Age-specific responses to climate identified in the growth of Quercus alba

The objective of this research was to determine whether the dendroclimatic responses of young Quercus alba (aged 29–126 years) differ from those of old Q. alba (149–312 years). We collected Q. alba increment cores across a range of size classes from Buffalo Mountain Natural Area Preserve, an oak-hickory forest in southcentral Virginia, USA. Tree cores were crossdated and raw ring widths were detrended to remove the influence of increasing circumference with age, microsite, and local stand dynamics. Standardized ring widths were averaged to develop two master chronologies from the 20 oldest and youngest trees. Ring-width indices were correlated with temperature, precipitation, and Palmer Drought Severity Index (PDSI). Annual tree-ring growth in old and young Q. alba was significantly correlated with precipitation from the previous growing season, but was not significantly correlated with temperature. Only the old trees showed a significant correlation between annual ring width and PDSI. These results may indicate that growth in old trees is more sensitive to drought than in young trees. If future climate change includes the predicted increase in mid-growing season droughts, tree-level responses are likely to be age-dependent with older trees experiencing relatively greater reductions in growth.     

近40年河北坝上地区杨树人工林径向生长对气候变化的响应差异

运用树木年轮气候学方法,研究近40年河北坝上地区健康和衰退小叶杨人工林径向生长对气候响应敏感性差异,揭示健康和衰退杨树生长与气候关系的时间变异规律。结果表明：（1）衰退杨树径向生长对温度、降水等气候因素响应较健康杨树敏感。衰退杨树年表中的气候信号较强,与当年生长季（4、8-10月）的气温因素呈显著负相关,与上一年休眠期（9月-当年1月）和当年生长季（7月）的降水和相对湿度呈显著正相关。健康杨树年表中气候信号较弱,主要与上一年冬季（12月）和当年生长季（4月）的气温因素呈显著负相关,与上一年生长末期（8-11月）降水和相对湿度呈显著正相关。（2）从各年表与帕默尔干旱指数（PDSI）的响应强度来看,衰退杨树生长更易受夏季干旱胁迫影响。衰退杨树年表与上一年9月-当年3月、6-10月的PDSI呈显著正相关,而健康杨树径向生长与PDSI呈弱的正相关。（3）1975-2017年间,随气温升高,健康和衰退杨树生长对温度的敏感性下降;健康杨树生长对降水和PDSI的敏感性较为稳定,适应能力强,而衰退杨树生长对降水和PDSI的敏感性增强,适应能力变弱。综上所述,干旱胁迫是限制衰退杨树生长的主要因素,而健康杨树生长受气候影响较弱,能适应当地气候条件。衰退杨树对气候变化响应较健康杨树明显,在气候变暖背景下,衰退杨树生长的气候限制因子由温度转变为水分,导致河北坝上地区遭受干旱灾害时发生退化的趋势更加明显。     

川西亚高山不同年龄紫果云杉径向生长对气候因子的响应

运用树木年轮气候学的基本方法,建立王朗自然保护区紫果云杉在集中分布上限区域的年轮宽度年表,选取差值年表分析不同年龄云杉的径向生长同逐月气候因子的相关及响应关系,结果显示:幼龄组云杉年表的敏感度高于中龄组和老龄组云杉,幼龄组云杉对生长季前及生长季的气温状况显著正相关;中龄组云杉年表仅与当年4月份和7月份的月平均最低气温显著正相关;老龄组云杉的年轮宽度指数同上年生长季(上年8月份)的月平均气温和月平均最低温显著负相关,上年生长季高温的"滞后效应"在老龄组云杉体现的更为突出;幼龄组与中龄组云杉对当年6月份降水持续增加显示出明显的负相关关系,上年12月份的降水会对幼龄组和老龄组云杉径向生长不利。研究表明幼龄组云杉包含的气候信息要优于中龄组和老龄组云杉,在该区域进行相关研究时应根据研究需要选取不同年龄跨度的云杉年表。     

