Early Summer Temperatures Research Articles

Dendroclimatic analysis of red pine affected by Diplodia shoot blight in different latitudinal regions in Michigan

Drought and intraspecific competition in red pine (Pinus resinosa Ait.) stands in Michigan have been implicated as predisposing factors for increased shoot blight risk caused by Diplodia pinea Desm. The overall objective of this study is to examine the interactive effects of drought, other climatic factors, and biotic factors (intraspecific competition) on productivity and growth of red pine forests affected by Diplodia shoot blight. This study incorporates a dendroclimatic approach that allows the retrospective examination of past annual diameter growth in relation to historical climate and the assessment of the potential impacts of future climate change. A total of 20 red pine stands were sampled in two latitudinal regions (the Upper Peninsula (UP) and the Lower Peninsula (LP) regions) of Michigan across two levels of initial stand density (low vs. high) and two levels of forest health condition (healthy vs. D. pinea affected). The full dendroclimatic relationships revealed in this study indicated that other climatic factors, in addition to summer drought stress, impacted red pine radial growth. Overall, red pine radial growth was generally more affected by precipitation and moisture index than solely by temperature variables. The radial growth response to climate depended on latitudinal region: summer moisture stress was more influential in the LP; cold spring and early summer temperatures negatively impacted growth more in the UP; and the degree of winter harshness was more of a factor in the UP. Crown damage caused by winter damage may have predisposed red pine stands to D. pinea affection by providing an easier entry point for fungal infection. Negative relations with precipitation in D. pinea affected stands may be due to increased dispersal of spores in D. pinea affected stands with significant rain and any increased storm and wind activity. Projections of radial growth under future scenarios of climate change indicate that climate warming has the potential to increase growth mainly in red pine stands in the UP region where growth has historically been limited by cool temperatures early in the growing season. Under the moisture index model, growth of red pine under the drier (A2) climate change scenario, only the D. pinea impacted high-density stands in the LP region are projected to show a significant decrease in growth by the middle (2041–2070) and final (2071–2100) projection periods. Model-based projections of forest growth in Michigan generally do not account for forest health issues such as invasive pathogens. The current study therefore provides a new understanding of the role of forest pathogens under future climate change.

Tree-growth response to climatic variability in two climatically contrasting treeline ecotone areas, central Himalaya, Nepal

Tree growth at the treeline ecotone is known to be sensitive to climate variability and is thus considered to be a worldwide biomonitor of climate change. However, our understanding of within-region variation in growth responses through space and time is limited. A dry south-facing slope dominated by Pinus wallichiana A.B. Jacks. and a wet north-facing slope dominated by Abies spectabilis (D. Don) Spach in Nepal, central Himalaya, were used to analyze the intersite (i.e., dry vs. wet sites) and intrasite (i.e., treeline vs. forest line elevations) tree-growth relationships, as well as response to monthly and seasonal temperature and precipitation at annual and bidecadal time scales. At both study sites and at two elevations within each site, growth can be strongly affected by growing-season and nongrowing-season factors; however, there are inconsistencies in terms of the climate–growth relationship across space and over time. At the dry site, only a weak positive growth response to summer temperature is observed. At both sites, there is a negative growth response to winter precipitation at both high and low elevations, and this response is markedly independent of the summer and winter temperature trends of the respective site. At the wet site, growth at the higher elevation is negatively correlated to the early summer temperature, whereas a positive growth response to spring precipitation is observed at the lower elevation, indicating a possible drought effect. The results illustrate how different climatic drivers may govern tree-growth responses both between sites with contrasting climates within a region and along elevational gradients within the treeline ecotone. This underlines the need for multiscale studies and a focus on multiple climate variables when analyzing treeline ecotone responses to climate change.

