Synanthropization of Vegetation in the Upper Belts of the Seminskii Range (the Altai Mountains)

Specific features of vegetation synanthropization under the effect of human activities and a long-term grazing load were studied in the subalpine and upper mountain-forest belts of the Seminskii Range.     

利用累积NDVI估算黄河流域年蒸散量

地表蒸散的准确估算在流域水资源的评价、干旱监测及农作物产量模拟研究中很重要,论文通过建立年蒸散量与累积NDVI及相对湿润指数之间的关系,利用1982～2000年8km分辨率的AVHRRNDVI资料及月平均气温和月降水量资料,对黄河流域近20年来地表蒸散的时空分布进行了分析,并利用水文站径流观测资料对估算结果进行了检验。结果表明,黄河流域多年平均年蒸散量是389mm,年际间变化很大,空间分布格局是东南部蒸散量最大,其次是兰州以上区间,宁蒙河段及鄂尔多斯高原蒸散量最小;全流域平均蒸散估算误差比较小,吻合比较好。     

TIMBER HARVEST IMPACTS ON SMALL HEADWATER STREAM CHANNELS IN THE COAST RANGES OF WASHINGTON1

ABSTRACT: We evaluated changes in channel habitat distributions, particle‐size distributions of bed material, and stream temperatures in a total of 15 first‐or second‐order streams within and nearby four planned commercial timber harvest units prior to and following timber harvest. Four of the 15 stream basins were not harvested, and these streams served as references. Three streams were cut with unthinned riparian buffers; one was cut with a partial buffer; one was cut with a buffer of non‐merchantable trees; and the remaining six basins were clearcut to the channel edge. In the clearcut streams, logging debris covered or buried 98 percent of the channel length to an average depth of 0.94 meters. The slash trapped fine sediment in the channel by inhibiting fluvial transport, and the average percentage of fines increased from 12 percent to 44 percent. The trees along buffered streams served as a fence to keep out logging debris during the first summer following timber harvest. Particle size distributions and habitat distributions in the buffered and reference streams were largely unchanged from the pre‐harvest to post‐harvest surveys. The debris that buried the clearcut streams effectively shaded most of these streams and protected them from temperature increases. These surveys have documented immediate channel changes due to timber harvest, but channel conditions will evolve over time as the slash decays and becomes redistributed and as new vegetation develops on the channel margins.     

南极菲尔德斯半岛植被微区CO2浓度的监测

在南极苔藓植被的微环境区内,CO₂的浓度在473.5mg·m^-3以上,大大高于全球CO2的平均浓度(356 mg·m^-3),可见苔藓等植被区可能是大气CO₂的源之一.这与特殊的南极条件下植被的生理生态特性有关.在苔藓分布区,CO₂浓度日变化的主要影响因素是光照和温度.菲尔德斯半岛变化无常的天气状况使得CO₂浓度昼夜变化规律出现局部波动,不同的天气状况也使CO₂浓度发生变化.研究表明:光照条件是CO₂浓度变化的主导影响因素,从CO₂浓度的季节变化中可以看出,CO₂浓度变化与大气温度呈负相关;与降水量和空气相对湿度呈正相关.本文首次给出了极地环境下植被微区的CO₂浓度变化及其影响因素,为极地温室气体的研究提供了新的材料.     

Changes in groundwater levels and the response of natural vegetation to transfer of water to the lower reaches of the Tarim River

Restoration and reconstruction of the degraded Tarim River ecosystem is an important challenge.A goal of an ecological water conveyance project is to protect and restore the natural vegetation in the lower reaches of Tarim River by transferring water from Bosten Lake,through the river channel,to the lower reaches.This study describes the changes in groundwater depth during the water transfer and the respondence of riparian vegetation to alterations in groundwater levels.The results indicate that groundwater depth along the Tarim River channel has a significant spatial-temporal component.Groundwater levels closest to the river channel show the most immediate and pronounced changes as a response to water transfer while those further away respond more slowly,although the observed change appears to be longer in duration.With a rise in the groundwater level,natural vegetation responded with higher growth rates,biomass and biodiversity.These favorable changes show that it is feasible to protect and restore the degraded natural vegetation by raising the groundwater depth.Plant communities are likely to reflect the hysteresis phenomenon,requiring higher water levels to initiate and stimulate desired growth than what may be needed to maintain the plant community.Because different species have different ecologies,including different root depths and densities and water needs,their response to increasing water availability will be spatially and temporally heterogenous.The response of vegetation is also influenced by microtopography and watering style.This paper discusses strategies for the protection and restoration of the degraded vegetation in the lower reaches of the Tarim River and provides information to complement ongoing theoretical research into ecological restoration in arid or semi-arid ecosystems.     

