Past, present and future distributions of Oriental beech (Fagus orientalis) under climate change projections.

Species distribution models can help predicting range shifts under climate change. The aim of this study is to investigate the late Quaternary distribution of Oriental beech (Fagus orientalis) and to project future distribution ranges under different climate change scenarios using a combined palaeobotanical, phylogeographic, and modelling approach. Five species distribution modelling algorithms under the R-package `biomod2`were applied to occurrence data of Fagus orientalis to predict distributions under present, past (Last Glacial Maximum, 21 ka, Mid-Holocene, 6 ka), and future climatic conditions with different scenarios obtained from MIROC-ESM and CCSM4 global climate models. Distribution models were compared to palaeobotanical and phylogeographic evidence. Pollen data indicate northern Turkey and the western Caucasus as refugia for Oriental beech during the Last Glacial Maximum. Although pollen records are missing, molecular data point to Last Glacial Maximum refugia in northern Iran. For the mid-Holocene, pollen data support the presence of beech in the study region. Species distribution models predicted present and Last Glacial Maximum distribution of Fagus orientalis moderately well yet underestimated mid-Holocene ranges. Future projections under various climate scenarios indicate northern Iran and the Caucasus region as major refugia for Oriental beech. Combining palaeobotanical, phylogeographic and modelling approaches is useful when making projections about distributions of plants. Palaeobotanical and molecular evidence reject some of the model projections. Nevertheless, the projected range reduction in the Caucasus region and northern Iran highlights their importance as long-term refugia, possibly related to higher humidity, stronger environmental and climatic heterogeneity and strong vertical zonation of the forest vegetation.

October to July precipitation reconstruction for Burabai region (Kazakhstan) since 1744.

The history of climate is crucially important for any part of the world to understand the nature of climate change. In this context, precipitation reconstruction is still lacking in northern Kazakhstan. The purpose of this study is to present a reconstruction for the total precipitation of October of the previous year to July of the current year in northern Kazakhstan. Pinus sylvestris L. (Scots pine) forests in Burabai Region are quite important to collect samples to study the climate history. A regional chronology, covering the years of 1702-2014 of Pinus sylvestris constructed by using 289/466 trees/cores was used in the reconstruction. The gridded climate data for the years of 1950-2014 were used in the calibration and verification process. High and significant correlations were obtained between tree-ring widths and October to July precipitation in Burabai Region. Based on this significant relationship, reconstruction was performed for the years of 1744-2014. Adjusted R2, F-value, sign test, and r value were found as 0.38, 39.7 (P ≤ 0.001), 47+/17, and 0.62 for reconstruction, respectively. The reconstruction showed that 43 dry and 42 wet years occurred during the years of 1744-2014. Only a one-time four-year duration of the wet period was determined covering the years 1978-1981. However, three of six very dry years occurred after the 1950s. As a conclusion, extremity in recent decades is getting an increase in Burabai region.

Influence of Climate on Radial Growth of Black Pine on the Mountain Regions of Southwestern Turkey.

In this study, we identified the most important climate factors affecting the radial growth of black pine at different elevations of the mountain regions of Southwestern Turkey (Sandiras Mountain, Mugla/Turkey). We used four black pine tree-ring chronologies, which represent upper and lower distribution limits of black pine forest on the South and North slopes of Sandiras Mountain. The relationships between tree-ring width and climate were identified using response function analysis. We performed hierarchical cluster analysis to classify the response functions into meaningful groups. Black pine trees in the mountain regions of Southwestern Turkey responded positively to a warmer temperature and high precipitation at the beginning of the growing season. As high summer temperatures exacerbated drought, radial growth was affected negatively. Hierarchical cluster analysis made clear that elevation differences, rather than aspect, was the main factor responsible for the formation of the clusters. Due to the mountainous terrain of the study area, the changing climatic conditions (air temperature and precipitation) affected the tree-ring widths differently depending on elevation.

A 200-year reconstruction of Kocasu River (Sakarya River Basin, Turkey) streamflow derived from a tree-ring network.

The Sakarya River Basin (SRB) contains one of the most important agricultural areas for Turkey. Here, we use a network of 18 tree-ring chronologies and present a reconstruction of the mean June-July Kocasu River discharge, one of the main channels in the SRB, during the period 1803-2002 CE, and place the short period of instrumental flows (since 1953 CE) into historical context. Over the past two centuries, we found 33 dry and 28 wet events and observed the longest wet period between the years 1880 and 1920. The driest years were 1845 and 1873, and the wettest years were 1859 and 1960. Our reconstruction showed that the extreme short-term drought events that occurred in recent years were minor compared to the severity and duration of droughts that occurred previous to instrumental data. We found four pre-instrumental severe and sustained low streamflow events during the periods 1819-1834, 1840-1852, 1861-1875, and 1925-1931, during which historical records show reduced agricultural production, death, famine, plague, economic crisis, and widespread human migrations. More concerning, however, are current hydroclimate conditions in the SRB, marked by decadal-scale mean flows that dip below the long-term mean (1803-1953) in the late 1970s and have since failed to recover. With the Mediterranean region currently likely experiencing the worst drought in the past ca 1000 years due to human-induced climate change, the future outlook of water resource availability in the SRB could prove catastrophic for human and natural systems.

Old World megadroughts and pluvials during the Common Era.

Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other "Old World" climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the "Old World Drought Atlas" (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. The OWDA matches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability.

An improved reconstruction of May-June precipitation using tree-ring data from western Turkey and its links to volcanic eruptions.

We developed a high quality reconstruction of May-June precipitation for the interior region of southwestern Turkey using regional tree-ring data calibrated with meteorological data from Burdur. In this study, three new climate sensitive black pine chronologies were built. In addition to new chronologies, four previously published black pine chronologies were used for the reconstruction. Two separate reconstructions were developed. The first reconstruction used all site chronologies over the common interval AD 1813-2004. The second reconstruction used four of the chronologies with a common interval AD 1692-2004. R² values of the reconstructions were 0.64 and 0.51 with RE values of 0.63 and 0.51, respectively. During the period AD 1692-1938, 41 dry and 48 wet events were found. Very dry years occurred in AD 1725, 1814, 1851, 1887, 1916, and 1923, while very wet years occurred in AD 1736, 1780, 1788, 1803, and 1892. The longest dry period was 16 years long between 1860 and 1875. We then explored relationships between the reconstructed rainfall patterns and major volcanic eruptions, and discovered that wetter than normal years occurred during or immediately after the years with the largest volcanic eruptions.