Several California crop disease climate models are in development and are available, including fire blight , scab , alternaria leaf blight , and brown rot . For the farmer, potential adaptation strategies for pests include choice of crop, growing season, manipulative cultural practices, fertilization, pest control, and irrigation, or a combination of these , many of which are currently used to control weeds in agriculture. Yet, there are often trade offs involved that can benefit pests as well . An effective adaptation plan depends on accurately casting predictions, but such predictions are difficult when the impact of undesirable organisms is based on a complex network of interacting factors. Maladaptation can result in negative effects that are as serious as the climate change-induced effects being avoided . Nonetheless, two endeavors stand out as productive methods of ultimately reducing the impact of invasive plants and weeds in California’s changing climate: an increase in our understanding of interactions in an ecosystem context and increased vigilance. Though many competition experiments have been conducted on the effect of rising CO2 on weed-crop competition , both our understanding of how such effects change in an ecosystem context and how such an effect interacts with other aspects of climate change is rudimentary and is insufficient to formulate respectable predictions in California’s future climate. This is further confounded by uncertainty associated with future precipitation patterns and those of El Niño events in California. As a second adaptation, increased vigilance will serve to identify new invaders early, thus dramatically increasing the potential for successful eradication . In terms of increased vigilance,nft hydroponic the “guilty until proven innocent” approach in which each threat is assumed to be dangerous, shows promise.
Where resources are limited, likely problem areas should be targeted, such as disturbed habitat, especially along roadsides and other dispersal corridors, and points of entry. The impact of climate change on pest and disease outbreaks is difficult to predict because it involves changes in both the vigor of the predator and the vulnerability of its prey. Plants do not experience climate change alone, but as part of a wider ecosystem incorporating their pests, pathogens, symbionts and competitors . Although arthropod pests and weeds do interact with each other, strategies aimed at managing one or other of these classes of threats, rarely consider such interactions . Furthermore the great diversity in commodities produced in California, coupled with the abundance of natural vegetation and weeds can provide an important refuge for pests and diseases causing microbes to survive in, at times when their primary crop host plant may be absent. Species with small geographic ranges are more vulnerable to climate change than widespread ones . This is also true of specialist versus generalist pest species. One possible adaptation is to modify planting dates or the selection of cultivars that are resistant to emerging pests and disease causing microbes. As with weeds this dictates the need for vigilance and accurate predictions of pest/disease outbreaks. Implementation of multifaceted pest and disease management strategies such as those applied in IPM will likely enhance the adaptive capacity of producers in a changing climate. Many of the strategies currently used to control disease and pest outbreaks will likely be successful in the climate of the future. Human responses to climate-induced pestilence need to be adaptive and inventive. Agricultural pest control is already a complex and expensive endeavor. For example, increased pesticides are an obvious adaptation; however, this approach has many drawbacks .
When combating Pierce’s disease, for example, in addition to conventional methods such as inspection, pesticides, and host removal, other technologies that are being employed to better control the disease in California, including biological control, sequencing the pathogen genome , and identification and breeding of disease resistant vines . In order to buffer against the unknown interacting effects of climate change, bet-hedging strategies should be used that reduce host pools such as maximizing spatial and temporal crop intra-specific genetic variation . The judicious use of genetic technologies may also prove important in stemming invasions and epidemics by adding to our range of available tools to deal with such challenges. Issues of precipitation are critical. A warmer drier California will likely have a very different pest, weed and disease landscape than a warmer wetter California. Furthermore, research is needed to understand the effects of climate change on the ecology and evolution of agricultural pests. The effects of climate variability on coevolution, virulence, and resistance to control methods are at best poorly understood. For example, does the efficacy of taxon-specific chemical control shift, if at all, in warmer and/or more variable environments? This question is important across all taxonomic levels, from vertebrate pests to microbial pathogens. Changes in competitive balance and trophic interactions are difficult to predict for future climates. Nevertheless, field experiments can be conducted across existing climate gradients representing current and future conditions. Such studies are lacking. Landscape surveys are also instructive in pointing out the value of non-crop habitat in pest control, and in determining spatial and temporal gradients that affect pest distribution . The effect of higher temperatures on overall abundance of herbivorous insects remains unknown in the absence of equivalent data of their natural enemies . Furthermore, efforts to link information specific to California weather to disease and pest outbreaks are limited in their number .
