Radial growth in Qinghai spruce is most sensitive to severe drought in the Qilian Mountains of Northwest China

Global warming and frequent extreme drought events lead to tree death and extensive forest decline,but the underlying mechanism is not clear.In drought years,cambial development is more sensitive to climate change,but in different phenological stages,the response rela-tionship is nonlinear.Therefore,the dynamic relationship between tree radial growth and climatic/environmental fac-tors needs to be studied.We thus continuously monitored radial growth of Qinghai spruce(Picea crassifolia Kom.)and environmental factors from January 2021 to November 2022 using point dendrometers and portable meteorological weather stations in the central area of the Qilian Mountains.The relationship and stability between the radial growth of Qinghai spruce and environmental factors were compared for different levels of drought in 2021 and 2022.The year 2022 had higher temperatures and less precipitation and was drier than 2021.Compared with 2021,the growing period in 2022 for Qinghai spruce was 10 days shorter,maximum growth rate(Grmax)was 4.5μm·d^(-1) slower,and the initiation of growth was 6 days later.Growth of Qinghai spruce was always restricted by drought,and the stem radial increment(SRI)was more sensitive to precipitation and air relative humidity.Seasonal changes in cumulative radial growth were divided into four phenological stages according to the time of growth onset,cessation,and maximum growth rate(Grmax)of Qinghai spruce.Stability responses of SRI to climate change were stronger in Stage 3 and Stage 4 of 2021 and stronger in Stage 1(initiation growth stage)and Stage 3 of 2022.The results provide important information on the growth of the trees in response to drought and for specific managing forests as the climate warms.

Variability in the climate-radial growth correlation of Pinus massoniana of different diameter classes

The physiological characteristics of trees change with age,suggesting that growth-related climate signals vary over time.This study aimed to clarify the impacts of different diameter classes on the chronological characteristics of Pinus massoniana Lamb.and its response to climatic factors.Chronologies of P inus massoniana were established in small diameter(14.1 cm),middle diameter(27.3 cm),and large diameter(34.6 cm)trees according to dendrochronology.The results show that:(1)radial growth of different diameter classes had varied characteristics and climate sensitivities;(2)radial growth of small diameter trees was affected by climatic factors of the previous and the current year,while large diameter trees were mainly affected by climatic factors of the current year;and(3)precipitation and temperature were key factors that restricted the radial growth of small and large diameter trees,respectively.

Radial growth and non-structural carbohydrate partitioning response to resin tapping of slash pine(Pinus elliottii Engelm.var.elliottii)

Slash pine(Pinus elliottii Engelm.var.elliottii)is a resin-producing species grown worldwide for significant economic benefits for wood production.Resin tapping cre-ates a carbon sink at the expense of carbon allocation for growth and consequently,wood production may be reduced.Non-structural carbohydrates comprising starch and sugars stored in plant organs,may serve as intermediate pools between assimilation and utilisation.However,the effect of resin tapping between tree growth and non-structural carbo-hydrates is not well understood.This study investigated(1)the effects of resin tapping on radial growth,(2)the effects of resin tapping on non-structural carbohydrate pools in different compartments,and(3)the feasibility of resin pro-duction without disruption of tree growth.Twenty one-year-old slash pines were subjected to resin tapping over two suc-cessive years.Non-structural carbohydrate concentrations in needles,branches,stem phloem,and roots of tapped and untapped trees in summer and winter were determined after the second year of resin harvest.The results showed that tapping had no significant effects on annual increments.Starch was the dominant non-structural carbohydrate frac-tion,regardless of tissues and season,and constituted up to 99%of the total non-structural carbohydrates in the phloem and roots.Glucose and fructose were the dominant sugars;sucrose was negligible.Compared with the controls,tapped trees showed 26%lower non-structural carbohydrate concen-tration in the phloem above the tapping wound in summer,which was attributable to the decreased abundance of starch,glucose,fructose,and sucrose.In winter,the altered non-structural carbohydrate profiles in the phloem above the tap-ping wounding were minimised as a result of recovery of the sugar concentrations.In contrast to free sugars,which accu-mulated substantially in needles and branches during winter,starch was enriched in the phloem,roots,and current-year needles.The results provide evidence for a localised effect of resin tapping,and highlight the observation that resin extrac-tion does not always cause a sacrifice in wood growth under a moderate resin-tapping intensity in slash pine plantations.

