The non‐cultivated habitat of the study area varied from oak woodland and mixed hardwood forests, to chaparral and grasslands in drier sites, as well as a distinct riparian vegetation surrounding waterways. Most of the non‐vineyard, non‐riparian forested land was mixed hardwood forest, dominated by a variety of oak species and interspersed with madrone , bay , buckeye , and the occasional Douglas fir . Several woody shrub species were found in the under story of the forest lands, including manzanita , ceonothus , and toyon , at times forming pure stands of chaparral shrubs where soils and exposure presented the ideal conditions. The riparian areas were characterized by a different suite of hardwood species, including maples , alders , cottonwoods , ash , and willows . In total, 29 woody species were recorded on the five ranches. In vineyard tracts, carbon was estimated for only the above ground woody portion of the vines, which are grown as a monoculture, planted in parallel rows that were also approximately two meters apart. Using a sampling regime based on a geographic information system , carbon was measured in soil from 44 pits that were 1 meter deep, and in above ground woody biomass, from 93 vegetation plots. The sampling points were located according to a representative set of sites on each of seven different habitat types. To estimate the carbon stored in a given tract, the average biomass per vine, calculated using allometric equations4 developed with age and main stem diameter, was multiplied by the number of vines in each tract . Similarly, field measurements combined with published allometric equations for native woody species were used to estimate woody biomass for the non‐vine species sampled on 10 x 30 m plots in forest lands. Soil carbon was estimated after combustion analysis of samples taken from the soil pits that were located in forested and vineyard lands. The data for the vegetation samples were integrated into a GIS together with remotely sensed imagery using a cluster analysis technique to produce a general land cover classification map with seven categories.

The amount of carbon stored on a given hectare of land was thus estimated to be a function of its habitat classification and the carbon values for the samples in that category . Soil carbon was estimated in a similar way, but samples were compared to existing soil maps from the national Soil Survey Geographic Database . These distribution maps, along with the sampled carbon values, were used to extrapolate carbon across the landscape to give both per hectare estimates of carbon stocks and total carbon estimates per ranch. The results of the study show two main conclusions with respect to carbon stocks : that per hectare, the top meter of soil holds substantially more carbon than the above ground woody vegetation, ranging from 5 times more in forests to 50 times more in vineyards, on average; and forest lands store more carbon in both soil and above ground woody vegetation than vineyards. On average, forested wild lands had 45 percent more total C/hectare than vineyards. That is, there are approximately12 times more above ground woody carbon and 6 percent more soil carbon per unit area in wild lands than in vineyards. Among wild land vegetation types, valley riparian habitats had the highest carbon stocks, and most of the carbon came from soil . This is most likely due to long‐term upland erosion, and subsequent deposition of organic material along the floodplains of the Russian River and its tributaries. The upland vegetation types had more variability in soil carbon stocks, but closed‐canopy mixed hardwood forest made the greatest contribution to C stocks .

For vineyard tracts, the age of the vines explained much of the variation in above ground C stocks and wood biomass. But even the largest vines contained only about one‐fourth of the wood biomass per hectare of the adjacent wooded wild lands.Planning ahead for climate change in agricultural landscapes involves more than crop management for reducing GHG emissions and coping with uncertain temperatures and precipitation . Land managers must have the capacity to respond to unforeseen change in natural resources as well. Integration of forest, other natural habitat and vegetation types, and agricultural ecosystems into complex landscapes is increasingly viewed as a way to increase the provision of multiple ecosystem services, including carbon storage, pest management, nutrient retention, erosion control, and water quality . Complex landscapes that are rich in biodiversity help to “keep options open” for alternative future management, even if such a strategy appears inefficient and sub-optimal in the present tense . In a mosaic approach for vineyard management, management objectives allow topography and habitat variability to determine the amount and configuration of vine tracts and wild lands. It was the landscape variability that also presented the greatest challenges to modeling carbon in this study. Combining GIS‐ and field‐based approaches was a useful way to sample and analyze vegetation‐based habitat types for their carbon stocks across the landscape . Variability in tree species composition and distribution within habitat types, as well as the many soil types showed the necessity of refined models to address heterogeneity for assessing C stocks. Two specific improvements would make for greater accuracy in future woody plant carbon estimates: a more comprehensive set of allometric equations for extrapolating above ground woody biomass of California tree species from field measurements such as diameter at breast height ; and understanding which environmental variables best explain the variation in above ground woody biomass and developing relevant procedures so carbon stocks can be accurately estimated on specific land holdings. Methods for improving the estimation of carbon stocks will be necessary if regulating bodies make carbon accounting mandatory or provide incentives for maximizing C storage. At present, however, most regulation is focused on emissions, such as AB 32. The U.S. Government has also taken an emissions control approach, such as when the U.S. Environmental Protection Agency declared carbon dioxide and five other GHGs to be air pollutants subject to regulation in 2009. In California, viable voluntary carbon offset projects must qualify for one of three categories: reforestation; improved forest management; or avoided conversion. This means that forest cover must increase by planting or management techniques, or land owners must demonstrate that forested land is at risk for conversion, and therefore its protection meets the requirement of additionality . In California in 2006, transportation, energy production,nft growing system and industry accounted for more than 80 percent of annual GHG emissions; whereas, agriculture collectively contributed only 6 percent . At first glance, it seems that paying for carbon storage on croplands in California would have only a small effect on reducing total GHG emissions and that high transaction costs would discourage any such policy, given the thousands of farms in the state. But marginal lands, remnant natural vegetation, and restored ecosystems within agricultural landscapes could potentially account for substantial carbon benefits in California, based on the results of this study, as well as provide a host of additional environmental benefits not measured here. At present, woody plants in agricultural landscapes are not eligible for carbon offsets in California’s forest protocol .

