High Treeline Research Articles

CLIMATE CHANGE EFFECTS ON HIGH-ALTITUDE WOODS IN THE ALTIPLANO

The keñua tree (Polylepis tarapacana), found at 5200 m a.s.l. in the Andes Mountains, grows at the highest treeline in the world. We measured the thermal conduction coefficient of keñua bark samples taken from different locations within the Andes Mountains. These measurements were used to find a correlation between environmental inputs and high altitude plant defence mechanisms. We found a new classification method to identify the origin of plant samples.

Isolated Trees in Two Tibetan Plateau Treelines Reveal Growth Plasticity to Harsh Conditions of the Little Ice Age

Trees greater than 150 years old growing in the current treelines were most likely isolated tree outposts above previous treelines of the Little Ice Age (LIA). An intuitive question is, how did these isolated trees grow at such a high elevation in the cold environment? Here, we tackle this question using tree-ring width data of the Northern Hemisphere’s highest treelines at 4900 m a.s.l. (Basu) and 4680 m a.s.l. (Langkazi) on the Tibetan Plateau. The results showed that an age-related exponential growth trend did not exist in most of the ring-width sequences of the sampled trees. The values of ring widths in the isolated trees had a similar pattern of probability distribution during and after the LIA. The coefficients of variation in ring widths of the isolated trees were significantly greater than those of the non-isolated trees in their common growth period. Synchronicity of annual change in radial growth among trees varied in time. These results indicated that the isolated trees in the LIA developed an adaptive ability to slow down radial growth rate and modulate growth synchronicity among individuals in cold stressful environments. Our study highlights growth plasticity in isolated trees above treelines for coping with harsh conditions in the LIA.

Indian Himalayan Timberline Ecotone in Response to Climate Change – Initial Findings

This article enumerates the findings of a team research on the Indian Himalayan timberline ecotone, with focus on three sites (located in Kashmir, Uttarakhand and Sikkim). Timberline elevation increased from west to east, was higher in the warmer south aspect than the cooler north aspect, and was generally depressed. Betula, Abies, Rhododendron and Juniperus were important treeline genera. The Himalaya has not only the highest treelines (Juniperus tibetica, at 4900 m), but also the widest elevational range (>1700 m). Remotely sensed data revealed that the timberline is a long, twisting and turning ecotone, traversing a length of 8–10 km per km horizontal distance. Surface temperature lapse rate in the monsoonal regions was lower (–0.53°C/100 m elevation) than generally perceived and varied considerably with season, being the lowest in December. The Himalayan treeline species are not water-stressed at least in monsoonal regions, predawn tree water potential seldom getting below –1 MPa. The upward advance of Rhododendron campanulatum (a krummholz species) may deplete alpine meadows with climatic warming. Tree-ring chronology indicated that winter warming may be favouring Abies spectabilis . Early snowmelt increased growth period and species richness. Treelines generally are stable in spite of decades of warming. Dependence of people on timberline was still high; so economic interventions are required to reduce the same.

Climatic and anthropogenic factors explain the variability of Fagus sylvatica treeline elevation in fifteen mountain groups across the Apennines

