Published online by Cambridge University Press: 05 June 2012
Introduction
The introductory chapter recognizes that tree mortality is both inevitable and desirable in a functioning forest. Imagining the development of a forest in the absence of mortality leads to the implausible scenario in which thousands of stems initially present attain increasingly larger diameters and grow outward to the point where they physically begin to interfere with their neighbors. The finite resources (sunlight, air, water, nutrients) available to individual trees would be insufficient to support continued growth and development. Severe competition between stems would constrain growth because all of the carbon fixed would be allocated for maintenance respiration, “freezing” the stand at this maximum attainable stem size in perpetuity – the ultimate stagnation. In reality, competition among individual trees leads to decline and ultimate death of those unable to compete. Site resources are focused on a smaller number of more vigorous competitors, and the implausible scenario is averted.
As the less competitive stems succumb to mortality and the stand thins out, the slope of the relationship (described in Chapters 1–3) between number of stems plotted against diameter (logarithmic scale) approaches −3/2. The multiple factors that contribute to mortality do not dissipate; a tenuous balance between site resources and the number of competing stems manifests itself through a sustainable diameter distribution. Catastrophic disturbances such as fire, windstorms, and attack by pests and pathogens may periodically upset the balance. As those disturbances subside and time passes, the balance tends to be re-established.
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