Effect of Climatic Factors on the Radial Growth of Teak （Tectona grandis L.F.） in Parakou and Tchaourou Districts in Northern Benin

Climatic factor＇s effect was studied on the radial growth of teak （Tectona grandis L.F.） by using the stem analysis of 36 trees distributed in 6 plantations in Parakou and Tchaourou districts in northern Benin. The results showed that the plantations of Parakou were in general more productive than those of Tchaourou. The annual average growth was estimated in the first five years at 0.86 cm/year for Parakou and 0.76 cm/year at Tchaourou. The analysis of the radial growth showed that a significant percentage of the variance was allotted to the growth model. It follows that a big part of the ring width was predetermined before the intervention of the other factors, in particular the climatic conditions. The percentage of the variance related to the climatic conditions was thus more reduced for the plantations of Tchaourou than those of Parakou. The radial growth was influenced by the conditions of humidity （evapotranspiration, humidity and rain） of February to May on the one hand and those from August to October on the other hand.

Response to Hydrothermal Change of Tree Radial Growth since 1990s in the Southern Taihang Mountains in Hebei Province

On the basis of the relationship between tree ring width of Pinus tabulaeformis in the southern Taihang Mountains in Hebei Province and climate factors, such as mean temperature, mean maximum temperature, mean minimum temperature and precipitation, we find that tree-ring width correlates positively and significantly with mean and maximum temperature in March and Spring, and with minimum temperature in March, April, Spring and Autumn. The sampling tree radial growth responds sensitively to spring temperature change.

Climate Factors of Vapour Pressure and Diurnal Temperature Influenced on Radial Growth of Scots Pine in Northeastern Mongolia

To find out the optimum conditions of growth in Scots pine (Pinus sylvestris var. mongolica), we analyzed the radial growth response relationship to climate factors in boreal forests. We present growth response from 3-sites Mg (Mangui), KYH (kheyihe), NM (Nanmu) from central Daxing’an mountains. Drought observed in 1920s-1930s years. We analyzed growth response from 1920-2016. Results specified that growth of scots pine did not vary with variation in sites. We measure the influence of vapour pressure and mean maximum and mean minimum diurnal temperature have been shown by correlations of different growing seasons. Most of warm temperature during June to September and growth of Scots pine show a significantly positive increase during winter season. Overall inconsistency in climate conditions of Daxing’an mountains due to Atlantic and Pacific oceans, affects the Asian moon soon and alternatively changes the local temperature and precipitation and vapour pressure and increases the drought severity.

Microenvironmental effects on growth response of Pinus massoniana to climate at its northern boundary in the Tongbai Mountains,Central China

The Tongbai Mountains is an ecologically sensi-tive region and the northern boundary of Pinus massoniana Lamb.To analyze the effect of different microenvironments on tree growth response to climate factors,we developed standard chronologies for earlywood width(EWW),late-wood width(LWW),and total ring width(TRW)of P.massoniana at two sampling sites on slopes with different orientations,then analyzed characteristics of the chronolo-gies and their correlations with climate variables from five stations in the region and with a regional normalized differ-ence vegetation index(NDVI).Statistical results showed that the TRW/EWW/LWW chronology consistency and charac-teristics(mean sensitivity,signal to noise ratio,expressed population signal)for trees growing on the southeastern slope were much higher than for trees on the northeastern slope.Correlations indicated that temperature in current March and August has a significant positive effect on TRW/EWW/LWW formation,and the effect on the northeastern slope was weaker than on the southeastern slope.Compared to temperature,precipitation has more complicated effects on tree growth,but the effect on the northeastern slope was also generally weaker than on the southeastern slope.Step-wise linear regression analyses showed that temperature in August was the main limiting factor at the two sampling sites.Similarly,the response of tree growth on the southeast-ern slope as determined by the NDVI is better than on the northeastern slope,and the TRW/EWW/LWW chronologies for the southeastern slope explained over 50%of the total NDVI variances in June.Overall,the results indicate that the difference in the climate response of P.massoniana at two sampling sites is clearly caused by differences in the microenvironment,and such differences should be properly considered in future studies of forest dynamics and climate reconstructions.

