Effects of Scale on Analyzing and Managing Risks to Forest Biodiversity
S. Hummel, G. Donovan, M. Hemstrom, T. Spies, and A. Youngblood
USDA Forest Service, Pacific Northwest Research Station
Summary: This paper contributes to the science of risk analysis by synthesizing the theoretical basis for its role in biodiversity management strategies. It contributes to the application of risk analysis in forest policy decisions by summarizing the current state of knowledge on estimating uncertainty at varying spatial and temporal scales in ways useful for simulation modeling. By considering both theoretical and applied aspects of risk analysis, the paper advances understanding of its strengths and limitations in forest ecology and management.
Approach: We summarize the key economic and ecological theories that underlie how risk is incorporated into contemporary strategies for managing biodiversity. By explaining the rationale for assessing risks to biodiversity associated with rare but severe disturbance events, the paper clarifies how these risks may change as the frequency and magnitude of the events change in different forest types. We use forest reserves in the interior northwestern US as an example to explore the implications of this change for land management. Reserves are one strategy for mitigating risks to biodiversity and in our example we explore the potential influence of altered fire regimes on the effectiveness of this strategy in interior, mixed-conifer forests.
Background: Risk analysis focuses on the problem of estimating the probabilities of rare events and the magnitude of their associated effects. One use of risk analysis is familiar to anyone who pays insurance premiums. Some types of insurance can be mandatory (malpractice, automobile), while other types are voluntary (life), and yet others subject to availability (flood, earthquake). Insurance doesn’t prevent loss. Instead, insurance spreads the risk of loss among members of a self-selected group who pool their funds so that compensation can be made to a member if an insured loss does occur. Funds come from premiums, which members pay based on calculations of the likelihood and damage of a specified future event and on their own personal risk factors. Insurance provides a way to manage risks that can be priced. The economic literature is replete with articles about risk management and ecologists have begun to borrow concepts from insurance when studying the contribution of biodiversity to ecosystem stability. Although no consensus has emerged, the ecological literature refers to biodiversity as a form of insurance. The insurance hypothesis proposes that ecosystems are insured against functional declines by the presence of many species, whose redundancies guarantee that some species will maintain key functions even if others fail. If this is true, then managing ecosystems to conserve biodiversity should help alleviate the deleterious consequences of natural and human-caused environmental threats. Many biodiversity conservation strategies are based – either implicitly or explicitly – on an assumption that the weight of evidence supports the insurance hypothesis. This paper examines the implications for biodiversity management if this assumption is wrong or if the frequency and severity of potential losses change with time and space.
Example: Forest reserves embody a biodiversity management strategy based on the insurance hypothesis. A decade ago, a network of reserves was established in the Pacific Northwest to conserve and develop a network of old-growth forests on federal land. Since then, increases in the amount of old forests in moist areas of the region have been documented. However, in drier areas east of the Cascade Range the amount of old forest is declining. We examine evidence for the adequacy of a reserve strategy to conserve the biodiversity of old forests in these drier areas, where changes in fire regimes and thus the probability of severe events directly affect key assumptions of the insurance hypothesis and calculations of risk. By reviewing the available literature on the variability of probabilities for disturbances like wildfire or insect epidemics at differing spatial scales we provide a summary that is of immediate value to anyone using simulation models for risk analysis.
Outcome: This paper will advance knowledge on the links among four of the conference topics: risk management across spatial and temporal scales, risk mitigation alternatives, uncertainty estimation and representation, and simulation modeling. It will show why this advance is important for contemporary land management decisions and environmental threat assessment by using forest reserves in the interior west as an example.
corresponding author:
Susan Hummel
USDA Forest Service
Pacific Northwest Research Station
620 SW Main Street, Suite 400
Portland, OR 97205
503-808-2084
shummel@fs.fed.us
Encyclopedia ID: p116