BackgroundFagus sylvatica forms the treeline across the Apennines mountain range, with an average elevation of 1589 m a.s.l. Previous studies evidenced that the current position of the treeline in the Apennines is heavily depressed as a result of a complex interaction between climatic factors and the past human pressure. In this study we correlated treeline elevation in the fifteen major mountain groups in the Apennines with selected climatic, geomorphological, and human disturbance variables in order to investigate in detail the site-specific features affecting the current treeline distribution.ResultsTreeline elevation was lowest in the North Italy (Apuan Alps), while the highest treeline was found in Central Italy (Simbruini). An absolute maximum treeline elevation of F. sylvatica exceeding 2000 m a.s.l. was found on 13 mountain peaks in Central and Southern Italy. Noteworthy, treeline elevation was largely lower on warmer south-facing slopes compared to northern slopes, with values several hundred meters lower in the Gran Sasso and Velino-Sirente. Although the causes of this pattern are still unknown, we argue that treeline elevation on south-facing slopes may be limited by the combination of climatic constraints (i.e. summer drought) and human disturbance. Evidence of a pervasive anthropogenic effect depressing treeline elevation was found in the North (Apuan Alps) Central (Gran Sasso, Velino-Sirente, Sibillini) and Southern part of Apennines (Pollino). By contrast, treeline elevation of the Laga, Simbruini, and Orsomarso mountain groups appears less affected by past anthropogenic disturbance. Finally, we recorded in the several mountain groups (i.e. Majella, Marsicani and Pollino) the coexistence of very depressed treelines just a few kilometers away from much higher treelines, among the highest ever recorded for F. sylvatica.ConclusionsFinally, we argue that F. sylvatica treeline across the Apennines is locally shaped both by the interaction of low temperatures experienced by the species in its earliest life stages in snow-free open spaces with summer soil water depletion and human disturbance.

The stability of spruce treelines on the eastern Tibetan Plateau over the last century is explained by pastoral disturbance

Most Tibetan people make their living through pastoralism, with livestock grazing being widespread throughout the Tibetan Plateau. The Tibetan Plateau is also home to the northern hemisphere’s highest treelines but the effects of human activities, in particular pastoralism, on these treelines and their influence on the treeline responses to climate change remain unclear. To disentangle the effects of pastoral disturbances and climate on treeline dynamics, we surveyed three plots at grazing-disturbed Balfour spruce (Picea likiangensis var. balfouriana) treelines in the Yushu region (eastern Tibetan Plateau) and compared this data with published results of five undisturbed spruce treeline sites. Spatiotemporal changes in the position and structure of treelines during the past 400 years were reconstructed using dendrochronology. Tree recruitment was significantly linked to long-term summer and winter temperature. Under low local population densities and grazing pressure but consistent climate warming, disturbed treelines shifted upwards by 23.9–82.6 m during the 1611–1910 period. However, under higher local population densities, increased grazing pressure and climate warming over the last century, disturbed treelines showed no significant upward shift. In contrast, undisturbed treelines shifted upward by 25–68.5 m over the last century, thus implying that pastoralism was suppressing treeline expansion in disturbed sites. Together, these results underscore the importance of anthropogenic disturbances in influencing the structure and position of alpine treelines on the Tibetan Plateau. The role played by human disturbance should be carefully considered when evaluating the potential for treeline advance under future climate warming.

Radiocarbon Constraints on the Age of the World’s Highest-Elevation Cave-Bear Population, Conturines Cave (Dolomites, Northern Italy)

AbstractWe report radiocarbon (14C) dates on bone samples of Ursus ladinicus, a small cave bear species well adapted to a life in the mountains, whose remains were found in Conturines Cave. Located at 2775 m asl in the Dolomites of northern Italy, this cave is by far the highest known cave bear site worldwide. Eleven 14C dates obtained by the Belfast and Oxford laboratories on samples showing good collagen preservation yielded consistent ages in excess of 46–50 ka BP. These results show that contrary to the previously held view these cave bear remains are older than Marine Isotope Stage 3, and likely date from a warm climate period with a high treeline, possibly the Last Interglacial.

Holocene treeline history of a high-mountain landscape inferred from soil charcoal: The case of Sierra de Gredos (Iberian Central System, SW Europe)

