In recent decades scientists worldwide have been puzzled by the seemingly rapid decline in the quality and health of many mature and old-growth forests, called 'novel forest decline'. Interestingly, forests which are quite removed from the impact of natural and human disturbances often seem to be suffering the worst. Because so many causes have been postulated for this decline, ranging from acid rain and global warming to pathogenic fungi and viruses, that most scientists now accept a multiple factor explanation for forest dieback. Indeed, it is common for forests in decline to be simultaneously affected by both environmental stresses (e.g., drought, acid rain, and soil acidification) and biological stresses (e.g., root rot, bark beetles, and budworms). Still, current approaches have yet to yield any unified set of mechanisms which can account for the similarity in the symptoms and etiology of forest decline globally.
A major breakthrough in our understanding of forest decline, including sudden oak death syndrome, has been achieved by approaching this problem from a systems' perspective. Complexity is a new theoretical arena, perhaps even a new paradigm in science, that defines the mechanisms by which natural systems self-organize and self-regulate. Applied to forest ecosystems, complexity emphasizes ecological interactions, synergistic couplings, and feedback connections among all the organisms in a forest.
Findings are summarized from more than 20 years of field and laboratory studies in biocomplexity of forest ecology and decline conducted at the University of Colorado and at the National Center for Atmospheric Research. Published research findings from Alaska, Colorado, Canada, Venezuela, Africa, China, and elsewhere show, unequivocally, that an intricate ecological subsystem, comprised of a suite of cryptogamic organisms, plays a central role in the decline and death of woody plants. This has allowed us to identify an underlying physiology of the forest, a physiology analogous to the immune system of an organism, but for an entire ecosystem. The pH balance, a critical parameter in this physiology, is found to shift as the result of successional changes in the ecosystem involving cryptogams, especially mosses. The onset of novel forest decline is observed to be closely associated with an increased cover of mosses, which are shown to kill fine "feeder" roots of plants. Symptoms of novel forest decline, globally, are observed to adhere closely to those expected with acidification and root mortality in these forests.