This situation deserves further recognition, not only to retain an important set of carbon stocks by avoided deforestation, but because incentives for managing a vineyard/wild land mosaic contribute toward other ecosystem services, such as threatened or endangered species habitat protection , water quality and storage capacity, soil erosion, and nutrient run‐off control. The importance of maintaining forest lands has been a major issue for scientists and policy makers concerned with global warming. Efforts to develop incentives to reduce deforestation have produced global campaigns like the United Nations REDD and REDD‐plus programs , as well as specific efforts to slow deforestation in key tropical forest biomes . A crucial issue in the global deforestation debate is the renewed recognition for the importance of forested lands that exist in agricultural landscapes that are not formally considered forests . In conclusion, for complex landscapes, high resolution spatial modeling is challenging and requires accurate characterization of the landscape by vegetation type, physical structure, sufficient sampling, and allometric equations that relate tree species to the landscape. While remote sensing techniques may improve the accuracy of carbon estimation, climate change policy in California shows a lack of focus on storage compared to emissions, and on agriculture compared to other sectors. These oversights may lead to missed opportunities for maximizing ecosystem services, including carbon storage, as well as for encouraging better farm stewardship and habitat conservation. Many types of agricultural landscapes have some fraction of their land out of production and in forests or other forms of conserved habitat. Yet this land is generally not being counted in carbon accounting protocols such as AB 32. As a result, land owners are not being recognized or rewarded for the role they are playing in storing carbon in forested lands. Furthermore, if such rewards or incentive programs did exist, it is highly likely that many producers would take an active role in reforesting parts of their land that is not in production, or planting hedgerows or other vegetation, in order to qualify for these programs.The Global Warming Solutions Act of 2006 has been a catalyst for greenhouse gas mitigation and has generated awareness of climate change adaptation in California’s agricultural sector. While agriculture accounts for only 6 percent of the state’s total GHG emissions, it has the potential to play a significant role in statewide mitigation efforts through the sequestration of carbon in soils and plant biomass and as a source of feed stock for renewable energy generation . Agricultural residues are a major, and largely untapped, renewable energy source for California . Statewide estimates suggest that the potential feed stock from agricultural residues is over 8.8 million tons of dry biomass per year . Various biomass‐derived fuels can be used to partially displace fossil fuel consumption and facilitate GHG mitigation. Since agriculture tends to be particularly vulnerable to climate change, market volatility, and urban development, some have argued that on‐farm energy generation using agricultural residues is a key way to link mitigation and adaptation to generate profitable co‐benefits .In short, mitigation strategies that integrate renewable energy sources into farm operations can themselves be viewed as an adaptation in response to climate change regulation. California’s net metering laws were established in 1995. They currently allow wind, solar, and some biogas installations to be connected to the energy grid through net metering accounts, provided they meet certain energy output and pollution‐control requirements . With the passage of AB 920,5 which became effective in 2011, residences, farms and businesses with renewable energy installations can also sell excess power back into the grid. In contrast, state policies have not previously allowed projects which generate electricity on‐farm from crop residues to participate in these net metering programs. However, the Renewable Energy Equity Act 6 which has been passed by the State Legislature, makes all forms of renewable energy eligible for California’s net metering program.