Radial growth response of Pinus densiflora and Quercus spp.to topographic and climatic factors in South Korea

Aims This study aimed to develop radial growth models and to predict the potential spatial distribution of Pinus densiflora(Japanese red pine)and Quercus spp.(Oaks)in South Korea,considering topographic and climatic factors.Methods We used a dataset of diameter at breast height and radial growth estimates of individual trees,topographic and climatic factors in systematic sample plots distributed over the whole of South Korea.On the basis that radial growth is attributed primarily to tree age,we developed a radial growth model employing tree age as an explanatory variable.We estimated standard growth(SG),defined as radial growth of the tree at age 30,to eliminate the influence of tree age on radial growth.In addition,SG estimates including the Topographic Wetness Index,temperature and precipitation were calculated by the Generalized Additive Model.Important Findings As a result of variogram analysis of SG,we found spatial autocorrelation between SG,topographic and climatic factors.Incremental temperature had negative impacts on radial growth of P.densiflora and positive impacts on that of Quercus spp.Precipitation was associated with positive effects on both tree species.Based on the model,we found that radial growth of P.densiflora would be more vulnerable than that of Quercus spp.to climatic factors.Through simulation with the radial growth model,it was predicted that P.densiflora stands would be gradually replaced with Quercus spp.stands in eastern coastal and southern regions of South Korea in the future.The models developed in this study will be helpful for understanding the impact of climatic factors on tree growth and for predicting changes in distribution of P.densiflora and Quercus spp.due to climate change in South Korea.

Hydrological Response of Populus euphratica Olve. Radial Growth in Ejinaa Banner, Inner Mongolia

Populus euphratlca Olve. is a dominant tree species in Ejlnaa Oasis of the lower reaches of the Helhe River, inner Mongolia, China. In recent years, the population of this species has shown signs of degradation that are suggested to be probably associated with the decrease of surface water. In this study, the history of river runoff In this region was examined with a dendrochronological study of P. euphratica from four sites. It Is found that tree-ring widths In the all sites have negative correlation with runoffs of all months at the Zhengylxla hydrological station. Principal component （PC） analysis of the tree-ring chronologies shows that the first PC （PC1） accounts for 49.98% of the total variances. The first PC Is found to have a significantly negative correlation with runoffs In March and April （- 0.52 and - 0.43, respectively, P 〈 0.05）. This negative correlation might be related to variations In the depth of underground water.

Larch growth across thermal and moisture gradients in the Siberian Mountains

Climate-driven changes in the thermal and moisture regimes may variously influence different tree species growth and ranges.We hypothesize that drought resistant Siberian larch(Larix sibirica Ledeb.)and precipitation-sensitive Siberian pine(Pinus sibirica Du Tour)responded differently to climate change along the elevational thermal and precipitation gradients.We studied the influence of air temperature,precipitation,soil moisture,and atmospheric drought(indicated by the drought index SPEI)on larch and pine growth along the southward megaslope of the West Sayan Ridge.We found that since 2000 climate change resulted in increasing larch and pine radial growth index(GI)(c.1.5–3times)within treeline(2000–2300 m)and timberline(1900–2000 m)ecotones,i.e.within high precipitation zones.Within the forest-steppe ecotone(1100–1200 m)in which L.sibirica is the only species,larch GI stagnated or even decreased.The total forested area increased since 2000 up to+50%in the high elevations,whereas in the low elevations(<1400 m)area changes were negligible.Within treeline and timberline,trees’GI was stimulated by summer temperature.Meanwhile,temperature increase in early spring reduces GI due to living tissue activation followed by tissue damage by desiccation.Within forest-steppe,larch radial growth was mostly dependent on soil moisture.Warming shifted dependence on moisture to the early dates of the growing period.Acute droughts decreased GI within forest-steppe as well as within treeline,whereas the drought influence on both species within highlands was insignificant.Within forest-steppe seedlings establishment was poor,whereas it was successful within treeline and timberline.Current climate change leads to stagnation or even decrease in Larix sibirica growth in the southern lowland habitat.In combination with poor seedlings establishment,reduced growth threatens the transformation of open lowland forests into forest-steppe and steppe communities.Meanwhile,in the highlands warming facilitated the growth of Siberian larch and pine and the increase of forested area.

