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1.
Evidence for global warming is inferred from spring advances in first-flowering in plants. The trend of average first-flowering times per year for the study group shows a significant advance of 2.4 days over a 30-year period. When 11 species that exhibit later first-flowering times are excluded from the data set, the remaining 89 show a significant advance of 4.5 days. Significant trends for earlier-flowering species range from -3.2 to -46 days, while those for later-flowering species range from +3.1 to +10.4 days. Advances of first-flowering in these 89 species are directly correlated with local increase in minimum temperature (T min).  相似文献
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内蒙古地区羊草草原植被对温度变化的动态响应   总被引:11,自引:1,他引:10       下载免费PDF全文
 1981~1994年连续14年内蒙古羊草草原温度随时间变化结果显示,该区域温度变化具有不对称性,冬季最低均温升高明显,而最高温及平均温度无明显增加趋势。羊草草原气候的变化主要表现在冬季最低温的增加,而不是平均温度的增加。羊草群落的结构和功能对冬季最低均温变化的响应研究表明,随着冬季最低均温的升高,阿尔泰狗哇花(Heteropappus altaicus)和冰草(Agropyron michnoi)的重要值及地上初级生产力将明显增加,而寸草苔(Cares duriuscula)则呈下降趋势,作为群落主要优势种的羊草(Leymus chinensis)和大针茅(Stipa grandis)及其它优势植物对冬季最低均温变化反应不明显。同时,群落的生物多样性指数(Simpson指数、Shannon-Wiener指数)、物种饱和度及地上初级生产力对冬季最低均温也均无显著相关,14年间冬季最低均温的变化并没有对群落的结构和功能产生明显影响。然而,因寸草苔和冰草等少数优势植物对冬季最低均温变化反应的敏感,温度变化的幅度增加或时间延续很可能造成少数优势种在群落中地位的改变,进而可能导致羊草群落结构和功能的变化。这表明在进行气候变化的模拟和模型研究时,不能仅简单地考虑平均温度增加的情况,而应确定主导影响因子,从而了解草原生态系统对全球变化的响应,选取适宜的模型参数。  相似文献
3.
气候变暖对内蒙古羊草草原建群种的影响   总被引:9,自引:2,他引:7  
通过对锡林郭勒盟锡林河流域羊草草原地区1981~1994年14年的温度观测和植被调查数据的逐年滑动平均处理,分析该地区气候和植被随时间的动态变化特征.结果表明,内蒙古羊草草原地区的气温在研究期内具有高低温变化不对称的特点,表现为全年最低温升高明显,最高温和平均温升高不明显.羊草草原的建群种羊草和大针茅对气温变化有不同的响应,最优建群种羊草的重要值和地上初级生产力随着最低温的升高有明显的下降趋势,次优建群种大针茅的重要值和地上初级生产力由于种间互补作用而略有升高.可以认为,如果这种趋势继续下去,大针茅有可能代替羊草,成为群落的最优建群种,使得群落的结构和功能发生改变.在研究与模拟羊草草原对温度变化的响应时,研究不同温度因子和年温度不同时段的变化特征,以及不同物种之间的竞争关系,有助于认识单个种群和整个生态系统对全球变化响应的机理.  相似文献
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Fluorescence characteristics and growth of seedling snow gum ( Eucalyptus pauciflora Sieb. ex Spreng.) during autumn and winter were related to variation in radiation and temperature regime in a fragmented forest. Seedlings were planted in four treatments along transects perpendicular to tree island edges to characterize plant responses to microclimates ranging from those of cleared areas to those beneath forest canopies. Three-dimensional mapping of seedling leaf display, in combination with information retrieved from hemispherical photographs about shading from overstory canopies, were used to calculate the intercepted amounts of direct radiation energy for unit area of leaves on clear days (IDRE) . IDRE was highest on the outside, most variable at the edges and lowest well inside the tree islands. Minimum temperature decreased with increasing view of the sky. Photoinhibition, measured as decrease in F v/ F m, was correlated with spatial and seasonal differences in weekly minimum temperature and IDRE . Seedlings in the open and under the most canopy cover, with low variability in IDRE in a scale of weeks, exhibited less variability in photoinhibition than those growing along forest edges. Seedlings in the open tended to be most photoinhibited and grew the most. The combination of increased IDRE with reduced minimum temperatures resulted in persistent and strong photoinhibition as the season progressed. Results are discussed in relation to the potential for seedling establishment following forest fragmentation.  相似文献
8.