西藏东部主要建群树种径向生长对极端干旱的响应差异

不同坡向、不同海拔树木生长对极端干旱事件的响应可能不同,然而这方面的认识不足。为此,选取西藏东部珠角拉山阴、阳坡的建群树种川西云杉 (Picea likiangensis var. rubescens) 和大果圆柏 (Juniperus tibetica),在不同海拔高度建立了树轮宽度年表,分析了径向生长的气候响应,以及对极端干旱事件的抵抗力和恢复力。结果表明:阳坡大果圆柏和阴坡川西云杉的树木生长对气候的响应存在相似性,均与前一年3-6月、11-12月气温显著正相关,与当年4-5月气温显著负相关,与当年4-5月降水和帕尔默干旱指数 (PDSI, Palmer Drought Severity Index) 显著正相关 (P <0.05)。阳坡大果圆柏的抵抗力显著低于阴坡川西云杉。随着海拔升高,阴坡川西云杉树木个体的抵抗力和恢复力均显著提高,而阳坡大果圆柏树木个体抵抗力、恢复力在不同海拔无显著区别。结合混合效应模型表明树木抵抗力主要受当年4-5月平均最高气温限制,树木恢复力主要受干旱事件后四年4-5月平均最高气温限制 (P <0.01),说明生长季高温引起的极端干旱是树木径向生长下降的主要原因。     

Short-term resin tapping activities had a minor influence on physiological responses recorded in the tree-ring isotopes of Chinese pine (Pinus tabuliformis)

Resin tapping might affect tree-ring growth, but details on the physiological responses of trees to resin tapping are still lacking, particularly for long-term responses. This study aimed to explore the physiological processes underlying resin-tapping of Chinese pine (Pinus tabuliformis) by using tree-ring stable isotopes. We compared tree-ring earlywood and latewood stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes in the pre-resin tapping and post-resin tapping period for tapped trees and compared their values between tapped and untapped trees and their responses to climate variables in a forest stand from 1984 to 2017. Furthermore, we used a dual isotope model to distinguish between the effects of the photosynthetic assimilation rate and stomatal conductance. Results indicated that tapped and untapped trees showed similar inter-annual variation for two isotopes, while the absolute values of tapped trees were slightly (P > 0.05) lower than tapped trees in the two years following resin tapping. Climate response analysis indicated that resin tapping had no significant effect on climatic sensitivity for either stable isotope. Earlywood stable isotopes were mainly influenced by temperature, relative humidity, and Palmer Drought Severity Index (PDSI) from May to July, while latewood isotopes were mainly influence by relative humidity form July to August and PDSI from July to September. The conceptual model results indicated that resin tapping lead to a slight, but not significant, decrease in the intrinsic water-use efficiency caused by increased stomatal conductance for the first two to three years following resin tapping. We conclude that tree-ring physiological responses could be less affected by short-term resin tapping activities.     

不同林龄樟子松人工林径向生长对气候及地下水位变化的响应

全球气候变化导致森林生态系统的结构与功能发生改变,甚至出现树木死亡与林分衰退的现象,研究林分生长对气候变化尤其是干旱事件的响应有助于预测未来气候变化下生态系统的稳定性。以辽宁章古台5个林龄的樟子松人工林为研究对象,分析了树木径向生长对气候因子与地下水位的响应,结果表明：秋季气温,尤其是最低气温显著影响樟子松林的生长(44年生林分除外);低林龄樟子松林(36、39年)生长与当年夏季及生长季内的降水显著正相关,而高林龄樟子松林(52年)生长则与当年春季尤其是当年2月与5月降水显著正相关;36、39、52年生樟子松人工林年表与当年夏季的Palmer干旱指数(PDSI)显著正相关,44、58年生樟子松人工林年表则与地下水位显著正相关。应对早期干旱(即1997年)时,樟子松人工林表现为随林龄增加,其抵抗力增加而恢复力降低;在随后的两个干旱事件中,高林龄樟子松林的抵抗力不再明显高于低林龄,可能是由于地下水位显著降低影响根系吸水;受累积干旱的影响,所有林龄樟子松人工林对2007—2008干旱事件的弹性力均小于1,径向生长量明显降低。地下水位是影响不同林龄樟子松人工林生长及对干旱抵抗力的重要因子,考虑...     

