Assessing alternative futures for agriculture in Iowa,U.S.A.

The contributions of current agricultural practices to environmental degradation and the social problems facing agricultural regions are well known. However, landscape-scale alternatives to current trends have not been fully explored nor their potential impacts quantified. To address this research need, our interdisciplinary team designed three alternative future scenarios for two watersheds in Iowa, USA, and used spatially-explicit models to evaluate the potential consequences of changes in farmland management. This paper summarizes and integrates the results of this interdisciplinary research project into an assessment of the designed alternatives intended to improve our understanding of landscape ecology in agricultural ecosystems and to inform agricultural policy. Scenario futures were digitized into a Geographic Information System (GIS), visualized with maps and simulated images, and evaluated for multiple endpoints to assess impacts of land use change on water quality, social and economic goals, and native flora and fauna. The Biodiversity scenario, targeting restoration of indigenous biodiversity, ranked higher than the current landscape for all endpoints (biodiversity, water quality, farmer preference, and profitability). The Biodiversity scenario ranked higher than the Production scenario (which focused on profitable agricultural production) in all endpoints but profitability, for which the two scenarios scored similarly, and also ranked higher than the Water Quality scenario in all endpoints except water quality. The Water Quality scenario, which targeted improvement in water quality, ranked highest of all landscapes in potential water quality and higher than the current landscape and the Production scenario in all but profitability. Our results indicate that innovative agricultural practices targeting environmental improvements may be acceptable to farmers and could substantially reduce the environmental impacts of agriculture in this region.This revised version was published online in May 2005 with corrections to the Cover Date.     

Tropical fruits: By J.A. Samson. Longman,London and New York, 1980, ix + 250 pp., $ 15

Plants have been regenerated from anthers of Primula obconica frozen in liquid nitrogen for 5 minutes, and cultured on synthetic media. There were two modes of plant development, directly from pollen-embryos, and indirectly through the differentiation of callus.     

Forest spread and phase transitions at forest-prairie ecotones in Kansas,U.S.A.

The spread of gallery forest habitat into upland areas is of substantial interest to resource managers because such spread has many implications for the management of grassland and forest habitats. This study used a dynamic percolation model to examine the potential rates of spread or invasion of forest in eastern Kansas. Aerial photos taken 16 years apart at the Fort Riley training base were used to calibrate a spatially explicit contagion model of forest spread to interpolate and extrapolate the forest spread processes. Results fit the actual pattern of spread well, as measured by both visual inspection and a multiscale fractal measure of pattern. Comparisons to a long-term fire-exclusion experiment in Geary County, Kansas, and to the Konza Prairie also provided validation. Both the simulation and the 100-year Geary County series showed an interesting pattern of forest spread. Spread was slow and steady until about 20% forest cover was reached, at which point the rate increased. We conclude that this self-accelerating response is due to spatial patterns created by the spreading forest that tend to accelerate the growth process after a critical point is reached. On the basis of theoretical study and experimental simulation of the percolation phase transitions, we suggest that fractal dimensions in a transient ecotone of binary mixtures (e.g., trees and grasses) should range between 1.56 and 1.8958, and the critical fractal dimension during ecotonal phase transitions should be 1.7951. This critical point of about 18.5% forest cover that we predicted was close to the observed result and might represent a phase transition at the forest-prairie ecotone.     

Landscape change with agricultural intensification in a rural watershed,southwestern Ohio,U.S.A.

Specialized cash grain production, emergent in the midwestern United States during the post-WWII era, typifies the Upper Four Mile Creek watershed in southwestern Ohio. This style of agriculture intensifies cropland use, with consequent increases in soil erosion and stream sedimentation - a serious problem in the lower reservoir, Acton Lake. Agricultural statistics and aerial photographs compiled between 1934 and 1984 were used to quantify agricultural dynamics and landscape change in the watershed, including land-use apportionment, diversity, and the structural configuration of forest, woodland, and old-field/brushland patches and corridors. A questionnaire sent to all land owners in the basin documented farm-level characteristics and factors that influence management decisions. Crop diversity (H) in Preble County, Ohio decreased from 1.42 in 1934 to 1.17 in 1982, as corn and soybeans dominated the landscape mosaic. Yields rose, but net profits were reduced by declining prices per bushel and increases in fertilizer and petroleum-based subsidies. Landuse diversity in the county also declined (H = 1.37 in 1934 tot 0.80 in 1982) in response to cropland expansion, whereas forest land in the watershed increased from 1605 to 2603 ha. Fragmentation declined and the landscape became polarized after 1956, with a concentration of agricultural patches in the upper watershed and forest-patch coalescence in stream gullies and state park land in the lower watershed. The questionnaire (~ 29% return) further supported, at the farm-level, observed regional trends toward expansion (farm coalescence and lease contracts) and specialization (conversion toward corn and soybeans). The most important factors influencing farm size and management were better equipment and family traditions. Thus, cultural and technological factors that operate at the farm-level, coupled with meso-scale variation in the physical conditions of a catchment basin, tend to influence landscape-level patterns more than regional socioeconomics and governmental policies.     

