as it is increasingly recognized that wood from sustainably managed forests is a socially and environmentally "green" product, I expect that total human demand on forests for wood and nonwood values will continue to rise even after population levels have stabilized. Forestry faces an ethical dilemma: how to balance the changing social and environmental needs and desires of today's generation against the needs and desires that we anticipate for our grandchildren, their grandchildren, and generations beyond. Forestry is defined as the art (skill), practice, science, and business of managing forest stands and forested landscapes to sustain the balance of values and environmental services desired by society. This definition requires that forest policies and practices change as society changes the balance of values that it desires, and responding to this change is the first responsibility of forestry. However, a second and equal responsibility is to reject current practices and oppose suggested changes that are not consistent with the ecology and sociology of the new desired balance of values and that will not provide our grandchildren and theirs with the range of values that we think they will want and need. Fulfilling these two key stewardship responsibilities of forestry requires that this profession have a sound understanding of the ecology of the values that are to be sustained. Although forestry is first and foremost about people and their needs, preferences, and desires and only second about ecology, biodiversity, and other currently politically correct topics, without a biological and ecological foundation, it is very unlikely that either the present or the future generations will have access to the resource values, nonresource values, and environmental services that they will want. This is the rationale for the science of forest ecology. Our science can certainly exist outside this utilitarian focus, but the prospect of another 3 to 5 billion humans in the time it takes for most trees that we plant today at temperate and northern latitudes to reach economic maturity (or provide the other values offered by trees of that age) requires that forest ecology also serve society's needs for an ecological foundation for a sustainable relationship between humans and forests. Since the first edition of the book (1987), great progress has been made in recognizing the importance of diversity: cultural diversity, economic diversity, biological diversity, and diversity in the way that we manage forests. Increasingly, forestry around the world is recognizing the importance of respecting the spatial diversity of forests. Forests differ in different climates, on different geologies and soils, aKimmins, J. P. is the author of 'Forest Ecology A Foundation for Sustainable Forest Management and Environmental Ethics in Forestry', published 2003 under ISBN 9780130662583 and ISBN 0130662585.