Under baseline conditions, agricultural land use comprised 46% of the study area. Vineyard, pasture, and row crops make up approximately a quarter each of this agricultural area, followed by grains , while alfalfa, rice, and orchards accounted for less than 4% each. Under the enhanced agriculture scenario, the agricultural footprint increased to 68% of the study area, and is reduced slightly in the restoration and urban scenarios to 44% and 43%, respectively. The developed/urban class accounted for 9% of the study area under baseline, and increased in the urban scenario to 16% of the study area by 2050 .The total amount of carbon stored on the landscape under baseline conditions was ~784,000 Mg C ha-1 , with the majority stored in row crops , riparian forests , and grassland . Carbon storage in other agricultural classes was less than 4%. Carbon storage increased by 83% from baseline in the restoration scenario to ~1.4 million Mg C ha-1, largely associated with a 4-fold increase in carbon stored in riparian forests . Areas adjacent to the Cosumnes River and its tributaries became increasingly important for this ecosystem service . In the restored landscape, the carbon stored in riparian forests accounted for 63% of the total, with proportionally less harbored in row crops and grasslands compared to baseline. In the enhanced agriculture scenario, carbon storage increased by 12% from baseline to 879,000 Mg C ha-1 ,ebb and flow bench with parcels that harbor increased carbon storage scattered throughout the study area . Compared to baseline, the proportion of carbon stored in row crops increased slightly, from 47% to 53% of all carbon stored in the study area, while the proportion of carbon stored in vegetation classes such as riparian forest and grasslands decreased by ~4% each.
In the urban scenario, carbon storage decreased from baseline by 6% to ~740,000 Mg C ha-1 . The AUC score for the BRT model performance was 0.672 . Variables with the highest relative importance for predicting Swainson’s Hawk nest sites included riparian forest, row crops, pasture, grassland, vineyards, and urban/ developed areas. We found a positive relationship between nest sites and the proportion of riparian forest, row crops, pasture, and grassland within the surrounding 25-ha landscape, and a generally negative relationship with vineyards and urban/ developed areas, matching expectations based on field surveys of habitat use. Baseline conditions showed areas adjacent to the Cosumnes River had the highest suitability for Swainson’s Hawk . The predicted landscape suitability for Swainson’s Hawk changed substantially from baseline under each of the three management scenarios. It increased the most under the enhanced agriculture scenario , followed by the restoration scenario . Parcels close to the Cosumnes River became more suitable in the restoration scenario, and parcels throughout the study area became more suitable under the enhanced agriculture scenario . As might be expected, landscape suitability declined under the urban scenario . The average suitability of each land-use scenario as calculated for each of the 15 focal bird species showed subtle changes. Average suitability across all species increased under the restoration scenario by 5% and increased slightly under the enhanced agriculture scenario , but overall suitability declined by 1% in the urban scenario . In addition, using a 5% change threshold, the restoration land-use scenario resulted in a more suitable landscape for nine out of the 15 bird species. One species, the Yellow-Breasted Chat , experienced a 5% increase in suitability under the urban scenario, and no species experienced an increase or decrease in suitability exceeding 5% in the enhanced agriculture scenario.
The total amount of nitrous oxide emission associated with baseline agriculture in the study area is approximately 50,506kg N2O. Row crops had the highest N2O emissions, accounting for 60% of the baseline emissions. The next highest emissions were associated with grain and vineyards , while pasture, orchards, and rice were less than 3%. The total amount of nitrates leached from agricultural lands is approximately 2.1 million kg N. Patterns of nitrogen leaching were similar to nitrous oxide emissions, with row crops ranking highest , followed by grain and vineyards . Again, pasture, orchard, and rice comprised less than 2% of the total. Areas of high leaching and emissions under baseline were scattered throughout the agricultural lands of the study area . In the enhanced agriculture scenario, total N2O emissions and nitrate leaching in the study area increased by about 20%, concentrated in the northwest area . Nitrous oxide emissions increased to approximately 60,000 kg N2O, and nitrate leaching to 2.6 million kg N . Similar to baseline conditions, row crops accounted for the greatest proportion of emissions and leaching. In the restoration scenario where agricultural lands were replaced by natural vegetation, total N2O emissions and nitrate leaching decreased by 3% , mostly in close proximity to the Cosumnes River . There was also an approximate 5% decrease in these figures in the urban scenario as agricultural land is developed; N2O emissions decreased to around 48,000kg N2O and nitrate leaching to 2 million kg N, respectively . Patterns of emissions and leaching among types of agriculture are similar to baseline across both the restored and urbanized landscapes. The total agricultural commodity value of the study area under baseline was ~$184 million , with a handful of high-value parcels scattered throughout the study area . Row crops accounted for almost half of this value , followed by vineyards . Agricultural types favored by the Swainson’s Hawk such as alfalfa, grains, and pasture each accounted for less than 3%.
