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  • 1
    Language: English
    In: Scientific reports, 2016-01-11, Vol.6 (1), p.19000-19000
    Description: Seasonal asymmetry in the interannual variations in the daytime and nighttime climate in the Northern Hemisphere (NH) is well documented, but its consequences for vegetation activity remain poorly understood. Here, we investigate the interannual responses of vegetation activity to variations of seasonal mean daytime and nighttime climate in NH (〉30 °N) during the past decades using remote sensing retrievals, FLUXNET and tree ring data. Despite a generally significant and positive response of vegetation activity to seasonal mean maximum temperature (Tmax) in ~22-25% of the boreal (〉50 °N) NH between spring and autumn, spring-summer progressive water limitations appear to decouple vegetation activity from the mean summer Tmax, particularly in climate zones with dry summers. Drought alleviation during autumn results in vegetation recovery from the marked warming-induced drought limitations observed in spring and summer across 24-26% of the temperate NH. Vegetation activity exhibits a pervasively negative correlation with the autumn mean minimum temperature, which is in contrast to the ambiguous patterns observed in spring and summer. Our findings provide new insights into how seasonal asymmetry in the interannual variations in the mean daytime and nighttime climate interacts with water limitations to produce spatiotemporally variable responses of vegetation growth.
    Subject(s): Geography ; Climate ; Plants - metabolism ; Seasons ; Daytime ; Asymmetry ; Temperature effects ; Vegetation ; Summer ; Drought ; Nighttime ; Diurnal ; Remote sensing ; Hemispheric laterality
    ISSN: 2045-2322
    E-ISSN: 2045-2322
    Source: Nature Open Access
    Source: Academic Search Ultimate
    Source: PubMed Central
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  • 2
    Language: English
    In: Ecology (Durham), 2014-09, Vol.95 (9), p.2453-2465
    Description: Birch ( Betula ) trees and forests are found across much of the temperate and boreal zones of the Northern Hemisphere. Yet, despite being an ecologically significant genus, it is not well studied compared to other genera like Pinus , Picea , Larix , Juniperus , Quercus , or Fagus . In the Himalayas, Himalayan birch ( Betula utilis ) is a widespread broadleaf timberline species that survives in mountain rain shadows via access to water from snowmelt. Because precipitation in the Nepalese Himalayas decreases with increasing elevation, we hypothesized that the growth of birch at the upper timberlines between 3900 and 4150 m above sea level is primarily limited by moisture availability rather than by low temperature. To examine this assumption, a total of 292 increment cores from 211 birch trees at nine timberline sites were taken for dendroecological analysis. The synchronous occurrence of narrow rings and the high interseries correlations within and among sites evidenced a reliable cross-dating and a common climatic signal in the tree-ring width variations. From March to May, all nine tree-ring-width site chronologies showed a strong positive response to total precipitation and a less-strong negative response to temperature. During the instrumental meteorological record (from 1960 to the present), years with a high percentage of locally missing rings coincided with dry and warm pre-monsoon seasons. Moreover, periods of below-average growth are in phase with well-known drought events all over monsoon Asia, showing additional evidence that Himalayan birch growth at the upper timberlines is persistently limited by moisture availability. Our study describes the rare case of a drought-induced alpine timberline that is comprised of a broadleaf tree species.
    Subject(s): Betula utilis ; precipitation ; alpine timberline ; drought ; climate sensitivity ; central Himalayas ; tree-ring width ; warming ; missing ring ; dendroecology ; pre-monsoon season ; Nepal ; Hardwood trees ; Dendroclimatology ; Climate change ; Climatology ; Precipitation ; Tree growth ; Timberlines ; Climate models ; Drought ; Growth rings
    ISSN: 0012-9658
    E-ISSN: 1939-9170
    Source: JSTOR Life Sciences
    Source: JSTOR Arts & Sciences I
    Source: Wiley Online Library All Journals
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  • 3
    Language: English
    In: Climatic change, 2016-01, Vol.134 (1), p.163-176
    Description: Semi-arid forests at the limit of their existence close to the Gobi Desert in Inner Asia might be vulnerable to warming-induced drought stress. Yet, not much is known about the impact of global-change-type droughts on these forests. Here, we show that warming-related tree mortality is recently taking place in high-elevation semi-arid Qinghai spruce (Picea crassifolia Kom.) forests of the north-eastern margin of the Tibetan Plateau (Qilian Mountains). Tree-ring samples were collected from 24 Qinghai spruce forest plots (20 m × 20 m) at three elevations (2600, 2700, 2800 m) along eight elevation transects on north-facing slopes. Three lines of evidence suggest that these forests are increasingly at risk of increased tree mortality as a consequence of global warming, (i) a strong precipitation and air humidity dependence of radial growth, (ii) increasing frequency of missing tree rings, and (iii) a rising tree mortality rate in recent decades. The recent drought episode on the north-eastern Tibetan Plateau may represent a precursor of future global-change-type drought events in large parts of Inner Asia. Warming-related tree mortality of the semi-arid forests may be interpreted as early-warning signs for the densely populated artificial oases surrounding the Gobi Desert, which largely depend on river run-off from the mountain forests on the edge of the Tibetan Plateau.
