升温突变对川西道孚林线川西云杉和鳞皮冷杉生长的影响

高山林线作为理想的全球气候变化监测器,是研究植被与气候变化关系的重要场所。利用川西道孚县高山林线川西云杉（Picea likiangensis var.balfouriana）和鳞皮冷杉（Abies squamata）的年轮宽度资料,基于树木年代学的方法,构建差值年表并通过升温突变前后（1995年前后）年轮指数与气候要素的相关分析,探讨了该区林线主要针叶树种的年轮响应变化,为研究青藏高原地区树木与气候响应关系提供研究基础。结果表明：（1）年尺度上,1995年气温突变前后川西云杉和鳞皮冷杉年轮指数和生长弹性时间变化趋势均不显著,没有发生显著的响应分歧现象。（2）月尺度上,升温突变前川西云杉年轮指数与前一年11月月均最高温、5-7月月均温、6月月均最高温、7月月均最低温呈显著正相关;鳞皮冷杉则与前一年11月月均温、11月月均最高温和12月月均温呈显著正相关;表明升温突变前林线树木生长分别受夏季和冬季温度控制;升温突变后川西云杉年轮指数与前一年11月月均温呈显著负相关,和当年2月降水量及7月月均最低温呈显著正相关;而鳞皮冷杉则与当年5月月均温和5月月均最低温呈显著负相关,与5月降水的正相关性达到最大;表明升温突变后林线川西云杉生长依然受夏季温度控制,而鳞皮冷杉生长则受到春季干旱胁迫的影响。未来气候若随着升温出现干暖化,则林线鳞皮冷杉可能会发生明显的响应分歧现象。     

Dendrochronology in Coniferous forests around Lake Rara,West Nepal

In two forest stands, one domonated byAbies spectabilis, and the other byPinus wallichiana-Picea smithiana, 198 cores were taken from 105 conifers in May 1983 and the annual ring widths were measured. The annual ring widths usually had significant similarities between cores taken from the same tree and with cores taken from different trees. these similarities increased with tree size. The climatic change affected the large trees more strongly than it did the small trees. Micro environmental changes, such as canopy gap affected the small trees more strongly. Annual ring widths were also correlated with the annual precipitations at Jumla 30 km south of the plots for a recent 20 year period. A multiple regression analysis between ring width and seasonal precipitation showed that the growth ofA. spectabilis was correlated primarily with the rain from May to August and secondarily with that from September to December in the previous year.     

大兴安岭林区南、北部天然樟子松生长对气候变化的响应差异

利用树木年代学方法,建立大兴安岭林区南、北部樟子松(Pinus sylvestris var.mongolica)年轮宽度年表,探讨樟子松径向生长对气候变化的响应差异。结果表明,南部(阿尔山、海拉尔)树轮宽度主要与当年4—9月的平均标准化降水蒸散指数SPEI(Standardized Precipitation Evapotranspiration Index)极显著正相关(r=0.639,P0.01),而北部(漠河、塔河)树轮宽度主要与同时期的平均最低温极显著正相关(r=0.488,P0.01)。说明南部樟子松径向生长主要受当年4—9月的水分限制,北部主要受同期平均最低温调控。两个地区树木生长对降水的响应一致,对当年4—9月(6月除外)的温度响应相反。近几十年来随着温度显著升高(P0.01),南部树木生长对4—9月平均最高温的负响应不断增强,而北部树木对同时段平均最低温的正响应更加明显。同时,南部樟子松生长量快速下降(r=0.612,P0.001),而北部生长量显著增加(r=0.474,P0.001)。研究发现,高温加剧干旱胁迫是南部樟子松生长量下降的主要原因,而北部樟子松生长量增加是受到4—9月平均最低温和降水量的相互作用。如果持续变暖,未来樟子松分布区可能北移。     

