长白山东坡不同海拔长白落叶松径向生长对气候变化的响应

为了解高山林线附近树木生长对气候变化的敏感性,选取长白山东坡火山喷发后形成的过渡性植物群落长白落叶松(又称黄花落叶松)(Larix olgensis)林为研究对象,并建立不同海拔高度长白落叶松的3个年轮宽度年表,研究不同生境长白落叶松径向生长对气候变化的响应,并利用冗余分析对不同海拔的年轮指数与气候因子的关系做进一步分析。主要结果如下:(1)高海拔年轮年表的统计特征更显著,比低海拔径向生长对气候因子的响应更加敏感;(2)高海拔径向生长主要受上年生长季前期和生长季气温的限制,尤其是上年6月和8月气温的限制作用,低海拔径向生长主要与降水量有关,受当年9月降水量和当年8月帕尔默干旱指数(PDSI)的共同影响;(3)林线内树木对气候响应的敏感性强于林线外,林线外小生境的异质性及干扰事件频发可能掩盖了树木对气候因子的敏感性,林线下方可能是检验林线处树木生长对气候响应平均状态的最佳位置;(4)不同海拔年轮年表与气候因子的冗余分析与响应函数分析的结果基本一致,进一步证明了冗余分析可以有效地量化树轮指数与气候因子的关系。该研究为全球变暖背景下长白山东坡长白落叶松林的管理及该区域气候重建提供了基础数据。     

长白山红松年轮细胞尺度参数对气候要素的响应

基于长白山低海拔区的红松年轮样本,建立树轮宽度和细胞尺度参数的7个标准年表;选取部分树轮年表与东岗气象站1959-2007年前一年9月到当年9月的月均气温、月均最高气温、月均最低气温、月降水量进行相关分析;并分析1988年气候突变前后红松年轮指数年表与气候要素的关系,结果表明:所建立的7个标准年表中,细胞个数与轮宽年表的相关性最好;降水和气温都是长白山低海拔区红松树木生长的限制因子,但树轮与降水的相关关系略好于气温,主要表现为与前一年9月和当年5、6月降水的相关达显著水平.细胞大小比轮宽能反映出更多气候信息,主要体现在细胞大小年表与当年3月气温和5月降水呈正相关关系,与当年5月气温呈负相关关系;1988年气温发生升高突变后,树轮对气候要素的响应发生了变化,主要表现为细胞大小对气候要素响应的敏感性降低,与气候要素相关的月份有所提前.     

气候变暖背景下不同海拔长白落叶松对气候变化的响应

为研究气候变暖背景下长白山北坡长白落叶松(Larix olgensis)径向生长对气候因子的响应,采集长白山北坡两个海拔(1400和900 m)的树芯,基于树木年代学理论建立了长白落叶松年轮宽度年表,分析了长白落叶松在两个时间段(1959—1993和1994—2009年)与气候因子的关系。结果显示:(1) 1959—2009年经历了一次突变性增温,突变年份为1993年;(2)高海拔长白落叶松与生长季前的平均气温和平均最高温(当年4月)呈显著正相关,与当年9月降水呈显著负相关。而低海拔长白落叶松径向生长主要受当年9月降水的影响;(3)经近十几年的快速升温,长白山落叶松生长对气候因子的响应发生了明显的变化。在突变增温前后,高海拔长白落叶松径向生长与生长季前气温的正相关性明显增强,而与生长季气温的相关性由正转负,与9月降水的负相关性增强。低海拔长白落叶松径向生长与9月降水的相关性减弱,与4月降水的相关性增强;(4) 1993年以后的快速升温使得高海拔长白落叶松生长量(BAI)显著增加,而低海拔长白落叶松生长的增长幅度不明显。因此,突变增温促进了高海拔长白落叶松的生长,而对低海拔长白落叶松的生长没有较大的影响。可以预测,若气候持续变暖,长白山落叶松的分布范围会逐渐扩大。     