Variation in benthic invertebrate abundance along thermal gradients within headwater streams of a temperate basin in Japan

To better understand the impacts of water temperature variation on stream invertebrates, we sampled benthic assemblages and measured water temperature monthly in headwater streams located in northeast Japan during 2011 and 2012. The sites in headwater streams had similar hydraulic and topographical settings, were free of man-made structures, and ranged in elevation from 100 to 850 m above sea level. The results of month-by-month analysis on the relationship between temperature and Plecoptera density revealed that the abundance declined with highly elevated temperatures in mid-summer (July, August). The strongest relationship between variation in Plecoptera abundance (June to October in 2012), however, and water temperature occurred during early summer (June). Thus, early summer temperatures contribute to greater seasonal increase in abundance, suggesting that snapshot data may be unreliable for detecting consistent relationships between the abundance and temperature. The degree of similarity in benthic fauna between sites was significantly negatively correlated with differences in water temperature but not correlated with geographical distance. These results suggest that faunal composition varies along the water temperature gradient rather than habitat connectivity in temperate headwater streams.

Exploring the impact of regional climate and local hydrology on Pinus sylvestris L. growth variability – A comparison between pine populations growing on peat soils and mineral soils in Lithuania

Aims To compare growth variability of Scots pine (Pinus sylvestris L.) ondifferent soil types, and to assess the potential of peat-soil pines for climatological and hydrological studies. Methods We used extensive dendrochronological analyses to investigate temporal and spatial responses of pines growing on peat soils and mineral soils in three regions of Lithuania. Results Significant correlations were observed between tree populations growing on similar soil types in different geographical regions, whereas synchronicity was absent between neighbouring stands growing on different soil types. At mineral soils, tree growth was significantly correlated with winter and early summer temperatures, whereas a more complex response was detected in peat-soil trees, presumably reflecting a multiannual synthesis of moisture variability and changing hydrology. Synchronous long-term peat soil tree-growth variations observed over large parts of the Baltics point to a possible regional hydrological forcing. Our results may therefore improve hydrological reconstructions using living and subfossil peat-soil trees, and could be of prime importance given the major influence peatland water-table fluctuations have on a range of environmental processes. Conclusion Results reveal that peat-soil pines are unsuitable for high-frequency climate reconstruction, but demonstrate their potential for the reconstruction of multi-annual to decadal hydrological fluctuations. Mineral-soil pines, by contrast, should be used for temperature reconstructions.

Recent climate warming of central China reflected by temperature-sensitive tree growth in the eastern Qinling Mountains and its linkages to the Pacific and Atlantic oceans

We have developed a 202-year tree-ring width chronology of Shensi fir (Abies chensiensis) growing in an open canopy forest at the treeline of the eastern Qinling Mountains. Climate response analyses revealed that the ring width of Shensi fir trees is primarily controlled by the range of temperature from February-June. The regression model that we used for statistical temperature reconstruction passed the leave-one-out cross-validation used in dendroclimatology, resulting in a quality-controlled February-June reconstruction for the eastern Qinling Mountains. The model accounts for 36.7% of the instrumental temperature variance during the period of 1960–2012. Warm springs and early summers occurred during AD 1870–1873, 1909–1914, 1927–1958 and 1997–2012, while the periods of AD 1874–1908, 1915–1926 and 1959–1996 were relatively cold. Spatial climate correlation analyses with gridded land surface data revealed that our temperature reconstruction contains a strong regional temperature signal for central China. The linkages of our temperature reconstruction with sea surface temperature in the Atlantic and Pacific oceans suggest the connection of regional temperature variations to large-scale ocean-atmosphere-land circulation. Preliminary analysis of links between large-scale climatic variation and the temperature reconstruction also shows that there is a relationship between extremes in spring and early summer temperature and anomalous atmospheric circulation in the Qinling Mountains. Overall, our study provides reliable information for the research of past temperature variability in the Qinling Mountains, China.