川西米亚罗林区主要树木生长对气候响应的差异

为分析青藏高原东缘半湿润区不同树种树木生长对气候变化的响应规律,于川西米亚罗林区海拔3000 m左右(低海拔)采集铁杉、岷江冷杉、紫果云杉,海拔4000 m左右林线位置(高海拔)采集岷江冷杉、四川红杉,共计182棵树木年轮样芯,建立了不同树种的树轮宽度年表,对不同树种的年轮指数与各月气候因子进行相关分析.结果表明： 在低海拔处,树木生长与4、5月气温呈负相关,与4、5月降雨呈正相关,受到春季干旱胁迫的影响;但树种之间存在显著差异： 铁杉的生长受春季干旱胁迫影响最严重,岷江冷杉次之,紫果云杉所受影响很小.在高海拔处,树木生长主要受生长季温度的影响,岷江冷杉年轮指数与当年2、7月最低气温呈显著正相关,与上一年10月最高气温亦呈正相关;四川红杉年轮指数与5月最高气温呈显著正相关,但与2月均温、3月最低气温呈显著负相关.近几十年青藏高原东北缘气候有干暖化趋势,如果这种趋势持续发生,低海拔紫果云杉长势将超过铁杉和岷江冷杉;高海拔处的升温更有利于岷江冷杉的生长.     

Climate response of Picea schrenkiana based on tree-ring width and maximum density

The effect of global warming on alpine forests is complex. It is crucial, therefore, to investigate the effects of climate change on the radial growth of trees at different altitudes. The tree growth–climate relationship remains poorly understood at large spatial scales in the Tianshan Mountains, China. Schrenk spruce (P. schrenkiana) is a unique tree species to this area. In this study, we collected tree-ring width and maximum density data from nine plots along an altitudinal gradient. Results showed that altitude affected both tree-ring width and maximum density. At high altitudes, tree-ring width was positively correlated with temperature in February of the current year. Tree-ring width was also positively correlated with precipitation in July of the previous year, and January and July of the current year, and negatively correlated with the monthly diurnal temperature range (DTR). At low altitudes, tree-ring width was negatively correlated with temperature in the early growing season and the growing season. Tree-ring width was positively correlated with precipitation in June and September of the previous year, and May of the current year. The tree-ring maximum density was positively correlated with temperature and the DTR of the growing season, and negatively correlated with precipitation in winter and growing season. Moving correlation analysis showed that the positive response of tree-ring width to precipitation in the growing season was enhanced over time at high altitudes. In the low-altitude trees, the negative response of tree-ring width to temperature in the growing season was reduced, while the positive response to precipitation in the growing season was enhanced. The positive response relationship between tree-ring maximum density and the temperature in July weakened over time. At low altitudes, the negative response of tree-ring maximum density to winter precipitation was strengthened, and a stable negative response to July precipitation was observed. As the climate becomes wetter and warmer in the Tianshan Mountains, our results suggest that the radial growth of trees may benefit at elevations above 2400 m a.s.l. There was no obvious elevation limit for the increase in tree-ring maximum density. These findings provide a basis for sustainable forest management under global climate change.     

Responses of ring widths and maximum densities of Larix gmelinii to climate on contrasting north- and south-facing slopes in central Siberia

An analysis was performed of the climatic responses of the radial growth of Larix gmelinii (Rupr.) Rupr. at two sites—both of which included contrasting north- and south-facing slopes—in Tura, central Siberia, with the development of ring width and maximum-density chronologies for each slope. Both residual and standard chronologies of ring widths were positively correlated with temperature from late May until mid June on all four slopes. By contrast, standard chronologies of ring widths were negatively correlated with precipitation during the winter (from October to April) and in May on the north-facing slope at site 1 and on the south-facing slope at site 2 respectively. The negative correlations with precipitation during the winter and in May on some of the slopes suggested that delayed snowmelt in early spring might inhibit the radial growth of L. gmelinii, and the effects of snow are likely to vary with topography. Both residual and standard chronologies of maximum densities were positively correlated with temperature in early July on all four slopes. Maximum densities were also positively correlated with precipitation during summer of the previous year on all the slopes. These suggest that no major differences exist in terms of responses of maximum density to climatic factors between the north- and south-facing slopes.     