阿尔泰山萨彦岭4种优势树种径向生长对气候因子的响应

气候变化深刻地影响森林树木的生长,而树种对气候变化敏感度的差异可能影响了气候变化下的森林生态系统响应。因此,研究优势树种间生长对气候变化的敏感度差异,对正确认识气候变化下林分生长动态及分布格局十分重要。基于树木年代学的方法,研究了阿尔泰山萨彦岭西伯利亚落叶松（Larix sibirica）、西伯利亚红松（Pinus sibirica）、西伯利亚冷杉（Abies sibirica）以及西伯利亚云杉（Picea obovata）4种优势树种的径向生长-气候关系。结果显示：（1）西伯利亚冷杉径向生长与上一年10-11月、当年1-9月的干旱指数、2-4月的降水显著正相关,与1月的平均温和最高温呈显著负相关关系,与当年4、6月份的水汽压正相关;（2）西伯利亚落叶松径向生长与上一年8月和当年8月的平均温、最高温以及当年8月的最低温显著负相关,而与当年6月的最低温则正相关,与8月份的水汽压显著负相关;（3）西伯利亚红松径向生长与3月降水、7月最低温、上一年10月的水汽压显著正相关;（4）西伯利亚云杉径向生长与6月平均温、最高温、水汽压正相关,与上一年10-11月、当年2-4月和9月的干旱指数正相关,同时与3、4月的降水量显著正相关。西伯利亚冷杉和西伯利亚云杉、西伯利亚云杉和西伯利亚落叶松、西伯利亚云杉和西伯利亚红松对于特定气候因子表现出相似的响应结果,与年表间相关性的结果一致。但差异也是明显的,西伯利亚冷杉和西伯利亚云杉对区域水分变化敏感,而西伯利亚落叶松和西伯利亚红松主要对区域温度变化敏感。综上所述,气候变化下,该区域优势树种对气候变化响应的差异可能导致区域林分动态和格局的改变,因此,多树种径向生长-气候关系研究有助于正确反映森林动态。研究结果可以为区域森林管理与生态保护工作提供理论依据。     

气候变暖抑制西藏拉萨河大果圆柏树木生长

西藏拉萨河作为雅鲁藏布江最大的支流,近几十年气温已显著上升,将可能从不同的程度上影响流域内植被的生长动态。以拉萨河流域主要分布的树种—大果圆柏(Sabina tibetica)为研究对象,采用树木年轮学的方法对大果圆柏进行了年轮采样和处理,建立了树木年表,探讨了大果圆柏过去的生长动态特征,并用相关分析、偏相关分析和滑动相关分析的方法分析了不同气候因子与树木年轮宽度指数的关系。研究结果表明,大果圆柏树木年轮宽度指数与前一年6—10月和当年3—7月的降水、相对湿度和帕默尔干旱指数(PDSI)呈显著的正相关关系,而与前一年6—9月和当年3—8月的平均温度和平均最高温度以及当年5—7月的平均最低温度均呈显著的负相关关系,表明了气候变暖引起的干旱胁迫是导致近几十年来大果圆柏树木径向生长下降的主要原因。在未来气候变暖背景下,拉萨河大果圆柏林将可能出现生长下降,甚至死亡的现象,将潜在驱动区域森林减少。     