Diversity, resource utilization, and phenology of fruiting bodies of litter-decomposing macrofungi in subtropical, temperate, and subalpine forests

The diversity, vegetative and reproductive characteristics, and phenology of litter decomposing macrofungi (LDM) were compared between humus forms and climatic regions. Fruiting bodies of LDM were examined for the forest floor of subtropical (ST), cool temperate (CT), and subalpine (SA) forests in Japan. Field surveys during one growing season yielded 35, 32, and 18 species in ST, CT, and SA, respectively. Species richness was generally higher in mull than in moder humus and in a warmer than in a cooler climate. A total of ten fungal families were observed, and species in the Mycenaceae dominated in the LDM assemblages at all study sites. A larger number of species fruited on deeper F layers of the forest floor in SA than in ST, where 74 % of species fruited directly on leaf litter. This observation was consistent with the analysis of radiocarbon content in fruiting bodies, implying that LDM tended to utilize older carbon accumulated at deeper layers of the forest floor in cooler climates. Seasonal changes in the fruiting frequency over a growing season exhibited similar two-peak patterns for all the study sites, coinciding with the periods of rainfall and increasing and decreasing air temperatures in early summer and autumn, respectively, but the fruiting period extended longer in a warmer than in a cooler climate.

Permanent forest plots show accelerating tree mortality in subalpine forests of the Colorado Front Range from 1982 to 2013

Broad-scale studies have documented widespread increases in tree mortality coincident with warming in the western U.S.A., but variability in patterns and agents of mortality is poorly documented based on multi-decadal observations of permanently marked trees, particularly in Rocky Mountain subalpine forests. The current study examines temporal variability in tree mortality based on monitoring >5000 permanently marked trees across a range of topographic positions and stand ages from c. 120 to >550years over a 31-year period in subalpine forests in the Colorado Front Range. This study documents accelerating rates of annual tree mortality for subalpine fir, Engelmann spruce, lodgepole pine, and limber pine from 1982 through 2013. Over the period from 1982 to 2013, annual mortality rates for all tree species combined increased from 0.36% to 1.03% in old stands (265 to >550years since stand-initiating fires) and from 0.30% to 0.72% in young stands (120years since fire). Tree populations at sites of topographically moister locations and where competition was less due to presence of canopy openings, experienced initially lower rates of tree mortality but all populations experienced higher mortality rates after c. 2008. In comparison with the 1953–1994 period, the frequency of extreme high temperatures in early summer increased after the mid-1970s and more markedly after 2000. Over time, the contribution of early summer (July) conditions to annual drought has increased. This pattern of climatic variability has been coincident with and conducive to a two and a half fold increase in the average annualized tree mortality rates for the total tracked tree population from the relatively cool and wet 1982–1994 period to the warmer and drier 2008–2013 period. Tree mortality attributable to bark beetles over the 1982–2013 period was minor, except for western balsam bark beetle (Dryocoetes confusus) which since 2008 has accounted for about 12% of the subalpine fir deaths. Overall, our findings indicate that even in the absence of lethal bark beetle outbreaks conifer mortality, apparently associated with moisture stress, has recently increased in subalpine forests in the Colorado Front Range.

Multiannual hydrological responses in Scots pine radial growth within raised bogs in southern Sweden

To explore interactions between climate and peatland hydrology, Scots pine ( L.) growing at four raised bogs in southern Sweden were subject to a dendroclimatological study. Radial tree growth reflecting climate and water table fluctuations over multiannual periods was detected as significant negative correlations between tree-ring width (TRW) chronologies and the preceding one to four years total precipitation or river discharge. Systematically stronger negative correlations were obtained when river discharge instead of precipitation was compared to radial tree growth. This indicates that river discharge reflect moisture variability of peat bogs better than what precipitation data does. Meanwhile, monthly precipitation and radial tree growth did not show any clear correlation, whereas spring and early summer temperatures had a positive influence on the tree growth. Our study shows that growth variability of bog pines in the Boreal zone reflect hydrological responses related to a synthesis of climate controlled moisture variability over several year periods.Pinus sylvestris

