Using InVEST to assess ecosystem services on conserved properties in Sonoma County, CA

Purchases of private land for conservation are common in California and represent an alternative to regulatory land-use policies for constraining land use. The retention or enhancement of ecosystem services may be a benefit of land conservation, but that has been difficult to document. The InVEST toolset provides a practical, low-cost approach to quantifying ecosystem services. Using the toolset, we investigated the provision of ecosystem services in Sonoma County, California, and addressed three related questions. First, do lands protected by the Sonoma County Agricultural Preservation and Open Space District (a publicly funded land conservation program) have higher values for four ecosystem services — carbon storage, sediment retention, nutrient retention and water yield — than other properties? Second, how do the correlations among these services differ across protected versus non-protected properties? Third, what are the strengths and weaknesses of using the InVEST toolset to quantify ecosystem services at the county scale? We found that District lands have higher service values for carbon storage, sediment retention and water yield than adjacent properties and properties that have been developed to more intensive uses in the last 10 years. Correlations among the ecosystem services differed greatly across land-use categories, and these differences were driven by a combination of soil, slope and land use. While InVEST provided a low-cost, clearly documented way to evaluate ecosystem services at the county scale, there is no ready way to validate the results. Ecosystem services, sometimes called “nature’s services,” are broadly defined as the ecosystem functions that benefit people (Daily 1997; Turner and Daily 2008). They are commonly grouped into four categories: supporting, provisioning, regulating and cultural services. Supporting services, such as nutrient recycling and soil formation, allow other ecosystem services to function. Provisioning services include food, raw materials, water and energy. Regulating services, such as carbon sequestration and water purification, regulate ecosystem processes. And cultural services, such as recreational opportunities, contribute to our quality of life. While the economic value of ecosystem services is often debated (Naidoo et al. 2008; Rockström et al. 2009), there is little doubt that the services are essential to human life (Daily 1997).