Gradual expansion of moisture sensitive Abies spectabilis forest in the Trans-Himalayan zone of central Nepal associated with climate change

Population structure and tree recruitment dynamics in the natural treeline ecotone of high mountains are strong indicators of vegetation responses to climate. Here, we examined recruitment dynamics of Abies spectabilis across the treeline ecotone (3439–3638 m asl) of Chimang Lekh of Annapurna Conservation Area in the Trans-Himalayan zone of central Nepal. Dendrochronological techniques were used to establish stand age structure by ring counts of adults, and by terminal bud scar count for seedlings and saplings. The results showed abundant seedling recruitment, higher regenerative inertia and colonization with a consistent range shift of the A. spectabilis treeline. The upward expansion of this sub-alpine treeline was found to be driven by a strong dependence of seedling recruitment and radial growth on snowmelt and precipitation as temperatures rise. The radial growth of A. spectabilis at the alpine timberline ecotone (ATE) and closed timberline forest (CTF) showed sensitivity to spring season (March–May) climate. Tree ring indices of CTF showed a strong positive correlation with spring and annual precipitation, and a significant negative correlation with spring and annual temperature, however, moisture sensitivity was less strong at ATE than CTF.     

秦岭中西部油松径向生长对气候因子的响应差异研究

在气候变暖背景下,树木径向生长对气候因子的响应会随区域干湿变化而有所差异。秦岭属于气候敏感区和生态脆弱区,南北气候特征差异明显,分析气候变化背景下树木径向生长对气候因子及干旱事件的响应,对准确预测未来气候变化对树木生长的影响至关重要。为探究该地区不同干湿环境下油松对气候因子及干旱事件响应的特点及差异,共采集秦岭中西部南北坡共4个样点的油松树轮样芯,利用树木年轮生态学的方法,分析各地油松年表与气候因子之间的关系,通过计算抵抗力、恢复力、恢复弹力等指标探究树木径向生长对干旱事件的应对能力,结果表明：1)在西部和北坡的3个样点,油松径向生长主要与前一年7—9月、当年5—7月的气温呈显著负相关,与当年5月降水呈显著正相关,在中部南坡油松径向生长主要与当年2—4月、9月气温呈显著正相关,与当年4月降水呈显著负相关;2)生长季气温升高所引发的水分亏缺,是研究区西部和北坡油松径向生长受限制的主要原因,且中部南坡油松生长受气温和干旱因子的制约要明显弱于其它3个样点;3)西部北坡油松对干旱的抵抗能力、恢复能力及恢复弹力均弱于西部南坡及中部北坡油松。在未来对研究区树木的管理与保护工作中,应更加关注西部北坡...     

Climatic factors affecting the tree-ring width of <Emphasis Type="Italic">Betula ermanii</Emphasis> at the timberline on Mount Norikura,central Japan

Tree-ring-width chronology of Betula ermanii was developed at the timberline (2,400 m a.s.l.) on Mount Norikura in central Japan, and climatic factors affecting the tree-ring width of B. ermanii were examined. Three monthly climatic data (mean temperature, insolation duration, and sum of precipitation) were used for the analysis. The tree-ring width of B. ermanii was negatively correlated with the December and January temperatures and with the January precipitation prior to the growth. However, why high temperatures and heavy snow in winter had negative effects on the growth of B. ermanii is unknown. The tree-ring width was positively correlated with summer temperatures during June–August of the current year. The tree-ring width was also positively correlated with the insolation duration in July of the current year. In contrast, the tree-ring width was negatively correlated with summer precipitation during July–September of the current year. However, these negative correlations of summer precipitation do not seem to be independent of temperature and insolation duration, i.e., substantial precipitation reduces the insolation duration and temperature. Therefore, it is suggested that significant insolation duration and high temperature due to less precipitation in summer of the current year increase the radial growth of B. ermanii at the timberline. The results were also compared with those of our previous study conducted at the lower altitudinal limit of B. ermanii (approximately 1,600 m a.s.l.) on Mount Norikura. This study suggests that the climatic factors that increase the radial growth of B. ermanii differ between its upper and lower altitudinal limits.     

