Tree Growth Decline Research Articles

Timescale Effects of Radial Growth Responses of Two Dominant Coniferous Trees on Climate Change in the Eastern Qilian Mountains

To explore the difference in the response of the radial growth of Pinus tabulaeformis and Picea crassifolia on different timescales to climate factors in the eastern part of Qilian Mountains, we used dendrochronology to select four different timescales (day, pentad (5 days), dekad (10 days), and month) for exploration. The primary conclusions were as follows: (1) According to an investigation of the dynamic correlations between radial growth and climate conditions, drought during the growing season has been the dominant limiting factor for radial growth across both species in recent decades; (2) climate data at the dekad scale are best for examining the correlations between radial growth and climate variables; and (3) based on basal area increment, P. tabuliformis in the study area showed a trend of first an increase and then a decrease, while P. crassifolia showed a trend of continuous increase (BAI). As the climate continues to warm in the future, forest ecosystems in arid and semi-arid areas will be more susceptible to severe drought, which will lead to a decline in tree growth, death, and community deterioration. As a result, it is critical to implement appropriate management approaches for various species based on the peculiarities of their climate change responses.

How to cope with drought and not die trying: Drought acclimation across tree species with contrasting niche breadth

Abstract Worldwide drought events have been reported to cause tree growth decline and mortality, thus altering the carbon (C) balance of forest ecosystems. While most of the attention has been focused on the physiological mechanisms associated with drought‐induced tree responses of a few species at specific locations, the ecological attributes of these species, like their niche breadth, may be also important in determining species’ sensitivity or resilience to drought. We postulated that wide‐niche breadth tree species should be more drought‐resilient than narrow‐niche breadth species. Using the most severe 2015–2016 El Niño drought event in the last 70 years in Patagonia, we determined pre‐ and post‐drought growth (BAI, basal area increment), C reserves in the form of non‐structural carbohydrate concentrations (NSCs = starch and soluble sugars), wood isotope (δ13C, iWUE and δ18O) signalling and xylem anatomy (mean vessel diameter, mvd) in eight angiosperm tree species of contrasting niche breadth across a sharp precipitation gradient in southern Chile. All species responded in unison after the drought with a non‐water‐conservative response, maintaining BAI and NSCs, decreasing δ13C, and increasing both mvd and the soluble sugars:NSCs ratio relative to pre‐drought time. Contrary to previous results reporting species‐specific drought responses, our results show unequivocally a functional coordination of organisms’ vital traits associated with a non‐water‐conservative strategy, and a drought‐induced acclimation based on starch conversion into soluble sugars in all of the tree species we examined, regardless of their niche breadth and habitat preference. We state that abiotic drivers such as drought may have selected similar interspecific responses provided that they operate at the community level rather than at the species level. These findings mark the need to revise current views about the ultimate interspecific functional coordination of organisms’ vital traits when facing more frequent and intensive drought events. A free Plain Language Summary can be found within the Supporting Information of this article.

The Effect of Foliar and Ground-Applied Essential Nutrients on Huanglongbing-Affected Mature Citrus Trees.