Unravelling the precise Holocene altitudinal fluctuation of the highland vegetation communities (>1800 m asl) in the Gredos Range (Central System, Spain) is challenging owing to the complexity of the long-term human-environmental interactions in the area. Aiming at improving the knowledge of these highland dynamics, a pedoanthracological analysis was conducted on six soil profiles located on the northern slope of the central sector of the Gredos Range, following an altitudinal transect between 2200 and 1700 m asl in the Las Pozas valley. The soil charcoal analysis revealed the long-term stability of the Leguminosae shrublands, which have dominated the landscape over 1800 m asl since the Early Holocene. The highest ancient timberline was stimated to be at approximately 1700 m asl in this valley, from the Early Holocene until the beginning of the Late Holocene. This ancient forest contained Pinus gr. sylvestris, with significant numbers of deciduous Quercus. However, scattered individuals or small groves of pioneer deciduous taxa (Betula sp., Populus sp., Salix sp., Maloideae and Prunus sp.) were found to have thrived over the timberline during the Early and Middle Holocene, especially between 1900 and 2000 m asl. The highest treeline was marked by Betula at 2100 m asl. Elevated values of charcoal concentration reflect the intense fire regime of the area. The pattern of fire events accumulation periods that can be inferred from the 23 dated charcoal samples is consistent with previous data, which supports an increase in fire frequency around 2000 cal yr BP, during the first reported period of significant human influence.

How wind affects growth in treeline Picea abies

Globally, treeline position is driven by temperatures during the growing season. Nevertheless, at regional scales, the position of uppermost tree stands also reflects other climatic factors, including wind action. It remains uncertain, however, how much do intense winds depress the treeline below its potential position. Our objective was to quantify the effect of wind speed on the possible depression of upper forest margins below the potential treeline in a windy mountain range with the treeline located close to summit areas. In the Giant Mountains, Czech Republic, growth parameters and symptoms of wind-induced loss of biomass were determined for Norway spruce (Picea abies [L] Karst.) in 70 plots distributed along a gradient of wind speed within the treeline ecotone. Wind speed was modelled for each plot. General linear models were applied to discern the effect of wind on tree growth. Our results show that high wind speeds are reflected in the presence of clonal tree islands and irregular tree crowns. Despite evident wind-induced biomass loss, radial growth was not significantly affected, and the effect of wind on height increment was limited only to parts of the stem from 2 m above ground. Considering that the height growth was substantially reduced by wind in about half of the treeline area, and wind was able to limit only growth of trees taller than 2 m, the overall wind-induced depression of highest treeline positions is probably low, even in windy mountain regions.

The Mass Elevation Effect of the Central Andes and Its Implications for the Southern Hemisphere's Highest Treeline

One of the highest treelines in the world is at 4810 m above sea level on the Sajama Volcano in the central Andes. The climatological cause of that exceptionally high treeline position is still unclear. Although it has been suggested that the mass elevation effect (MEE) explains the upward shift of treelines in the Altiplano region, the magnitude of MEE has not yet been quantified for that region. This paper defines MEE as the air temperature difference in summer at the same elevation between the inner mountains/plateaus (Altiplano) and the free atmosphere above the adjacent lowlands of the Andean Cordillera. The Altiplano air temperature was obtained from the Global Historical Climatology Network-Monthly temperature database, and the air temperature above the adjacent lowlands was interpolated based on the National Center for Environmental Prediction/National Center for Atmospheric Research Reanalysis 1 data set. We analyzed the mean air temperature differences for January, July, and the warm months from...

The Origin and Development of the Central European Man-made Landscape, Habitat and Species Diversity as Affected by Climate and its Changes – a Review

The Origin and Development of the Central European Man-made Landscape, Habitat and Species Diversity as Affected by Climate and its Changes – a Review

Comparison of COFECHA and TSAPWIN from Dendroclimatology for Climate Change and Taiwan Fir (Abies kawakamii) Growth Pattern in Alpine Central Taiwan