Early summer temperature changes in the southern Altai Mountains of Central Asia during the past 300 years

June–July mean temperature was reconstructed back to 1698 for the southern Altai Mountains in eastern Central Asia using four temperature series based on tree-ring widths. The reconstruction explains 48% of the variation in the observed temperature from 1962 to 2003. Warm periods occurred during 1714–1732, 1753–1776, 1800–1840, 1866–1886, 1893–1911, and 1943–1969, while the periods of 1708–1713, 1733–1752, 1777–1799, 1841–1865, 1887–1892, 1912–1942, and 1970–1993 were relatively cold. Power spectral and wavelet analyses demonstrated the existence of significant 50-, 14-, 2.8-, and 2.5-year cycles of variability. The results of a spatial correlation analysis suggested that this temperature reconstruction contains climatic signals for a large area of Central Asia. After employing a 21-year low-pass filter, the coherence of the newly reconstructed series with a regional temperature reconstruction for Central Asia and also with a local temperature reconstruction for the Zajsan Lake area of East Kazakhstan indicates that our temperature reconstruction captures broad-scale regional climatic variations in the low-frequency domain.

Early summer temperatures reconstructed from black pine (Pinus nigra Arnold) tree-ring widths from Albania

The first regional chronology of black pine ( Pinus nigra Arnold) from Albania, its response to climate and a 428-year long reconstruction of June–July temperatures for the 1583–2010 period are presented. Samples were collected at five locations from the north to the south of Albania. We constructed a 552-year long Pinus nigra chronology with sufficient sample depth for potential climate reconstruction from 1583 to 2010 (428 years). Response to precipitation was significant only for July of the current year (0.23), while a clear temperature response to the May–August period was identified, with July having by far the highest correlation (−0.47). When combined, June–July temperatures had the highest correlation of all tested combinations ( r = −0.63), explaining almost 40% of the tree-ring width variability. The test of the climate signal temporal stability using a 31-year running correlation highlighted the very stable relationship between tree-ring indices and June–July temperatures. The spatial extent of the regional Pinus nigra chronology tested, using a field correlation function, showed very high spatial correlation over a large part of the Balkan Peninsula and even southern Italy. Based on high explained variance between tree-ring indices and June–July temperatures and significant values of reduction of error (RE) and coefficient of efficiency statistics (CE; 0.62 and 0.25 in the calibration period), a linear model was developed, with June–July temperatures reconstructed for the 1583–2010 period. Our reconstruction and identified extreme years were compared with various temperature, drought and precipitation reconstructions from nearby regions, as well as data from documentary archives. We confirmed a high degree of similarity of our reconstruction with other reconstructions and documentary data.

Coherent pan‐Asian climatic and isotopic response to orbital forcing of tropical insolation

AbstractThe oxygen‐18 isotope composition of calcite in stalagmites across southern and eastern Asia are highly correlated to one another on orbital time scales: large negative excursions are coincident with maxima in summer insolation in the subtropics of the Northern Hemisphere (NH). These isotopic excursions reflect changes in the precipitation‐weighted isotopic composition of precipitation, δ18Op. We present results from two core experiments using an isotope‐enabled climate model—the“high‐insolation” and “low‐insolation” experiments—in which the model is forced by extrema in NH summer insolation. Compared to the low‐insolation experiment, the high‐insolation climate features profound, large‐scale changes in the pattern of monsoon precipitation spanning from Africa to Southeast Asia that are due to changes in the relative contributions of temperature and moisture to the near‐surface equivalent potential temperature θe. Under high insolation, a more rapid increase in land surface temperature in early summer causes the greatest θe (and hence precipitation) to shift from the oceans in low insolation (such as today) to be over land in high insolation (such as the early Holocene). The model captures the general pattern of isotopic excursions seen in caves spanning from Israel to western China, including large drops in δ18Op over eastern Tibet (−7‰), the Arabian Peninsula, and northeast Africa (−4‰). Although there are large changes in precipitation over Tibet, the change in δ18Op is due to changes in the δ18O of water vapor that is delivered and subsequently precipitated; it does not inform on local precipitation amount or intensity.