The fate of foliar and ground-applied essential nutrients is the least studied topic under citrus greening or Huanglongbing (HLB)-affected citrus, which is inherently suffering from severe root decline because of HLB-associated problems. The objective of this study was to evaluate if ground-applied coupled with foliar spray of essential nutrients can reverse the decline in tree growth and understand the fate of the nutrients in the soil-root-tree interfaces. The treatments were arranged in a split-split plot design in which nitrogen (N) was ground-applied in 20 splits biweekly and Mn, Zn, and B were foliar and /or ground-applied in three splits following the spring, summer, and late summer flush seasons. Soil nutrients in three depths (0–15, 15–30, and 30–45 cm), root, and leaf nutrient concentrations of the essential nutrients, leaf area index (LAI), and tree canopy volume (TCV) data were studied twice (spring and summer) for two years. A significantly higher soil NH4-N and NO3-N concentrations were detected in the topsoil depth than the two lower soil depths (15–30 and 30–45 cm) indicating lesser nutrient leaching as trees received moderate (224 kg ha−1) N rate. Except for soil zinc (Zn) concentration, all the nutrient concentrations were significantly higher in the topsoil (0–15 cm), compared with two lower soil depths indicating that Zn was intricate by changes in soil environmental conditions, root acquisition, and/or leaching to lower soil depth. Leaf N concentration significantly increased over time following seasonal environmental fluctuations, tree growth, and development. Thus, leaf N concentration remained above the optimum nutrient range implying lower N requirement under irrigation scheduling with SmartIrrigation, an App used to determine the daily irrigation duration to meet tree water requirement and split fertigation techniques. Root Manganese (Mn) and Zn concentrations were significantly higher in the root tissues of the treated than the control trees and translocated to the leaves accordingly. Meanwhile, a significantly higher LAI for trees budded on Swingle (Swc) rootstock however, larger TCV for trees budded on Volkameriana (Volk) rootstocks. The trees had significantly larger TCV when the trees received a moderate N rate during early study years and under foliar 9 kg ha−1 coupled with the ground 9 kg ha−1 Mn and Zn treatments during the late study years. Therefore, split ground application of 224 kg ha−1 of N, foliar applied 9 kg ha−1 coupled with ground-applied 9 kg ha−1 Mn and Zn were the suggested rates to sustain the essential leaf nutrient concentration within the optimum ranges and improve the deterioration of vegetative growth associated with HLB-induced problems of citrus trees.

The Kroof experiment: realization and efficacy of a recurrent drought experiment plus recovery in a beech/spruce forest

AbstractForest ecosystems play a central role in global water and carbon cycles, yet the impact of global climate change, in particular drought, on trees and forests is poorly understood. Therefore, there is an urgent need for forest‐scale experiments in improving our understanding of trees’ responses to extreme drought events and subsequent recovery under field conditions. Here, we present the design and efficacy of a novel throughfall exclusion experiment with retractable roofs in a mature forest allowing for flexible drought and recovery periods. A total of 12 plots (144 ± 26 m2 on average) with 3–7 European beech and Norway spruce trees each were established by root trenching to a depth of one meter, four years prior to the experiment. Subsequent installation of roofs (n = 6) allowed for the removal of throughfall precipitation and almost a complete non‐availability of soil water in the upper 70 cm during five subsequent growing seasons, that is, 2014–2018. This reduction in available soil water resulted in pre‐dawn leaf water potentials down to −1.8 MPa in mature trees. Stem diameter growth decreased by 30% in beech and 70% in spruce, and fine root abundance was reduced by 57% in beech and 73% in spruce compared with controls. After only one growing season, the mycorrhizal community composition changed in response to drought. Careful watering of hydrophobic forest soils in early summer of 2019 resulted in recovered pre‐dawn leaf water potentials of drought‐stressed trees within one week. Recovery of stem diameter growth, however, did not occur within the same growing season and remained reduced by 33% in beech and 69% in spruce compared with controls. The implemented throughfall exclusion system imposed recurrent seasonal drought events on a mature beech/spruce forest with high efficacy. Shifts in community composition of mycorrhizae in parallel to tree growth decline advocate for a more holistic view on forest‐scale drought and watering experiments, particularly in light of more frequently predicted drought events in future. The perennial nature of mature trees and their subsequent slow recovery from drought, that is, over multiple growing seasons, argues for more long‐term experiments that span several years.