区域气温和降水对关帝山不同海拔华北落叶松径向生长的耦合效应

为揭示区域气温和降水在不同海拔对山地林区林木径向生长的耦合效应,在关帝山林区孝文林场和庞泉沟国家自然保护区外围4个不同海拔选取立地条件相似的华北落叶松(Larix principis-rupprechtii Mayr.)人工林设置调查样地,采集典型样木样芯,采用建立年表的方法,获取年轮宽度指数,结合区域气温和降水进行相关性分析和单年分析。结果表明:在研究地区4个海拔上华北落叶松的径向生长均与区域气温和降水量有密切关系,但不同海拔响应机制不同;在1600 m海拔处,年轮宽度指数与当年4月气温极显著负相关,与当年9月降水量显著正相关;在1800 m海拔处,年轮宽度指数与上年6月气温显著负相关,降水量显著正相关;在2000 m海拔处,年轮宽度指数与当年9月气温和当年3月降水量显著负相关;在海拔2200 m处,年轮宽度指数与上年8月气温显著正相关,降水量显著负相关;随着海拔的升高,气温逐渐降低,降水量增加,两者对华北落叶松径向生长的耦合效应也发生变化,当海拔到达2000 m时,生长季降水量的增加使耦合效应关系发生转换。     

玉龙雪山不同针叶树种树轮宽度年表特征及其与气候因子的关系北大核心CSCD

为揭示滇西北高原树木径向生长与气候关系的规律,该研究分别在玉龙雪山采集高山松(Pinus densata)、云南松(Pinus yunnanensis)和云南铁杉(Tsuga dumosa)年轮样本,建立3个树种树轮宽度差值年表,将年轮指数与气候因子进行响应分析和冗余分析,以明确影响玉龙雪山树木径向生长的主要气候因子,为该区域森林生态系统的管理保护提供依据,并为探讨气候变化背景下滇西北森林动态提供依据。结果表明:(1)所建立的3个树种树轮宽度差值年表具有较少的低频变化,且离散程度较低、逐年变化共性较高,可代表采样点树木的年轮特征;高山松、云南松和云南铁杉差值年表的平均敏感度依次分别为0.21、0.22和0.17,样本总体代表性分别为0.96、0.96和0.94,均高于0.85的阈值,说明年表中信息具有代表性。(2)响应分析结果显示,高山松径向生长与当年2月的降水量呈显著正相关关系;云南松径向生长与当年5月的平均气温和最高温呈显著负相关关系,与当年10月平均气温呈显著正相关关系;云南铁杉径向生长与当年1月和5月的降水、当年10月相对湿度均呈显著正相关关系,与当年5月最高气温呈显著负相关关系。(3)冗余分析结果显示,当年1月降水、2月降水、5月干旱指数对3个树种均具有促进作用,且5月干旱指数的显著相关性最强;当年10月降水的增加有利于高山松和云南铁杉的径向生长,但对云南松径向生长具有抑制作用。研究认为,当年冬季降水、5月湿润条件以及10月降水是影响玉龙雪山3个树种径向生长的重要环境因子;若干暖化趋势加剧,将不利于滇西北高原3个树种的生长,从而影响区域森林生态系统结构和功能。     

帽儿山地区兴安落叶松人工林树木年轮气候学研究

通过帽儿山兴安落叶松（Larix gmelinii）人工林树木年轮样本和气象资料,对该地区兴安落叶松进行了树木年轮气候学研究,结果表明：过去50年年均温度上升达到了显著水平（p<0.05）,平均温度每10年约上升0.4℃,年平均最高气温每10年约上升0.3℃,年平均最低气温每10年约上升0.5℃,但是年降水量随着年份变化不显著（p>0.05）。从月均温度来看,所有月份均出现明显上升趋势,其中冬季2月份温度上升最为明显,达到0.9~1℃/10年,而夏季（6~8月）上升的较小,达到0.2~0.7℃/10年;多数月份降雨量随年龄变化不显著（p>0.05）。在这一气候变暖过程中,早材及总年轮宽度生长随着夏季（6~7月）温度上升而下降,春季(5月)温度的升高而升高,晚材随着秋季（9月）温度上升而增加,导致在年水平上,年轮生长随着年均温的变化不显著（p>0.05）。降雨量在未来气候变化过程中,没有稳定的变化趋势,但是对年轮影响明显,在年水平上,早材与年轮的生长均受降水量的影响较大(p<0.05)。如果未来东北地区气候变暖趋势明显,而降水量变化不明显,春季和秋季温度升高导致的年轮生长增加会被夏季过高温度抑制年轮生长所抵消,因此,落叶松林径向生长受到的影响可能不大。     

