Growth dynamics of tree-line and lake-shore Scots pine (Pinus sylvestris L.) in the central Scandinavian Mountains uring the Medieval Climate Anomaly and the early Little Ice (original) (raw)
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Frontiers in Ecology and Evolution, 2014
Trees growing at their altitudinal or latitudinal distribution in Fennoscandia have been widely used to reconstruct warm season temperatures, and the region hosts some of the world's longest tree-ring chronologies. These multi-millennial long chronologies have mainly been built from tree remains found in lakes (subfossil wood from lake-shore trees). We used a unique dataset of Scots pine tree-ring data collected from wood remains found on a mountain slope in the central Scandinavian Mountains, yielding a chronology spanning over much of the last 1200 years. This data was compared with a local subfossil wood chronology with the aim to (1) describe growth variability in two environments during the Medieval Climate Anomaly (MCA) and the early Little Ice Age (LIA), and (2) investigate differences in growth characteristics during these contrasting periods. It was shown that the local tree-line during both the MCA and early LIA was almost 150 m higher that at present. Based on living pines from the two environments, tree-line pine growth was strongly associated with midsummer temperatures, while the lake-shore trees showed an additional response to summer precipitation. During the MCA, regarded to be a period of favorable climate in the region, the tree-ring data from both environments showed strong coherency and moderate growth variability. In the early LIA, the two chronologies were less coherent, with the tree-line chronology showing more variability, suggesting different growth responses in the two environments during this period of less favorable growing conditions. Our results indicate that tree-ring width chronologies mainly based on lake-shore trees may need to be re-evaluated.
Trees growing at their altitudinal or latitudinal distribution in Fennoscandia have been widely used to reconstruct warm season temperatures, and the region hosts some of the world's longest tree-ring chronologies. These multi-millennial long chronologies have mainly been built from tree remains found in lakes (subfossil wood from lake-shore trees). We used a unique dataset of Scots pine tree-ring data collected from wood remains found on a mountain slope in the central Scandinavian Mountains, yielding a chronology spanning over much of the last 1200 years. This data was compared with a local subfossil wood chronology with the aim to (1) describe growth variability in two environments during the Medieval Climate Anomaly (MCA) and the early Little Ice Age (LIA), and (2) investigate differences in growth characteristics during these contrasting periods. It was shown that the local tree-line during both the MCA and early LIA was almost 150 m higher that at present. Based on living pines from the two environments, tree-line pine growth was strongly associated with mid-summer temperatures, while the lake-shore trees showed an additional response to summer precipitation. During the MCA, regarded to be a period of favorable climate in the region, the tree-ring data from both environments showed strong coherency and moderate growth variability. In the early LIA, the two chronologies were less coherent, with the tree-line chronology showing more variability, suggesting different growth responses in the two environments during this period of less favorable growing conditions. Our results indicate that tree-ring width chronologies mainly based on lake-shore trees may need to be re-evaluated.
Validation of the supra-long pine tree-ring chronologies from northern Scandinavia
We empirically demonstrate that acceptance thresholds for a dendrochronological cross-match of at least t=6 for oak and at least t=7 for pine are required when constructing independent tree-ring master chronologies. These thresholds are far above the "thresholds for significant matches" of t=3.5 or t=4 adopted forty years ago, which are still regarded appropriate for the dating of archaeological samples. We also validate the supra-long Scots pine chronologies from northern Scandinavia using these tightened criteria and our crossdating software CDendro. The Finnish and Swedish pine chronologies were built by two concurrent teams of scientists working with wood from different places and with different methods. Both teams arrived at the same conclusion regarding the overall dendro signal for the past 7500 years. Our reassessment confirms this conclusion, and demonstrates that both teams worked on a firm level of confidence when accepting dendrochronological matches. This validation is vital for the credibility of our hypothesis about general errors in the European oak masters, errors which were probably caused by using pre-dating with other methods in cases when sufficient dendrochronological confidence levels could not be reached.
An 854-Year Tree-Ring Chronology of Scots Pine for South-West Finland
Studia Quaternaria, 2014
A near-millennial tree-ring chronology (AD 1147-2000) is presented for south-west Finland and analyzed using dendroclimatic methods. This is a composite chronology comprising samples both from standing pine trees (Pinus sylvestris L.) and subfossil trunks as recovered from the lake sediments, with a total sample size of 189 tree-ring sample series. The series were dendrochronologically cross-dated to exact calendar years to portray variability in tree-ring widths on inter-annual and longer scales. Al though the studied chronology correlates statistically significantly with other long tree-ring width chronologies from Finland over their common period (AD 1520-1993), the south-west chronology did not exhibit similarly strong mid-summer temperature or spring/early-summer precipitation signals in comparison to published chronologies. On the other hand, the south-west chronology showed highest correlations to the North Atlantic Oscillation indices in winter/spring months, this associatio...
Dendrochronologia, 2004
This work seeks to analyse the importance of summer-temperatures on the tree-ring growth of Scots pine (Pinus sylvestris L.) during the past three centuries. Three living-tree chronologies, subfossil pine chronology and one composite tree-ring chronology were constructed from latitudinal and altitudinal forest-limits of pine in northern Finland and compared with meteorological data comes from three localities. These data include early instrumental temperature observations from 18 th and 19 th centuries. The modern meteorological data covers the period from 1860 to present. Response functions were derived by means of Pearson correlations using five subperiods as follows: 1738±1748, 1802±1822, 1825±1835, 1861±1926 and 1927±1992. It was demonstrated that the correlations between ringwidths and midsummer (July) temperatures did not vary significantly as a function of time. Early-(June) and late-summer (August) mean temperatures were secondary in relation to midsummer temperatures in controlling the radial growth. Early-summer temperatures governed pine radial growth most clearly during the 19 th century, whereas late-summer temperatures had strongest influence on ring-widths during the 18 th century and later part of the 20 th century. There was no clear signature of temporally reduced sensitivity of Scots pine ring-widths to midsummer temperatures over the periods of early meteorological observations. Subfossil pine chronology, constructed using pines recovered from small lakes along the forest-limit zone, showed a consistent pattern of response to summer-temperatures in relation to living-tree chronologies.