Impact of Nutrients and Temperature on Algal Growth and Relative Abundance of Xixi Wetland, China

This paper focused on eutrophication and algal succession problems of freshwater ecosystems. Water samples of the Xixi Wetland were sampled in the late autumn and early winter of 2013, and then analyzed for nitrogen and phosphorus species and chlorophyll-a indicators. Artificial climate chamber was used to simulate the nitrogen input and global warming scenario, to study the effect of nutrients (ammonia and nitrate) addition and temperature on the algal growth. The results show that the water quality of the wetland is good with TP, ammonia, and TN during the study period. Interaction impact of nutrients addition and temperature increase the relative abundance of cyanobacteria significantly (p<0.01), the total biomass was found to be more sensitive to ammonia addition. Therefore, it is especially important to pay more attention on this wetland during the algal bloom sensitive period of increasing temperature in early summer.

Mechanism of early-summer low-temperature extremes in Japan projected by a nonhydrostatic regional climate model

We investigated the mechanisms associated with projected early-summer low-temperature extremes in Japan at the end of the 21st century by means of a well-developed nonhydrostatic regional climate model under the A1B scenario provided by the Intergovernmental Panel on Climate Change-Special Report on Emission Scenario. The projected surface air temperature reveals that even in a climate warmer than that at present, extremely low daily minimum temperatures in early summer are comparable to those in the present climate at several locations. At locations where future low temperatures are remarkable, the temperature drop at night is larger in the future than at present. This temperature drop results from mainly two heat fluxes: upward longwave radiation and latent heat flux. In the future climate, upward longwave radiation increases owing to high temperature at the surface around the time of the sunset. In addition, the upward flux of latent heat increases owing to low relative humidity just above the surface. These dryer conditions are associated with lower relative humidity at 850hPa, suggesting the effects of synoptic systems. These two fluxes act to reduce the surface temperature, and hence surface air temperature.

Legacy effects of habitat degradation by Lesser Snow Geese on nesting Savannah Sparrows

Increased growth of the midcontinental population of Lesser Snow Geese (Chen caerulescens caerulescens) has led to overgrazing and habitat degradation at their Arctic and sub-Arctic breeding grounds. This habitat degradation has been shown to induce a trophic cascade that negatively affects plant, insect, and other avian species that share these habitats. In conjunction with a long-term study of the impacts of Lesser Snow Geese on habitat, we examined the dual influences of climate and long-term habitat change on the nesting occurrence of Savannah Sparrows near Churchill, Manitoba, Canada. Using multistate occupancy models, we found that variability in early-summer temperature and precipitation modulated year-to-year variability in nesting occurrence and detection probabilities. Extreme warm and wet conditions in early summer can benefit breeding Savannah Sparrows across the landscape. However, such events have not been prevalent enough to override the ~80% decline in Savannah Sparrow nesting occurrence over 36 yr. This dramatic decline can be attributed to the legacy of Lesser Snow Goose foraging, which has led to an 84% reduction in preferred shrub habitat for nesting Savannah Sparrows. Management actions targeted at reducing Lesser Snow Goose abundance and habitat restoration will be needed to allow sympatric Savannah Sparrows and functionally similar species to recover.