秦岭不同龄组巴山冷杉径向生长对气候因子的响应差异

秦岭地区树轮气候学研究已经引起众多学者的重视,但年龄因素对调节树木径向生长-气候响应关系的研究尚未在当地得到广泛关注。运用树轮气候学方法,建立秦岭牛背梁国家级自然保护区低、中、高3个龄组巴山冷杉(Abies fargesii)的树轮宽度差值年表,探究不同龄组巴山冷杉径向生长与覆盖研究区的0.5°×0.5°分辨率格点气候要素之间的响应关系,以期解译年龄差异对巴山冷杉树木径向生长-气候响应特征的潜在影响。结果表明：不同龄组巴山冷杉差值年表统计特征值存在明显差异,平均敏感度和样本总体代表性随年龄增大而递减,但标准差、样本间平均相关系数和第一特征根变异解释量均以中龄组最低,信噪比却以中龄组最高;春季(3—5月)降水的增加以及秋季(9—11月)气温的升高对低龄组巴山冷杉径向生长的促进作用最强,对中龄组树木生长的促进作用明显减弱,而对高龄组树木生长几乎没有影响;气温对巴山冷杉径向生长的促进作用随树龄增高而增强,差值年表与当年2月、8月、上年5月平均温、平均最高温的相关系数均呈现随龄级增大而逐渐递增的趋势。年龄因素对牛背梁国家级自然保护区巴山冷杉径向生长-气候响应关系存在明确影响,随着年龄的增加,巴...     

祁连山东部青海云杉死亡和存活个体径向生长对气候变化的响应差异

研究建立了祁连山东部青海云杉(Picea crassifolia)存活个体与死亡个体的树轮宽度年表和断面生长增量(BAI)序列,对青海云杉存活个体与死亡个体的径向生长特征及其对气候要素的响应关系进行了比较,尝试厘清青海云杉径向生长与气候要素之间的响应机制。结果表明:青海云杉死亡个体的径向生长速率明显低于存活个体(P ＜ 0.001),尤其是在20世纪80年代快速升温后,这一差距进一步加大,青海云杉死亡率也大幅增加。在1951-1986年期间,青海云杉径向生长主要受生长季前(上一年9月到当年2月)干湿状况的影响;而在1987-2020年期间,青海云杉径向生长则更多受生长季(当年6-8月)干湿状况的影响。并且与活树相比,死树对区域干湿状况表现出更高的敏感性,对气温的负响应也更强。随着气候变暖加剧,高温及其带来的干旱胁迫已成为区域内限制青海云杉径向生长的主要气候因素,青海云杉的死亡率可能会继续升高。     

Growth responses of an African savanna tree, <Emphasis Type="Italic">Bauhinia thonningii</Emphasis> Schumacher,to defoliation,fire and climate

This study investigated the growth responses to defoliation, fire-exposure and climate factors of a widespread Africana savanna tree, Bauhinia thonningii Schumacher, at a site in central Zambia. Experimental trees (n = 47) were either exposed to fire (n = 12) in the first half of the dry season or protected from fire (n = 35). Some of the fire-protected trees (n = 12) were subjected to artificial defoliation in two consecutive years. Phenological responses (bud break, leaf flush and leaf production) to fire-exposure and defoliation were monitored on permanently marked sample shoots over a 2-year period. Radial tree growth (diameter at 1.3 m above ground) was measured annually over a 7-year period from 1998 to 2005. During the first two years, defoliation and fire-exposure advanced the onset of bud break and leaf flush but fire-exposed trees produced significantly less leaves than did trees protected from fire, probably because scorching caused more severe shoot die-back than is normal. Leaf production was also significantly affected by experimental treatments and their interaction with year. Although treatments had significant short-term effects on radial growth, previous-year growth significantly influenced current-year growth, thereby confirming the existence of autocorrelation in the time-series growth data of B. thonningii. The interaction between previous-year growth and climate factors explained a significant proportion (25–40%, P < 0.001) of the variance in annual tree growth. Variogram models predicted that a 2-year manual defoliation treatment would shorten the longer-term growth cycle while continuous fire-exposure extended the cycle by one year. The results are useful for the management of savanna trees.     

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.     