天山中西段不同地区雪岭云杉径向生长对气候变暖的响应差异

为研究乌苏和石河子地区雪岭云杉（Picea schrenkiana）径向生长对气候变暖的响应差异状况,利用响应函数及滑动相关分析等树轮气候学方法,研究了2个地区森林下限雪岭云杉径向生长与气候因子的响应关系。结果表明：乌苏和石河子地区雪岭云杉生长均与生长季的气候因子呈显著相关关系。但乌苏和石河子地区雪岭云杉生长对当地气候因子的响应也存在差异,乌苏地区雪岭云杉径向生长与上一年7、9月平均气温呈显著负相关,与当年8月降水、上一年9月及当年8月平均相对湿度和上一年7~10月的scPDSI呈显著正相关。石河子地区雪岭云杉径向生长与当年1月平均湿度和当年1、2月的scPDSI呈显著正相关。此外,乌苏地区树轮宽度指数具有与温度升高而下降的“分离现象”,而石河子地区树轮宽度指数具有与温度升高相一致的趋势。升温导致的水分胁迫是造成乌苏地区雪岭云杉径向生长与温度变化趋势相反的重要因素。生长季的温度和降水的增加对石河子地区雪岭云杉径向生长有促进作用。乌苏地区雪岭云杉径向生长对5~7月平均气温和降水量变化敏感性上升;石河子地区雪岭云杉径向生长对5~7月降水量变化敏感性上升,而对5~7月平均气温变化敏感性下降。结果显示,气候变化的区域差异是造成乌苏和石河子地区雪岭云杉径向生长趋势不同以及各年表序列对温度和降水变化敏感性变化的主要气候因素。     

千山油松年轮宽度年表的建立及其与气候的关系

以千山油松为样本,建立了年轮宽度标准化年表、差值年表和自回归年表.结果表明,油松年轮宽度与5—7和9—11月温度指标的相关性较高,且与低温呈正相关,其中与7月的极端最低温、9月的平均最低温显著相关.3种年表与上年12月和当年1月的极端最低温、1月的平均最低温呈显著相关,且其与全年、上年12月、当年5月的降水量显著相关,与4月的降水量极显著相关.油松与水汽压、相对湿度的月和年指标均有较强的相关性.蒸发的年指标和绝大部分月指标对油松生长具有负效应,其中4—7月最明显.油松年表的窄化突变佐证了1800年以来的30次主要的旱灾年历史记录.千山油松的生长受全球或半球尺度气候变化的影响.年表与太阳活动存在显著的11、23和50年左右的公共周期,与地磁指标在10、20和45年左右存在共同的周期变化.     

Treeline dynamics in relation to climatic variability in the central Tianshan Mountains, northwestern China