Evaluating temporal variation in Citizen Science Data against temporal variation in the environment

Citizen Science Data (CSD) is increasingly contributing to the assessment of biodiversity and ecosystems. However, there is a need to evaluate the usefulness of CSD for different purposes. Ideally, CSD from populations should be evaluated against independent population data collected using a proper sampling design, but such data are lacking for almost all species. We propose an approach for evaluating CSD against environmental data. First, an evaluation model is formulated based on knowledge of how environmental variables affect population dynamics. Second, the hypotheses of the evaluation model are tested statistically. Support for the evaluation model is interpreted as support for the CSD. We applied the approach to six longhorn beetle species using Swedish data from 1930–2000. The evaluation model assumed that early summer temperature affects larval development time. We found support for the evaluation model in two species, and some evidence in its favour in one species. This suggests that the CSD from these species reflect true inter‐annual variation. We also found statistical evidence for population trends in three to four species. In two of these, the evaluation model was supported thus providing particular support for the trend estimates. Lack of support for the evaluation model may be due to biological inaccuracy, the general characteristics of CSD, or low resolution of the environmental evaluation data. We also discuss alternative environmental data for evaluating CSD.

Early-summer temperature variations over the past 563 yr inferred from tree rings in the Shaluli Mountains, southeastern Tibet Plateau

We developed a tree-ring chronology (AD 1446–2008) based on 75 cores from 37 Abies squamata Mast. trees from the Shaluli Mountains, southeastern Tibet Plateau, China, using signal-free methods, which are ideally suited to remove or reduce the distortion introduced during traditional standardization. This chronology correlates best with regional temperatures in June–July, which allowed us to develop a June–July temperature reconstruction that explained 51.2% of the variance in the instrumental record. The reconstruction showed seven cold periods and five warm periods. Cold periods were identified from AD 1472 to 1524, 1599 to 1653, 1661 to 1715, 1732 to 1828, 1837 to 1847, 1865 to 1876 and 1907 to 1926. Warm intervals occurred from AD 1446 to 1471, 1525 to 1598, 1716 to 1731, 1848 to 1864, 1877 to 1906 and 1927 to present. The reconstruction agrees well with nearby tree-ring-based temperature reconstructions. Spatial correlation analyses suggest that our reconstructions provide information on June–July temperature variability for the southeastern Tibetan Plateau and its vicinity. Spectral analyses revealed significant peaks at 2–6, 10.7, 51.2, 102.2 and 204.8yr. The temperature variability in this area may be affected by ENSO, the Pacific Decadal Oscillation and solar activity.

Radial growth variations of black pine along an elevation gradient in the Cazorla Mountains (South of Spain) and their relevance for historical and environmental studies

In southern Spain, the Cazorla Mountains (500–2,100 m a.s.l.) have supplied construction timber from black pine (Pinus nigra Arn.) for buildings and ships since at least the Middle Ages. To establish the age and provenance of wooden cultural heritage originating from this area, well-replicated long-span chronologies are needed. Old-living trees occur at high elevations, whereas many historical timbers originated from lower altitudes; hence, crossdating possibilities were questionable. To assess the potential of this species for the development of a multi-millennia tree-ring data set with living trees and historical timbers for the western Mediterranean, we developed four ring-width chronologies along the circa 1,000 m altitudinal range of black pine in these mountains and examined crossdating patterns and climate–growth responses along with altitude and through time. Teleconnections with other Iberian and Mediterranean tree-ring data were also tested. A well-replicated chronology spanning AD 1331–2009 was obtained at the upper site, while lower elevations delivered shorter chronologies. Similarity among chronologies and responses to climate were dependent on elevation. Tree-ring width was negatively related to temperature in previous late summer and positively to February–March, whereas precipitation had an opposite effect; some negative influence of early summer temperature was also observed. However, growth responses were rather unstable throughout the twentieth century. These chronologies showed good tele- and heteroconnections with conifer chronologies from Iberia, northern Morocco and Turkey, evidencing the existence of a common macroclimatic signal, which also varied along with elevation. The relevance of these results for dendrohistorical studies is discussed.