Age-related climate sensitivity in Pinus Edulis at Dinosaur National Monument,Colorado, USA

The influence of tree age on climate sensitivity is of central importance in dendrochronology. Recent research has highlighted the disparate nature of age-dependent growth responses across species and geographic locations. We compared growth sensitivity and the influence of climate in Pinus edulis (Piñon) of varying ages at Dinosaur National Monument (DINO, northwestern Colorado, USA. Piñon is a particularly good species for this study because of its long life-span and climate sensitivity, and the DINO site is at the northern extreme of the current distribution. We evaluated changes in climate-growth relationships in piñon using total ring-width measurements and running averages of chronology statistics, mean sensitivity (MS) and coefficient of variation (CV), and we investigated growth response to climate variability as trees age. These measures indicated initial low growth sensitivity, increasing as trees reached mid-life stages, approximately 200–250 years, then relatively constant sensitivity from 250-800+ years. First order partial auto correlation (PAC1) declined throughout the life stages of piñon at DINO. The trend in declining autocorrelation leads to higher MS values in the older age classes. Greater year to year variation indicates less persistence in the study population, hence lower autocorrelation.We investigated the degree to which this relationship could be explained by the summer Palmer Drought Severity Index (PDSI) and whether this relationship varied with tree age. The strength of the tree-ring growth response to PDSI was at a maximum during the first two centuries of growth (R² = 0.54). between two and six centuries (R² = 0.48), after which we detected a decline in the sensitivity of tree growth to PDSI with increasing age (R² = 0.41). This study adds to the literature on age-related climate sensitivity in trees; our findings indicate that age-related changes in climate-tree-ring growth responses should be considered when climate variables are reconstructed from tree-ring width chronologies, and specifically from Pinus edulis.     

Drought-driven growth reduction in old beech (Fagus sylvatica L.) forests of the central Apennines, Italy

Productivity of old‐growth beech forests in the Mediterranean Basin was measured by average stem basal area increment (BAI) of dominant trees at two mountain sites in the Italian Apennines. Both forests could be ascribed to the old‐growth stage, but they differed markedly with regard to elevation (1000 vs. 1725 m a.s.l.), soil parent material (volcanic vs. calcareous), mean tree age (less than 200 years vs. 300 years), and stand structure (secondary old‐growth vs. primary old‐growth forest). Drought at the two sites was quantified by the self‐calibrated Palmer Moisture Anomaly Index (Z‐index), and by the self‐calibrating Palmer Drought Severity Index (PDSI) for summer (June through August) and the growing season (May through September). Dendroclimatological analyses revealed a moisture limitation of beech BAI at interannual (water availability measured by Z‐index) and decadal scales (water availability measured by PDSI). Both BAI and water availability increased from 1950 to 1970, and decreased afterwards. Trees were grouped according to their BAI trends in auxological groups (growth‐type chronologies), which confirmed that growth of most trees at both sites declined in recent decades, in agreement with increased drought. Because BAI is not expected to decrease without an external forcing, the patterns we uncovered suggest that long‐term drought stress has reduced the productivity of beech forests in the central Apennines, in agreement with similar trends identified in other Mediterranean mountains, but opposite to growth trends reported for many forests in central Europe.     

Spatial and age-dependent tree-ring growth responses of Larix gmelinii to climate in northeastern China

Tree-ring width chronologies from 276 Larix gmelinii cores taken in northeastern China were used to analyze spatial and age-dependent growth–climate response relationships. Tree radial growth from five localities showed similar patterns, while exhibiting different tree-ring growth responses to local climate. The rotated principal component analysis (RPCA) indicated that tree age, growing season moisture conditions, and ambient air temperature variations resulted from location differences (e.g., longitude, latitude, and altitude), which could explain the non-stationary spatial climate–growth relations observed. The study tested the fundamental assumption that the climate–growth of L. gmelinii was age independent after the removal of size trends and disturbance signals. The age-related climate–growth relationship might potentially improve the veracity of past climate reconstructions. Bootstrapped correlation function analyses suggested that the response of L. gmelinii radial growth to climate differed between trees ≥150 years old and <150 years old. Mean sensitivity and standard deviation for trees increased with age in the <150 years old tree class; whereas trees ≥150 years old had no significant relationship with age. These results showed that the assumption of age-independent climate–growth relationship is invalid at these sites. Physiological processes and/or hydraulic constraints dependent on tree age, together with detrending techniques could be the possible causal factors of clear age-dependent responses. These results suggested the importance of incorporating trees of all ages into the chronology to recover a detailed climatic signal in a reconstruction of L. gmelinii for this region.     