Tree growth decline as a response to projected climate change in the 21st century in Mediterranean mountain forests of Chile

Global Climate Models project that observed climate trends are likely to be preserved and the number of extreme events will be increasing during the rest of the 21st century, which may have a detrimental impact on forest ecosystems. These impacts may include forest decline and widespread dieback of the most vulnerable biomes, such as the Mediterranean Forest of Central Chile (MFCC). Nothofagus macrocarpa and Austrocedrus chilensis are two canopy-dominant, endangered tree species in the mountains of MFCC. Here, we project tree growth of these species based on tree-ring width chronologies, a simplified version of a process-based model, and climate change projections. We used the tree ring information derived from ~400 trees from 12 sites distributed across MFCC in combination with the simplified version of process-based Vaganov-Shashkin tree-growth model (VS-Lite) to forecast changes in tree growth for the next four decades. Tree growth projections were made on the basis of monthly values of temperature and precipitation from the output of 35 climate models based on two ensembles of CO 2 emission scenarios of the IPCC AR5 (RCP 8.5: higher-emission scenario, and RCP 2.6: lower-emission scenario). For the MFCC region these scenarios result in temperature rise ranging between 0.5 °C and 2.0 °C, and a precipitation decrease between 5% and 20% by the year 2065, as related to historical conditions. Our results showed that the VS-Lite model is capable of reproducing tree growth decline during the recent extreme dry period, i.e. 2010–2018, which supports its use for tree growth projections in the MFCC region. According to the modeling results, we find that tree growth in both N. macrocarpa and A. chilensis forests distributed in the MFCC region will be adversely affected by future climate changes, mainly starting from the year 2035, under both scenarios. Our work provides evidence of the degree of vulnerability of Mediterranean mountain forests in central Chile according to current climate change projections. The projected decline in tree growth indicates serious risks in the dynamics and survival of these forests relatively soon, so alerts are given about this situation which may require to counteract the deleterious effects of global change on vegetation in this region. • A VS-Lite model was used to project radial growth from two mountain tree species of Central Chile Mediterranean forests. • The tree-growth model was robustly calibrated and validated for its use in future growth projections under climate change. • A significant tree growth decline in response to climate change is projected in Central Chile by 2065.

Water and Soil Nutrient Dynamics of Huanglongbing-Affected Citrus Trees as Impacted by Ground-Applied Nutrients

The decrease in the rate of inflow and outflow of water—and thereby the uptake of plant nutrients as the result of Huanglongbing (HLB or citrus greening)—leads to a decline in overall tree growth and the development of nutrient deficiencies in HLB-affected citrus trees. This study was conducted at the University of Florida, Southwest Florida Research and Education Center (SWFREC) near Immokalee, FL from January 2017 through December 2019. The objective of the study was to determine the effect of rootstocks, nutrient type, rate, and frequency of applications on leaf area index (LAI), water relations (stomatal conductance [gs], stem water potential [Ψw], and sap flow), soil nutrient accumulation, and dynamics under HLB-affected citrus trees. The experiment was arranged in a split-split plot design that consisted of two types of rootstocks, three nitrogen (N) rates, three soil-applied secondary macronutrients, and an untreated control replicated four times. LAI significantly increased in response to the secondary macronutrients compared with uncontrolled trees. A significantly greater gs, and thus a decline in Ψw, was a manifestation of higher sap flow per unit LA (leaf area) and moisture stress for trees budded on Swingle (Swc) than Cleopatra (Cleo) rootstocks, respectively. The hourly sap flow showed significantly less water consumption per unit LA for trees that received a full dose of Ca or Mg nutrition than Ca + Mg treated and untreated control trees. The soil nutrient concentrations were consistently higher in the topmost soil depth (0–15 cm) than the two lower soil depths (15–30 cm, 30–45 cm). Mobile nutrients: soil nitrate–nitrogen (NO3-N) and Mg2+ Mg2+, Mn2+, Zn2+, and B leached to the lower soil (15–30 cm) depth during the summer season. However, the multiple split applications of N as Best Management Practices (BMPs) and optimum irrigation scheduling based on reference evapotranspiration (ETo) maintained soil available N (ammonium nitrogen [NH4-N] and NO3-N) below 4.0 mg kg−1, which was a magnitude 2.0–4.0× less than the conventional N applications. Soil NH4-N and NO3-N leached to the two lower soil depths during the rainy summer season only when trees received the highest N rate (280 kg ha−1), suggesting a lower citrus N requirement. Therefore, 224 kg ha−1 N coupled with a full Ca or Mg dose could be the recommended rate for HLB-affected citrus trees.