Aim Climate variability may be an important mediating agent of ecosystem dynamics in cold, arid regions such as the central Tianshan Mountains, north‐western China. Tree‐ring chronologies and the age structure of a Schrenk spruce (Picea schrenkiana) forest were developed to examine treeline dynamics in recent decades in relation to climatic variability. Of particular interest was whether tree‐ring growth and population recruitment patterns responded similarly to climate warming. Location The study was conducted in eight stands that ranged from 2500 m to 2750 m a.s.l. near the treeline in the Tianchi Nature Reserve (43°45′?43°59′ N, 88°00′?88°20′ E) in the central Xinjiang Uygur Autonomous Region, northwestern China. Methods Tree‐ring cores were collected and used to develop tree‐ring chronologies. The age of sampled trees was determined from basal cores sampled as close as possible to the ground. Population age structure and recruitment information were obtained using an age–d.b.h. (diameter at breast height) regression from the sampled cores and the d.b.h. measured on all trees in the plots. Ring‐width chronologies and tree age structure were both used to investigate the relationship between treeline dynamics and climate change. Results Comparisons with the climatic records showed that both the radial growth of trees and tree recruitment were influenced positively by temperature and precipitation in the cold high treeline zone, but the patterns of their responses differed. The annual variation in tree rings could be explained largely by the average monthly minimum temperatures during February and August of the current year and by the monthly precipitation of the previous August and January, which had a significant and positive effect on tree radial growth. P. schrenkiana recruitment was influenced mainly by consecutive years of high minimum summer temperatures and high precipitation during spring. Over the last several decades, the treeline did not show an obvious upward shift and new recruitment was rare. Some trees had established at the treeline at least 200 years ago. Recruitment increased until the early 20th century (1910s) but then decreased with poor recruitment over the past several decades (1950–2000). Main conclusions There were strong associations between climatic change and ring‐width patterns, and with recruitments in Schrenk spruce. Average minimum temperatures in February and August, and total precipitation in the previous August and January, had a positive effect on tree‐ring width, and several consecutive years of high minimum summer temperature and spring precipitation was a main factor favouring the establishment of P. schrenkiana following germination within the treeline ecotone. Both dendroclimatology and recruitment analysis were useful and compatible to understand and reconstruct treeline dynamics in the central Tianshan Mountains.     

Comparing Juniperus virginiana tree-ring chronologies from forest edge vs. forest interior positions in the Cedars Natural Area Preserve in Virginia, USA

We created two eastern red cedar master chronologies, one from trees growing along the edge of grassy openings and another from trees growing within the intact forest canopy. Correlation coefficients were calculated between ring width indices from two time periods (1895–1949 and 1950–2001) of the residual chronology and temperature, precipitation, and Palmer Drought Severity Indices (a standardized measure of dryness). The two time periods represented younger and older eastern red cedar. The younger, interior eastern red cedar had significant, positive correlations between ring width index (RWI) and June and November precipitation, March temperature, and Palmer Drought Severity Index (PDSI) from May through December. There were significant, negative correlations between RWI and May, June, and December temperature and May through July PDSI from the previous year. For the older, interior eastern red cedar significant, positive correlations existed between RWI and precipitation from the previous June, October, and December, and PDSI from July. Significant, negative correlations existed between RWI and January precipitation and May temperature. For the edge eastern red cedar within the earlier time segment (1895–1949) there was only one significant dendroclimatic correlation and this was a negative correlation with December temperature. For the edge eastern red cedar within the later time segment (1950–2001) there were significant, positive correlations between RWI and precipitation from June, September, October, and December of the previous year, March precipitation from the current growing season, and PDSI from July. There were significant, negative correlations between RWI and precipitation from January and November, temperature from the previous June, temperature from May and December, and PDSI from June of the previous year. Thus, eastern red cedar from the interior had more significant correlations to climate than trees growing along the edge. This result does not match other studies that have found edge trees to be more responsive to climate than interior trees. Perhaps this difference can be explained by some of the variations in the significant dendroclimatic correlations between the earlier and later time periods. The differences between the two time periods (within a single site) imply that the environmental conditions of trees changed over time. These differences may be a result of tree encroachment into the forest openings which creates a constantly changing environment for the eastern red cedar and results in some of the high variability of dendroclimatic relationships identified in this study. These results imply that trees growing in communities without stable edges, i.e. where the environment around the trees is in a constant state of flux, would be unsuitable for climatic reconstruction because they do not conform to the uniformitarian principle.     

嵩山地区油松人工林树轮宽度对气候因子的响应

以河南登封嵩山地区不同坡向的油松人工林为对象,分别建立了跑马岭、峻极峰及区域油松差值年表。结果表明: 跑马岭油松年表的质量高于峻极峰油松年表;跑马岭油松年表和峻极峰油松年表都包含较高的气候信息,都与当年2月平均气温、生长季末期(9—10月)平均气温和平均最高温呈显著正相关,与当年5月的平均最高温呈显著负相关;跑马岭和峻极峰油松径向生长对气候响应有一定的差异,跑马岭油松径向生长主要与3月平均最低温和9月降水量呈显著正相关,而峻极峰与5月降水量和9月平均最低温呈显著正相关;区域油松年表包含了更多的气候信息。利用多元回归分析方法能较好地模拟出油松树轮宽度生长的限制因素是多个月的温度,尤其是当年9月平均气温,这与相关分析结果一致。本研究可以为本地区森林保护和生态建设提供基础服务。     