气候对天山中部不同海拔天山云杉径向生长的影响

为研究气候因子对天山中部不同海拔天山云杉(Picea schrenkiana var.tianschanica)径向生长的影响,在天山中部新疆农业大学实习林场内设置低、中、高3个海拔梯度(1900、2200、2500 m)进行年轮样芯取样,利用树木年轮学方法,选用1955—2022年研究区温度、降水、标准化降水蒸散发指数、帕默尔干旱指数等气象数据,与所测年轮数据进行分析。结果表明:低海拔天山云杉年轮宽度与前一年6月和当年6—8月温度、前一年8月降水以及当年6—9月帕默尔干旱指数呈显著正相关(P<0.05)。中海拔天山云杉年轮宽度与前一年6月温度、8月降水以及前一年6—8月标准化降水蒸散发指数呈显著正相关(P<0.05)。高海拔天山云杉年轮宽度与当年1月温度、前一年11月至当年3月标准化降水蒸散发指数呈显著负相关(P<0.05),与当年6—7月降水呈显著正相关(P<0.05)。因此,在林区内,天山云杉生长与环境的干湿状况随海拔变化存在密切的关系。降水是促进低海拔天山云杉径向生长的关键因素,温度和降水共同作用中海拔天山云杉生长,温度对高海拔天山云杉径向生长的影响高于降水。

天山雪岭云杉径向生长响应气候变化的海拔分异

【目的】探究天山中部地区不同海拔雪岭云杉径向生长变化趋势、对气候因子的响应以及应对干旱胁迫的生态弹性,为预测气候变化下天山雪岭云杉林沿海拔梯度的群落发展趋势提供理论参考。【方法】在天山北坡中段雪岭云杉森林的下林线、林带中部、上林线处采集雪岭云杉树芯样品,建立3个树轮标准年表,计算胸高断面积增量,分析雪岭云杉径向生长与气候因子的关系,采用抵抗力、恢复力和恢复弹力分析雪岭云杉对干旱胁迫的响应。【结果】在过去61年,研究区各海拔雪岭云杉径向生长均受到明显抑制,受抑制程度表现为下林线处最重,林带中部次之,上林线处较轻;不同海拔影响雪岭云杉径向生长的主控气候因子存在差异,下林线主要与当年4—7月气温显著负相关(P<0.05),与上一年6月和当年4、6月降水量及上一年8月至当年9月自校准帕默尔干旱指数(scPDSI)显著正相关(P<0.05);林带中部主要与上一年6—8月和当年3—4、6—7月气温显著负相关(P<0.05);上林线主要与当年2和6—7月气温显著正相关(P<0.05),与上一年8月和当年4月降水及上一年6月至当年5月scPDSI显著正相关(P<0.05);雪岭云杉径向生长对气候因子的响应在海拔梯度和时间梯度上均有差异,由下林线至上林线,与气温的负相关性及与降水和scPDSI的正相关性均依次减弱。在时间梯度上,与气温的相关性逐渐减弱,与降水和scPDSI的正相关性逐渐加强。不同海拔雪岭云杉应对干旱胁迫的生态弹性具有差异,抵抗力和恢复弹力表现为上林线>林带中部>下林线,恢复力表现为下林线>林带中部>上林线;下林线雪岭云杉对干旱较敏感,遭受干旱胁迫时生长下降明显;在抵抗力与恢复力反向平衡关系未打破时,下林线雪岭云杉不受干旱遗留效应影响。【结论】因研究区升温迅速而降水增加缓慢,各海拔雪岭云杉遭受干旱胁迫越来越严重,其中下林线雪岭云杉径向生长降幅最大,抵抗力最小,生长衰退风险最高。

