HALF A CENTURY OF CROPLAND CHANGE*

ABSTRACT. The census concept of total cropland is a better measure of effective agricultural land than is total farmland, which includes extensive areas of woodland owned by farmers. The cropland area of the United States dropped from 478 million acres in 1949 to 431 million acres in 1997, for a net loss of less than 1 million acres, or roughly one‐fifth of 1 percent, per year. In the midwestern agricultural heartland most counties changed less than 5 percent in the half‐century, and more counties gained than lost. The West was a crazy quilt of change, and in the East most counties lost more than 10 percent. Major metropolitan counties lost a few percentage points more than did adjacent areas, but at a lower rate per capita than the nation as a whole. Most of the loss of cropland was in marginal agricultural counties with soils of low inherent fertility and topography unsuited to modern farm machinery. The loss of cropland to suburban encroachment may be cause for intense local concern, but attempts to thwart development cannot be justified on grounds of a net national loss of good cropland.     

What can we learn about changing ethnic diversity from the distributions of mixed-race individuals?

It is hypothesized that self-defined mixed-race persons live in residentially mixed areas in the largest metropolitan areas in California. The hypothesis is tested by examining the distribution of mixed-race persons among ethnically and racially diverse and nondiverse neighborhoods in the San Francisco and Los Angeles Metropolitan Areas. The research confirmed that mixed-race individuals are more likely to live in areas with ethnic diversity and that the tendency is greater for the mixed-race population in the San Francisco–Oakland Metropolitan Areas than in the Los Angeles Metropolitan Area. Mixed-race individuals live in neighborhoods which are diverse with mixes of all four major ethnic and racial groups, and in “well-off” (but not the most affluent) neighborhoods. The study also shows that the mixed-race population is youthful. The association of mixed-race individuals and racially integrated neighborhoods will have important implications for the evolving nature of spatial integration in California specifically, and the United States more generally.     

Siberian Village: Land and Life in the Sakha Republic

Bella Bychkova Jordan and Terry G. Jordan‐Bychkov. Minneapolis: University of Minnesota Press, 2001. xii and 140 pp., maps, photos., glossary, notes, refs., and index. $32.95 cloth (ISBN 0‐81663‐5692). Reviewed by Glen M. MacDonald, Department of Geography, University of California, Los Angeles, Los Angeles, CA.     

Expanding Local Water Supplies: Assessing the Impacts of Stormwater Infiltration on Groundwater Quality

In urban regions, the increased volume of stormwater runoff that results from the impermeable urban landscape is a potential source of water supply, particularly for groundwater recharge. One concern regarding infiltration of stormwater is its potential impact on groundwater quality. To further evaluate this, an extensive monitoring program was conducted in and around Los Angeles, California, over a six-year period. Samples collected from stormwater runoff, the vadose zone, and groundwater were analyzed for constituents of concern including metals, nutrients, organics, bacteria, and emerging contaminants. Findings indicate no degradation of groundwater quality as a result of intentional infiltration. At sites with shallow groundwater, concentrations of some constituents decreased over the period of the study.     

Modelling the impacts of cropland displacement on potential cereal production with four levels of China’s administrative boundaries

Cropland displacement, as an important characteristic of cropland change, places more emphasis on changes in spatial location than on quantity. The effects of cropland displacement on global and regional food production are of general concern in the context of urban expansion. Few studies have explored scale-effects, however, where cropland is displaced not only within, but also outside, the administrative boundary of a certain region. This study used a spatially explicit model (LANDSCAPE) to simulate the potential cropland displacement caused by urban land expansion from 2020 to 2040 at four scales of the Chinese administration system (national, provincial, municipal, and county levels). The corresponding changes in potential cereal production were then assessed by combining cereal productivity data. The results show that 4700 km² of cropland will be occupied by urban expansion by 2040, and the same amount of cropland will be supplemented by forest, grassland, wetland, and unused land. The potential loss of cropland will result in the loss of 3.838×10⁶ tons of cereal production, and the additional cropland will bring 3.546×10⁶ tons, 3.831×10⁶ tons, 3.836×10⁶ tons, and 3.528×10⁶ tons of potential cereal production in SN (national scale), SP (provincial scale), SM (municipal scale), and SC (county scale), respectively. Both SN and SC are observed to make a huge difference in cereal productivity between the lost and the supplemented cropland. We suggest that China should focus on the spatial allocation of cropland during large-scale displacement, especially at the national level.     

