Evidence synthesis as the basis for decision analysis: a method of selecting the best agricultural practices for multiple ecosystem services

Agricultural management practices have impacts not only on crops and livestock, but also on soil, water, wildlife, and ecosystem services. Agricultural research provides evidence about these impacts, but it is unclear how this evidence should be used to make decisions. Two methods are widely used in decision making: evidence synthesis and decision analysis. However, a system of evidence-based decision making that integrates these two methods has not yet been established. Moreover, the standard methods of evidence synthesis have a narrow focus (e.g., the effects of one management practice), but the standard methods of decision analysis have a wide focus (e.g., the comparative effectiveness of multiple management practices). Thus, there is a mismatch between the outputs from evidence synthesis and the inputs that are needed for decision analysis. We show how evidence for a wide range of agricultural practices can be reviewed and summarized simultaneously (“subject-wide evidence synthesis”), and how this evidence can be assessed by experts and used for decision making (“multiple-criteria decision analysis”). We show how these methods could be used by The Nature Conservancy (TNC) in California to select the best management practices for multiple ecosystem services in Mediterranean-type farmland and rangeland, based on a subject-wide evidence synthesis that was published by Conservation Evidence (www.conservationevidence.com). This method of “evidence-based decision analysis” could be used at different scales, from the local scale (farmers deciding which practices to adopt) to the national or international scale (policy makers deciding which practices to support through agricultural subsidies or other payments for ecosystem services). We discuss the strengths and weaknesses of this method, and we suggest some general principles for improving evidence synthesis as the basis for multi-criteria decision analysis

Effects of cover crops on multiple ecosystem services: Ten meta-analyses of data from arable farmland in California and the Mediterranean

Cover crops are considered to be beneficial for multiple ecosystem services, and they have been widely promoted through the Common Agricultural Policy (CAP) in the EU and Farm Bill Conservation Title Programs, such as the Environmental Quality Incentives Program (EQIP), in the USA. However, it can be difficult to decide whether the beneficial effects of cover crops on some ecosystem services are likely to outweigh their harmful effects on other services, and thus to decide whether they should be promoted by agricultural policy in specific situations. We used meta-analysis to quantify the effects of cover crops on five ecosystem services (food production, climate regulation, soil and water regulation, and weed control) in arable farmland in California and the Mediterranean, based on 326 experiments reported in 57 publications. In plots with cover crops, there as 13% less water, 9% more organic matter and 41% more microbial biomass in the soil, 27% fewer weeds, and 15% higher carbon dioxide emissions (but also more carbon stored in soil organic matter), compared to control plots with bare soils or winter fallows. Cash crop yields were 16% higher in plots that had legumes as cover crops (compared to controls) but 7% lower in plots that had non-legumes as cover crops. Soil nitrogen content was 41% lower, and nitrate leaching was 53% lower, in plots that had non-legume cover crops (compared to controls) but not significantly different in plots that had legumes. We did not find enough data to quantify the effects of cover crops on biodiversity conservation, pollination, or pest regulation. These gaps in the evidence need to be closed if cover crops continue to be widely promoted. We suggest that this novel combination of multiple meta-analyses for multiple ecosystem services could be used to support multi-criteria decision making about agri-environmental policy

Best management practices for multiple ecosystem services: subject-wide evidence synthesis and multi-criteria decision analysis