长白山北坡不同海拔红松径向生长-气候因子关系对气温突变的响应

树木径向生长受复杂环境的影响。为预测气候变化背景下未来红松(Pinus koraiensis)径向生长动态变化,在长白山北坡采集3个海拔梯度(745、1134、1280 m)红松树轮样芯,运用树木年轮学研究方法,分析不同海拔红松径向生长-气候因子关系对气温突变的响应差异。结果表明:(1)通过对采样点附近气象站气温数据的M-K检验发现,年均温在1987年发生显著突变;(2)低海拔红松径向生长主要受当年生长季6—7月降水的影响,中、高海拔红松径向生长主要受当年7月平均最低气温的影响;(3)气温突变以后,低海拔红松径向生长-气候因子关系较为稳定,中海拔红松径向生长对前一年11月降水量的响应关系发生显著改变,高海拔红松径向生长对当年5月降水量的响应关系发生显著改变。因此,气温突变背景下,低海拔红松树轮年表更适用于区域气候重建等研究。同时随着气温持续升高,低海拔红松径向生长可能呈现下降趋势,中、高海拔红松径向生长可能呈现先增加后下降的趋势。     

天山东部不同海拔西伯利亚落叶松对气候变暖的响应分析

利用树木年轮气候学方法,探讨了在气候变暖情景下,天山东部上中下限西伯利亚落叶松(Larix sibirica)树木径向生长与气候因子之间的响应关系,并利用冗余分析对其关系进行了验证。结果表明:不同海拔的差值年表(RES)要比标准年表(STD)的特征参数大,具有更高的信噪比和平均敏感度,含有较多的环境信息且更能代表树木总体变化;海拔2 160 m处的年表(L1)在快速升温(1985年)后,树木年轮宽度与降水和温度的相关性明显减弱;海拔2 430 m处的年表(L2)在两个时段内与降水和温度的关系均较弱;海拔2 700 m处的年表(L3)在1985~2013年时段内对降水和气温的正响应均增强。树木径向生长对单月气候因子的响应在前一年11、12月份显著性更高,当年6、7月份气温与树轮宽度指数具有更高的相关性。气候变暖使树木径向生长不断减小的特征在低海拔地区表现更为明显。上中下限西伯利亚落叶松对气温升高的敏感性降低。高海拔地区西伯利亚落叶松的径向生长主要受温度的影响,而中低海拔地区主要受降水与温度的共同影响。     

玉龙雪山不同海拔丽江云杉径向生长对气候变异的响应

为研究滇西北高原树木径向生长与气候关系随海拔的变化规律,分别在玉龙雪山低、中、高海拔采集丽江云杉(Picea likiangensis)年轮样本,建立了不同海拔丽江云杉树轮宽度残差年表,将年轮指数与气候因子进行响应分析、冗余分析以及滑动响应分析。结果表明:玉龙雪山丽江云杉径向生长受气温和降水共同影响,但不同海拔径向生长响应模式存在差异。其中当年1–3月降水与不同海拔丽江云杉径向生长均呈显著正相关关系;当年生长季后期降水与中、低海拔树木生长呈显著负相关关系,与高海拔树木生长呈显著正相关关系;中、低海拔树木生长还受当年春季干旱胁迫;而当年7月气温升高促进高海拔丽江云杉生长。冗余分析与响应分析结果基本一致,说明冗余分析能够有效量化树轮宽度指数与气候因子的关系。滑动响应分析显示气温和降水在小时间尺度上的变化也会影响树木生长。结合不同海拔丽江云杉生长对气候因子的响应模式及未来气候预测,玉龙雪山高海拔丽江云杉生长将得到加强,而中、低海拔丽江云杉生长则表现出不确定性。     

Radial growth responses of Picea likiangensis to climate variabilities at different altitudes in Yulong Snow Mountain,southwest China

为研究滇西北高原树木径向生长与气候关系随海拔的变化规律, 分别在玉龙雪山低、中、高海拔采集丽江云杉(Picea likiangensis)年轮样本, 建立了不同海拔丽江云杉树轮宽度残差年表, 将年轮指数与气候因子进行响应分析、冗余分析以及滑动响应分析。结果表明: 玉龙雪山丽江云杉径向生长受气温和降水共同影响, 但不同海拔径向生长响应模式存在差异。其中当年1-3月降水与不同海拔丽江云杉径向生长均呈显著正相关关系; 当年生长季后期降水与中、低海拔树木生长呈显著负相关关系, 与高海拔树木生长呈显著正相关关系; 中、低海拔树木生长还受当年春季干旱胁迫; 而当年7月气温升高促进高海拔丽江云杉生长。冗余分析与响应分析结果基本一致, 说明冗余分析能够有效量化树轮宽度指数与气候因子的关系。滑动响应分析显示气温和降水在小时间尺度上的变化也会影响树木生长。结合不同海拔丽江云杉生长对气候因子的响应模式及未来气候预测, 玉龙雪山高海拔丽江云杉生长将得到加强, 而中、低海拔丽江云杉生长则表现出不确定性。     