FARMLAND CONVERSION: NATIONAL LESSONS FOR IOWA*

Between 1967 and 1975, United States cropland declined 30.5 million acres, of which 8 million acres were prime farmland. The rising gross farm product continues to outweigh such losses owing to short-term adjustments such as irrigation, but longer-term measures to conserve farmland are widely urged. Even Iowa, where urban growth is modest, is incurring some loss of superior farmland. Experience in other states offers certain lessons to Iowa: discourage unnecessary municipal annexations; evaluate the impact of public investments on farmland; expand tax preferences for agriculture; and assist counties to improve their land planning and regulatory efforts.     

THE UNUSUAL STORMS OF FEBRUARY 1992 IN SOUTHERN CALIFORNIA

During February 1992, a series of relatively warm storms passed eastward across southern California, yielding intense precipitation that triggered widespread mass movement, flooding, property damage, and loss of life. These storms were triggered by an intense low pressure system (976 mb) off northern California which deepened as its eastward progress was initially blocked by a high pressure ridge (1040 mb) across western North America. Between February 10 and 13, large areas of Ventura and Los Angeles counties experienced cumulative precipitation of 200–400 mm with intensities reaching 40–50 mm hr^-1. Mass movement, mainly as soil slips that transformed downslope into debris flows, occurred where cumulative precipitation exceeded 300 mm and when sustained intensities exceeded 25 mm hr^-1. Stream response was rapid, particularly in urban areas where impermeable surfaces and storm drains fed concrete stream channels. The canalized upper Los Angeles River and Arroyo Simi exceeded all previous discharges for over 43 and 36 years of record, respectively. Other streams, from the large Santa Clara River to modest Malibu Creek, yielded recurrence intervals for the peak discharge of between 8 and 24 years, but the rapidity of flooding everywhere was remarkable. Whereas main trunk streams, canalized or not, responded predictably, the storm series emphasized the problems of poorly controlled development of potentially unstable hillsides and floodable lowlands and indicated a need to reassess the assumptions upon which such development is permitted. [Key words: climatology, cyclonic storm, geomorphology, mass movement, flooding, California].     

Planning for Peri-urban Agriculture: a geographically-specific,evidence-based approach from Sydney

Agriculture on the fringes of cities across the Global North is increasingly perceived as making an important contribution to urban sustainability. As Australian cities continue to expand and encroach on their peri-urban peripheries, there is rising concern about loss of farmland to housing. Such concerns are especially urgent in the Sydney Basin, due to population growth, and topographical and land-use constraints. Accounting for the Basin's farmlands, however, remains opaque, not unrelated to difficulties in acquiring reliable data on the area and value of Sydney's agricultural industries. The problem is not simply that there are no data available but rather that the nature of existing data is (often hotly) contested. Critical questions for urban planners therefore remain unanswered, including: is peri-urban agriculture as important as advocates suggest? Are metropolitan food supplies under threat? If peri-urban farmland is important, what should be done to preserve it? In collating and analysing existing Australian Bureau of Statistics (ABS) and non-ABS data on Sydney agriculture between 1992 and 2011, we outline the need for more reliable and consistent longitudinal data to enable better planning for Sydney's farmland into the future. Notwithstanding limitations of available data sources, our findings reveal trends in Sydney Basin agriculture that invite debate on many assumptions about the nature of peri-urban agriculture. These findings emphasise the importance of geographically specific, evidence-based analysis as a basis for planning for peri-urban agriculture.     

珠江三角洲地区未来海平面上升及风暴潮增水的耕地损失预测

珠江三角洲地区是中国海岸带中风暴潮灾害最集中的区域之一。在全球气候变化和海平面上升的影响下,风暴潮灾害将对该地区农业生产造成巨大的损失。在借鉴相关经验与研究的基础上,建立风暴潮增水灾害耕地产量损失评估模型,选择广东省珠江三角洲地区为研究区域,以该地区的DEM、土地利用等数据为基础,通过实地调研获取当地的作物种植结构、轮作方式、作物单产、不同淹没高度下不同作物的损失率等数据资料,基于未来海平面上升及风暴潮增水的不同时间情景,估算并分析了2030、2050及2100年珠三角地区耕地受灾范围的空间分布特征及产量损失变化情况。结果表明：受气候变化的影响,未来珠三角地区风暴潮影响下的耕地淹没面积比重不断上升,其中阳江、佛山和东莞等地耕地淹没面积从2030年到2100年增加较为明显,广州和珠海的耕地淹没面积增加幅度则较为缓和。从耕地淹没造成的农业产量损失来看,蔬菜、稻谷和花生等主要作物的损失产量比重呈现增加趋势,且蔬菜的增幅最大,其次是稻谷。其中广州、江门、阳江等地稻谷、花生、蔬菜的损失产量比重均表现为持续上升。     