Recent decline of high altitude coniferous growth due to thermo-hydraulic constrains: evidence from the Miyaluo Forest Reserve, Western Sichuan Plateau of China

Tree growth decline has been reported in many places around the globe under the context of increasingly warming climate, and strengthening drought intensity is detected to be the primary factor for such decline, particularly in northern forest sites, as well as arid and semi-arid areas. Yet, the forest growth decline in high altitude, high mountain sites certainly merits investigation. Here, we reported faxon fir (Abies fargesii var. faxoniana) forest growth decline (slope = -0.64) at the tree line (4150 m above sea level) in Miyaluo Forest Reserve (MFR) at the Western Sichuan Plateau, southwestern China since 2000. We investigated the cause of tree growth decline by applying dendrochronological approaches. We took tree-ring samples from fir trees at the tree line and developed tree-ring width (TRW) chronology. The tree growth – climate relationship analysis showed that maximum temperature (Tmax) was the primary factor limiting the radial growth of fir trees in the investigated area. The moving correlation analysis indicated the strengthening positive influence of Tmax, spring precipitation, and cloud cover during winter and monsoon period on radial growth since 2000s. Our results have shown that both thermal and hydraulic constrains accounted for the radial growth decline of fir trees at the tree line of MFR in the western Sichuan Plateau.

Climate sensitivity of conifer growth doesn’t reveal distinct low–high dipole along the elevation gradient in the Wolong National Natural Reserve, SW China

Recent climate warming is usually hypothesized to cause tree growth decline in the semi-arid regions where forests are particularly vulnerable to warming induced increases of water deficit. But there is still a large knowledge gap of climate warming effects on tree growth of cold temperate forest in the sub-humid region. Here we assess how climate warming has affected tree growth in the Wolong National Natural Reserve, Southwestern China, where recent warming might not cause tree growth decline because of the cold-humid climatic conditions. Tree-ring data from four co-dominant coniferous species (Larix potaninii var. macrocarpa, Tsuga chinensis, Abies faxoniana and Juniperus saltuaria) along an elevation gradient (from 2700 m to 3700 m) all imprinted temperature signals, and were both positively and significantly correlated with instrumental record of temperature data during the analyzed period of 1954–2010. Furthermore, the rising temperature since 1980 induced pervasive tree growth increases and stronger temperature signals for the coniferous species along the elevation gradient. The tree-ring chronology recorded a strong coherence with instrumental temperature since 1980 and was successful to keep up with the pace of climate warming rate. If climate warming continues, further increases in forest growth could be expected, and the terrestrial carbon sink will be strengthened for the local forest ecosystem in the future.

Forecasting Forest Vulnerability to Drought in Pyrenean Silver Fir Forests Showing Dieback

Forest dieback is manifested as widespread loss of tree vigour, growth decline and high mortality rates. Forest dieback is becoming increasingly frequent and extended, particularly in drought-prone regions. This is the case of the south-western Spanish Pyrenees, where keystone species such as Silver fir reach their xeric and southern distribution limits. While dieback of this species has been widely documented in this area, we still lack methodologies to forecast the vulnerability of these forests in response to increasing drought stress so as to anticipate their potential dieback in the future. Here we study multiple features of Silver fir forest and trees to evaluate whether previous growth rates and their growth trends are valid predictors of forest dieback. Further, we validate our methodology revisiting two Silver fir sites sampled two decades ago. The defoliation degree was strongly related with radial growth, and growth trends differed between moderately to highly defoliated trees and non-defoliated trees. Forests showing dieback, i.e. those in which 25% of the sampled trees showing defoliation > 50%, were located at low elevation and received less rainfall in summer than forests showing no dieback. Trees showing high defoliation presented lower growth rates than non-defoliated trees. Moreover, we ratified that defoliation has increased considerably over the last two decades in one of the two revisited sites, but we were unable to accurately forecast growth trends in both sites, particularly in the site not showing dieback. The retrospective assessment of growth rates and trends offers valuable information on the vulnerability of Silver fir trees to drought. However, we are still far from being able to forecast the vulnerability of Silver fir forest to increasing drought. A systematic monitoring of growth across a wide tree-ring network of sites might provide valuable information to advance in this direction.