When a farm is managed for one ecosystem service, such as soil conservation, what happens to other ecosystem services? For example, if cover crops are used to reduce erosion or increase fertility, what happens to below-ground biodiversity or water quality? If management practices cause trade-offs between multiple ecosystem services, which practices cause the fewest trade-offs? Based on the methods developed by the Conservation Evidence project (www.conservationevidence.com), we show how subject-wide evidence synthesis, expert assessment, and multi-criteria decision analysis can be used to make transparent and evidence-based decisions about which management practices are the best for multiple ecosystem services. We reviewed the evidence for the effects of twenty farmland management practices (e.g., cover cropping or riparian restoration) on seven ecosystem services (crop production, soil and water regulation, climate regulation, pollination, pest regulation, and biodiversity conservation) in agroecosystems with Mediterranean climates. For each publication that we reviewed, we summarised the effects of each practice on each ecosystem service for which there was quantitative evidence. A group of conservationists and agronomists assessed the evidence that we summarised (scoring each practice for benefits and harms to each service, and scoring the certainty of the evidence), and assigned each practice to an effectiveness category for each service (e.g., “likely to be beneficial” or “trade-offs between benefits and harms”). Based on the scores from this expert assessment, we used multi-criteria decision analysis to make a structured decision about which practices were the best for which combinations of ecosystem services and cost. We also developed an online decision-support tool that allows users to make their own decisions, based on the evidence, by stating their relative preferences for cost, crop production, and other ecosystem services.peerReviewe

The Development of 70-Year-Old Wieslander Vegetation Type Maps and an Assessment of Landscape Change in the Central Sierra Nevada

Assessing dominant land cover change is critical to understanding the terrestrial consequences of climate change. This study created digital maps from a portion of a heritage vegetation survey of California, the Wieslander Vegetation Type Map survey of the 1930s. Digital maps were produced for a 30,236 km2 area of the Sierra Nevada. These historical data were compared with CalVeg, a 1996 vegetation map produced by the US Forest Service. In addition, the extent of Pinus ponderosa forests on the Placerville quadrangle was compared to a historical map from 1850 as well as the 1934 map.At low elevations, blue oak (Quercus douglasii) and foothill pine (Pinus sabiniana) areas have largely converted to grasslands. At about 1000 meters elevation, the lower edge of the “Yellow Pine Belt” (dominated by Pinus ponderosa) has retreated upslope about 180 meters between 1934 and 1996, and by 526 meters since 1850. Grazing, competition by nonnative grasses, and fire occurred on only 42% of the total area of change.The authors hypothesize failure of conifer seedling establishment due to earlier Sierra snowmelts caused by warmer temperatures. The lower edge of the Sierran conifer belt appears to be sensitive to climate change, a conclusion with implications for the water‐holding capacity of the mountains

The Development of 70-Year-Old Wieslander Vegetation Type Maps and an Assessment of Landscape Change in the Central Sierra Nevada

Assessing dominant land cover change is critical to understanding the terrestrial consequences of climate change. This study created digital maps from a portion of a heritage vegetation survey of California, the Wieslander Vegetation Type Map survey of the 1930s. Digital maps were produced for a 30,236 km2 area of the Sierra Nevada. These historical data were compared with CalVeg, a 1996 vegetation map produced by the US Forest Service. In addition, the extent of Pinus ponderosa forests on the Placerville quadrangle was compared to a historical map from 1850 as well as the 1934 map.At low elevations, blue oak (Quercus douglasii) and foothill pine (Pinus sabiniana) areas have largely converted to grasslands. At about 1000 meters elevation, the lower edge of the “Yellow Pine Belt” (dominated by Pinus ponderosa) has retreated upslope about 180 meters between 1934 and 1996, and by 526 meters since 1850. Grazing, competition by nonnative grasses, and fire occurred on only 42% of the total area of change.The authors hypothesize failure of conifer seedling establishment due to earlier Sierra snowmelts caused by warmer temperatures. The lower edge of the Sierran conifer belt appears to be sensitive to climate change, a conclusion with implications for the water‐holding capacity of the mountains

Groundwater sustainability in the San Joaquin Valley: Multiple benefits if agricultural lands are retired and restored strategically

Restoring habitat in retired farmland could reduce water demand and provide ecosystem services for farmers and local communities