Spatiotemporal wetland changes and their threats in North Central Ethiopian Highlands

Wetlands are important environmental resources for rural livelihoods in Ethiopia. The study investigated spatiotemporal change of wetlands, drivers and effects in North Central Ethiopian Highlands. Landsat satellite imageries of 1984, 1993, 2000, and 2013 were used to analyse wetland changes over the last three decades. Practical observations, interviews and discussions with local communities and officers were also conducted to address the main objective. Furthermore, secondary data on crop yields were collected to supplement the primary data. The study shows that wetlands have been converted into built‐up areas and farmlands. Wetlands in the study area experienced annual loss across the entire study period. Consequently, the area size of wetlands decreased from 7.4 per cent in 1984 to 2.6 per cent in 2013. About 66 per cent of the total wetlands was lost within 30 years mainly due to farmland encroachment and urban expansions. The highest rate of wetland change was recorded between 2000 and 2013. Such wetland changes increased conflicts among land users. However, the converted wetlands increased short‐term benefits due to wetland recession agriculture. To conclude, wetland resources are under enormous threats, and challenge the sustainability of livelihoods. Thus, integrated and adaptive wetland restoration policies could improve the degraded wetlands.     

中国耕地与未来30年食物需求、保障及对策

在未来的 30年中 ,中国的人口将继续增长 ,至 2 0 30年达到峰值 1 6亿 ,净增 3亿左右。随着社会经济的发展 ,人民生活水平的提高 ,人均食物需求的量与质越来越高。届时中国食物的保障能力受到国际社会的普遍关注。中国到 2 0 30年 ,满足上述食物需求量 ,食物主要来自耕地的生产潜力和非耕地的食物替代生产两方面。在政策非常强有力、一切从保护耕地出发、严格控制耕地占用和维持动态平衡的条件下 ,到 2 0 30年 ,中国耕地面积可保持 1 31× 1 0 6 hm2。而中国到 2 0 1 0年、 2 0 30年年人均需求粮食分别为 42 0 kg和460 kg,这两个基期年分别需求粮食总量为 5 796× 1 0 8kg和 7360× 1 0 8kg。研究认为 2 0 1 0年、 2 0 30年中国耕地动态变化后食物保障能力分别在 93%和 87%。非耕地资源食物替代是补充食物生产和缓解耕地压力的重要途径。 2 0 30年其食物替代能力可达到 90 0 0 0×1 0 3t,其中草业 3380 0× 1 0 3t,木本粮油 1 70 0 0× 1 0 3t,水域 2 5 82 0× 1 0 3t,野生生物 1 340 0× 1 0 3t,非耕地的事物替代能力达到约 1 0 %。中国食物生产与发展的四个保证 ,一是有效的保护耕地政策 ,二是科学技术进步与科技投入 ,三是构建食物生产体系与保障体系 ,四是高效利用水资源的技术与措施。     

The Disappearance of Dense Fog in Los Angeles: Another Urban Impact?

Incidences of dense fog have been gradually disappearing from large cities around the world. In Los Angeles, the climate records show that dense fog may become another extinct specie. In the last 50 years, dense fog has been reduced by about half at two, busy, coastal Los Angeles airports. Not one, but two factors, can be seen as possible causes. Both the downtown Los Angeles urban heat island and the city's air pollution clean-up show a significant relationship to decreasing fog. This study correlates monthly and annual dense fog data recorded at Los Angeles International and Long Beach International airports since the 1950s with downtown Los Angeles temperature and particulate air pollution data. The El Niño—Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) values also explain interannual dense fog variability, with PDO showing a stronger relationship. Coastal sea surface temperatures also closely follow dense fog frequencies. Recent coastal cooling, since 1998, associated with a shift to the cool phase of PDO, has been associated with a rise in dense fog incidences.     