The effect of towns on plant phenology, i.e. advancement of spring development compared with a rural environment, via the urban heat island (UHI) phenomenon, has been shown for many towns in many countries. This work combines experimental and observational methodology to provide a better and deeper view of climatic habitat in an urban context with a view to understanding the relationship between plant development and urban climate on the intra-urban scale (by taking into account town structure). A dense network of 17 meteorological stations was set up in Rennes, France, enabling us to identify and quantify climatic changes associated with the UHI. Meanwhile, phenological observations were made during early spring (March and April) in 2005 on Platanus acerifolia and Prunus cerasus to study the relationship between climatic and phenological data. The results show that there is both a climatic gradient and a developmental gradient corresponding to the type of urbanisation in the town of Rennes. The town influences plant phenology by reducing the diurnal temperature range and by increasing the minimum temperature as one approaches the town centre. The influence of ground cover type (plants or buildings) on development is also shown. The developmental phases of preflowering and flowering are influenced to differing extents by climatic variables. The period during which climatic variables are effective before a given developmental phase varies considerably. The preflowering phases are best correlated with the mean of the minimum air temperature for the 15-day period before the observation, whereas flowering appears to be more dependent on the mean of the daily diurnal temperature range for the 8 days preceding the observation.  相似文献
9.
Several North American broad-leaved tree species range from the northern United States at 47°N to moist tropical montane forests in Mexico and Central America at 15–20°N. Along this gradient the average minimum temperatures of the coldest month (T Jan), which characterize annual variation in temperature, increase from –10 to 12°C and tree phenology changes from deciduous to leaf-exchanging or evergreen in the southern range with a year-long growing season. Between 30 and 45°N, the time of bud break is highly correlated with T Jan and bud break can be reliably predicted for the week in which mean minimum temperature rises to 7°C. Temperature-dependent deciduous phenology—and hence the validity of temperature-driven phenology models—terminates in southern North America near 30°N, where T Jan>7°C enables growth of tropical trees and cultivation of frost-sensitive citrus fruits. In tropical climates most temperate broad-leaved species exchange old for new leaves within a few weeks in January-February, i.e., their phenology becomes similar to that of tropical leaf-exchanging species. Leaf buds of the southern ecotypes of these temperate species are therefore not winter-dormant and have no chilling requirement. As in many tropical trees, bud break of Celtis, Quercus and Fagus growing in warm climates is induced in early spring by increasing daylength. In tropical climates vegetative phenology is determined mainly by leaf longevity, seasonal variation in water stress and day length. As water stress during the dry season varies widely with soil water storage, climate-driven models cannot predict tree phenology in the tropics and tropical tree phenology does not constitute a useful indicator of global warming.  相似文献
10.
Although using hourly weather data offers the greatest accuracy for estimating growing degree-day values, daily maximum and minimum temperature data are often used to estimate these values by approximating the diurnal temperature trends. This paper presents a new empirical model for estimating the hourly mean temperature. The model describes the diurnal variation using a sine function from the minimum temperature at sunrise until the maximum temperature is reached, another sine function from the maximum temperature until sunset, and a square-root function from then until sunrise the next morning. The model was developed and calibrated using several years of hourly data obtained from five automated weather stations located in California and representing a wide range of climate conditions. The model was tested against an additional data-set at each location. The temperature model gave good results, the root-mean-square error being less than 2.0 °C for most years and locations. The comparison with published models from the literature showed that the model was superior to the other methods. Hourly temperatures from the model were used to calculate degree-day values. A comparison between degree-day estimates determined from the model and those obtained other selected methods is presented. The results showed that the model had the best accuracy in general regardless of the season. Received: 25 October 2000 / Revised: 2 July 2001 / Accepted: 2 July 2001  相似文献
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