Under different environments, trees has recorded signals of a variety of types (Schweingruber, 2007). The ring width change implies climate information and the growing season. Through analyzing tree ring, we can understand how climate change affects the growth of trees. Studying the relationship between limiting factor and ring width is able to reconstruct the weather in the past or predict the future weather. The average temperature has increased 0.8 C from 1866 in global (Bluemle, 1999). Climate change and global warming cause lots of effect in global. With the rise of temperature, forest vegetation is moving high latitude and high altitude. The tree–line of alpine forest was immigrating upward on altitude (Kullman, 1998). Taiwan fir (Abies kawakamii H.) is the highest forest in Taiwan (Flora of Taiwan, 1994). Climate is the main factor that affects vegetation distributes in the long– term. Temperature and precipitation were the most effective (Walther, 2003). Taiwan fir grows on the timberline, where temperature and precipitation are growth– limiting factors. Because the growing of Taiwan fir is controlled by the growth–limiting factors, by studying the ring width growth, the study tried to understand how climate affects trees. The mean sensitivity of Taiwan fir is around 0.14, it is a fine material for studying the climate response (Tsou, 1998). Crossdating aims to synchronize growth ring series by aligning patterns in ring width (Pilcher, 1990). To facilitate the crossdating process, numerous methodologies and computer software have been developed. Computer software were such as COFECHA (Holmes, 1983), and TSAPWin (Rinntech, 2009). COFECHA standardizes the raw data of ring width, and provides the correlation test of the whole series and each segments (by default 50–ring). Default standardization include cubic smooth spline (rigidity 32 rings), autoregressive modeling and logarithmic transformation. TSAPWin displays the ring width in line graph, and provides synchrony test of each series. TSAPWin also combines the ring width measurement. With this function, it can easily measure and analyze. Radial growths of trees were influenced by temperature and precipitation in the cold high tree–line zone, and Comparison of COFECHA and TSAPWIN from Dendroclimatology for Climate Change and Taiwan Fir (Abies kawakamii) Growth Pattern in Alpine Central Taiwan

Long-term geobotanical observations of climate change impacts in the Scandes of West-Central Sweden

In the context of projected future human-caused climate warming, the present study reports and analyses the performance of subalpine/alpine plants, vegetation and phytogeographical patterns during the past century of about 1 °C temperature rise. Historical baseline data of altitudinal limits of woody and non-woody plants in the southern Scandes of Sweden are compared with recent assessments of these limits at the same locations. The methodological approach also includes repeat photography, individual age determinations and analyses of permanent plots. At all levels, from trees to tiny herbs, and from high to low altitudes, the results converge to indicate a causal association between temperature rise and biotic evolution. The importance of snow cover phenology is particularly evident. Treeline advance since the early-20th century varies between 75 and 130 m, depending on species and site. Tendencies and potentials for further upshift in a near future are evident from the appearance of young saplings of all tree species, growing 400–700 m atop of the treeline. Subalpine/alpine plant species have shifted upslope by average 200 m. In addition, present-day repetitions of floristic inventories on two alpine mountain summits reveal increases of plant species richness by 58 and 67%, respectively, since the early-1950s. Obviously, many plants adjust their altitudinal ranges to new climatic regimes much faster than generally assumed. Nevertheless, plants have migrated upslope with widely different rates. This produces non-analogous alpine plant communities, i.e. peculiar mixtures of alpine and silvine species. The alpine region is shrinking (higher treeline), and the character of the remaining alpine vegetation landscape is changing. For example, extensive alpine grasslands are replacing snow bed plant communities.

Highest Treeline in the Northern Hemisphere Found in Southern Tibet

Three new records of the highest treelines in the northern hemisphere are presented here, based on the definition of a “tree.” The tree species with the highest treeline in the northern hemisphere is Juniperus tibetica Kom. The highest forest stand is located at 4900 m in southeast Tibet. The highest tree stands of Juniperus indica Bertol. in the Himalaya were found in northern Bhutan at 4750 m. Information from such observations is decisive for the development of hypotheses on the limits of tree growth. We compare the present findings with findings on highest treelines in other mountain areas worldwide and draw some conclusions.