The changing patterns of cropland conversion to built-up land in China from 1987 to 2010

Over the past few decades, built-up land in China has increasingly expanded with rapid urbanization, industrialization and rural settlements construction. The expansions encroached upon a large amount of cropland, placing great challenges on national food security. Although the impacts of urban expansion on cropland have been intensively illustrated, few attentions have been paid to differentiating the effects of growing urban areas, rural settlements, and industrial/transportation land. To fill this gap and offer comprehensive implications on framing policies for cropland protection, this study investigates and compares the spatio- temporal patterns of cropland conversion to urban areas, rural settlements, and industrial/ transportation land from 1987 to 2010, based on land use maps interpreted from remote sensing imagery. Five indicators were developed to analyze the impacts of built-up land expansion on cropland in China. We find that 42,822 km² of cropland were converted into built-up land in China, accounting for 43.8% of total cropland loss during 1987–2010. Urban growth showed a greater impact on cropland loss than the expansion of rural settlements and the expansion of industrial/transportation land after 2000. The contribution of rural settlement expansion decreased; however, rural settlement saw the highest percentage of traditional cropland loss which is generally in high quality. The contribution of industrial/transportation land expansion increased dramatically and was mainly distributed in major food production regions. These changes were closely related to the economic restructuring, urban-rural transformation and government policies in China. Future cropland conservation should focus on not only finding a reasonable urbanization mode, but also solving the “hollowing village” problem and balancing the industrial transformations.     

LAND‐USE DYNAMICS BEYOND THE AMERICAN URBAN FRINGE*

ABSTRACT. A deficiency common to both the historical debates over loss of agricultural land and the current discussions of urbanization and sprawl is a limited understanding of land‐use dynamics beyond the urban fringe. Data aggregated at the county level poorly capture the fine‐grained pattern of land‐use change beyond the dynamic urban‐rural interface. Furthermore, current urban‐based definitions are poorly suited to delineate these areas, and low‐density, exurban land use is difficult to measure using existing land‐cover databases. Urbanization and the conversion of once‐agricultural or other natural resource lands to other uses has traditionally been tracked using urban areas, as delimited in the U.S. census. Urban densities are typically defined as areas with more than 1,000 people per square mile, or 1.6 people per acre (U.S. Census Bureau 2000). Assuming an average of 2.5 people per housing unit, this translates to roughly 0.7 units per acre, or approximately 1 unit per 1.6 acres. The analytical units used in the census, however, both overbound and underbound areas with urban densities. About one‐third of urban areas in 1990 comprised lower‐than‐urban housing density, thanks to overbounding. But, then, one‐third of locations that had urban‐level housing densities failed to be included in urban areas as a result of underbounding, which, if counted, would have constituted another 18 million acres of urban area. An increase over time of the average number of acres required per housing unit in exurban and higher‐density locations occurred in roughly one‐third of U.S. counties from 1960 to 1990 and persisted from 1990 to 2000. In 2000 roughly 38 million acres were settled at urban densities, and nearly ten times that much land was settled at rates from low, exurban density (as low as one house per 40 acres) to higher rates (up to one per 10 acres). This represents a continuing encroachment on land previously given over to other uses—habitat or agriculture. Practitioners of natural resource management need to recognize the ubiquity of exurban development and better incorporate the fine‐scale patterns of land use beyond the urban fringe.     

中国农村转型与耕地保护机制

我国农村和城市的发展都处在转型时期，对土地的需求将进一步扩展，而开发边际土地的余地已经有限，未来耕地食物安全的形势将更趋势严峻，因而保护耕地成为我国的基本国策，但实际上由于缺乏保护机制，耕地仍在继续向效益更高的其它土地用途转移，因此，保护耕地的根本大计在于建立机制，保护耕地的经济机制是提高农业的比较经济效益，耕地生态服务功能的价值实现至关重要，在政策管理机制方面，要强化政府在耕地保护中的作用，规范土地管理行为，明确独立于市场的政府土地管理目标，并以法律形式固定的规划作为实现目标的手段，城市发展要加强内涵集约度。     

Large-scale immigration and political response: popular reaction in California

Over the past 3 years, the level of political debate has grown over the nature and extent of the recent large-scale immigration to the US in general, and to California in particular. California's Proposition 187 to deny welfare benefits to illegal immigrants brought national attention to the immigration debate, and no doubt influenced recent decisions to significantly change the US's welfare program. The author studied the vote on Proposition 187 in the November 1994 California election to better understand the nature of reaction to large-scale immigration and recent arguments about anti-immigrant sentiment and nativism. The only counties which voted against the proposition were Sonoma, Marin, San Mateo, Santa Cruz, Yolo, Alameda, and Santa Clara, as well as the population of San Francisco. The vote generated political responses from across the border as well as within California. Statements from Mexican and other Central American governments reflected their concern over the possibility of returning populations, for whom there are neither jobs nor public services in their countries of origin. Findings are presented from a spatial analysis of the vote by census tracts in Los Angeles County.     