Drought-induced tree growth decline in the desert margins of Northwestern China

Water deficiency is the primary limiting factor for tree growth in arid and semi-arid areas. Droughts associated with rising temperatures have increased in severity and frequency globally over the past few decades, making the trees in the drought-prone sites first be affected by water shortages. However, our understanding of tree growth status in these areas, and of their response to drought, is currently insufficient; especially in the context of global warming. Here, we studied 94 Chinese pine (Pinus tabulaeformis) and 86 spruce (Picea crassifolia) trees from different altitudes [2,100–2400 m above sea level (a.s.l.)] distributed at the desert margins of Northwestern China to explore tree growth and drought response from multiple perspectives using dendroecological approaches. Significant growth decline, across all tree species and altitudes, was detected in response to an interdecadal trend towards a drier climate. Moreover, the extent of tree growth decline, the proportion of affected trees, and the degree of moisture dependence have all tended to increase in each sample site, most likely due to enhanced drought severity and duration in recent decades. The more sensitive and susceptible trees were found at lower elevations (drier sites) and may signify a higher vulnerability to heating-induced drought stress. Tree resistance to drought showed strong negative correlation with drought severity across all sample sites. However, the connection between post-drought tree resilience and drought intensity is weak, perhaps because the samples were all collected from living trees, while those that had died were not sampled. The priority for future work should be to combine surviving and dead trees simultaneously, thus achieving a more representative view of tree resilience to drought; this will improve our knowledge of forest dynamics and even ecosystem succession in these vulnerable and sensitive environments.

Neighbourhood diversity mitigates drought impacts on tree growth

Abstract Biodiversity is considered to mitigate detrimental impacts of climate change on the functioning of forest ecosystems, such as drought‐induced decline in forest productivity. However, previous studies produced controversial results and experimental evidence is rare. Specifically, the biological mechanisms underlying mitigation effects remain unclear, as existing work focuses on biodiversity effects related to the community scale. Using trait‐based neighbourhood models, we quantified changes in above‐ground wood productivity of 3,397 trees that were planted in a large‐scale tree diversity experiment in subtropical China across gradients of neighbourhood diversity and climatic conditions over a 6‐year period. This approach allowed us to simultaneously assess to what extent functional traits of a focal tree and biodiversity at the local neighbourhood scale mediate the growth response of individual trees to drought events. We found that neighbourhood tree species richness can mitigate for drought‐induced growth decline of young trees. Overall, positive net biodiversity effects were strongest during drought and increased with increasing taxonomic diversity of neighbours. In particular, drought‐sensitive species (i.e. those with a low cavitation resistance) benefitted the most from growing in diverse neighbourhoods, suggesting that soil water partitioning among local neighbours during drought particularly facilitated most vulnerable individuals. Thus, diverse neighbourhoods may enhance ecosystem resistance to drought by locally supporting drought‐sensitive species in the community. Synthesis. Our findings demonstrate that mechanisms operating at the local neighbourhood scale are a key component for regulating forests responses to drought and improve insights into how local species interactions vary along stress gradients in highly diverse tree communities.

