We assessed differences between habitat types, as in previous studies, and did not detect consistent differences between organic and conventional farms; however, our analysis of the effects of specific farm practices on bats was much more informative . We documented significant overlap in practices between organic and conventional farms included in the study , which may explain why we did not detect strong differences between farm management types that mask the influence of local farm practices and characteristics on bats. We found greater bat activity in natural areas compared to farms,highlighting the importance of conservation of natural habitat patches within intensive agricultural landscapes. This finding is consistent with previous studies in mixed annual cropping systems in the US and vineyards in North America . Our finding that diversity was marginally significantly higher in natural habitat than on conventional farms may be explained by differences in local habitat features. Conventional farms had the least variation within site types, with large monocultures of annual crops and little non-crop vegetation, creating open habitat dominated by T. brasiliensis. Natural vegetation sites comprised a range of vegetation forms spanning mixed riparian vegetation to oak woodlands, offering habitat niches for more diverse species. We found no evidence of differences in species richness between site types,fodder growing system as the same species were usually documented across clustered sites.
However, we did find that bat community composition differed between natural habitat and farms,but not between organic and conventional farms.Our finding that farms with more crop varieties had greater activity of all bat species and clutter-adapted bats is the first evidence that bats respond to herbaceous plant diversity on farms. The effect of crop diversity on bats has not been previously tested, and we are not aware of other studies that have documented effects of on-farm herbaceous plant diversity. Most similarly, a study comparing bat activity between farm field margins planted in mixed grasses and conventionally managed field margins did not find a significant effect on bat activity . In contrast to previous studies, we found no evidence that bat activity was positively correlated with proximity to linear habitat . However, difference in the extent and configuration of linear habitat in European farmlands compared to the CCR may explain why our findings conflict with previous literature. Differences in woody vegetation that would impact environmental clutter did not predict clutter-adapted bat activity. If proximity to linear habitat in- fluenced bat activity, it may have been necessary to monitor at a linear edge and at increasing distance into a crop field. To link our findings of the relationship between crop diversification, bat activity, and insect biomass, we focus on clutter-adapted bats. Our finding that crop diversity was significantly correlated with higher clutter-adapted bat activity and greater biomass of Lepidoptera, and that greater biomass of this important insect prey order was significantly positively correlated with higher bat activity, suggests that crop diversification impacts bats via changes in populations of insect prey .
Farms with higher crop diversity also tended to have more noncrop herbaceous cover and weedy field margins as farms often employed a suite of diversified practices. On-farm vegetative diversity can provide critical insect food and habitat resources that are not found in simple monocultures, increasing insect abundance , and improving foraging habitat for bats. The frequency of pesticide use decreased the biomass of Diptera, and Coleoptera, which account for 20–40% of the summer diet of M. yumanensis and T. brasiliensis, in California , the two most common species in the study region. Higher application rates of pesticides and use of synthetic agrochemicals in conventional systems has been suggested as the mechanism driving increased insect abundance and bat activity on organic farms . Because bat activity increased with crop diversity and activity of clutter-adapted bats increased with Lepidoptera biomass, we suggest that both vegetative diversity and pesticide applications drive changes in insect populations and bat activity. Previous studies also demonstrate a positive correlation between bat activity and insect biomass in pastures, linear habitat, and crop fields in agricultural landscapes and show that bats track and feed on populations of insect pests . Of course, the correlation between bat activity and insect biomass is a two-way relationship. Bats may be attracted to higher quality on-farm foraging areas with greater insect biomass, in turn consuming more insects and suppressing insect population levels on these farms, which may explain why we did not see a correlation between open-space bats and insect biomass.
Despite this two-way relationship between bats and insects, our findings provide evidence that crop diversification and less frequent pesticide use increase insect prey and bat activity on farms. The influence of crop diversification on bat activity does not depend on the amount of semi-natural habitat surrounding the farm. Although a few studies in tropical agroforestry systems have confirmed an interaction between local and landscape scale agricultural intensification , Froidevaux et al. found that the effects of local vineyard management were not dependent on landscape complexity. Moreover, we found that crop diversity is a better predictor of bat activity on farms than semi-natural habitat density. Similarly, Kelly et al. did not find strong effects of seminatural habitat density on bat activity on farms. Bat activity in remnant semi-natural habitat is higher is agricultural landscapes with more semi-natural habitat , but the effects of landscape-scale factors on bat ecology have not been extensively studied in temperate, annual cropping systems .Hedgerows, woodland patches, and scattered trees can support bat conservation in agricultural landscapes . A focus on the importance of structural, woody vegetation to bat conservation reflects species’ specific roosting requirements that are not provided by farms, and the potential for structural vegetation to increase habitat connectivity for species with structure-bound ecologies. The conservation of woody vegetation is undoubtedly important to the long-term conservation of bats in agricultural landscapes. However, because the addition of woody, perennial vegetation is often not a feasible management strategy for growers in intensive agricultural systems, we suggest that including a complementary focus on improving the quality of bat foraging habitat offers additional management options in agricultural landscapes. Intensive agricultural systems provide inconsistent food resources to bats, whereas the maintenance of natural habitats can help to ensure stable food resources . Similarly, diverse on-farm and within-field vegetation can help to ensure consistent food resources for bats without negatively affecting production practices or increasing pest problems. The addition of herbaceous plant diversity can be designed through species selection and timing of planting to support desired insect communities . On-farm plant diversity can improve pest suppression, enhance populations of beneficial insects, reduce crop damage, and increase crop yields .Twenty-five years after the publication of the first IPCC Assessment Report, it is instructive to step back and ask what we have learned about the economic impacts of climate change to the agricultural sector, not just from a technical standpoint, but from a conceptual one. California is an ideal focus for such an analysis both because of its strong agricultural sector and proactive climate policy. After passing the 2006 Global Warming Solutions Act,chicken fodder system the state has sponsored research to complete three climate change assessments, with the fourth assessment report in progress at the time of submitting this paper. This effort to study adaptation appears to be relatively more prolific than in many other global sub-regions, particularly over the past decade .
