利用1988-2010年青藏高原东北部地区5个站点牧草生育期地面观测数据,分析了近20年代表性牧草返青、开花、黄枯期及生长季的变化趋势,并通过偏相关分析探讨了气温和降水对牧草生育期的关系。结果表明,近20年青藏高原东北部牧草生育期北部推迟南部提前的特征明显。南部的三江源区域返青、开花与黄枯期总体呈显著提前趋势,其中曲麻莱羊茅返青期提前的倾向率达到-4 d/10 a,开花期为-13 d/10 a,黄枯期达到-9 d/10 a,且均通过0.01的显著性检验水平。北部环青海湖区域的海北西北针茅生育期则表现出一定的推迟趋势。生长季长度北部地区延长,而南部除甘德(垂穗披碱草)外均呈明显缩短趋势。近20 a 黄枯期的变化幅度明显大于返青期,使得生长季长度的变化更多地受黄枯期变化的影响。1月和3月气温是影响研究区牧草返青最主要的气候因子,气温增高返青提前。开花期南北差异明显,北部与同期气温呈明显负相关关系,南部则主要与开花前2-3个月的降水量密切相关,降水增多大部地区开花期提前。此外,降水也是各地牧草黄枯的主要影响因子。
英文摘要:
The Qinghai-Tibet Plateau (QTP) is usually regarded as an ideal place to study the response of natural ecosystems to climate change because this mountainous region supports one of the most fragile environments within the global ecosystem. After the QTP experienced a distinct warming in recent decades, scientists have realized that a remarkable variation in vegetation in the QTP could potentially result from climate change. In this paper, the temporal variation of phenology for the alpine Gramineae was analyzed for the dates of the onset of growth in spring, blossoming, and withering from 1988 to 2010 based on the observations from five in-situ sites in the northeastern QTP. Additionally, the relationships between temperature or precipitation and the duration of the growth period for alpine Gramineae were investigated using the stepwise regression and partial correlation analysis. Seasonal trends were found to be advancing significantly in the last20 years in the southern QTP, which includes the Three-Rivers Source Area for the dates of onset, blossoming and withering of grasses. Specifically, the trendsare -4d/10a for onset, -13d/10a for blossoming, and -9 d/10a for withering in the Qumalai fescue grassland, all of which are statistically significant (P< 0.01).Additionally, the Haibei Stipa sareptanavar krylovii grassland, which is in the northern portion of the study area, experienced increasing trends that is totally different with Qumalai for all three phenological events in the last decade. Furthermore, the results revealed significant geographical differences in the observed changes in phonological trends between northern and southern portions of the study area, with a significant advance in the south portion and a weak delay in the northern area for the onset, blossoming and withering of grasses as well as for the overall length of the growing season. The trend in the growing season is similar to that in phenology, with the growing season becoming shorter in the southern area and being extended in the northern area; but the length of the growing season is mainly dominated by the changes of withering dates because the range of phonological change is significantly greater in the withering dates than in the onset dates. Although the onset dates show an advanced trend, which is an advantage in lengthening the growing season, a significant advance of withering dates eliminates the contribution of the earlier onset of the growing season and shortens the overall growing season. The onset dates of alpine grass are strongly related to air temperatures in January and March with negative correlations in the northeastern QTP, while warming air temperatures in January and March lead an advanced onset of growth in grasses. The blossoming dates for the same period in the north have a negative correlation with air temperature, while precipitation with a lead-time of 2 to 3 months is the major factor in southern portion. Moreover, precipitation is an important indicator that influences the withering dates. Precipitation is strongly negatively correlated with withering dates and the previous one to three months of precipitation at Xinhai Station in the northern area, but a weak positive correlation exists between withering dates and precipitation in June with a 2- monthlead time at Gande and Henan stations in the southern area. This indicates that the withering dates will be delayed for a few days when the averaged precipitation occurs in June in the southern area and the significant advance in the withering dates will occur with the above averaged precipitation in May in the northern part of the northeastern QTP.