A Critique of Silviculture: Managing for Complexity

To a restoration ecologist, the title of this book offers the best of both worlds: applying empirically rooted, practical approaches of silviculture to restore or sustain complex systems, rich with redundancy and resilience. I think it's fair to say that the authors' goal was to deliver on the promise of their title. Their path to this end is a long and winding one, sometimes frustrating, and in the end, they don't deliver all the title promises.

The Society of American Foresters defines silviculture as "the art and science of controlling the establishment, growth, composition, health, and quality of forests and woodlands to meet the diverse needs and values of landowners and society on a sustainable basis" (Adams et al. 1994). A Critique of Silviculture argues that the reality has been substantially narrower, focused on trees to the near exclusion of other forest organisms, on the concept of uniform stands, on an agricultural research model, on stands without sufficient thought about smaller and larger landscape units, and on predictability of outcomes.

The authors begin their argument in chapter 1 going back nearly 2,000 years with a very interesting discussion of the ways that human needs, especially population pressures and shifting (in space and time) demand for wood products, shaped the development of silviculture as a discipline in Europe. They explain the emergence of the concept of a stand, or relatively homogeneous block in the forest, as the basis for management and also as the reason for a tendency to focus management toward single-species, even-aged stands, regardless of natural conditions. For many readers, this will be new material. It's interesting, for example, to learn that the concept of the stand may have originated from the need to protect regeneration from grazing pressure.

From there, however, the authors focus on a near caricature of silviculture. They admit as much for at least parts of their discussion (see page 88). As the discipline of forestry grew in the United States throughout the 20th century, it necessarily adapted to local conditions, local history, and complex mixtures of species. The work of Roach (1977) and Marquis (1981), for example, specifically addresses the challenges of managing complex mixtures of species with different silvical characteristics and retaining legacy trees after harvest, and Smith's (1962) widely used silviculture textbook has devoted a growing section to silviculture of mixed stands through several revisions and reprintings. Yet A Critique of Silviculture focuses almost exclusively on the silviculture research and practice associated with single-species plantations.

Despite the caricature of silviculture at the heart of the book, the details of the critique will stimulate silviculturists to useful self-examination. It provides vivid descriptions of the ways that language and tradition can shape one's view of the forest. Some of the criticisms are familiar—the overemphasis on trees to the exclusion of other plants and structures, such as dead wood, and the gap between the uniform conditions sought and used for research plots and the high variability encountered in natural forests. The familiar criticisms are well developed here and are good reminders to those who work to bring change to the forest, whether for wood production, improvement of wildlife habitat, or restoration of fully functioning ecosystems, that the forest is a varied and complex place.

While it is not completely new, I found the section on the unintended consequences of "applying an agricultural approach to silviculture research" to be the most valuable in the book. The criticisms of the ways in which research design can influence or limit scientific thinking apply well beyond silviculture. Later in the book when describing recent large-scale silvicultural experiments, the authors explain how silviculturists and others are working to expand the boundaries of research and analysis methods. They are very critical of research results that focus on mean responses, implying that variability around mean responses is omitted from silvicultural research reports, or even, at one point, suggesting that plot-based sampling is ill-suited to characterizing spatial variability and heterogeneity. It is this kind of overstatement that undermines the potential utility of the book.

One criticism of silviculture, however, may be of particular interest to restoration ecologists. The authors believe that an emphasis on predictability is a shortcoming of silviculture. They suggest that the emphasis on predictability necessarily pushes practitioners to simplify the systems in which they work, and offer examples of transitions from natural to planted regeneration as examples of the negative consequences of a focus on predictability. Unfortunately, the authors fail to adequately address the reality that all work in forests—independent of objectives—involves decisions about the allocation of scarce resources. Without some predictions and measures of variation around those predictions, allocation decisions are essentially wishful thinking. Recognition of the risks of simplification does not have to mean forgoing predictions of response to management actions.

Through chapters 3 and 4, the authors turn their attention, not nearly as critically, to the development of the ecological concept of complexity. The social context of this discussion is the late 20th century evolution of society's perceptions about forests, especially public forests. The authors adopt attitudes about public forests with a one-size-fits-all zeal, failing to acknowledge the question of whether there are still forests that might be better served by a narrow range of management objectives and treatments:

The focus of silviculture in managed forests should shift toward maintaining a full suite of possible outcomes so that the forest can readily adapt to new and modified conditions created by or following disturbance, be they from human or natural causes, or both. In doing so, silviculturists need to accept that some of the advantages and benefits of the traditional silviculture approach may be lost, and understand that "novel" benefits will be gained, many of which we may not currently anticipate.

These shifts may be very appropriate where the management objective is primarily restoration of degraded landscapes, especially when combined with the authors' emphasis on measuring more than trees in assessing restorations. The book is frustratingly short, however, on concrete suggestions about new silvicultural practices that might be adopted by silviculturists with a restoration ecology bent. The implied strategies are more passive than silviculture has traditionally been, showing respect for natural variation at multiple scales. What help is that for a team working to restore a degraded landscape, where some investment is clearly called for? There is limited advice on analyzing treatment responses at finer and coarser scales than treatments are likely to be applied. The chapter also argues for the development of statistical models of forest behavior to support management decisions. The book's emphasis shifts from tools for managing complex systems to tools for better describing them, and this is where the authors fall short. Concluding principles at the end of chapter 5 boil down to the importance of considering more elements than trees, and accepting a wider range of outcomes than the authors believe silviculturists have traditionally accepted or strived for. This is good advice for silviculturists and restoration ecologists alike (and they are sometimes the same people), but it is not really new, as the literature cited attests. In a subtle but important reference near the end of the book, the authors acknowledge that "because of their manipulative nature, many silvicultural studies are better suited than observational studies often used by ecologists to investigate the basic mechanisms of ecosystem responses to treatments or disturbances."

In their introduction, Puettman, Coates, and Messier state that the book "provides . . . a road map to a new philosophical and practical approach to silviculture that endorses managing forests as complex adaptive systems." They do provide a road map to a new philosophical approach (although the novelty may be mainly in contrast to their caricature of silviculture rather than to the rich diversity of current research and practice). As for directions to new practice, I recommend returning to a classic silviculture textbook. As early as 1962, a leading textbook on silviculture told its readers: "Skillful practice itself is a continuing and informal kind of research in which new ideas are constantly applied and old ideas tested for validity. The observant and inquiring forester will find many of his questions about silviculture answered by the results of accidents of nature and earlier treatments of the forest" (Smith 1962, 2). This is good advice for silviculturists and restoration ecologists alike, whether managing for bioenergy production, ecological restoration, or some other social need.