Abies spectabilis shows stable growth relations to temperature,but changing response to moisture conditions along an elevation gradient in the central Himalaya

A better understanding of growth-climate responses of high-elevation tree species across their distribution range is essential to devise an appropriate forest management and conservation strategies against adverse impacts of climate change. The present study evaluates how radial growth of Himalayan fir (Abies spectabilis D. Don) and its relation to climate varies with elevation in the Manaslu Mountain range in the central Himalaya. We developed tree-ring width chronologies of Himalayan fir from three elevational belts at the species’upper distribution limit (3750−3900 m), in the middle range (3500−3600 m), and at the lower distribution limit (3200−3300 m), and analyzed their associations with climatic factors. Tree growth of Himalayan fir varied synchronously across elevational belts, with recent growth increases observed at all elevations. Across the elevation gradient, radial growth correlated positively (negatively) with temperature (precipitation and standardized precipitation-evapotranspiration index, SPEI-03) during the summer (July to September) season. However, the importance of summer (July to September) temperatures on radial growth decreased with elevation, whereas correlations with winter (previous November to current January) temperatures increased. Correlations with spring precipitation and SPEI-03 changed from positive to negative from low to high elevations. Moving correlation analysis revealed a persistent response of tree growth to May and August temperatures. However, growth response to spring moisture availability has strongly increased in recent decades, indicating that intensified spring drought may reduce growth rates of Himalayan fir at lower elevations. Under sufficient moisture conditions, increasing summer temperature might be beneficial for fir trees growing at all elevations, while trees growing at the upper treeline will take additional benefit from winter warming.     

柴达木盆地东缘青海云杉树轮细胞结构变化特征及其对气候的指示

基于青海柴达木盆地东缘山地青海云杉生长上限的树轮样本,在获取树轮宽度数据的同时,获取了细胞特征指标,包括细胞个数和细胞大小,建立了树轮早材、晚材、整轮的细胞个数标准年表和细胞大小的最大值、最小值年表,并通过与附近茶卡气象站过去31年（1970—2000年）逐月降水量和温度的相关分析和响应函数分析,从细胞尺度探讨了青海云杉生长与外界气候要素的关系.结果表明：早材细胞个数与冬半年（上年10月至当年3月）温度之间呈正相关关系;晚材细胞个数除了与11月和12月最低温度呈显著正相关外,还与生长季中7月和8月平均温度呈显著相关关系;早、晚材细胞个数同时与7月的降水量呈显著负相关.早材细胞个数与5月的降水量呈正相关关系.对于早材最大细胞大小的年表来说,其变化与2月的降水量变化有很好的一致性,而晚材最小细胞的大小与8月降水量的变化同步.细胞个数和细胞大小不仅记录了树轮宽度所记录的温度变化信息,还额外记录了一定的降水信息,说明不同的树木生长指标能够记录不同的气候信息.利用同一地点同一树种不同类型的树轮指标,能够提取多种气候要素的变化信息,这对将来从同一样点的树轮资料中提取更丰富的气候信息以及发掘树轮气候学的潜力具有一定意义.     

Occurrence of Diaphanosoma excisum (Sars) on a sandy beach at Balramgari (Orissa), India

The occurrence of Diaphanosoma excisum (Sars), a freshwater cladoceran, in benthic samples of an intertidal sandy beach is reported. Population density was seasonal. A relatively high density was recorded from June to September (south-west monsoon season) with a maximum (46 ind 10 cm^–2) in September at a depth of 10–15 cm of sediment. A sudden decline occurred during north-east monsoon (October to January), and in the fair season (February to May), the cladocerans disappeared. Mean density varied (P<0.001) with sediment depth and season and showed a contagious dispersion. Abundance was negatively correlated with salinity (r = –0.76) but positively with POC (r =0.79) and mean grain size of the sediment (r = 0.93). The density of D. excisum was highest in fine sand.