芦芽山华北落叶松(Larix principis-rupprechtii)树轮宽度年表对气候因子的响应

在芦芽山地区采集3个不同海拔的华北落叶松(Larix principis-rupprechtii),在传统去趋势的基础上,采用"signal-free"方法对拟合曲线进行修正,避免了中等频率的气候信息引起的拟合偏差,最终建立3个不同海拔树轮宽度标准年表(STD)。同时以10a为界对上述年表进行滤波处理,得到3个低频年表。年表特征值表明,随着海拔升高,年轮平均轮宽变窄,敏感性和高频信息增强,低频信息减弱,这可能与逐渐恶劣的生境有关。中、低海拔年表的低频信息更一致,中、高海拔的高频信息更接近,而高、低海拔无论是标准年表还是高频、低频年表相似性均较差。树轮气候响应分析显示,低海拔STD年表与5月最低温负相关最为显著,STD和低频年表均与5、6月份土壤温度显著负相关,说明生境暖干,树木主要受生长季的干旱胁迫;中海拔STD年表与当年5月最高温正相关最为显著,STD和低频年表与土壤温度相关均不显著,说明生境逐渐变得冷湿,生长季的低温成为树木生长的限制因子;高海拔STD年表与气象要素相关不显著,低频年表与当年4月土壤温度正相关,说明高海拔最为冷湿,并有季节性冻土分布,生长季的土壤低温成为树木生长的限制因子。因此,全球变暖的趋势将更有利于高海拔树木的生长,而低海拔树木的干旱胁迫进一步加剧。     

芦芽山阳坡不同海拔华北落叶松径向生长对气候变化的响应

为研究树木生长对气候变化的响应状况,选取芦芽山阳坡的3个海拔高度建立了华北落叶松(Larix principis-rupprechtii)的树轮宽度年表。年表的统计参数表明,3条年表均为研究气候信息的可靠资料。结果表明,芦芽山阳坡华北落叶松的径向生长和生长与气候的关系均具有海拔差异,中海拔(2440 m)和高海拔(2540 m)的华北落叶松具有相似年际生长变化,而二者均与低海拔(2330 m)华北落叶松的年际生长不同。低海拔华北落叶松的生长与4月平均气温和上一年11月降水量显著负相关,而中海拔和高海拔的生长均与上一年10月平均气温和6月降水量显著负相关。通过年表与气候因子之间的滑动相关分析发现,3个海拔高度华北落叶松生长与气候因子的关系均不稳定,生长与气温条件之间的显著相关关系是随着气温升高而出现的。气温的升高引起了华北落叶松生长与气温因子关系的海拔差异,以及径向生长的海拔差异。这一结果对于气候变化对植被垂直梯度影响的研究具有一定参考价值。     

不同去趋势方法的新疆东天山高低海拔雪岭云杉树轮宽度年表对气候的响应

利用新疆东天山高低海拔雪岭云杉(Picea schrenkiana Fisch.et Mey.)年轮样本,采用样条函数法、负指数函数法和区域曲线法3种去趋势方法研制树轮宽度标准化年表,通过分析不同去趋势方法的新疆东天山高低海拔云杉树轮宽度标准化年表特征、年表与气候响应的关系和年表间在不同频域互相关,及其与其它资料对比发现:(1)3种去趋势法对东天山年表质量影响较小,低海拔树轮年表含有更多可靠的气候变化信息。(2)高海拔的雪岭云杉树木径向生长与6—9月平均气温均呈显著正相关,其中标准化树轮年表与7月平均气温相关系数达0.553(P0.01,n=58),夏季温度可能是东天山高海拔雪岭云杉径向生长的主要限制因子;低海拔雪岭云杉树木径向生长与春季降水显著正相关,同时与春季平均气温显著负相关,春季高温和缺水共同作用的春旱可能是影响低海拔雪岭云杉径向生长的主导因子,且负指数函数年表对气候响应更敏感。(3)区域曲线法能够保留树轮标准化年表中更多低频信息,但优势不明显。高低海拔标准化年表在低频域相关系数较大,并和历史干旱事件有很好的对应。在东天山高低海拔雪岭云杉的去趋势方法研究中,负指数函数法比样条函数法和区域曲线法更适合。     

