The fractional multinomial logit model indicates that perennial crops are more likely to increase in response to annual precipitation. However, the panel fixed effects model shows a negative relationship between the share of perennial crops and annual precipitation, but it is not significant. Both models have consistent climate-induced acreage decisions for remaining climate normal. For instance, on average, the growing degree days during summer is positively associated with an increase in perennial crop shares. The average winter chill hours have a negative association with the share of perennial crops, as shown by both models.In Figure 1, we present the estimated marginal effects calculated at various levels of the climate normal distribution, such as the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles. During the summer, the share of perennial crops peak at between 50 and 75 percentiles of degree days, and then decline at higher percentiles of 90 and 95 percentiles of degree days . During winter, nft growing system the share of perennial crops decreases at all levels of degree day distribution . In contrast, annual crop shares decrease during the summer and increase with an increase in winter degree days.
These plots suggest that increased degree days during summer favor planting perennial crops rather than annual crops. The share of perennial crops increases when annual precipitation is below or at the median distribution of annual precipitation, but decreases when annual precipitation is above the median distribution . While the annual crop share increases at all levels of annual precipitation, as indicated by the upward slope of marginal effects of annual crops shares. Finally, perennial crops shares decrease at higher levels of distribution of chill hours during winter, particularly sharply between the 25th and 75th percentile of distribution of chill hours . To estimate the long-term climate effects on acreage decisions for almonds, pistachios, and nuts, the widespread cash crops in the Valley, we divided the perennial crops in our sample into almonds, pistachios, and nuts, and other tree crops. Appendix Table A6 presents the marginal effects assessed using average climate normal for the shares of almonds, pistachios, nuts, and other tree crops separately. The acreage decision of almonds, pistachios, and nuts crops on average has a negative association with chill hours during winter and degree days. While degree days during summer and annual precipitation positively correlate with an increase in the share of other tree crops. Next, we explore spatial heterogeneity in how climate-induced acreage decisions are made in different parts of the Central Valley. To explore spatial heterogeneity empirically, we ran separate fractional multinomial logit regressions for the northern, central, and southern parts of the Central Valley to obtain the average marginal effects.
Appendix Table A7 reports the results. The results indicate that the share of perennial crops increases in response to growing degree days during summer in the northern parts of the Central Valley. An increase in annual precipitation is positively associated with the share of perennial crops grown in all parts of the Central Valley. Winter chill hours only affect the central and southern parts of the Central Valley, resulting in a decrease in perennial crop shares. In contrast, the share of annual crops decreases in response to the growing degree days during summer only in the northern parts of the Valley. An increase in winter degrees days is positively associated with the share of annual crops grown in all parts of the Central Valley. Lastly, an increase in precipitation is negatively associated with the share of annual crops in the northern parts of the Central Valley.As mentioned in the data section, the changes in crop type acreage derived from cropland data layer are more reliable during 2010-2017 than during all the study periods .We test the robustness of our main results by limiting our study period to 2010-2017 and defining our climate normal over 30 years. Quantitatively, marginal effects evaluated at mean values of climate normal are comparable to the main results with full sample for the years 2008-2021 and climate normal defined over 27 years . For instance, the share of perennial crops is positively associated with long-term degrees days during summer and annual precipitation.
Contrarily, during summer , degrees days and annual precipitation have a negative impact on the share of annual crops. Finally, an increase in winter chill hours has a negative association with the planting of perennial crops. Next, there may be a concern about farmland parcels near each other that may have unobserved characteristics that are correlated across space and may potentially influence growers’ land-use decisions. We address this concern by utilizing geo-referenced parcel locations to create a new variable, the average distance between a parcel and its five closest neighbors, then use this variable as an additional regressor in our main specification. The new distance variable could be used as a proxy for acreage decisions in nearby parcels, which could impact planting decisions within the own parcel. We report the marginal effect of crop type shares evaluated at mean values of climate normal in columns 2 and 4 of Appendix Table A8. The estimated coefficients are comparable to the main results in Table 2, suggesting that unobserved characteristics related to neighboring parcels are not a major concern in our study region.From a policy perspective, we explore the spatial heterogeneity of our projection results. Panel B and C of Table 4 report the results. We observe that projected degree days and total precipitation have different effects on the share of agricultural land use in the northern, and central and southern parts of the Central Valley. The projected increase in degrees during summer , on average, negatively affects perennial crops in the northern parts of the Central Valley. The perennial crop shares in the central and southern parts of the Central Valley is expected to be negatively affected during both summer and winter due to projected increase in degree days. The annual crop share is expected to be negatively impacted by the degree days during summer in all parts of the Central Valley, but positively impacted by the degree days during winter. A decrease in projected chill hours in winter is expected to increase planting of perennial crops throughout the Central Valley, with a higher percentage in the northern parts. Finally, projected total precipitation is expected to increase the share of perennial crops and decrease the share of annual crops in the Central Valley. This paper examines growers’ revealed adaptation in land-use adjustments and changing cropping patterns in California in response to climate change. We provide estimates of long-run adaptive responses to climate-induced changes in California’s agriculture. Using parcel-level data, we provide microlevel evidence of the impact of climate change on agricultural land use. This study exploits parcel-level variations in crop types to estimate the impact of climate change on irrigated agriculture by shifting crops, which capture growers’ behavioral response to long-run adaptation. We find that growers in the Central Valley are transitioning from annual crops to perennial crops in response to changing climates. Specifically, vertical hydroponic nft system perennial crops have a positive association with long-term degree-days in summer and total precipitation, while negative association with winter chill hours. We demonstrate that growers are more likely to plant new acres of perennial crops on less suitable land and may potentially shift available irrigation water to high-revenue crops. Moreover, our projection results suggest that an increase in total precipitation and decrease in winter chill hours in northern and central and southern parts of Central Valley will potentially be associated with an overall increase in perennial crop shares. From a policy perspective, switching to high-value crops, which are also long-term water-demanding crops, may be in contrast to the potential water savings of a crop-switching strategy . This study quantifies the changes in climate-induced agricultural land use, including crop switching, and contribute to the literature on agricultural-climate interactions in California and other water stressed agricultural regions globally.Insects pollinate many plant species, including several major crops. Bees are the single most important insect pollinator group and can be a limiting factor for the success of plant reproduction . Consequently, there is strong inter- and intra-specific competition among plants for the attention of pollinators.