将乐国有林场杉木径向生长及其对气候的响应

【目的】杉木是我国南方特有的用材树种,其具有良好的绿化效果,同时也具有较高的经济价值。本文主要对不同时间尺度上杉木径向生长动态及其与气候因子的关系展开研究,为科学经营研究区杉木提供参考依据。【方法】本研究利用径向生长测量仪对福建省将乐国有林场杉木进行了为期4年(2017年7月—2021年6月)的连续监测,对其径向生长量进行分析,确定生长季,同时进行偏相关分析及滑动相关分析探究温度、湿度、降水量等气候因子对杉木径向生长的影响。【结果】(1)杉木具有周期性的日径向改变,主要体现在3个阶段(第1个阶段是收缩、第2个阶段是恢复、第3个阶段是增长);杉木径向变化的季节动态经历了低谷期、上升期和稳定期;杉木的径向变化年际间存在差异,但径增长的时间序列和累积变化趋势基本是一致的。(2)拟合并分析杉木累积径向生长曲线可以确定福建将乐杉木的生长季为每年2—9月。(3)平均相对湿度、降水量、最低温度和平均温度是主要的影响因子,且杉木净增量与降水量具有显著正相关的关系,温度在适宜杉木径向生长的范围内越高越利于生长,但高于或低于这个范围均会起抑制作用;滑动相关分析结果表明随着生长季时间的变化,相关系数呈现先增加后减少的趋势。【结论】杉木径向生长与相对湿度、降水量、温度等气候因子有密切联系,因此研究杉木的径向变化特征和对气候因子的响应,为更好地规划目标树种的生存策略提供了重要的技术路径和参考模型。

澜沧江源区高山柏径向生长对气候变化的响应

为探究澜沧江源区气候变化对高山柏(Sabina squamata)径向生长的影响,在该区巴青县、杂多县和囊谦县分别对高山柏进行采样。运用树木年轮学方法测定3个样地高山柏逐年树轮宽度和胸高断面积增量(BAI),建立高山柏树轮宽度标准年表并分析其对气候变化的响应。研究结果表明,1986—2019年,澜沧江源区年平均温度呈快速上升趋势(0.43℃/10a,P<0.01),年平均最低气温(0.57℃/10a,P<0.01)的上升速率明显高于年平均最高气温(0.33℃/10a,P<0.01),而年降水量呈不显著的上升趋势(2.39mm/a,P>0.10)。气候变暖背景下,澜沧江源区高山柏树轮宽度呈上升趋势(P<0.01),2000—2019年生长速率((0.37±0.16) mm/a)较1986—1999年((0.20±0.09) mm/a)增加了85%;BAI亦上升显著,在1986—1999年一直呈上升趋势((12.16±5.16) mm^(2)/a),2000—2019年处于平稳快速生长阶段((22.49±8.84) mm^(2)/a),表现出稳定且持续的生长能力。高山柏树轮宽度标准年表与气候因素的相关性显示:澜沧江源区高山柏径向生长对温度的响应明显强于降水,与多数月份(上年6月—当年10月)的降水呈不显著正相关,而与多数月份的温度呈显著正相关。与月平均最高温度和平均温度相比,高山柏径向生长与月平均最低温度的相关性更为显著(P<0.01)。在气候暖湿化背景下,近30年澜沧江源区高山柏径向生长进入快速生长时期,树轮宽度和BAI均呈快速生长特征,表明该区域气候条件更加适宜高山柏生长。