Lettuce, tomatoes, rice, and almonds have increased in acreage by more than 50% in the last 30 years, while two major crops of past production eras, barley and sugar beets, have declined by almost 100% during this period. Major shifts in production areas have occurred; for example, almond production in California has moved northwards over the past several decades. Within California, as the climate warms, production patterns will shift latitudinally northward, to higher elevations, or out of the state. A warmer and drier climate and expanding growing seasons could benefit olive and citrus production by extending their cultivation range northward . If crops are to decline or disappear from the Californian landscape with climate change, it is most likely to be those that use large amounts of water to produce crops of limited economic value . Many commodities in California have experienced highs and lows during the last century.Wheat production, for example, declined steadily through the 20th century due to bunt and stem rust diseases, loss of foreign markets, and competition with irrigated crops, until the 1970s when new disease-resistant varieties were introduced . For grapes, prohibition in 1919 caused a nearly total demise of the wine grape industry, which had already experienced shifts in production due to outbreaks of the invertebrate pest, phylloxera, by that time. The industry has now obviously rebounded to the point of being one of the main drivers of agricultural land use change in California.

For apricots, statewide production has decreased steadily in the past 40 years, especially since shifts, spurred by urbanization in the Santa Clara Valley, occurred due to less advantageous weather conditions in the San Joaquin Valley, but competition with foreign markets also decreased the demand for dried fruit products. Potato production historically has moved extensively around the state, experiencing fluctuations in production due to tuber-borne diseases and changes in processed vs. fresh consumption patterns. These examples show that California agriculture has the capability and agility to maintain agriculture productivity despite obstacles related to urbanization, pest and market changes for individual crops. Yet, the concern is that a changing climate may accelerate the rate at which producers must cope with specific management problems that arise, especially heat waves, water scarcity, and pests . A sequence of unfavorable years may force these land users to switch from horticultural to lower-income field crops, or to sell land for urbanization or ranchettes with affiliated small-scale agricultural enterprises. If the supply of a given commodity decreases due to climate change, and the price of that commodity increases, producers with the capacity to maintain production due to their microclimate or to technological ability may increase their profits . But, less capable producers will suffer greater losses, especially for high-input crops with large costs of production. Economic analysis of the trade offs between different production ratios of field vs. horticultural crops suggest that a shift towards more acreage of crops with lower input costs, such as field crops, compared to higher-input horticultural crops, could be advantageous in the long-run, despite lower maximum profit per acre, due to greater reliability of yield and income each year.Land use changes are driven not only by environmental factors such as climate, topography, and soil characteristics, but also by synergetic combinations of the five fundamental land use drivers . First, resource scarcity, which can lead to an increase in the pressure of production on resources, has profound implications for land use change.

It has been suggested that climate change may have either a “fertilization” effect, leading to increased yields or a “land-area” effect on crop production that would reduce arable land area and, subsequently, production . Water resources will likely be the primary environmental variable determining shifts in crop distribution since California’s water reserves are largely allocated for cropland irrigation . The loss of prime agricultural land to urbanization may also move production areas to lower quality soils, and to areas without sufficient water supplies . Second, changing opportunities and constraints, which are created by local, as well as national markets and policies, can also impact new land uses. Agriculture in California has been historically “demand-driven,” with food production goals of exporting products to the rest of the U.S. and international markets bringing huge profits to California. Depending on the cost of production and supply, either consumers or producers could gain from climate change . Climate change-induced alterations in agricultural productivity in one region can affect productivity in another region , such as the recent loss of California garlic production to China , possibly leading to collapses in one set of product markets that might trigger collapses or changes in those production systems . Third, outside policy intervention, motivated by improving or worsening agricultural conditions in different areas affected by climate change, could lead to protectionist policies seeking to improve domestic production and increase subsidies for irrigation or other inputs . Such policies can have the long-term effect of slowing economic growth, encouraging unsustainable practices, and/or increasing food insecurity. Nevertheless, incentives can potentially give rise to experimentation with new crops and products . Fourth, loss of adaptive capacity associated with increases in climate variability can greatly determine shifts in land use. Adaptation is defined by the IPCC as ‘adjustments in practices, processes or structures in response to actual or expected climatic stimuli or their effects, with an effort to reduce a system’s vulnerability and to ease its adverse impacts’. Adaptive capacity refers to a system’s increased options and capacity to reorganize after change or disturbance,hydroponic nft channel which is conferred by resilience, and is enhanced by diversification within agricultural landscapes, as well technology and access to information that increase options for successful responses . In California, for example, vegetable growers tend to minimize risks by diversifying production , while 70% of orchard producers produce only one commodity and are much more likely to rely on crop insurance as a risk-management tool . Both finding ways to produce the same crop at a profit, and relocating employment outside of agriculture, may be considered adaptation . Lastly, changes in social organization and attitudes towards climate change consequences might play a large role in determining land use shifts.