Variability of climate–growth relationships along an elevation gradient in the Changbai Mountain, northeastern China

In order to explore climate–growth relationships at different elevations, tree-ring width chronologies of larch (Larix olgensis) were developed from three sampling sites on the northern slope of the Changbai Mountain, northeastern China. There were no consistent trends in statistical characteristics of the tree-ring chronologies along the elevation gradient, since trees in the forest interior had a complacent growth pattern. Monthly mean temperature and monthly total precipitation were used for the analysis. Correlation analysis indicated that temperatures in winter had negative correlations with tree growth (previous November, December and current March for the low-, mid- and high-elevation sites, respectively). The correlations between tree growth and June temperature varied from weakly negative at low elevations to significantly positive at high elevations. Precipitation in June of the growth year had negative relationship with the high-elevation chronology. However, high precipitation was associated with low temperature in early growing season, further supporting that temperature is a growth-limiting factor at high elevations. Our results suggest that along the elevation gradient, L. olgensis may respond in different ways to local climate change.     

Different trends and divergent responses to climate factors in the radial growth of Abies georgei along elevations in the central Hengduan Mountains

Climate change has been unprecedented in the last half-century. Tree growth dynamics and responses to climate warming at different elevations vary by study area due to regional diversity in site-specific climatic conditions in the central Hengduan Mountains. A. georgei is the dominant species in high-elevation montane forests in the central Hengduan Mountains. To study the response of A. georgei radial growth to climate and identify tree growth trends at different elevations, tree-ring width chronologies at four elevations across the subalpine A. georgei forest belt were built and growth-climate relationships were analyzed. The primary findings of this study were as follows: (1) radial growth rates of A. georgei decreased with elevation; (2) warming alleviated the limitation of low temperatures and abundant precipitation on tree radial growth at the highest sampling site; and (3) unlike at other elevations, the trend of trees basal area increment (BAI) at the lowest sampling site showed a significant decline over the past 20 years. This suggests the presence of an elevational inflection point, likely between 3800 m and 4000 m, where tree growth trends diverge. These results confirmed that A. georgei at higher elevation in the central Hengduan Mountains currently benefits from higher temperatures. However, the effects of drought on A. georgei at lower elevations would cause radial growth to decrease with climate warming. Therefore, it is critical to establish effective management strategies based on how A. georgei responds to climate change at various elevations.     

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.     

Anomalous temperature–growth response of Abies faxoniana to sustained freezing stress along elevational gradients in China’s Western Sichuan Province

A network of ten Faxon fir tree-ring width chronologies was constructed from sites ranging in elevation from 3,000 to 3,450 m in the Wolong Natural Reserve in Western Sichuan Province, China. The site chronologies display significant inter-site correlations (mean R = 0.647, p < 0.001) and the first principal component (PC1) accounts for 68.32 % of the total variation of the chronologies, implying a high degree of similarity in growth variation among the elevation gradients. Correlation analysis using monthly climate data indicates that the radial growth response of Faxon fir along the elevation gradients is markedly similar to common climatic signals, such as sunshine duration (positive) and cloud cover (negative), from January to March. Thus, it appears that winter freezing stress, which is caused by low solar radiation and high cloudiness, is the major environmental factor regulating the growth of trees across the elevational gradients. In addition, the site chronologies have no elevation-dependent growth responses to temperature or precipitation. Irrespective of the elevational differences of the sample sites, an anomalous reduction in radial growth occurred consistently since the 1960s, diverging from the instrumental temperature records since the 1990s. The cause of this divergence may be ascribed to the recent accelerated winter freezing stress and its role in controlling radial growth.     