亚热带杉木径向生长对气候因子的响应

杉木(Cunninghamia lanceolata)是亚热带地区主要造林树种之一,其在区域碳循环和缓解气候变化中起着重要的作用。以亚热带地区6个站点(荆关、马鬃岭、分宜、将乐、东风、高峰)杉木人工林为研究对象,建立树轮标准化年表,分析树木年轮年表与气候因子的关系,解析不同研究区杉木径向生长对气候变化的响应机制,探讨不同站点杉木对干旱事件的响应策略,为该地区杉木人工林的经营管理提供理论依据。研究结果表明,6个研究区杉木树轮宽度对气候变化的平均敏感度大于0.15,样本总体代表性大于0.85,均处于可接受水平,表明6个站点的杉木样本具有区域代表性,适用于进行气候相关分析。杉木径向生长主要与生长季的平均温度和降水量、上一年夏季的最低温度正相关,与当年夏季最高温度负相关,高峰站点的径向生长与7-10月的相对湿度显著正相关,其他地点径向生长与月相对湿度相关性较弱,分宜、东风和高峰站的径向生长与干旱指数显著正相关,其他地点的杉木树轮宽度与干旱指数相关性较弱。干旱事件对6个站点杉木生长均产生了负面影响,胸高断面积增长(Basal area increment, BAI)呈先上升后下降的趋势,在生长后期,6个研究点的BAI出现不同程度的衰退现象。第二次干旱发生后,杉木对干旱事件的应对能力更强。亚热带纬度较低的地区杉木受到干旱的影响较大,温暖而湿润环境下的杉木对干旱事件的抵抗力较小,恢复力较高。

六盘山南坡不同密度华北落叶松人工林年内径向生长动态及其影响因素

[目的]探究不同密度下华北落叶松人工林林分径向生长的季节变化特征及其对环境因子的响应,为准确评估和预测未来区域尺度上华北落叶松人工林树木径向生长和森林动态、实现可持续管理与多功能维持提供科学依据。[方法]在宁夏六盘山南部香水河小流域,设置4种不同密度华北落叶松样地,使用树木生长尺对华北落叶松年内径向生长过程进行监测,并同步监测气象因子、土壤温度和湿度。[结果]表明:(1)在生长季时间尺度,华北落叶松径向变化呈“S”型,径向变化呈相对稳定、快速增大、涨缩波动3个阶段的时间格局,快速增大阶段主要发生在6月初—7月下旬,DOY152—210。(2)在544、742、999和1020株·hm^(-2)的密度下,生长季节内华北落叶松林平均累积径向生长量分别为1070±230μm、775±181μm、518±214μm和494±124μm;随林分密度的增加,华北落叶松年内累积径向生长量呈下降趋势,其快速增大阶段缩短;(3)混合效应模型分析结果表明,华北落叶松径向生长主要受土壤水分和平均气温控制,但林分密度和生长时期对年内径向生长也有显著影响;同时考虑林分密度、生长时期、树木大小以及气象因子等变量的模型可解释72.0%的方差,但排除林分密度和生长时期因素后,树木大小和气象因子共同仅能解释46.4%的方差。[结论]超过2/3的华北落叶松径向生长发生在快速生长期;华北落叶松平均累积径向生长量随密度增大而减小;林分密度、生长时期、树木大小和气象因子共同调控树木的年内径向生长。

黄土高原中部降水对乔灌木气候响应敏感性的影响

基于黄土高原中部地区降水梯度上(绥德447mm,延安531mm,宜君603mm)的乔灌木年轮材料,通过树木年轮气候学方法分析了不同降水条件下,乔木刺槐(Robinia pseudoacacia)、山杏(Armeniaca sibirica),灌木酸枣(Ziziphus jujuba)、白刺花(Sophora davidii)径向生长的气候敏感性差异。结果表明:(1)绥德、宜君酸枣标准年表的相关统计参量明显偏低,个体生长一致性较差,年轮材料中包含的气候信息较少,这表明绥德和宜君地区的酸枣对本地气候条件已高度适应,径向生长受气候影响较小。(2)刺槐、山杏、酸枣、白刺花均在森林草原过渡带(延安)表现出较高的气候敏感性,气候要素对各物种径向生长的解释率在该地区最高。除绥德、宜君酸枣外,各样点的乔灌木气候--生长关系均存在“时滞效应”。整体上研究区内酸枣气候敏感性最差。在绥德和宜君地区,灌木气候敏感性明显弱于乔木。(3)乡土物种山杏、酸枣、白刺花在三个采样点均对长期干旱胁迫不敏感,对当地环境具有较强的生态适应性。人工物种刺槐在延安地区,从上年生长季末至当年生长季结束持续对干旱胁迫响应敏感,而在绥德和宜君地区则对干旱胁迫不敏感。刺槐、山杏、白刺花在宜君地区与温度的响应特征整体上发生明显趋势转换,温度对刺槐、白刺花的负反馈减弱正反馈增强,而对山杏的正反馈减弱负反馈增强。