URBAN SPACES OF AMERICAN INDIANS IN THE EXILES

Released in 1961, The Exiles is a low‐budget docudrama that chronicles the lives of three American Indians over a period of twelve hours in a downtown Los Angeles neighborhood in the late 1950s. Contemporary neorealist filmmaking appears to have influenced the film, whereas itsg narrative is ethnographic in form. An examination of the film and its dialogue reveals the ways in which American Indians who recently migrated from their reservation to the city have socially constructed the urban spaces within the framework of the physical setting provided to them. The nature of the engagements of the male and female protagonists with the sites and with other American Indians in this small urban sphere provides substantive clues to the nature and level of their respective transitions into the realm of the white‐dominated society of Los Angeles and beyond.     

绿洲农户生产效率差异评价及改进策略——以张掖市制种玉米为例

绿洲农业是中国西北干旱区农业的精华,面临自然要素稀缺和生态环境脆弱的双重限制。基于制种玉米种植农户数据,在采用数据包络分析法（DEA）测算生产效率的基础上,依据测算结果对冗余投入要素进行改进模拟,得出以下结论：该地区制种玉米生产效率均值为0.863 3,且小规模农地效率值最高,大规模农地效率值最低。针对冗余投入要素的改进模拟后,提出了主要针对贡献率高的生产要素优化的建议。     

耕地资产社会保障功能的空间分异研究——不同农业类型区的比较

在中国人多地少和土地产权二元结构背景下,耕地资源一直是农民的“命根子”,其社会保障功能被认为是社会的稳定器,但近年来这一观点受到越来越多的质疑。目前中国农户耕地的社会保障功能还有多大,迫切需要利用详实的数据进行系统性、定量化的测算。基于此,把拥有承包权的耕地看作农户的一项资产,论文选取都市农业区、集约农业区、平原主粮作物区和山地主粮作物区4类典型农业区,实地调查1025户农户家庭,旨在揭示耕地社会保障功能的空间分异规律。结果表明:作为家庭农业的生产资料,耕地投入农业生产所获收益占家庭总收入的比重在各区最高为50%,其中山区不足7%;作为一项养老保障,家庭耕地资产收益对养老需求的贡献率均不足30%,山区甚至不及3%;作为金融抵押品,若以20万元资金需求为例,户均耕地资产可贷款额度均不超过资金需求的20%,而山区仅为1%。现阶段农户耕地资产的社会保障价值已十分微弱,这有助于给出对新时期农村土地保障功能的科学判断。随着城镇化的推进,不同农业类型区农户的耕地收益及资产价值均不断下降,尤其是在农地利用边际化胁迫下的山区,如何减缓山区耕地弃耕撂荒和耕地资产贬值,无疑是乡村振兴战略实施过程中需要重点关注的问题。     

中国耕地利用变化驱动下的粮食生产:安全格局分析(英文)

自从1978年改革开放以来,随着经济的迅速发展,中国的耕地利用格局发生了很大的变化。耕地数量和质量的变化直接导致粮食生产的变动。本文利用来自政府部门的农业统计数据,分析了1978-2004年间中国耕地利用水平的时空动态格局,并通过构建"粮耕弹性系数"来反映耕地利用变化与粮食生产的互动关系。研究结果表明:耕地投入的增加和质量的提升在一定程度上缓解了1978年以来我国耕地资源严重流失给粮食生产安全带来的压力;自改革开放以来,中国耕地利用水平呈现由经济快速发展带来的普遍性提升局面,并随着经济发展程度由东南沿海向内陆递减,耕地利用水平的提升速率也呈现由东南沿海向内陆梯级递减态势。然而,耕地集约利用程度的不断提升,并不一定会带来粮食产量的持续稳定增长。耕地集约利用增长的边际效用递减特性,使得中国粮食生产安全的保障已逐步由耕地集约利用水平的提升转向了耕地面积的保护,由此导致耕地资源的数量成为了左右粮食生产安全的关键,这也为当今中国制定严格的耕地保护目标和战略提供了现实的科学依据。