Suppression of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) on Pastured Cattle Using an Abamectin-lmpregnated Cattle Ear Tag

Abstract Ear tags containing 8% abamectin and 20% piperonyl butoxide were applied to pastured cattle to evaluate efficacy against southern cattle ticks, Rhipicephalus (Boophilus) microplus (Canestrini), during a 40-wk field study. Temperature fluctuations had an important impact on effectiveness of the tags. The first 19 wks, during spring and early summer (March-June) temperatures were optimum for tick survival, producing high tick numbers on treated animals (9 - 63 ticks) which were not different from untreated animals. During this time tags provided ≤ 53.7% control. By contrast, during the summer through midfall (July-October), high temperatures caused dramatic natural declines in the tick population, but tick numbers on treated animals were always lower (0 - 3 ticks) than untreated animals (4 - 16 ticks). Control during this period was 72 - 100%, indicating tags had a negative impact on tick survival beyond the natural attrition caused by high temperatures. During the last 9 wks (midOctober to midDece...

Predictable signals of seasonal precipitation in the Yangtze–Huaihe River Valley

ABSTRACTAn effort is made to identify the ‘more predictable’ signals in seasonal precipitation in the Eastern Yangtze–Huaihe River Valley of China based on the observations recorded for the period of 1951–2004 at a network of 23 stations in this region. A recently developed methodology for decomposing the interannual variance of seasonal mean climate fields is applied to precipitation time series at the stations. This allows the total interannual variance to be separated into the variance of a slow component, or predictable signal, and the variance of a more noisier component of rainfall associated with intraseasonal variability. The potential predictability (signal‐to‐total ratio) is generally moderate in this region and is lower during winter from January to March (JFM) and higher in summer from May to July (MJJ) and autumn from November to January (NDJ). Empirical orthogonal function (EOF) analysis is then applied to the predictable‐, intraseasonal‐ and total‐covariance matrices, respectively. Leading EOF modes of the total component more often resemble the EOF modes of the intraseasonal component when the potential predictability is lower and vice versa. Temporal variation of the leading modes in the predictable components is more closely linked to the interannual variability of Eastern Pacific sea surface temperature (SST) in early summer (MJJ), North Atlantic SST in late summer (JAS) and El Niño/Southern oscillation in late autumn (NDJ). The rainfall SST connections found in these seasons persist throughout the entire 54‐year period. The predictable rainfall modes also have apparent linkages to the intensity and position of the Western Pacific subtropical high during the early summer and late autumn with more rainfall occurring in the region when the height pattern is more intensive and extends further west. During the late summer, the predictable rainfall variability is accompanied by a large variation of tropospheric advection from north of the region, indicating the impact of an anomalous atmospheric circulation associated with the variation of summer North Atlantic Oscillation.

Growth response of Sabina tibetica to climate factors along an elevation gradient in south Tibet

We examine the climate significance in tree-ring chronologies retrieved from Sabina tibetica Kom. (Tibetan juniper) at two sites ranging in elevation from 4124 to 4693m above sea level (a.s.l.) in the Namling region, south Tibet. The study region is under the control of semi-arid plateau temperate climate. The samples were grouped into high- and low-elevation classes and standard ring-width chronologies for both classes were developed. Statistical analysis revealed a decreasing growth rate yet increasing chronology reliability with increasing elevation. Overall, correlation analyses showed that radial growth in S. tibetica at the study sites was controlled by similar climatic factors, regardless of elevation; these factors comprised early winter (November) and early summer (May–June) temperatures as well as annual precipitation (July–June). Slight differences in the correlation between tree growth along the elevation gradient and climate variables were examined. The correlations with early winter temperature varied from significantly positive at the low-elevation site to weakly positive at the high-elevation site, whereas the correlations between radial growth and early summer temperature increased from weakly negative at the low-elevation sites to strongly negative at the high-elevation sites. The abundant precipitation through the year may have masked variations in tree growth on different elevation aspects. Our results will aid future dendroclimatological studies of Namling tree rings in south Tibet and demonstrate the potential of S. tibetica Kom. for improving our understanding of environmental impacts on tree growth.