    Subject(s): Earth Sciences ; Climate Change/Climate Change Impacts ; Atmospheric Sciences ; Deforestation ; Environmental aspects ; Climatic changes ; Tibet ; Forest dynamics
    ISSN: 0165-0009
    E-ISSN: 1573-1480
    Source: Alma/SFX Local Collection
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  • 4
    Language: English
    In: The New phytologist, 2011-05-01, Vol.190 (3), p.760-769
    Description: As one of the world's highest natural tree lines, the Smith fir (Abies georgei var. smithii) tree line on the southeastern Tibetan Plateau is expected to vary as a function of climate warming. However, the spatial patterns and dynamics of the Smith fir tree line are not yet well understood. Three rectangular plots (30 m × 150 m) were established in the natural alpine tree-line ecotone on two north-facing (Plot N1, 4390 m asl; Plot N2, 4380 m asl) and one east-facing (Plot E1, 4360 m asl) slope. Dendroecological methods were used to monitor the tree-line patterns and dynamics over a 50-yr interval. The three study plots showed a similar pattern of regeneration dynamics, characterized by increased recruitment after the 1950s and an abrupt increase in the 1970s. Smith fir recruitment was significantly positively correlated with both summer and winter temperatures. However, Smith fir tree lines do not show a significant upward movement, despite warming on the Tibetan Plateau. The warming in the past 200 yr is already having a significant impact on the population density of the trees, but not on the position of the Smith fir tree line.
    Subject(s): Trees ; Climate change ; Population ecology ; Age structure ; Forest ecology ; Timberlines ; Global warming ; Ecotones ; Tree age ; Seedlings ; southeastern Tibetan Plateau ; recruitment ; age structure ; Abies georgei var. smithii ; dendroecology ; tree‐line dynamics ; climate change ; Geography ; Temperature ; Abies - physiology ; Time Factors ; Abies - anatomy & histology ; Ecosystem ; Abies - growth & development ; Seasons ; Trees - growth & development ; Regeneration - physiology ; Tibet ; Population Dynamics ; Global temperature changes
    ISSN: 0028-646X
    E-ISSN: 1469-8137
    Source: JSTOR Life Sciences
    Source: Elektronische Zeitschriftenbibliothek - Frei zugängliche E-Journals
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  • 5
    Language: English
    In: Trees (Berlin, West), 2019-08-01, Vol.33 (4), p.973-975
    Description: Quantitative wood anatomy represents a tool to investigate paleoclimatic signals on a seasonal to sub-seasonal basis.
    Subject(s): Life Sciences ; Plant Pathology ; Plant Anatomy/Development ; Forestry ; Agriculture ; Plant Physiology ; Plant Sciences ; Life Sciences & Biomedicine ; Science & Technology ; Mountain ecology ; Alpine ecosystems
    ISSN: 0931-1890
    E-ISSN: 1432-2285
    Source: Web of Science - Science Citation Index Expanded - 2019〈img src="http://exlibris-pub.s3.amazonaws.com/fromwos-v2.jpg" /〉
    Source: Alma/SFX Local Collection
    Source: ProQuest Central
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  • 6
    Language: English
    In: American journal of botany, 2019-10, Vol.106 (10), p.1386-1391
    Description: Premise The resumption of stem growth varies across the ontogenetic development of trees. Compared with younger trees, older ones have thicker outer bark with a temperature‐insulating effect that could potentially prevent the stem from warming in the spring. However, the question of whether xylogenesis in old trees is influenced by the thick bark still remains unresolved. Methods We investigated the onset of xylogenesis across the ontogenetic development of Smith fir (Abies georgei var. smithii) trees in the Sygera Mountains, southeastern Tibetan Plateau. The outer bark of older trees was also removed. Xylogenesis was monitored in microcores we collected every 3 days during May and June in 2017. Results Xylogenesis began in late May in young (〈50 yr) and mature (50–100 yr) trees, 1 week earlier than in adult (〉100–150 yr) and old (〉150–200 yr) trees. Older (〉200 yr) trees had the latest onset of xylogenesis, 2 weeks after young trees. The resumption of xylogenesis was similar between the control and bark‐removed trees. Conclusions Growth resumption was delayed in older and bigger trees. Outer bark did not affect the onset of xylogenesis, which indicated that the delayed resumption of growth during the lifespan of trees could be more related to endogenous factors than to an insulating effect of the thick bark of older individuals.