With respect to insect-pollinated crops, pollinator visitation is required to obtain maximal seed and fruit production. Consequently, pollination facilitates higher yields even when a crop plant is self-compatible. Tomato provides a good example of the relationship between pollination and yield. Bumblebees are important pollinators of tomato and other Solanum species that utilize an unusual pollination system called ‘buzz-pollination’ . Buzz-pollinated flowers provide excess pollen as a reward to foraging bumblebees that feed it to their developing larvae. Although domesticated tomato is to a large extent ‘self-fertilizing’, buzz-pollination by bumblebees or by manual application of mechanical vibration ‘wands’ is required for maximal seed production, which in turn promotes increased fruit yield . Cucumber mosaic virus , one of the major viral pathogens of tomato, is a positive sense RNA virus that encodes five proteins including the 2b protein, which is a viral suppressor of RNA silencing. Bees do not transmit CMV but the virus is vectored by several aphid species. Virus infection causes dramatic changes in plant host metabolism . CMV-induced metabolic changes include qualitative and quantitative alterations in the emission of volatile compounds and in certain host species this makes infected hosts more attractive to aphid vectors. It is not known if the virus-induced alterations in host volatile emission that influence aphid behavior can also affect plant-pollinator interactions. Most bee-plant interaction studies have focussed on the effects of visual cues. Therefore, the influences of floral and non-floral volatiles on bee-mediated pollination are less well understood. In contrast, the floral odors that attract moth pollinators have been more extensively researched. In this study we determined that CMV infection induced changes in olfactory cues emitted by Arabidopsis thaliana and tomato plants in ways that could be perceived by the bumblebee Bombus terrestris, and confirmed in tomato that this was associated with quantitative and qualitative changes in the blend of plant-emitted volatile organic compounds . We also elucidated a role for the host microRNA pathway in regulating the emission of bee-perceivable olfactory cues. Our data indicated that bumblebees possess an innate preference for olfactory signals emitted by CMV-infected tomato plants and we mathematically modeled what the possible wider implications of this might be if a similar preference occurred in wild host plants under natural conditions.In ‘free-choice’ assays, bumblebees encountered flight arenas containing ten tomato plants concealed within towers designed to allow odors to diffuse out but prevent the bees from seeing or touching the plants . Cups that were placed on top of towers hiding plants of both treatment groups offered bumblebees the identical ‘incentive’ of a 30% sucrose solution. Nonetheless, when presented with mock-inoculated and CMV-infected tomato plants, bumblebees preferred to visit the towers that were hiding infected plants . Bumblebees showed similar preferences for flowering and non-flowering CMV-infected plants, indicating that leaves were the main source of attractive volatiles . Bumblebees also displayed a preference for CMV-infected tomato plants over plants infected with CMVΔ2b, a viral mutant lacking the gene for the 2b VSR , a factor that also influences CMV-plant-aphid interactions.The results obtained in free-choice assays with tomato plants infected with CMVΔ2b suggested that the 2b protein, which is a VSR, may be exerting effects on the metabolism of plant volatiles by interfering with host small RNA pathways. The model plant Arabidopsis is the best higher plant system to use to investigate the effects of small RNA pathways. However, whilst Arabidopsis plants emit potentially pollinator-influencing volatiles, this species is not bee-pollinated. Consistent with this, bumblebees showed no significant difference in preference for volatiles emitted by CMV-infected versus mock-inoculated Arabidopsis plants in free-choice assays . An alternative approach to investigate the ability of bees to recognise differences in olfactory or other stimuli is to set up a differential conditioning or ‘learning curve’ assay. A differential conditioning assay can reveal whether bees can perceive cues that would not normally induce any behavioural responses and that could not be studied in free-choice assays. In our differential conditioning assays, cups on towers offered bumblebees either a 30% sucrose solution ‘reward’ for choosing one treatment group or a ‘punishment’ for choosing the other group.