Coping With Extreme Events: Growth and Water‐Use Efficiency of Trees in Western Mexico During the Driest and Wettest Periods of the Past One Hundred Sixty Years

AbstractUnderstanding how trees respond to extreme events is important to predict how climate change will impact forests in the future. In this study, we report changes in radial growth and tree‐ring carbon (δ13C) and oxygen (δ18O) stable isotope ratios of Pseudotsuga menziesii (Douglas‐fir) in western Mexico. Tree growth was compared with δ13C and δ18O ratios recorded during dry and wet periods caused by El Niño‐Southern Oscillation since 1850. The three driest and three wettest events during the studied period caused tree growth decline of up to 50% followed by 6–10 years of slow recovery until baseline growth was regained. Wet events resulted in up to 17% growth increase, a positive effect that persisted for no more than 3–5 years. Stable isotope ratios recorded physiological adjustments that in some cases correlated significantly with tree growth. Excursions in tree‐ring Δ13C and δ18O isotope ratios suggest that trees cope with dry and wet periods with proportional but divergent adjustments in photosynthesis versus stomatal conductance. Notably, the intrinsic water‐use efficiency—that is, the ratio between carbon assimilation and water loss through transpiration—was positively correlated with tree basal growth only during dry periods. We found no significant correlations between growth and intrinsic water‐use efficiency during wet periods. Contrary to expectations, rising CO2 levels over the past ~160 years did not affect tree growth response to precipitation variability.

Recent tree growth decline unprecedented over the last four centuries in a Tibetan juniper forest

Forest structure and function are subject to risks of growth declines from intensified drought and frequent extreme events related to climate warming. Knowledge of tree growth declines will help anticipate future responses of forests to climate change. In this study, we investigated tree growth declines over the last four centuries in a juniper forest on the eastern Tibetan Plateau. By analyzing the radial growth trajectories of individual trees, we identified two events of intense growth decline, one in 1817–1830 and the other in 1969–1999 over the past four centuries. The intensity of the recent decline was unprecedented in the period under study. Ring-width chronology showed a positive correlation with self-calibrating Palmer Drought Severity Indices and a negative correlation with mean monthly temperatures in May and June. The recent intensified growth decline may have been due to temperature-induced frequent droughts in the study area. Our findings suggest that trees in this juniper forest may face a higher risk of growth decline and even mortality under continued climate warming.

Modeling regional drought-stress indices for beech forests in Mediterranean mountains based on tree-ring data

Due to the recent spread of forest die-off worldwide, concerns arise about the relative influence of specific climate parameters on tree growth decline in semi-arid environments, such as the Mediterranean mountain forests. As temperatures increase, drought may reduce tree productivity and survival across these forest ecosystems. Drought-induced tree growth decline can be interpreted as an early-warning signal of forest vulnerability. Here, we modeled the relationship between tree-ring width index (RWI) of beech populations in mountain forests of south-central Italy and the standardized precipitation evapotranspiration index (SPEI) derived from local weather stations. The aim of the research was to propose a procedure to determine the tipping point of drought severity triggering tree decline in beech forests. We focused on the cumulative water balance over the previous 1 month, which was particularly appropriate in relationship with the soil water conditions of these Mediterranean mountains. Under drier conditions, the correlation between RWI and SPEI was stronger, soil water supply (early fall of current year) and atmospheric evaporative demand (late spring of current year) being the dominant factors limiting tree growth of southern beech populations.

Cumulative Drought Stress Leads to a Loss of Growth Resilience and Explains Higher Mortality in Planted than in Naturally Regenerated Pinus pinaster Stands

The assessment of the long-term impacts of drought on tree growth decline using tree-ring analyses may be used to test if plantations are more vulnerable to warming after successive droughts, leading to a “cumulative stress” effect. We selected 76 Pinus pinaster trees (declining and non-declining trees), and basal area increments over the last 20 years (BAI20) were calculated to build the chronologies for the stand types and vigor classes. Resistance, recovery and resilience indices were calculated. Pearson correlations, analyses and Partial Least-Squares regression were used to analyze the relationships among the response and environmental variables. We found a negative and significant relationship between mean temperature for May and June of the current year and growth in the naturally regenerated stands. This negative effect on growth under warm spring conditions was more noticeable in plantations than in naturally regenerated stands. A negative trend along time was found for the resilience index in planted stands. Evapotranspiration, maximum temperature and annual radiation showed significant and negative correlations with the growth of declining trees from planted stands, indicating they are susceptible to drought stress. Declining trees in planted stands showed a loss of growth resilience, specifically a negative trend after successive droughts.