Elevation-specific tree-ring chronologies of Norway spruce and Silver fir in Southern Germany
Dendrochronologia, 2012
Tree-ring (TR) chronologies are important instruments for the dating and provenance analyses of historical wood, as well as for climate reconstructions. However, radial growth patterns differ between tree species and growing environments. Therefore chronologies are more or less specific for a certain tree species, region and elevation. Chronologies that are restricted to more confined regions could extend the possibilities for dating, dendroprovenancing and regional climate reconstructions.
Tree-ring (TR) chronologies are important instruments for the dating and provenance analyses of historical wood, as well as for climate reconstructions. However, radial growth patterns differ between tree species and growing environments. Therefore chronologies are more or less specific for a certain tree species, region and elevation. Chronologies that are restricted to more confined regions could extend the possibilities for dating, dendroprovenancing and regional climate reconstructions.
Trees, 2013
Tree-ring chronologies are important indicators of pre-instrumental, natural climate variability. Some of the longest chronologies are from northern Fennoscandia, where ring width measurement series from living trees are combined with series from sub-fossil trees, preserved in shallow lakes, to form millennial-length records. We here assess the recent ends of such timeseries by comparing climate signals and growth characteristics in central and northern Sweden, of (1) trees growing at lakeshore microsites (representing the source of sub-fossil material of supra-long chronologies), with (2) trees collected in dryer micro-sites several meters ''inland''. Calibration trials reveal a predominating June-September temperature signal in N-Sweden and a weaker but significant May-September precipitation signal in C-Sweden. At the micro-site level, the temperature signal in N-Sweden is stronger in the lakeshore trees compared to the inland trees, whereas the precipitation signal in C-Sweden remains unchanged among the lakeshore and inland trees. Tree-rings at cambial ages [40 years are also substantially wider in the lakeshore micro-site in C-Sweden, and juvenile rings are more variable (and wider) in the dryer micro-site in N-Sweden (compared to the adjacent micro-sites). By combining the data of the various micro-sites with relict samples spanning the past 1,000 years, we demonstrate that growth rate differences at the micro-site scale can affect the low frequency trends of millennial-length chronologies. For the supra-long chronologies from northern Fennoscandia, that are derived from sub-fossil lake material, it is recommended to combine these data with measurement series from only lakeshore trees.
Dendrochronologia, 2012
The common growth signal and spatial synchrony of nine chronologies of tree rings (Pinus sylvestris L.) from the Baltic Sea region were studied using moving correlations with time windows of 50 and 100 years. Drifts from synchrony to asynchrony and again back to synchrony across several centuries were observed. The chronologies showed higher (or lower) coefficients of correlations and correspondingly gentler (or steeper) declines in spatial synchrony in certain periods. In accordance with research into other ecological phenomena, the origin of the spatial synchrony was found to relate to the intensity of the westerly circulation over the Atlantic and Europe as described by the North Atlantic Oscillation (NAO) index. The tree rings from all of the analysed subregions were found to be wider, identifying faster periods of growth, when there was a positive NAO during the extended winter season from December to March that preceded the period of growth. Previous studies showed that the NAO index can be linked with the growth of tree rings because of factors in the local climate that affect growth, such as temperature and precipitation. Moreover, the spatial synchrony showed multidecadal fluctuations that were correlated with variations of a similar scale in the reconstructed NAO index. However, a high degree of spatial synchrony was observed during the 20 th century in the presence of values of NAO index that were strongly negative. A more detailed view was provided by maps of the correlations in which spatial changes were demonstrated in the growth of pines between the 12 th and the 20 th century. These results could be used as background information in the development of improved proxy-based reconstructions of the NAO index (or other similar meteorological variables), which could also be inferred from tree ring data relating to earlier centuries.
Climate Dynamics, 2011
Dendroclimatological sampling of Scots pine (Pinus sylvestris L.) has been made in the province of Jämtland, in the west-central Scandinavian mountains, since the 1970s. The tree-ring width (TRW) chronology spans several thousand years and has been used to reconstruct June-August temperatures back to 1632 BC. A maximum latewood density (MXD) dataset, covering the period AD 1107-1827 (with gap 1292-1315) was presented in the 1980s by Fritz Schweingruber. Here we combine these historical MXD data with recently collected MXD data covering AD 1292-2006 into a single reconstruction of April-September temperatures for the period AD 1107-2006. Regional curve standardization (RCS) provides more low-frequency variability than ''non-RCS'' and stronger correlation with local seasonal temperatures (51% variance explained). The MXD chronology shows a stronger relationship with temperatures than the TRW data, but the two chronologies show similar multi-decadal variations back to AD 1500. According to the MXD chronology, the period since AD 1930 and around AD 1150-1200 were the warmest during the last 900 years. Due to large uncertainties in the early part of the combined MXD chronology, it is not possible to conclude which period was the warmest. More sampling of trees growing near the tree-line is needed to further improve the MXD chronology.