Timm Kroeger

Urban forests and pollution mitigation: analyzing ecosystem services and disservices.

The purpose of this paper is to integrate the concepts of ecosystem services and disservices when assessing the efficacy of using urban forests for mitigating pollution. A brief review of the literature identifies some pollution mitigation ecosystem services provided by urban forests. Existing ecosystem services definitions and typologies from the economics and ecological literature are adapted and applied to urban forest management and the concepts of ecosystem disservices from natural and semi-natural systems are discussed. Examples of the urban forest ecosystem services of air quality and carbon dioxide sequestration are used to illustrate issues associated with assessing their efficacy in mitigating urban pollution. Development of urban forest management alternatives that mitigate pollution should consider scale, contexts, heterogeneity, management intensities and other social and economic co-benefits, tradeoffs, and costs affecting stakeholders and urban sustainability goals.

Water funds and payments for ecosystem services: practice learns from theory and theory can learn from practice

Payments for ecosystem services (PES) are emerging worldwide as important mechanisms to align investments in human and natural well-being. PES projects are often defined as voluntary transactions where well-defined environmental/ecosystem services (or land uses likely to secure those services) are bought by a minimum of one service buyer, from a minimum of one service provider, if and only if the service provider continuously secures service provision (conditionality). Further criteria of PES include limiting additional objectives and ensuring that payments reward behaviour that would otherwise not occur (additionality). Together these best practices for PES are increasingly accepted as the most efficient means to achieve desired outcomes and are guiding funding for PES projects. We used a series of water funds (watershed-oriented PES projects based on a trust fund model) to examine how theoretical best practices could inform and improve practice and also how theory could learn from practical efforts. We conclude that thoughtful consideration is required when evaluating the promise of a PES approach against a theoretical ideal. We found that requiring conditionality may limit the use of creative finance mechanisms such as trust funds that can provide long-term benefits for conservation and human well-being, and that requiring additionality can exclude benefits from social diffusion and result in the inefficient targeting of PES funds. Finally, public–private partnerships in water funds lead to multiple additional/side objectives but partnerships are likely to lower transaction costs and provide transparent, long-term landscape-scale watershed management.

Reforestation as a novel abatement and compliance measure for ground-level ozone.

Significance Despite often decadeslong control efforts, in many regions of the world ambient concentrations of ground-level ozone threaten human and ecosystem health. Furthermore, in many places the effects of continuing land use and climate change are expected to counteract ongoing efforts to reduce ozone concentrations. Combined with the rising cost of more stringent conventional technological ozone controls, this creates a need to explore novel approaches to reducing tropospheric ozone pollution. Reforestation of peri-urban areas, which removes ozone and one of its precursors, may be a cost-effective approach to ozone control and can produce important ancillary benefits. We identify key criteria for maximizing the ozone abatement and cost effectiveness of such reforestation and the substantial potential for its application in the United States. High ambient ozone (O3) concentrations are a widespread and persistent problem globally. Although studies have documented the role of forests in removing O3 and one of its precursors, nitrogen dioxide (NO2), the cost effectiveness of using peri-urban reforestation for O3 abatement purposes has not been examined. We develop a methodology that uses available air quality and meteorological data and simplified forest structure growth-mortality and dry deposition models to assess the performance of reforestation for O3 precursor abatement. We apply this methodology to identify the cost-effective design for a hypothetical 405-ha, peri-urban reforestation project in the Houston–Galveston–Brazoria O3 nonattainment area in Texas. The project would remove an estimated 310 tons of (t) O3 and 58 t NO2 total over 30 y. Given its location in a nitrogen oxide (NOx)-limited area, and using the range of Houston area O3 production efficiencies to convert forest O3 removal to its NOx equivalent, this is equivalent to 127–209 t of the regulated NOx. The cost of reforestation per ton of NOx abated compares favorably to that of additional conventional controls if no land costs are incurred, especially if carbon offsets are generated. Purchasing agricultural lands for reforestation removes this cost advantage, but this problem could be overcome through cost-share opportunities that exist due to the public and conservation benefits of reforestation. Our findings suggest that peri-urban reforestation should be considered in O3 control efforts in Houston, other US nonattainment areas, and areas with O3 pollution problems in other countries, wherever O3 formation is predominantly NOx limited.