Long-term changes in the tree radial growth and intrinsic water-use efficiency of Chuanxi spruce (Picea likiangensis var. balfouriana) in southwestern China

Elevated CO2 level in the atmosphere is expected to improve the tree growth rates and intrinsic water-use efficiency (iWUE). Although current results inferring from tree rings found the tree growth decline in water-limited area, it is still unclear whether spruce trees in humid southwestern China benefit from the increasing CO2. In this study, tree-ring width data were used to investigate the tree radial growth rate of Chuanxi spruce (Picea likiangensis var. balfouriana). Moreover, combining with the tree-ring carbon isotope date, we analyzed the physiological responses of Chuanxi spruce to rising CO2 concentrations in the atmosphere (Ca) associated with climatic change in southwestern China. From 1851 to 2009, iWUE of Chuanxi spruce rose by approximately 30.4%, and the ratio of atmospheric CO2 to leaf intercellular CO2 concentration (Ci/Ca) showed no significant trend in the study area. The result suggested that Chuanxi spruce used an active response strategy when Ca was significantly increased. iWUE showed a significant increasing trend in parallel with tree radial growth, indicating that the increasing iWUE resulted in an increase in radial growth. These results suggest that spruce forests in southwestern China have not shown declining trends under increasing Ca and climate change scenarios, in contrast to trees growing in water-limited areas. Therefore, spruce forests benefit from the increasing CO2 in the atmosphere in the humid areas of southwestern China.

Are Scots pine forest edges particularly prone to drought-induced mortality?

Climate change is expected to exacerbate the frequency of drought-induced tree mortality world-wide. To better predict the associated change of species composition and forest dynamics on various scales and develop adequate adaptation strategies, more information on the mechanisms driving the often observed patchiness of tree die-back is needed. Although forest-edge effects may play an important role within the given context, only few corresponding studies exist. Here, we investigate the regional die-back of Scots pine in Franconia, Germany, after a hot and dry summer in 2015, thereby emphasizing possible differences in mortality between forest edge and interior. By means of dendroecological investigations and close-range remote sensing, we assess long-term growth performance and current tree vitality along five different forest-edge distance gradients. Our results clearly indicate a differing growth performance between edge and interior trees, associated with a higher vulnerability to drought, increased mortality rates, and lower tree vitality at the forest edge. Prior long-lasting growth decline of dead trees compared to live trees suggests depletion of carbon reserves in course of a long-term drought persisting since the 1990s to be the cause of regional Scots pine die-back. These findings highlight the forest edge as a potential focal point of forest management adaptation strategies in the context of drought-induced mortality.

Anthropogenic nitrogen deposition ameliorates the decline in tree growth caused by a drier climate.

Most forest ecosystems are simultaneously affected by concurrent global change drivers. However, when assessing these effects, studies have mainly focused on the responses to single factors and have rarely evaluated the joined effects of the multiple aspects of environmental change. Here, we analyzed the combined effects of anthropogenic nitrogen (N) deposition and climatic conditions on the radial growth of Acer saccharum, a dominant tree species in eastern North American forests. We capitalized on a long-term N deposition study, replicated along a latitudinal gradient, that has been taking place for more than 20yr. We analyzed tree radial growth as a function of anthropogenic N deposition (ambient and experimental addition) and of summer temperature and soil water conditions. Our results reveal that experimental N deposition enhances radial growth of this species, an effect that was accentuated as temperature increased and soil water became more limiting. The spatial and temporal extent of our data also allowed us to assert that the positive effects of growing under the experimental N deposition are likely due to changes in the physiological performance of this species, and not due to the positive correlation between soil N and soil water holding capacity, as has been previously speculated in other studies. Our simulations of tree growth under forecasted climate scenarios specific for this region also revealed that although anthropogenic N deposition may enhance tree growth under a large array of environmental conditions, it will not mitigate the expected effects of growing under the considerably drier conditions characteristic of our most extreme climatic scenario.