Riparian plant composition in an urbanizing landscape in southern California,U.S.A.

In coastal southern California, natural riparian corridors occur in a landscape mosaic comprised of human land uses (mainly urban and suburban development) interspersed among undeveloped areas, primarily native shrublands. We asked, does the composition of the landscape surrounding a riparian survey point influence plant species distribution, community composition, or habitat structure? We expected, for example, that invasive non-native species might be more abundant as the amount of surrounding urbanization increased. We surveyed 137 points in riparian vegetation in Orange County, California, along an urbanization gradient. Using logistic regression we analyzed 79 individual plant species’ distributions, finding 20 negatively associated and 12 positively associated with the amount of development within a 1-km radius around the survey points, even after accounting for the effects of elevation. However, after summarizing plant community composition with Detrended Correspondence Analysis we observed that, overall, community composition was not statistically correlated with the amount of development surrounding a survey point once the association between development and elevation was taken into account. Non-native species were not particularly associated with increasing development, but instead were distributed throughout vegetation and urbanization gradients. However, the extent of the tree and herb layers (structural attributes) was associated with development, with the tree layer increasing and the herb layer decreasing as urbanization increased. Thus, although the degree of surrounding urbanization appears to influence the distribution of a number of individual plant species, overall composition of the community in our study system seemed relatively unaffected. Instead, we suggest that community composition reflected larger-scale environmental conditions, such as stream order and other variables associated with elevation, and/or regional-scale disturbances, such as historic grazing or enhanced atmospheric deposition of nitrogen.     

5个美国扁桃品种的微繁殖

对5个引进的美国扁桃品种Bulgaria1、Nonpareil、Fritz、Prize和Neplus的微繁殖进行了研究。以单芽茎段作为外植体,所用启动培养基为MS 0.5～1.0mg/LBA 0～0.1mg/LIAA,增殖培养基为MS 0.5～2.0mg/LBA 0.1mg/LIAA 0.5mg/LGA3,壮苗培养基为MS 0.1mg/LBA 162.14mg/LPG。生根培养方法为100mg/LIBA溶液浸渍60min后接入无任何生长激素的1/2MS上暗培养2周,或在1/2MS 100mg/LIBA 200mg/L柠檬酸上培养12h转入无任何生长激素的1/2MS上暗培养8d。采用试管苗基部遮光可代替暗培养,但生根率略低而地上部分生长更健壮。     

美国佛罗里达州新育成的2个兔眼蓝莓品种

介绍了美国佛罗里达州最新育成并注册的2个兔眼蓝莓品种。“佛罗里达玫瑰”（Florida Rose）2002年注册,该品种生长势强健,丰产,5月下旬成熟,平均单果重1．3g,果肉硬、味甜略酸,种子少。可供应鲜果市场和用于加工,也可做观赏果树;“味美”（Savory）2003年注册,该品种长势极强健,丰产,5月下旬成熟,平均单果重2．0g,果实微蓝色,甜略带酸味,可供应鲜果市场和用于加工。     

美国密歇根州最新育成的3个高灌蓝莓品种

介绍了美国密歇根州立大学2004年注册的3个最新育成的高灌蓝莓品种。其中德雷珀中晚熟、丰产;利珀蒂晚熟,丰产;奥罗拉极晚熟、丰产。3个品种均适合在北高灌蓝莓适栽区栽培,能耐-20℃低温．果实硬度大,贮期长。     

Ecotonal changes and altered tree spatial patterns in lower mixed-conifer forests, Grand Canyon National Park, Arizona, U.S.A.

This research analyzes patch development and determines tree spatial patterns along the lower mixed-conifer ecotone on the North Rim of Grand Canyon National Park in Arizona (U.S.A.). Patterns of patch development were interpreted from spatial analyses, based on tree age and size, and past records of disturbance and climate. Five plots in the ecotone between mixed conifer forests and monospecific stands of ponderosa pine (Pinus ponderosa) were studied for patterns of patch development. The methods used include: (1) size-structure analyses, to compare species patch development; (2) dendrochronological dating of tree establishment; (3) tree ring master chronology, to determine periods of suppressed growth, compared to a Palmer Drought Severity Index; and (4) spatial analyses by species composition, size and age, with univariate and bivariate analyses of spatial association and spatial autocorrelation. We found an increased density of shade-tolerant and fire-intolerant species namely clusters of pole-sized white fir, and fewer large ponderosa pine. This revised version was published online in May 2005 with corrections to the Cover Date. This revised version was published online in July 2006 with corrections to the Cover Date.