Trends in vital signs for Greater Yellowstone: application of a Wildland Health Index.
The Earth's remaining tracts of wildlands are being altered by increased human pressure and climate change. Yet, there is no systematic approach for quantifying change in the ecological condition of wildland ecosystems. This paper applies a Wildland Health Index (WHI) to evaluate trends in ecological vital signs in the Greater Yellowstone Ecosystem (GYE). Components of the WHI include criteria for judging ecosystem health, vital signs consistent with these criteria, monitoring at spatial scales relevant to the ecosystem, evaluating trends in condition, and communicating with decision makers. The GYE, while large, intact, and with substantial management capacity, is undergoing increasing human pressure and climate change. Thus, assessment of trends in ecological health is needed to prioritize management. We synthesized current knowledge to evaluate trends in stressors and vital signs of ecosystem function, composition, and structure for 1970 to present and forecasted to 2100. Results were summarized in a WHI Scorecard to illustrate trends in the higher level vital signs of interest to policy makers. We found that human population has doubled, and housing density has tripled in the GYE since 1970 and both are projected to double again by 2050. Human development is now estimated to cover 31% of the GYE. Temperature has warmed 0.8°C since 1950 and is projected to increase 2.5-5.3°C by 2100. These changes in land use and climate have reduced snowpack and stream flows, increased stream temperatures, favored pest outbreaks and forest die-off, fragmented habitat types, expanded invasive species, and reduced native fish populations. Large mammal populations, in contrast, have been increasing in numbers and expanding in range. These trends differ among land allocation types. The WHI Scorecard rated 6 of 9 vital signs as relatively stable or improving in national parks and designated wilderness. On private lands, in contrast, five vital signs were rated as deteriorating. Confidence in our evaluation is not high because of lack of monitoring across the full GYE. While the National Park Service has a rigorous monitoring program, fewer vital signs are tracked on other federal lands and still fewer on private lands. Thus, trends in ecological condition are not evaluated across the entire GYE nor widely reported in the media. We recommend that the WHI approach be systematically applied across the GYE and other large wildland ecosystems in the United States to better inform management to sustain these wildlands.