    Subject(s): cell differentiation ; cambium ; wood formation ; manipulative experiment ; secondary phloem ; xylem growth ; dendroecology ; ontogeny ; subalpine forest ; tree ring ; Life Sciences & Biomedicine ; Plant Sciences ; Science & Technology ; Trees ; Xylem ; Plant Bark ; Seasons ; Abies
    ISSN: 0002-9122
    E-ISSN: 1537-2197
    Source: Web of Science - Science Citation Index Expanded - 2019〈img src="http://exlibris-pub.s3.amazonaws.com/fromwos-v2.jpg" /〉
    Source: Wiley Online Library All Journals
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  • 7
    Language: English
    In: Annals of botany, 2015-03-01, Vol.115 (4), p.629-639
    Description: A series of studies have shown that temperature triggers the onset of xylogenesis of trees after winter dormancy. However, little is known about whether and how moisture availability influences xylogenesis in spring in drought-prone areas. Xylogenesis was monitored in five mature Qilian junipers (Juniperus przewalskii) by microcore sampling from 2009 to 2011 in a semi-arid area of the north-eastern Tibetan Plateau. A simple physical model of xylem cell production was developed and its sensitivity was analysed. The relationship between climate and growth was then evaluated, using weekly wood production data and climatic data from the study site. Delayed onset of xylogenesis in 2010 corresponded to a negative standardized precipitation evapotranspiration index (SPEI) value and a continuous period without rainfall in early May. The main period of wood formation was in June and July, and drier conditions from May to July led to a smaller number of xylem cells. Dry conditions in July could cause early cessation of xylem differentiation. The final number of xylem cells was mainly determined by the average production rate rather than the duration of new cell production. Xylem growth showed a positive and significant response to precipitation, but not to temperature. Precipitation in late spring and summer can play a critical role in the onset of xylogenesis and xylem cell production. The delay in the initiation of xylogenesis under extremely dry conditions seems to be a stress-avoidance strategy against hydraulic failure. These findings could thus demonstrate an evolutionary adaptation of Qilian juniper to the extremely dry conditions of the north-eastern Tibetan Plateau.
    Subject(s): ORIGINAL ARTICLES ; Juniperus - growth & development ; Climate ; Rain ; Snow ; Droughts ; Seasons ; Tibet ; Wood - growth & development ; standardized precipitation evapotranspiration index ; wood formation ; onset of xylogenesis ; drought ; Juniperus przewalskii ; SPEI ; xylem production rate ; juniper ; Original ; Semi-arid forest ; xylem differentiation
    ISSN: 0305-7364
    E-ISSN: 1095-8290
    Source: JSTOR Ecology & Botany II
    Source: Academic Search Ultimate
    Source: PubMed Central
    Source: Alma/SFX Local Collection
    Source: Oxford Journals 2016 Current and Archive A-Z Collection
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  • 8
    Language: English
    In: Annals of botany, 2009-09, Vol.104 (4), p.665-670
    Description: Background and Aims Shrubs and dwarf shrubs are wider spread on the Tibetan Plateau than trees and hence offer a unique opportunity to expand the present dendrochronological network into extreme environments beyond the survival limit of trees. Alpine shrublands on the Tibetan Plateau are characterized by rhododendron species. The dendrochronological potential of one alpine rhododendron species and its growth response to the extreme environment on the south-east Tibetan Plateau were investigated. Methods Twenty stem discs of the alpine snowy rhododendron (Rhododendron nivale) were collected close to the tongue of the Zuoqiupu Glacier in south-east Tibet, China. The skeleton plot technique was used for inter-comparison between samples to detect the growth pattern of each stem section. The ring-width chronology was developed by fitting a negative exponential function or a straight line of any slope. Bootstrapping correlations were calculated between the standard chronology and monthly climate data. Key Results The wood of snowy rhododendron is diffuse-porous with evenly distributed small-diameter vessels. It has well-defined growth rings. Most stem sections can be visually and statistically cross-dated. The resulting 75-year-long standard ring-width chronology is highly correlated with a timberline fir chronology about 200 km apart, providing a high degree of confidence in the cross-dating. The climate/growth association of alpine snowy rhododendron and of this timberline fir is similar, reflecting an impact of monthly mean minimum temperatures in November of the previous year and in July during the year of ring formation. Conclusions The alpine snowy rhododendron offers new research directions to investigate the environmental history of the Tibetan Plateau in those regions where up to now there was no chance of applying dendrochronology.