气候变暖抑制西藏拉萨河大果圆柏树木生长

PDF HTML阅读 XML下载 导出引用 引用提醒 气候变暖抑制西藏拉萨河大果圆柏树木生长 DOI: 10.5846/stxb201807131522 作者: 作者单位: 成都理工大学 旅游与城乡规划学院,中国水利水电科学研究院水电可持续发展研究中心;中国水利水电科学研究院水电可持续发展研究中心,中国科学院生态环境研究中心 城市与区域生态国家重点实验室,呼伦贝尔市环境监测中心站,中国科学院地理科学与资源研究所生态网络观测与模拟重点实验室,呼伦贝尔市生态环境监测站 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2016YFC0502102）；西藏自治区科技支撑项目（Z2016C01G01/08） Climate warming decelerates growth of Sabina tibetica in Lhasa River area of Tibet Author: Affiliation: Chengdu University of Technology,,State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要: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。 Abstract:Lhasa River, situated in Qinghai-Tibet Plateau, is the largest tributary of the Yarlung Zangbo River. This region has experienced high warming rates in recent decades, which could have an effect on vegetation growth dynamics. Here, we used dendroclimatological techniques to sample and dispose tree cores of Sabina tibetica in Lhasa River area of Tibet and built standard ring-width index chronology. We assessed the dynamics of tree growth of Sabina tibetica over the past decades, and conducted correlations, partial correlations and moving correlation analysis to analyze the relationship between tree ring-width index chronology and climatic factors. Our results indicated that ring-width index (RWI) had strong positive correlations with total precipitation, relative humidity and Palmer Drought Severity Index (PDSI) from June to October of the previous year and from March to July during the current year's growing season, but significant negative associations with mean temperature and mean maximum temperature from June to September of the previous year and from March to August in the current year, and mean minimum temperature from May to July in the current year. Furthermore, drought because of climate warming had primary influence on tree growth decline in recent decades. If climate warming continues in Lhasa River area, further tree growth decline and increases in tree mortality may occur, potentially driving regional forest loss. 参考文献 相似文献 引证文献

Use of tree rings as indicator for groundwater level drawdown caused by tunnel excavation in Zhongliang Mountains, Chongqing, Southwest China

Tunnel excavation causes geological, hydrological, environmental and social changes. The effects of groundwater level changes caused by tunnelling on tree growth have been poorly understood. Dendrochronology was used to evaluate the impact of groundwater level drawdown on tree growth. Tree cores of Masson pines were collected from the areas affected by tunnel construction in the Zhongliang Mountains of Chongqing in south-western China to study the effects of tunnel excavation on the growth rate of trees by comparing with tree cores collected from unaffected areas. Excavation and early operation of the first tunnel in the Zhongliang Mountains from 1968 to 1984 caused a groundwater table drawdown in both karst aquifer and non-karst aquifer. The lowered groundwater table significantly reduced the growth rate of pine trees, and the low growth rate remained for 15 years. The effect was experienced up to at least 1 km from the tunnel axis. The decline in tree growth was higher in karst than in non-karst areas, though the effects on the trees of the karst areas were lagging. The high precipitation in 1998 contributed to groundwater recovery, after which the tree growth recovered moderately but not to the original level. Groundwater leakage of the recently excavated tunnels did not affect pine trees heavily, probably because the pines had adapted to the new hydrogeological conditions and new strategies in tunnel inflow management were adopted in the recently excavated tunnels. The use of tree growth rate as an indicator of groundwater table change in tunnelling areas offers a new option to study environmental impacts and the extent of tunnelling effects.