三峡库区典型消落带淹水后草本植被的自然恢复特征

消落带是影响水库生态环境安全的关键区域。利用生物调查方法,对三峡库区典型缓坡型消落带草本植被的自然恢复情况进行了初步研究。结果表明：（1）研究区植被主要为一年生和多年生草本植物,共有29种,其中空心莲子草、狗牙根、稗草、苍耳、狗尾草、鬼针草和马唐是消落带的优势种类,且空心莲子草和狗牙根是消落带成陆初期的建群种。消落带植物群落多呈斑块状集中分布,沿145～175 m高程梯度从下往上大致可分为4条植物带：空心莲子草 狗牙根带、稗草带、苍耳 马唐 狗尾草带和一年生杂草带。（2）淹水后消落带草本植物群落在没有人为干预的情况下可自然恢复,只是群落结构趋于简单,植物物种多样性显著降低。（3）植物群落的物种多样性、地上生物量和盖度均沿水位梯度带从下往上呈先增后减的抛物线状变化,即消落带下部＜消落带上部＜消落带中部。三者的变化趋势有着高度的相关性,并且都与淹水时间呈负相关。（4）沿水位梯度带植物群落的均匀度指数差异不显著,其他物种多样性指数以及地上生物量差异显著     

嘉陵江流域植被覆盖时空变化特征

归一化植被指数(Normal Difference Vegetation Index,NDVI)能够反映植被的繁茂程度,可用来揭示环境的演化,并且能在全球变化研究中起到“指示器”的作用。目前利用NDVI研究植被变化多集中于陕西、甘肃、新疆等地区,对嘉陵江流域的植被变化趋势及其影响因素研究很少。利用线性相关分析方法分析GIMMS NDVI数据,借助于地理信息系统软件,分析嘉陵江流域植被覆盖的时空变化规律。研究结果如下：（1）嘉陵江流域在1982～2006年植被覆盖呈微弱上升趋势,与我国其它地区一致,但增长速率大小不一样;（2）嘉陵江流域植被覆盖明显优于黄土高原、西北地区,存在明显的空间差异,南部地区小于北部地区;（3）植被变化也存在空间差异,南部地区多呈增加趋势,而北部地区多呈减少趋势;（4）嘉陵江流域植被覆盖及其变化与气候变化和人类活动均有密切关系。基于分析,发现嘉陵江流域在人类活动和气候变化的双重影响下,环境向有利的方向发展。     

SIMULATED RELATIONSHIPS BETWEEN SPECTRAL REFLECTANCE,THERMAL EMISSIONS,AND EVAPOTRANSPIRATION OF A SOYBEAN CANOPY1

ABSTRACT: A canopy reflectance model is incorporated into a routine for simulating water and energy flows in the soil-plant-atmosphere system. The reflectance model is structured tocalculate canopy albedo throughout each simulation period and to determine spectral reflectances at a specified time during the day. Spectral vegetation indices are then calculated from the reflectances and related to the evapotranspiration and thermal response of the canopy. The canopy reflectance model is also used to establish the photo-sytheticaily active radiation load at various depths in the canopy. Stomatal resistances are calculated using these radiation values and integrated to give the minimum canopy resistance. Actual canopy resistance is obtained by adjusting minimum canopy resistance for environmental stresses such as leaf water potential and leaf temperature. Using data for a soybean canopy, canopy evapotranspiration and temperatures are simulated for a range of leaf area index values and compared with the corresponding spectral vegetation indices. The resuits indicate that the normalized difference spectral index has an inverse linear relationship with canopy temperature, concurring with results obtained from satellite observations. The possibility of using a spectral vegetation index and thermal observations together to parameterize surface moisture availability for evapotranspiration is considered.     

A PRECIPITATION ESTIMATION TECHNIQUE FOR DEVELOPING ISOHYETS IN AN ARID AREA USING VEGETATION AND TOPOGRAPHIC PARAMETERS1

A technique is presented for developing an isohyet map for the Hualapai Valley, a closed hydrologic basin of about 315 square miles in the northwestern Great Basin in Nevada. In this basin there is practically no climatic data, and in the northwest Great Basin there are too few stations for determination of rainfall on a detailed basis. Using a vegetational typing to represent a range in elevation and precipitation, an initial mean annual rainfall is determined for selected points on a grid pattern. This rainfall is then modified by using topographic parameters of slope, orientation, exposure, and rainfall shadow effect. The resulting point determinations of mean annual rainfall are then smoothed using a trend surface analysis, and an isohyetal map is drawn from the smoothed points. The technique provides an estimated accuracy of one inch of mean annual precipitation and one mile of resolution on isohyets.     

SOIL-MOISTURE EFFECTS OF CONVERSION OF SAGEBRUSH COVER TO BUNCHGRASS COVER1

Precipitation, soil moisture, runoff, and vegetation were measured on two, 5- to 10-acre, big sagebrush (Artemisia tridentata) watersheds and two, equally small, beardless bluebunch wheatgrass (Agrophron inerme) watersheds that were converted from big sagebrush in 1967. The watersheds are located near Wolcott, Colorado, at an elevation of 7,200 feet, and are mantled with 2 to 3 feet of silty clay soils. Annual precipitation was about 13.5 inches; about 9 inches occurred as rain or snow from April through October and about 4.5 inches accumulated as a snowpack from November through March. Evapotranspiration was about 2 inches greater in 1968 and 1 inch greater in 1969 from the sagebrush watersheds than from the grass watersheds. With a mature stand of grass in 1970 and 1971 the differences in evapotranspiration were within the range of differences measured during the 3-year calibration period when all four watersheds were sagebrush. Water use was similar in the top 1 foot of soil but slightly more water was used by the grass in the 1- to 2-foot zone and more water being used by the sagebrush below 2 feet. Soil-water potential data indicated that only the big sagebrush used a small amount of water from the fractured shale at depths below 40 inches. Sagebrush used more water in August and September than the grass.