黄土高原羊圈沟小流域人工物种和自然物种径向生长对气候变化的响应差异

为揭示黄土高原人工和自然物种径向生长对气候变化的响应差异,在延安羊圈沟小流域分别获取人工和自然物种的树木年轮材料并构建标准年表,其中人工物种为刺槐(Robinia pseudoacacia)和柠条(Caragana korshinskii),自然物种为山杏(Armeniaca sibirica)和荆条(Vitex negundo var.heterophylla),并对年表中的气候信号进行了统计分析。结果表明:1)人工物种年表中的气候信号较强,主要表现在5—8月份,与温度呈负相关关系(刺槐:r=-0.427—-0.511,P0.05;柠条:r=-0.227—-0.738,P0.05),与降雨则呈正相关关系,但相关系数未达到显著性水平;自然物种年表中的气候信号较弱,与温度和降雨的相关关系均较低;2)不同于自然物种,人工物种树轮年表还与去年夏季(7—9月份)温度(负相关)和降水(正相关)存在相关关系,表明人工物种树木生长对气候因子存在一定滞后性;3)人工物种树轮年表与PDSI干旱指数在各月份均维持正相关关系,在生长季(刺槐4—9月、柠条4—8月)达到显著水平(刺槐:r=0.481—0.704,P0.05;柠条:r=0.314—0.610,P0.05);而自然物种年表与PDSI干旱指数的相关关系较弱,均未达到相关性水平。从各年表与气候要素(温度、降雨、PDSI)响应强度来看,黄土高原人工物种树木生长受水分胁迫显著,且以刺槐最为明显,其次是柠条;自然物种树木生长则没有明显干旱胁迫的影响,仅山杏生长受一定水分胁迫影响,荆条生长则与各气候要素关系较弱,水分胁迫对其生长的影响已很小。本研究的结果表明黄土高原人工物种生长明显受到水分条件限制,而自然恢复物种生长则受水分条件影响较小,能适应黄土高原干旱半干旱气候条件。     

Age-dependent responses of tree-ring growth and intra-annual density fluctuations of Pinus pinaster to Mediterranean climate

Dendrochronology generally assumes that climate–growth relationships are age independent once the biological growth trend has been removed. However, tree physiology, namely, photosynthetic capacity and hydraulic conductivity changes with age. We tested whether the radial-growth response to climate and the intra-annual density fluctuations (IADFs) of Pinus pinaster Ait. varied with age. Trees were sampled in Pinhal de Leiria (Portugal), and were divided in two age classes: young (<65 years old) and old (>115 years old). Earlywood and tree-ring width of young P. pinaster trees were more sensitive to climate influence while the response of latewood width to climate was stronger in old trees. Young trees start the growing season earlier, thus a time window delay occurs between young and old trees during which wood cells of young trees integrate environmental signals. Young trees usually have a longer growing season and respond faster to climate conditions, thus young P. pinaster trees presented a higher frequency of IADFs compared with old trees. Most of the IADFs were located in latewood and were positively correlated to autumn precipitation. The radial-growth response of P. pinaster to climate and the IADFs frequency were age dependent. The use of trees with different age to create a tree-ring chronology for climate studies can increase the resolution of climatic signals. Age-dependent responses to climate can also give important clues to predict how young and old trees react to climate change.     

