David A. Keiser

Disentangling the mechanisms underlying functional differences among decomposer communities

Summary 1. Home-field advantage (HFA) is a commonly used sports analogy, which has seen recent growth within the ecosystem ecology literature. It is most often invoked in litter transplant studies, where local adaptation (HFA) explains higher decomposition rates of leaf litter on ‘home’ soil communities. 2. In exploring the mechanisms driving functional differences among soil decomposer communities, a consistent quantitative framework is lacking. 3. We review methods for calculating HFA, propose a consolidated regression approach and demonstrate why HFA must be calculated along with a new ‘ability’ metric if we are to test definitively the competing hypotheses that soil decomposer communities are functionally equivalent versus dissimilar. We demonstrate that qualitative interpretations of HFA differ when the ability of a decomposer community is calculated simultaneously with HFA. For example, communities may differ in their ability to degrade litter in the absence of HFA, or apparent HFA may instead be caused by differing abilities, changing our ecological interpretation of the factors generating functional differences among decomposer communities. 4. Synthesis: We propose a single, statistical approach to help evaluate how and why soil decomposer communities differ in functional abilities. Our approach should help formalize mechanistic interpretations of why soil community composition commonly influences litter decomposition rates.

The low but uncertain measured benefits of US water quality policy

US investment to decrease pollution in rivers, lakes, and other surface waters has exceeded

Air pollution and visitation at U.S. national parks

1.9 trillion since 1960, and has also exceeded the cost of most other US environmental initiatives. These investments come both from the 1972 Clean Water Act and the largely voluntary efforts to control pollution from agriculture and urban runoff. This paper reviews the methods and conclusions of about 20 recent evaluations of these policies. Surprisingly, most analyses estimate that these policies’ benefits are much smaller than their costs; the benefit–cost ratio from the median study is 0.37. However, existing evidence is limited and undercounts many types of benefits. We conclude that it is unclear whether many of these regulations truly fail a benefit–cost test or whether existing evidence understates their net benefits; we also describe specific questions that when answered would help eliminate this uncertainty.

Integrated Assessment Models of the Food, Energy, and Water Nexus: A Review and an Outline of Research Needs

Ozone levels in U.S. national parks are similar to those of U.S. cities, and are negatively associated with visitation. Hundreds of millions of visitors travel to U.S. national parks every year to visit America’s iconic landscapes. Concerns about air quality in these areas have led to strict, yet controversial pollution control policies. We document pollution trends in U.S. national parks and estimate the relationship between pollution and park visitation. From 1990 to 2014, average ozone concentrations in national parks were statistically indistinguishable from the 20 largest U.S. metropolitan areas. Further, relative to U.S. cities, national parks have seen only modest reductions in days with ozone concentrations exceeding levels deemed unhealthy by the U.S. Environmental Protection Agency. We find a robust, negative relationship between in-park ozone concentrations and park visitation. Still, 35% of all national park visits occur when ozone levels are elevated.