Treeline dynamics in relation to climatic variability in the central Tianshan Mountains, northwestern China

ABSTRACTAim Climate variability may be an important mediating agent of ecosystem dynamics in cold, arid regions such as the central Tianshan Mountains, north‐western China. Tree‐ring chronologies and the age structure of a Schrenk spruce (Picea schrenkiana) forest were developed to examine treeline dynamics in recent decades in relation to climatic variability. Of particular interest was whether tree‐ring growth and population recruitment patterns responded similarly to climate warming.Location The study was conducted in eight stands that ranged from 2500 m to 2750 m a.s.l. near the treeline in the Tianchi Nature Reserve (43°45′−43°59′ N, 88°00′−88°20′ E) in the central Xinjiang Uygur Autonomous Region, northwestern China.Methods Tree‐ring cores were collected and used to develop tree‐ring chronologies. The age of sampled trees was determined from basal cores sampled as close as possible to the ground. Population age structure and recruitment information were obtained using an age–d.b.h. (diameter at breast height) regression from the sampled cores and the d.b.h. measured on all trees in the plots. Ring‐width chronologies and tree age structure were both used to investigate the relationship between treeline dynamics and climate change.Results Comparisons with the climatic records showed that both the radial growth of trees and tree recruitment were influenced positively by temperature and precipitation in the cold high treeline zone, but the patterns of their responses differed. The annual variation in tree rings could be explained largely by the average monthly minimum temperatures during February and August of the current year and by the monthly precipitation of the previous August and January, which had a significant and positive effect on tree radial growth. P. schrenkiana recruitment was influenced mainly by consecutive years of high minimum summer temperatures and high precipitation during spring. Over the last several decades, the treeline did not show an obvious upward shift and new recruitment was rare. Some trees had established at the treeline at least 200 years ago. Recruitment increased until the early 20th century (1910s) but then decreased with poor recruitment over the past several decades (1950–2000).Main conclusions There were strong associations between climatic change and ring‐width patterns, and with recruitments in Schrenk spruce. Average minimum temperatures in February and August, and total precipitation in the previous August and January, had a positive effect on tree‐ring width, and several consecutive years of high minimum summer temperature and spring precipitation was a main factor favouring the establishment of P. schrenkiana following germination within the treeline ecotone. Both dendroclimatology and recruitment analysis were useful and compatible to understand and reconstruct treeline dynamics in the central Tianshan Mountains.

Growth, demography and carbon relations of Polylepis trees at the world's highest treeline

Summary Growth, reproductive success and non‐structural carbon pools in Polylepis tarapacana Philippi trees were examined across a transect between 4360 and 4810 m altitude on Nevado Sajama, Bolivia. The mean −10‐cm soil temperature of 5·4 °C under trees at the treeline during the 265‐day growing season matched the threshold temperature found at other subtropical and tropical treelines. Beyond 4400 m Polylepis is restricted to the warmer and drier equator‐facing slopes, suggesting a direct thermal limitation of tree growth. Maximum tree height, annual shoot increment and mean tree‐ring width decreased with altitude. Trees near the upper range limit reached a maximum tree height of 3·3 m and a maximum stem diameter of 34 cm. The smallest tree‐height classes dominated populations at all altitudes, and the uppermost site revealed the highest proportion of seedlings. Tree‐size demography indicates a critical phase for tree establishment during the sapling stage, when trees emerge from sheltered niches near the ground. No evidence of a depletion of mobile C stores (sugars, starch and lipids) was found in any tissue type with increasing elevation, suggesting a limitation of C investment (growth) rather than C acquisition (photosynthesis) at treeline.