Dendrochronological analysis of Sequoia sempervirens in an interior old-growth forest

Dendrochronological studies of large and old Sequoia sempervirens are limited by access and complex crossdating, but core sampling at regular height intervals along the main trunks of five standing trees allowed for reconstruction of growth, height, and age while providing within-tree replication for crossdating. We developed a crossdated ring-width chronology (1453–2015) for redwoods growing in an easternmost old-growth forest in the Napa Range of California, determined aboveground tree attributes, investigated the inter-annual climate-growth relationships since the late 19th century, and documented long-term growth trends. Age, height, f-DBH (functional diameter at breast height), and aboveground biomass of these co-dominant trees ranged from 241 to 783 years, 45.7 to 61.5 m, 117.0 to 226.9 cm, and 9.34 to 33.62 Mg, respectively. Bootstrapped correlation and response function analysis showed radial growth positively related to May through August Palmer Drought Severity Index (PDSI) and negatively related to maximum June temperature (r ≥ │0.47│, P < 0.0001), explaining 33.3% of ring-width variation. Bootstrapped correlations over a moving 40-year window indicated strengthening relationships with PDSI and minimum temperature. The long-term growth trend, reflected by the size-detrended metric of residual wood volume increment (RWVI), varied over time and showed an average one-year decrease of 13.3% for 20th and 21st century droughts. A fire detected in August 1931 corresponded with a one-year decrease in RWVI of 43.1% followed by >100% increase within five years. Growth dynamics for redwoods in this interior forest provide a point of comparison for redwoods previously studied in old-growth forests along the latitudinal gradient, highlighting range-wide trends and site-specific differences in responses to climate and fire.     

昌岭山两个优势树种径向生长对气候变化的响应

在气候变暖背景下,树木径向生长对气候变化的响应存在不稳定性。利用采自祁连山东部余脉昌岭山两个优势树种油松和青海云杉的树轮样芯,建立树轮宽度标准年表,通过分析树轮宽度年表与气候要素的相关关系,探讨两个树种径向生长对气候变化的响应。结果表明：（1）油松年表比青海云杉年表包含更多的气候信息,其平均敏感度、标准差、信噪比和样本对总体的代表性等统计量均高于青海云杉标准年表。（2）气候要素对不同树种径向生长限制程度不同,油松径向生长主要与降水（前一年9月和当年3-8月）和气温（前一年9月）有关,但对降水的响应更为敏感,而青海云杉径向生长则受到气温（当年9月）和降水（前一年9月、当年3月和7月）的共同作用。（3）气温突变后,油松和青海云杉年表与各气温要素的相关性显著增强,而青海云杉年表与气温要素的相关性变化更明显,指示了青海云杉径向生长对气温的响应更不稳定。（4）生长季平均最低气温的升高诱导的干旱胁迫是油松和青海云杉树木径向生长-气温响应变化的主要原因。     

Sex-related,growth–climate association of Araucaria angustifolia in the neotropical ombrophilous woodlands of Argentina

Araucaria angustifolia is a dioecious dominant tree in araucaria forests in Brazil and Argentina, South America. The species is nowadays critically endangered by deforestation and global climate change. The goal of this study was to analyse the dynamics of radial growth in this species and its association with climatic variables, according to the sex, at its western range boundary in Argentina. Standard dendrochronological techniques were applied on stem disks from female and male trees. Xylem anatomical anomalies made the tree-ring dating process difficult. Female and male trees showed growth patterns that changed over time, not being significant in the 1950–1990 period and highly significant from the 1990s onwards (p < 0.1) when female trees had a higher growth rate. Female and male trees showed a different association with climatic variables. No significant effect of temperature and precipitation was identified on female trees. For male trees, rainfall had a positive effect in August, before the growing season, and a negative effect at the end of the growing season (March). Temperature had a negative effect on male trees, before and during the growing season (February and January, respectively). No effect of SOI was detected on both sexes. Results emphasised the usefulness of A. angustifolia for dendrochronological studies and the value of dioecious species for the study of sex-related growth–climate association.