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Dryad

Multiple Benefits from Agricultural and Natural Land Covers in the Central Valley, CA

Abstract

The data and code provided in this repository are associated with the technical report on the "Multiple Benefits from Agricultural and Natural Land Covers" project and were prepared by the authors for the Migratory Bird Conservation Partnership. MBCP partner organizations include The Nature Conservancy, California Audubon, and Point Blue Conservation Science.

Executive Summary

The Central Valley of California is one of the most heavily modified landscapes in the world, with millions of acres of semi-arid grassland and desert transformed into an irrigated crop production powerhouse through large-scale infrastructure and irrigation projects. Despite its reputation as an agricultural “sacrifice zone”, it remains an area of conservation focus for its varied, unique, and vibrant ecosystems, from rare vernal pools and serpentine grasslands to the extensive networks of riverine systems, riparian forests, and wetlands that converge at the Sacramento-San Joaquin Delta. While the importance of these natural areas for human-valued functions such as water supply and quality regulation, biodiversity, culture, and recreation is well established, the dominance of agricultural land covers in the Central Valley underscores the need to understand to what extent they contribute to or detract from similar valued ecosystem functions beyond crop production.

Much of the information that is available on the potential benefits from agricultural and natural land covers is not centralized. Instead, disparate reports from research activities that vary in geographic location, scope, and timeframe constitute the bulk of the literature. Furthermore, most studies implement a particular suite of metrics to characterize benefits or tradeoffs provided by a land cover depending on the objectives of the study. Therefore, a synthesis of information on multiple benefits that aggregates metrics into a single database with comparable units of measure is an important step towards incorporating multiple benefits research into concerted planning and policy making efforts for a multifunctional Central Valley landscape.

We performed a rapid evidence assessment following a consistent search strategy and pre-determined inclusion/exclusion criteria. We limited the results of the literature search to peer-reviewed publications from 2010-2020 with a geographic focus on the Central Valley, including the Sacramento-San Joaquin Delta. We extracted published, quantitative estimates of land cover associated benefits and/or tradeoffs and compiled a database consisting of metrics on: 1) climate regulation (e.g., greenhouse gas emissions, carbon storage/sequestration), 2) economy (e.g., livelihoods, production value), 3) environmental quality (e.g., pollution, pesticide load), 4) water (e.g., water quality, water use), and 5) wildlife, specifically value for avian conservation. We also consulted a panel of experts in the fields of agricultural ecology and conservation to assess: 1) avian conservation value, and 2) vulnerability to the impacts of climate change of each of the land covers. Finally, we produced a spatially-explicit model using publicly-available datasets to visualize the distribution of ecosystem benefits and tradeoffs, including carbon storage potential, air and water quality, groundwater recharge, and socio-cultural benefits.

We found that the agricultural land covers most likely to be associated with multiple benefits were alfalfa, rice, and rangelands/pastures. Alfalfa was associated with benefits such as carbon sequestration and managed aquifer recharge potential, along with minor support for biodiversity, although tradeoffs such as nitrous oxide emissions from mature stands and high consumptive water use were also noted. Flooded rice systems were notable for their high value for wildlife, particularly migrating and wintering bird species, along with their economic value in the form of relatively high wages for agricultural labor, although methane emissions and consumptive water use were also a concern. Rangelands and pastures (i.e., grasslands managed for livestock production) had high potential benefits for climate regulation via carbon storage and sequestration in soils and belowground biomass, along with high value for biodiversity and support of valuable agricultural pollination services. In contrast, annual field crops such as tomatoes, corn, and cotton were the most likely to be associated with tradeoffs such as greenhouse gas emissions, nitrate leaching hazard, and heavy pesticide use. Natural land covers such as wetlands and riparian areas were mostly associated with benefits such as carbon storage (particularly in riparian areas) and pollutant mitigation (in the case of wetlands), while some tradeoffs in greenhouse gas emissions were noted.

The spatial distribution of benefits and tradeoffs was highly heterogeneous, although in many cases a north-south trend was evident with areas in the northern Central Valley/Sacramento Valley exhibiting more relative benefits than areas in the southern Central Valley/San Joaquin Valley. The former is noted for the concentrated production of rice, along with a mixture of tomatoes, alfalfa, and orchard crops such as almonds and walnuts. The latter, on the other hand, is associated with most of the Central Valley’s annual production of annual row crops (e.g., cotton), oranges and lemons, table grapes, and deciduous perennial tree crops such as pistachios, almonds, peaches, and prunes. Carbon storage patterns were particularly distinctive, with hotspots in the highly organic soils of the Sacramento-San Joaquin Delta and the former Tulare lakebed.

Our ability to draw general conclusions on the relative benefits or tradeoffs associated with Central Valley land covers was limited by the single-intervention nature of most of the quantitative research available on benefit/tradeoff related metrics. Experimental designs often must restrict activities to a single or few related land covers and investigate the impacts of an intervention on the metric of interest. For the purposes of cross-system comparisons, there were very few studies that addressed variability in benefit/tradeoff metrics across multiple land covers from a multiple benefits or multi-functional landscapes perspective. Studies reviewed for many land covers were focused on a few key metrics of known importance for that land cover, e.g., methane emissions in rice, rather than a broader survey of potential benefits and tradeoffs. Furthermore, most experimental analyses are spatially biased and not representative of the entire Central Valley landscape. These challenges highlight the need for more research on human-valued benefits across land covers from a multiple benefits perspective, preferably with a common set of metrics and indicators relevant to most or all of the land covers under consideration.

This report synthesizes the most recent, Central-Valley-specific literature available on multiple benefit and tradeoff metrics. Section I presents individual land cover profiles, with details on both the quantitative estimates for benefit metrics available in the literature as well as other land-cover-relevant metrics not included in benefit/tradeoff analysis. Section II presents results for spatial models of benefits and tradeoff metrics, including carbon storage, air, water, and habitat quality, groundwater recharge potential, and socio-cultural benefits, across the Central Valley. Finally, Section III provides further details on a cross-land cover benefit/tradeoff analysis using data extracted from the published literature, along with the results of expert panel scoring on relative avian conservation value and climate change vulnerability among land covers. Appendices are included for detailed coverage of methods for the rapid evidence assessment, benefit/tradeoff analyses, and index development.