Raptor Use of Artificial Perches in California Rangelands in Fall

Most raptor species rely on perches for hunting, resting, preening and roosting and in many agricultural areas the availability of adequate perches can limit raptor abundance and diversity. This has negative implications for both raptor conservation and the natural pest control services they can provide for farmers. Installing artificial perches on agricultural lands can therefore benefit both raptors and farmers. However, installing perches under current guidelines is difficult on California’s 38 million acres of rangelands, where rocky soil can be restrictive to anchoring poles belowground. We developed a novel method for modifying existing fenceposts to support raptor perches. These raptor perches are relatively light, easy to construct, can be transported in multiple pieces and assembled in the field. We installed 16 artificial raptor perches in four representative habitats on a California ranch to 1) determine if raptors will use artificial perches in each habitat; 2) test raptor preferences for different perch configurations; and 3) observe which raptor species utilize perches. Here, we share our perch design as well as our results from monitoring perches between August and November 2017. We found that American kestrels, great horned owls, barn owls, and red-tailed hawks utilized perches, as did a number of non-raptor species. Perch use by raptors was highest in an irrigated pasture and at a mid-elevation grassland site located on a hill. Perches at a low-elevation, unirrigated pasture with no slope and perches located in higher elevation oak woodland sites were used significantly less. In all habitats raptors preferred to utilize 15-foot perches over 20-foot perches. Raptors rarely utilized a lower perch when two were available on a single pole, suggesting that this added feature is not necessary to attract the species we observed

Raptor Use of Artificial Perches in California Rangelands in Fall

Most raptor species rely on perches for hunting, resting, preening and roosting and in many agricultural areas the availability of adequate perches can limit raptor abundance and diversity. This has negative implications for both raptor conservation and the natural pest control services they can provide for farmers. Installing artificial perches on agricultural lands can therefore benefit both raptors and farmers. However, installing perches under current guidelines is difficult on California’s 38 million acres of rangelands, where rocky soil can be restrictive to anchoring poles belowground. We developed a novel method for modifying existing fenceposts to support raptor perches. These raptor perches are relatively light, easy to construct, can be transported in multiple pieces and assembled in the field. We installed 16 artificial raptor perches in four representative habitats on a California ranch to 1) determine if raptors will use artificial perches in each habitat; 2) test raptor preferences for different perch configurations; and 3) observe which raptor species utilize perches. Here, we share our perch design as well as our results from monitoring perches between August and November 2017. We found that American kestrels, great horned owls, barn owls, and red-tailed hawks utilized perches, as did a number of non-raptor species. Perch use by raptors was highest in an irrigated pasture and at a mid-elevation grassland site located on a hill. Perches at a low-elevation, unirrigated pasture with no slope and perches located in higher elevation oak woodland sites were used significantly less. In all habitats raptors preferred to utilize 15-foot perches over 20-foot perches. Raptors rarely utilized a lower perch when two were available on a single pole, suggesting that this added feature is not necessary to attract the species we observed

Understanding the contribution of habitats and regional variation to long-term population trends in tricolored blackbirds.

Population trends represent a minimum amount of information required to assess the conservation status of a species. However, understanding and detecting trends can be complicated by variation among habitats and regions, and by dispersal connecting habitats through source-sink dynamics. We analyzed trends in breeding populations between habitats and regions to better understand the overall dynamics of a species' decline. Specifically, we analyzed historical trends in breeding populations of tricolored blackbirds (Agelaius tricolor) using breeding records from 1907 to 2009. The species breeds itinerantly and ephemerally uses multiple habitat types and breeding areas, which make interpretation of trends complex. We found overall abundance declines of 63% between 1935 and 1975. Since 1980 overall declines became nonsignificant and obscure despite large amounts of data from 1980 to 2009. Temporal trends differed between breeding habitat types and were associated with regional differences in population declines. A new habitat, triticale crops (a wheat-rye hybrid grain) produced colonies 40× larger, on average, than other breeding habitats, and contributed to a change in regional distribution since it primarily occurred in a single region. The mechanism for such an effect is not clear, but could represent the local availability of foodstuffs in the landscape rather than something specific to triticale crops. While variation in trends among habitats clearly occurred, they could not easily be ascribed to source-sink dynamics, ecological traps, habitat selection or other detailed ecological mechanisms. Nonetheless, such exchanges provide valuable information to guide management of dynamic systems