Holocene climate of the Kola Peninsula; evidence from the oxygen isotope record of diatom silica

Holocene climate variability was studied in a lake sediment record covering the last c . 9000 years from Lake Chuna on the Kola Peninsula, north-west Russia, using the oxygen isotope composition of diatom silica (δ 18O diatom). The evaporation of the lake waters is likely to be minimal, and thus the isotopic composition of the lake waters recorded by the δ 18O diatom reflects the isotopic composition of summer precipitation. Overall the δ 18O diatom signal seems to record a predominance of the polar Arctic air mass bringing cold summer air temperatures immediately after the last glaciation and again after 4000 years to present time. The Atlantic maritime air mass is likely to have supplied warm summer rainfall especially in the mid Holocene. The pattern is broadly consistent with a quantitative pollen reconstruction from Chuna Lake which suggests higher mean July temperatures from deglaciation to 5500 years BP with a rather steep decline to lower temperatures after 4000 years BP. Our results support the general regional scenario of a mid Holocene warm period deduced from the higher tree line, vegetation changes and glacier fluctuations in Fennoscandia. However, the δ 18O diatom record from the Kola Peninsula suggests a relatively cold early-Holocene with a gradual shift to warmer conditions to a maximum at around 5000–4000 years BP assuming that the modern δ precipitation–temperature relationship has been constant throughout the Holocene.

Glacier contraction during the middle Holocene in the western Italian Alps: Evidence and implications

Radiocarbon dates of peat from the top and base of a bog exposed by recent retreat of Rutor Glacier show that the glacier front terminated upvalley from the bog from 8400 until at least 6000 B.P. The evidence is consistent with botanical data that point to a high tree line during the interval and to reconstructed mean July temperatures at least 4 °C warmer than present temperatures. If the mass-balance history of the glacier is typical of other glaciers in this region, it is likely that average equilibrium-line altitudes during the interval of contraction remained above those of the present and well above those of subsequent neoglacial ice advances.

Holocene glacial and tree-line variations in the White River Valley and Skolai Pass, Alaska and Yukon Territory

Complex glacier and tree-line fluctuations in the White River valley on the northern flank of the St. Elias and Wrangell Mountains in southern Alaska and Yukon Territory are recognized by detailed moraine maps and drift stratigraphy, and are dated by dendrochronology, lichenometry, 14C ages, and stratigraphic relations of drift to the eastern (1230 14C yr BP) and northern (1980 14C yr BP) lobes of the White River Ash. The results show two major intervals of expansion, one concurrent with the well-known and widespread Little Ice Age and the other dated between 2900 and 2100 14C yr BP, with a culmination about 2600 and 2800 14C yr BP. Here, the ages of Little Ice Age moraines suggest fluctuating glacier expansion between ad 1500 and the early 20th century. Much of the 20th century has experienced glacier recession, but probably it would be premature to declare the Little Ice Age over. The complex moraine systems of the older expansion interval lie immediately downvalley from Little Ice Age moraines, suggesting that the two expansion intervals represent similar events in the Holocene, and hence that the Little Ice Age is not unique. Another very short-lived advance occurred about 1230 to 1050 14C yr BP. Spruce immigrated into the valley to a minimum altitude of 3500 ft (1067 m), about 600 ft (183 m) below the current spruce tree line of 4100 ft (1250 m), at least by 8020 14C yr BP. Subsequent intervals of high tree line were in accord with glacier recession; in fact, several spruce-wood deposits above current tree line occur bedded between Holocene tills. High deposits of fossil wood range up to 76 m above present tree line and are dated at about 5250, 3600 to 3000, and 2100 to 1230 14C yr BP. St. Elias glacial and tree-line fluctuations, which probably are controlled predominantly by summer temperature and by length of the growing and ablation seasons, correlate closely with a detailed Holocene tree-ring curve from California, suggesting a degree of synchronism of Holocene summer-temperature changes between the two areas. This synchronism is strengthened by comparison with the glacier record from British Columbia and Mt. Rainier, Likewise, broad synchronism of Holocene events exists across the Arctic between the St. Elias Mountains and Swedish Lappland. Finally, two sequences from the Southern Hemisphere show similar records, in so far as dating allows. Hence, we believe that a preliminary case can be made for broad synchronism of Holocene climatic fluctuations in several regions, although further data are needed and several areas, particularly Colorado and Baffin Island, show major differences in the regional pattern.