    Subject(s): alpine shrub ; Rhododendron nivale ; South-east Tibetan Plateau ; climate/growth association ; cross-dating ; dendroclimatological potential ; growth ring ; Dendroclimatology ; Climate change ; Subshrubs ; Precipitation ; Plant growth ; Shrubs ; Timberlines ; Climate models ; Growth rings ; Dendrochronology ; Geography ; Climate ; Rhododendron - anatomy & histology ; Wood - anatomy & histology ; Snow ; Time Factors ; Ecosystem ; Rhododendron - growth & development ; Tibet ; Meteorology ; growth association ; climate ; Original
    ISSN: 0305-7364
    E-ISSN: 1095-8290
    Source: JSTOR Ecology & Botany II
    Source: Academic Search Ultimate
    Source: PubMed Central
    Source: Alma/SFX Local Collection
    Source: Oxford Journals 2016 Current and Archive A-Z Collection
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  • 9
    Language: English
    In: Global change biology, 2013-08, Vol.19 (8), p.2500-2510
    Description: Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi‐arid settings. Here, we assess how climate warming has affected tree growth in one of the world's most extensive zones of semi‐arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi‐arid forests, where growing season water stress has been rising due to warming‐induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi‐arid sites is corroborated by correlation analyses comparing annual climate data to records of tree‐ring widths. These ring‐width records tend to be substantially more sensitive to drought variability at semi‐arid sites than at semi‐humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007–2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi‐arid forests.
    Subject(s): tree growth decline ; forest die-off ; drought ; semi-humid ; semi-arid ; tree ring ; Inner Asia ; semi‐humid ; forest die‐off ; semi‐arid ; Pinaceae - growth & development ; Global Warming ; Mongolia ; Trees - physiology ; Species Specificity ; Droughts ; China ; Siberia ; Trees - growth & development ; Pinaceae - physiology ; Climate ; Global temperature changes ; Growth ; Analysis ; Mortality ; Forests and forestry ; Statistics
    ISSN: 1354-1013
    E-ISSN: 1365-2486
    Source: Alma/SFX Local Collection
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  • 10
    Language: English
    In: Global change biology, 2018-11, Vol.24 (11), p.5549-5559
    Description: Among forest ecosystems, the alpine treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long‐term Himalayan treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan treelines, being good locations for testing if, in addition to temperature, precipitation mediates treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in treeline dynamics in 20 plots located at six alpine treeline sites, dominated by two tree species (birch, fir), and situated along an east–west precipitation gradient in the central Himalayas. Our reconstructions evidenced that treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine treelines and promote downward treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing treeline dynamics. Based on 20 treeline plots along an east–west precipitation gradient in the central Himalayas, this research showed that treelines shifted upward in response to recent climate warming, but their shift rates were mediated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine treelines and promote downward treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing treeline dynamics.
    Subject(s): central Himalayas ; treeline shift ; Alpine treeline ; tree recruitment ; climate change ; Global Warming ; Rain ; Trees - physiology ; Time Factors ; Nepal ; Altitude ; Plant Dispersal ; Analysis ; Alpine ecosystems ; Mountain ecology ; Environmental aspects ; Air pollution ; Global warming ; Rain and rainfall
    ISSN: 1354-1013
    E-ISSN: 1365-2486
    Source: Alma/SFX Local Collection
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