Concerted efforts are needed to monitor and compile data, including historical records. The development and validation of prescriptive control models depend on these data. Currently, climate disease models in California are developed on an as-needed basis with temporary funding often provided by private agricultural interests . Hence, no long-term efforts or programs exist. Increased development is necessary in the use of continuing programs such as the disease warning systems recommended by Wu et al. . Long-term sharing, coordination, and modeling of pest outbreak and environmental data among the diverse climate regions within California would greatly improve our understanding and ability to prepare for, adapt to, and mitigate against future pest risks and disease causing agents. Pests and pathogens that may become significant in California agriculture need to be identified and appropriate quarantine and inspection measures implemented to avoid introduction. Looking to other regions where the climate is similar to that predicted for California in the coming century will also likely be instructive.Land use refers to the management regime humans impose on the biophysical attributes of the earth’s surface. Temperature or rainfall patterns associated with climate change may alter land use and land-cover distributions ,nft system and consequently basic patterns of productivity, stability, and sustainability in agroecosystems . Conversely, the effects of human-induced greenhouse gas fluxes and C sequestration that is attributed to land use and management can, in turn, impact the rate and magnitude of climate change . For example, cultivation of forest and grassland soils accounts for approximately 25% of the net loss of C in the United States, while N fertilization, no-till farming, and grassland restoration have only slightly reduced these losses . Issues of agricultural land use change are particularly interesting in regions with Mediterranean-type climates; they have typically experienced high population growth, urban expansion, and decreasing self-sufficiency in terms of producing their own food, due also to the export value of the many specialty commodities they produce. In California, these issues raise questions related to the sustainability of agriculture, both economically and environmentally. Given the potential growth of California’s population to 9 million people by the end of the century, urbanization is probably the single largest factor driving land use change in California’s agricultural landscapes, farmland loss, and the increasing utilization of wetlands and riparian corridors that serve as wildlife corridors .
Urbanization could result in a loss of 35% of the prime agricultural land in San Joaquin Valley counties, and much of the remaining agricultural land in coastal counties, even when climate change is not considered in the projections . This section will 1) introduce the approaches commonly used to assess climate change effects on land use, 2) discuss the fundamental drivers of land use change, and 3) evaluate knowledge gaps in current mitigation and adaptation strategies for climate change-induced land use shifts in California.Climate change impact assessments commonly employ a hierarchy of models which, ideally, are integrated to simulate the most important processes, interactions, and feed backs in the systems. At the top of the hierarchy are Global Circulation Models , which simulate global climatic patterns on a grid with cells sized between 2 and 9° longitude and/or latitude and several vertical layers thick. Results from GCMs are then used as inputs to biophysical models, which also rank at the top tier of the hierarchy. Outputs from biophysical models are subsequently used as inputs to economic models at, for example, the farm level . Models at the regional scale are more suitable to estimating climate change effects on land use. While some GCM predict gains of 20-50% in potential agricultural land for North America , regional models provide projections at greater resolution and detail. Regional models have forecast that certain crops will be forced to shift out of their current geographical range due to increasing temperatures , but these losses in productivity may be partially offset by increased productivity from increased CO2 levels . Other crops especially C4 plants might suffer lower yields due to elevated atmospheric CO2 levels , though California produces few C4 commodity crops. As Section 6 points out, less is known about how temperature and CO2 concentrations affect key developmental phases of horticultural crops, and thus their vulnerability to climate change. Climate analogs can provide some insights into land use change. Using the hot, dry decade of the 1930s as an analog of the possible climate that might occur in the Missouri, Iowa, Nebraska, and Kansas region as a consequence of climate change, Easterling and Apps modeled crop responses. They found that farm management changes and slight increases in productivity of some crops, for example, irrigated wheat, could eliminate 80% of the negative impact of the analog climate, thus minimizing potential land use change. In California, an analogy of climate change, the drought of 1987-1991 demonstrated that farmers increased their reliance on ground water, adopted water-conserving technologies, reduced water use per acre, moved away from water intensive crops, and fallowed more land . The drought instigated the official approval of water trading and demonstrates how extreme events can trigger rapid changes in land use and social institutions that increase adaptation to climate change. Different approaches have been used to predict climate change impacts on the agricultural landscape, sometimes resulting in very different outcomes. The first approach is a process-based one that arbitrarily or synthetically forecasts a specific climatic change by varying temperature, precipitation, or another model parameter and is likened to a simple sensitivity analysis .Some weaknesses of this approach include 1) the utilization of significant amounts of primary data that are constrained in time and/or space; 2) requisite stable equilibrium conditions; 3) omission of changes in crop physiology and ecosystem productivity, adaptive human behavior, and land use; and 4) neglect of interactions with land use and responses to environmental change . The California SWAP/CALVIN model is similar to this approach, and it predicts relatively feasible changes in terms of crop management and land use change to maintain crop productivity . A second approach models the responses of crops and farmer behavior based on extrapolation of responses of varying climates observed at other sites to the system of interest, and does not necessarily consider unique adaptations that may increase success during transition to a new climate regime . This latter approach is more akin to the approach of Hayhoe et al. . In this case, predicted effects of climate change on wine grape production are more negative than what would be indicated by the SWAP/CALVIN model, suggesting more problems associated with adaptation, and greater changes in land use patterns. Thus, different potentials for land use change emerge from different modeling efforts. More work is needed to improve the accuracy of modeled forecasts of climate change, and to produce results that are accessible and will allow a wide range of user communities in agriculture to adapt to climate change.