One examples is the Standard Williamson Act and the newer Farmland Security Zone , which compensate landowners for 10-20 year commitments to agricultural land use by property tax reductions . Another example is the USDA Cost-Sharing and Reserve Programs which compensate farmers for practices that increase water and air quality, wildlife habitat, or grassland conservation. Another issue is that cultural values, and even just the belief that climate change is actually taking place, strongly motivate the social response to climate and land use change . Stakeholders need to decide which risks should be retained and managed adaptively versus which risks should be shared through risk sharing contracts. Social and economic impacts of climate change must be evaluated at larger scales than site-specific studies, i.e., landscape or regional scales, to provide useful information .Agricultural land in California has gradually shifted to urban or other non-agricultural uses, driven by population growth and non-agricultural force. From 1990-2000, approximately 500,000 acres were converted from agricultural to non-agricultural uses . In one view, this trend towards less agricultural land will have minor effects on the total productivity and economic value of California agriculture. Essentially, this view builds on the high degree of past success that California has had in developing production strategies and markets for a diverse array of different types of commodities, as exemplified in Figure 8.2 by the changing geographic distribution of the top 10 counties in terms of agricultural production since 1929. A recent analysis predicts that although there will be a 10 percent net loss of farmland and irrigation water resources by 2030, this will be offset by yield growth attributable to climate change, crops with high value per acre, and growth in production per acre due to technological improvement . Climate change is assumed to increase yields of California crops by approximately 15%, based on the predictions using the simple quadratic models that were described in Section 5 . The demand for California vegetables, fruit and nuts is expected to grow, and cotton, alfalfa, and irrigated pasture acreage in the state is likely to shift to these crops. As long as relative prices and policy adjustments favor these shifts, and technological advances increase, a gradual increase is predicted in the value of food production in California, and net food exports to the rest of the world is expected to expand rather than contract. Alternatively, such successful adaptation of California agriculture to climate change might require a more cautious approach. There may be surprises in terms of weather events, for example, short-term heat waves floods, or pest outbreaks. Recent modeling has shown that California will experience longer heat waves, and more summer heat waves based on fine-scale, regional processes . In fact, extreme events may dictate outcomes from climate change more definitively than the expectation that gradual increases in mean temperatures and CO2 fertilization effects will reliably boost crop productivity. Adaptive capacity and resilience may be enhanced by taking a cautious strategy that acknowledges the need for land use changes that will assure productivity during gradual changes in climate, but also when extreme weather events, or unexpected surprises, occur. Based on the ecological literature, diversification is a key element to resilience in response to change or disturbance. Biodiversity, for example, can provide “insurance” or a buffer against environmental fluctuations . Since different species respond differently to change, more species can lead to more predictable aggregate community or ecosystem properties. Although certain species may appear to be functionally redundant for an ecosystem process at a given time, they may no longer be redundant through time. Based on this analogy, and the recognition that diversity in crops and farming systems lend economic and ecological resilience at the landscape level , it seems reasonable to adopt a diversification strategy as one element in the necessary technological advances for agriculture to cope with climate change in California. But while crop diversification can act to reduce farm business risks, there are start-up costs and problems for achieving economies of scale. Other risk-reducing strategies, such as crop insurance or the securing of off-farm income, may be readily available and preferred by producers . Another issue is the loss of wetlands, riparian corridors, and the fragmentation of farmland that is predicted to occur in California’s agricultural landscapes during the next century due to urbanization, as well as to water projects that must build levees and storage reservoirs to cope with higher stream flows . Not only do impacts on species protected by the Endangered Species Act, but impacts on other ecosystem services provided by these habitats, for example, water filtration, soil retention, or erosion regulation, need to be considered in planning land use strategies. Thus, it will be necessary to address whether adaptations to climate change by growers and institutions, will be at the expense of sustainable land use practices and extant natural ecosystems .