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Habitats
Terrestrial and freshwater habitat
How important is land cover conversion as a stressor? And how has land
cover changed in the Puget Sound watershed?
Essay by: Nick Georgiadis, University of Washington Puget Sound Institute
The 2014 Puget Sound Pressures Assessment
Ecosystem recovery should be, and often is, informed by the best available science. Typically, the
source of the best available information is peer-reviewed scientific literature. However,
questions often arise and major decisions must be made for which there is no vetted guidance in
the scientific literature, and no time to study the issue directly. For example, among the first
questions asked by recovery practitioners about an ecosystem like Puget Sound are: Of the many
human pressures on the ecosystem, which present the greatest threats? And On which
pressures should recovery effort be focused? Typically, answers are not to be found in technical
journals, rather, they reside inside the crania of specialists and experts who are familiar with
diverse components of the ecosystem. The process of carefully asking the right questions of
experts, and classifying their informed answers, is known as ‘expert elicitation’. The trick is to
draw opinions as objectively as possible, from as many experts as possible, and synthesize their
responses as systematically as possible. While the products may not be as well-supported as,
say, the results of an incisive experiment, they are infinitely superior to abject guesses, and serve
very well, if by default, as the best available information.
Expert elicitation was recently used to list and rank human actions and effects that are injurious
to the Puget Sound ecosystem, often referred to as “stressors”. Details of the exercise are
intricate and lengthy, but it was thorough: in the end, 61 experts rated the impact of a total of 47
stressors on a total of 60 “endpoints” – the species and habitats that humans value the most,
and aspire to conserve or restore. The assessment yielded scores quantifying how severely each
stressor affects each endpoint. These scores were summed to yield overall rankings of stressor
impact, and of endpoint vulnerability.
Results were published online in a report entitled The 2014 Puget Sound Pressures Assessment
(PSPA; McManus et al., 2014), and were revealing about the relative impacts of stressors on
terrestrial, freshwater, and marine environments.
Land cover conversion featured prominently among stressors with the greatest potential
impacts across all environments:
Conversion of land cover for natural resource production
Non-point source conventional water pollutants
Conversion of land cover for transportation & utilities
Shoreline hardening
Non-point source, persistent toxic chemicals in aquatic systems
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