Under the enhanced agricultural scenario, revenue increased by 48% to ~$273 million , with revenues from row crops accounting for an even higher proportion of the total revenue . The restoration scenario resulted in a 4% decrease in agricultural revenue , while the urbanization scenario resulted in a 5% decrease .Our analysis examined a highly productive agricultural landscape and quantified how different land-management scenarios compared in terms of carbon storage, biodiversity values, ecosystem disservices, and agricultural returns at the parcel scale. More specifically, we looked at the trade offs under different land-use change scenarios, and evaluated whether positive benefits in financial agricultural returns were at the expense of biodiversity and other services. Underlain by the projected changes in land-cover types in 2050, our estimates indicated that the restoration scenario had multiple positive benefits from a conservation and environmental management perspective, similar to the conservation scenario generated by Nelson et al. . Restoration yielded substantial positive outcomes for carbon storage and habitat for Swanson’s Hawk, as well as 15 other focal bird species . Concurrently, ecosystem disservices decreased , and agricultural returns also decreased . Furthermore, the amount of agricultural land in the study area only decreased slightly under the restoration scenario. At the other extreme, urbanization had consistently negative effects on the landscape, and resulted in decreased carbon storage and landscape suitability for all bird species , along with a loss in financial agricultural returns . The only positive effect from a conservation and environmental management perspective was the reduction in nitrous oxide and nitrogen leaching . From a land-use planning viewpoint, however, these relatively negative effects of expanding the urban footprint would need to be examined in the context of alternatives for meeting the housing needs of local cities . The enhanced agriculture scenario was developed based on favoring the kinds of crops commonly protected or expanded as part of Swainson’s Hawk conservation and mitigation efforts. Although managing for a single species is not ideal, in some cases it is a necessity because mitigation for habitat loss or affected protected species demands it. In other cases, a single-species approach might be pursued by management if a keystone species is identified. Either way, evaluating the effect of this strategy on ecosystem services and disservices, agricultural returns,4x8ft rolling benches and potential multi-species benefits is valuable for management. By 2050, we estimated that the enhanced agricultural landscape had a highly positive effect on Swanson’s Hawk habitat value , higher even than the restoration scenario . Landscape suitability for the 15 focal bird species also increased marginally, i.e., favorable crop types for the Swanson’ hawk were also more suitable for some of these bird species. Agricultural returns increased by almost 50%. In contrast to other studies , we found carbon storage benefitted as well , owing to a replacement of grasslands with row crops, pastures, grains, and alfalfa with higher levels of carbon storage . However, these gains came at a cost, with increases in nitrous oxide emissions and nitrogen leaching by about one fifth . The approach and scenarios used in this study provide a framework which can be adaptively modified in the future to inform land utilization. Clearly, many different or complex management scenarios could be explored. Our intent was to evaluate a range of feasible options to demonstrate the effects of major restoration on the one hand to urban growth on the other, with the enhanced agriculture scenario in the middle. One future modification, for example, would be to optimize the configuration of native and adjacent agricultural land in the restoration scenario to increase connectivity across the landscape. Alternatively, future analyses could also account for carbon storage in urban green spaces, or the value of retaining mature trees to provide nesting habitat for a listed species in the urban scenario.
In addition, other services such as groundwater could be assessed, which is particularly relevant given the recently implemented Sustainable Groundwater Management Act, or recreation, given the high visitation rates of the study area. To improve estimates of ecosystem services associated with agricultural areas, better information is needed on crop rotations over time . The study area also harbors a few registered organic farms and some contracted organic production, such as rice cultivation. Future modifications of our approach could incorporate organic land management, given the association between organic practices and decreased ecosystem disservices. Although cultivation is largely conventional, compared to many parts of California it is highly diversified, with many different types of crops across small parcels. This spatial configuration makes farm scaping practices and buffer habitats a realistic option, which, in turn, can substantially affect carbon storage and biodiversity in agricultural lands . Estimates of the focal ecosystem services could also be improved by additional data, for example, including below-ground carbon storage estimates for the forest class, estimates of soil carbon, or nitrous oxide emissions for natural habitats. Our findings using the 15 focal bird species, although subtle, indicated that management actions for the Swainson’s Hawk yielded benefits for other bird species; however, it would be useful to assess how well this was reflected in other taxonomic groups. A number of studies from central California indicate that insects might respond similarly to the restoration scenario. For example, insectary hedgerows favor beneficial insects over pests by a ratio of three to one , with the highest numbers of insects correlated with the length of flowering period. Another study found that pollination by native bees depended on the proportion of natural habitat within 1 to 2.5km from the farm site . The authors compared rates of pollination of watermelon in Yolo County, California and found that farms with ≤1% natural habitat within 1 km experienced greatly reduced diversity and abundance of native bees compared to farms with ≥30% natural habitat within 1km, meaning that pollination services by native bees had to be supplemented by imported colonies of European honey bees. This study represents one of the few ecosystem services studies conducted at a spatial scale that is relevant to the on-the-ground decision-making of land managers, county planners, and conservation practitioners. Using parcels instead of pixels is useful because changes such as cropping patterns or fertilizer application occurs by these units. The identification of parcels that exhibit consistent, beneficial changes in carbon and biodiversity from baseline conditions across all scenarios may represent focal areas for targeted protection that constitute “no regrets” opportunities for conservation investment. In contrast, conflicted parcels that harbor both beneficial services and disservices might require land-owners and municipalities to work together to develop a management strategy that optimizes the value for beneficial ecosystem services. By restoring habitat, conservation biologists and restoration ecologists seek to promote the reassembly of diverse ecological communities, while also enhancing the ecosystem services these communities provide . Restoration of pollinator communities is of particular concern because pollinators play a critical role in plant reproduction in both natural and agricultural systems .