竞争压力下栓皮栎受气候影响的生长特征及其干旱适应性

为评估竞争压力下气候对栓皮栎(Quercus variabilis Bl.)径向生长的影响及树木对干旱的适应性,以太行山南麓地区混交林中的栓皮栎为研究对象,考虑不同竞争强度与竞争主要来源,结合月气象因子及干旱稳定性指标,分析竞争对栓皮栎径向生长的作用特征。结果表明:研究区栓皮栎径向生长主要受当年6-8月份的气候因子影响。竞争强度分组分析后发现,竞争强度的加剧削弱了栓皮栎径向生长对上一年温度的滞后响应,同时增加了对夏季相对湿度的敏感性。竞争显著提高以种间竞争为主的栓皮栎的干旱抵抗力(R_(t));相反,竞争压力对以种内竞争为主的栓皮栎的干旱恢复力(R_(c))、弹性力(R_(s))造成了负面影响。当竞争主要来自种间时,栓皮栎径向生长表现出更高的气候敏感性与干旱抵抗力。竞争调节了气候对栓皮栎生长的影响模式及干旱适应性程度,种间及种内的竞争调节作用是非等效的。

昌岭山油松年内径向生长特征及其对气候的响应

利用树木径向生长记录仪对甘肃昌岭山油松径向生长进行了连续三年动态监测,通过平均值法提取了油松净径向生长数据,利用Gompertz函数对油松径向生长曲线进行拟合,分析了油松年内径向生长特征,并结合气象资料分析了油松径向生长对温度和降水的响应,探讨了油松径向生长开始时间与温度的关系以及气候影响油松径向生长的机制。结果表明:(1)油松年内径向生长速率先增大后减小,最大值出现5月下旬到6月上旬,主要生长时间集中在5—8月。两棵油松径向生长开始时间较一致,出现在4月上旬和中旬,但结束时间存在较大差异。(2)生长期油松径向生长与平均气温、最高气温和最低气温均呈负相关,与降水呈正相关,但相关性强弱存在年际差异。(3)昌岭山地区油松径向生长开始的平均气温阈值在7℃左右。生长季温度会通过影响水分条件间接对油松径向生长造成影响,异常充沛的降水可能是2019年6月两棵油松净径向生长量偏多的主要原因。

Growth response of Abies spectabilis to climate along an elevation gradient of the Manang valley in the central Himalayas

The Himalayas are characterized by a broad gradient of bioclimatic zones along their elevation.However,less is known how forest growth responds to climatic change along elevation.In this study,four standard treering width chronologies of Himalayan fir(Abies spectabilis)were developed,spanning 142–649 years along an elevation gradient of 3076–3900 m a.s.l.Principal component analysis classified the four chronologies into two groups;the ones at lower elevations(M1 and M2)and higher elevations(M3 and M4)show two distinct growth trends.Radial growth is limited by summer(June–August)precipitation at M3,and by precipitation during spring(March–May)and summer at M4.It is limited by spring temperatures and winter precipitation(December–February)at M1.Tree-ring width chronologies also significantly correlate with winter and spring Palmer Drought Severity Index(PDSI)at M1,and with summer PDSI at M3 and M4.Thus,Himalayan fir growth at high elevations is mainly limited by moisture stress rather than by low temperatures.Furthermore,the occurrence of missing rings coincides with dry periods,providing additional evidence for moisture limitation of Himalayan fir growth.