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Partnering with nature: How one city’s growth could be greened

In working with nature in cities, stormwater filtration from bioswales is only the beginning.

Human life depends on the services provided by healthy ecosystems. As described in the UN-backed Millennium Ecosystem Assessment, these services include the provisioning of resources such as food, fiber, and raw materials; regulating services such as water filtration, storm buffering, and climate stabilization; supporting services such as soil formation, photosynthesis, and pollination; and cultural services that are spiritual, aesthetic, and recreational.

Human activities can impede ecosystem functions, thereby reducing flows of services. For instance, impervious pavement impairs watershed function, thereby diminishing services such as fish abundance. Prioritizing for production or harvest of a single commodity, such as food or fiber, can diminish other services in that same ecosystem, such as erosion prevention or soil formation, as well as undermine overall ecosystem resilience.

Approaches to working with nature, however, can enable, rehabilitate, and restore ecosystem functions. Designs for on-site stormwater interception and infiltration can effectively reduce the imperviousness of built environments. Food production techniques can maintain or improve yields while bolstering species richness and abundance, enhancing soil fertility, and increasing carbon sequestration. In the Pacific Northwest, restorative forestry can effectively provide timber harvests while supporting other ecosystem services.

Practices and frameworks for working with nature to improve ecosystem functions, increase flows of services, and bolster the resilience of coupled human-natural systems include permaculture, agroecology, ecological forest management, ecological design, and green infrastructure.

Recently, Ecotrust looked at how the Portland Metro area could better utilize ecosystem services. In an urbanizing world, there are huge potential economic, social and environmental benefits to investing in ecosystem services in or near metropolises. While much research has been devoted to economic valuations of un-priced ecosystem services, cities and regions are in the early stages of incorporating these values into planning.

Ecotrust’s own experiences with ecosystem service projects and valuations, including the development of spatial and economic analyses for marine planning deliberations, lead us to seek to better understand these types of research questions and public engagement processes.

For Portland, we developed a set of scenarios to explore the potential for meeting social goals through management for ecosystem services across the greater region. We focused on three services of significance to the rural-urban context: carbon sequestration, stormwater interception, and food production. Our questions were:

  •  What percentage of the region’s climate change commitments could be met through biological sequestration — trees and other plant matter?
  • What percentage of the city’s stormwater management commitments could be met via green infrastructure?
  • What percentage of the region’s food needs could be satisfied with regional production?

For carbon sequestration, we examined current carbon storage and new sequestration potential in stream-side riparian buffers in The Intertwine Alliance’s regional parks and open spaces, as well as new sequestration potential in the urban forest canopy within the city of Portland.

For stormwater interception and infiltration, we examined the additional potential for tree planting in the urban tree canopy at the scale of City of Portland combined sewer system (which covers about one-third of the city), leaving aside for the moment additional potential of other public and private management options such as bioswales, ecoroofs, downspout disconnections, and rain gardens.

For food production, we looked at the landscape potential to satisfy regional needs from agricultural production lands in the tri-county Clackamas, Multnomah, Washington area, without considering the potential of community gardens or other production within urban areas. Nor did we consider the availability of farming inputs.

Based on plausible scenarios for working with nature, we developed the following estimates:

New carbon sequestration in the region’s riparian areas and urban forests could sequester 485,472 metric tons of CO2 per year by 2050, meeting 2.1 percent of Oregon’s greenhouse gas reduction targets on a current per capita basis. Stormwater interception by new urban forest canopy could meet 6.3 percent to 14.8 percent of city’s projected infrastructural needs by 2040. We found no specific targets for regional food production to satisfy regional demand, but based on a preliminary analysis of landscape suitability, we estimated that the region could supply current regional consumption for most crop categories, with the exception of meat products.

The full report, Partners with Nature, lays out our assumptions and conclusions in more detail.

By definition, our findings are partial and exploratory, and this exercise is as much about framing questions as it is about arriving at quantitative estimates. Each of these scenarios could be re-considered within a participatory or planning context, under differing assumptions or more detailed projections for climate, population, and other anticipated changes. We consider this report an invitation to more in-depth, place-based scenario development that supports shared goals, practices for working with nature and resilience building, in Portland and across the globe.