Vocal variation in <Emphasis Type="Italic">Chiroxiphia boliviana</Emphasis> (Aves; Pipridae) along an Andean elevational gradient

Bird vocalizations are likely shaped both by natural and sexual selection. Here we test the sensory-drive hypothesis, which states that communication signals diverge as a direct adaptation to the signaling environment and can evolve to minimize degradation and maximize transmission. We examined the effects of elevation and other habitat variables on variation in vocalizations of Chiroxiphia boliviana (Aves, Pipridae) along an elevational gradient (1300–2500 m) in cloud and humid montane forests in the Andes of Bolivia. We also conducted sound transmission experiments to determine if reverberation and attenuation changed along the gradient. Reverberation increased at higher elevations, and attenuation decreased at higher elevations and increased for higher frequencies. We recorded vocalizations from ~?50 individuals throughout the elevational gradient and examined variation in duration and bandwidth of short calls (used as contact calls between males), 2 display calls (advertisement for females) and 2 types of male–male duets (including interval times between males). Duration of short calls, display 1 and duet 1 increased with elevation. Bandwidth of short calls increased at mid-elevation categories and decreased at high elevations, whereas bandwidth of display 1 and duet 1 decreased with elevation. We also directly related the transmission properties to vocalizations and found that bandwidth of short calls decreased with reverberation and attenuation, bandwidth of display 2 decreased with reverberation, and duration of duet 1 both increased and decreased with attenuation (at 3 and 4 kHz, respectively). This study suggests that vocalizations by C. boliviana may be adapted to the habitat transmission properties along the elevational gradient; and perhaps that increasing song length and concentrating energy within a narrow bandwidth may lead to an increase in amplitude and improvement in transmission. Overall, our results support the sensory-drive hypothesis and suggest that this form of selection is likely common along tropical elevational gradients.     

Growth response of Abies georgei to climate increases with elevation in the central Hengduan Mountains,southwestern China

Climatic harshness is expected to increase at higher elevations; however, elevational trends of tree radial growth response of high-elevation forests to climate change need to be investigated at different locations because of existing local variability in site-specific climatic conditions. We developed tree-ring width chronologies of Yunnan fir (Abies georgei) along elevation gradients at two sites in the central Hengduan Mountains (HM). High-elevation forests of A. georgei showed growth synchronicity and common growth signals along elevation gradients, indicating a common climatic forcing, although tree radial growth rates decreased with increasing elevation. Radial growth of Yunnan fir showed positive correlations with summer temperatures and February precipitation and moisture availability, but were negatively correlated with spring temperatures. The strongest positive relationship indicated summer (July) mean and minimum temperatures are the most important growth determining climatic factors for tree radial growth in the cold environment of HM, and this relationship revealed a clear elevational trend with stronger correlations at higher altitudes. In contrast, tree radial growth was negatively correlated with June precipitation and moisture availability. The whole study period 1954–2015 was split in two sub-periods of equal length. Comparing the early sub-period (1954–1984) to the later sub-period (1985–2015), tree growth response to the summer temperatures strongly increased, while it became weaker to June precipitation and moisture availability. High-elevation Yunnan fir forests in the HM currently benefit from elevated growing season temperatures under humid summer conditions. However, increasing temperatures may induce drought stress on tree radial growth if the observed decreasing trend in humidity and precipitation continues.     

Plant population differentiation and climate change: responses of grassland species along an elevational gradient

Mountain ecosystems are particularly susceptible to climate change. Characterizing intraspecific variation of alpine plants along elevational gradients is crucial for estimating their vulnerability to predicted changes. Environmental conditions vary with elevation, which might influence plastic responses and affect selection pressures that lead to local adaptation. Thus, local adaptation and phenotypic plasticity among low and high elevation plant populations in response to climate, soil and other factors associated with elevational gradients might underlie different responses of these populations to climate warming. Using a transplant experiment along an elevational gradient, we investigated reproductive phenology, growth and reproduction of the nutrient‐poor grassland species Ranunculus bulbosus, Trifolium montanum and Briza media. Seeds were collected from low and high elevation source populations across the Swiss Alps and grown in nine common gardens at three different elevations with two different soil depths. Despite genetic differentiation in some traits, the results revealed no indication of local adaptation to the elevation of population origin. Reproductive phenology was advanced at lower elevation in low and high elevation populations of all three species. Growth and reproduction of T. montanum and B. media were hardly affected by garden elevation and soil depth. In R. bulbosus, however, growth decreased and reproductive investment increased at higher elevation. Furthermore, soil depth influenced growth and reproduction of low elevation R. bulbosus populations. We found no evidence for local adaptation to elevation of origin and hardly any differences in the responses of low and high elevation populations. However, the consistent advanced reproductive phenology observed in all three species shows that they have the potential to plastically respond to environmental variation. We conclude that populations might not be forced to migrate to higher elevations as a consequence of climate warming, as plasticity will buffer the detrimental effects of climate change in the three investigated nutrient‐poor grassland species.