Assessing adaptation potential — the institutional, technological, and management instruments for adjusting to actual or expected climatic change and its effects — represents an important turning point in the climate impacts literature. The important role of responsive decision-making by farmers and institutions is recognized for the first time as the key ingredient to dampening the effects of climate change . Adaptation was simply mentioned as an optimistic afterthought in earlier studies, which suggested that agriculture would fully or mostly adjust in the long term — although there was sparse detail on how it would do so . When adaptation was directly included in the modeling framework, economists found that the estimated welfare damages from climate change documented in previous studies declined . In colloquial terms, this is a shift from modeling the “dumb” farmer to modeling one with reasonable economic agency. There are four key concepts linked to the idea of adaptation: vulnerability, adaptive capacity, economic welfare, and economic efficiency. In the IPCC literature, adaptation is connected to the foundational concept of vulnerability, defined as the propensity for agricultural systems to be affected by future climatic changes . Vulnerability can also be defined endogenously as the ability of farmers and institutions to respond and adapt to, and recover from such changes . This latter definition is synonymous with the concept of adaptive capacity, or the ability of a system to moderate potential damages and take advantage of adaptation and mitigation opportunities to reduce vulnerability of the system to climatic changes . Adaptation dampens welfare losses caused by climate change. The relationship of adaptation with vulnerability is more complex, and better represented as that of trade-offs. For example, changing the crop mix in favor of high value crops may reduce vulnerability to water scarcity, but it may increase vulnerability to heat tolerance. Finally, the concept of efficient adaptation has been defined as a situation where the costs of effort to reduce climate-induced damages is less than the resulting benefits from adapting . Given the central role of farmer and institutional responsiveness, how do recent agro-economic assessments suggest that specific adaptations may improve economic welfare and reduce vulnerability? What is economically efficient adaptation in the short and long-run? What are the limits to the agricultural sector’s adaptive capacity? This is certainly not the first review of climate impact assessments to California agriculture. Smith and Mendelsohn highlighted the importance of regional climatic impacts to several economic sectors in California , integrating across range of modeling approaches . The agricultural impacts are calculated by the Statewide Agricultural Production model under wet and dry scenarios. The results echo those of more recent SWAP studies, suggesting that field crop usage will decline by the end of the century under a dry scenario, though the decline in revenues will be partially offset by increased production of high-value crops. Prior to Smith and Mendelsohn , several notable studies examined the state of the knowledge of climate assessments at the US level . In particular, Lewandrowski and Schimmelpfennig integrate the knowledge from both programming and econometric studies of the agricultural sector. Other reviews have focused on the technical details of the different modeling approaches without discussing the results of the various studies . Following the pioneering work of Smith and Mendelsohn , this paper also focuses on California. The state is a leader in agricultural production, with $53.5 billion in sector cash receipts in 2014. California accounts for roughly 2/3 of US fruit/nut production, and 1/3 of US vegetable production . Roughly 1/3 of California cropland, or 9 million acres, is irrigated , making the state’s agricultural sector highly vulnerable to changes in groundwater and surface water supply . Several programming and econometric studies have been published after Smith and Mendelsohn , that operationalize the concept of adaptation . This paper begins with a review of regional impacts of climate change to California agriculture. It is followed by a review of the results from recent programming and econometric studies. The final section synthesizes the results from these studies, addressing lessons learned about vulnerability,adaptation, and adaptive capacity; and how these relate to economic welfare and Efficiency.Observational studies indicate that average daily temperature and daily minimum temperatures, particularly during the winter season, have increased in California . Average daily temperature in the US Southwest for the previous decade has been higher than any decade observed in the previous century . Barnett et al. find that daily minimum temperatures in winter have increased between 0.28– 0.43 C per decade from 1950–1999. Not just magnitude, but an increased rate of warming has been observed. Karl et al. suggest that the US Southwest has experienced the most rapid rate of warming in the nation. Observed precipitation patterns are fundamentally more complex and variable than temperature, exhibiting a high degree of variability across space and time. Trenberth et al. indicate that annual precipitation has decreased in the southwestern United States for the period 1901–2005.