Accelerated Recent Warming and Temperature Variability Over the Past Eight Centuries in the Central Asian Altai From Blue Intensity in Tree Rings

Warming in Central Asia has been accelerating over the past three decades and is expected to intensify through the end of this century. Here, we develop a summer temperature reconstruction for western Mongolia spanning eight centuries (1269–2004 C.E.) using delta blue intensity measurements from annual rings of Siberian larch. A significant cooling response is observed in the year following major volcanic events and up to five years post-eruption. Observed summer temperatures since the 1990s are the warmest over the past eight centuries, an observation that is also well captured in Coupled Model Intercomparison Project (CMIP5) climate model simulations. Projections for summer temperature relative to observations suggest further warming of between ∼3°C and 6°C by the end of the century (2075–2099 cf. 1950–2004) under the representative concentration pathways 4.5 and 8.5 (RCP4.5 and RCP8.5) emission scenarios. We conclude that projected future warming lies beyond the range of natural climate variability for the past millennium as estimated by our reconstruction

Is eastern Mongolia drying? A long-term perspective of a multidecadal trend

Temperatures in semiarid Mongolia have rapidly risen over the past few decades, and increases in drought, urban development, mining, and agriculture have intensified demands on limited water resources. Understanding long-term streamflow variation is critical for Mongolia, particularly if alterations in streamflow are being considered and because of the potential negative impacts of drought on the animal agriculture sector. Here, we present a temporally and spatially improved streamflow reconstruction for the Kherlen River. We have added 11 new records in comparison with two in the original 2001 reconstruction. This new reconstruction extends from 1630 to 2007 and places the most recent droughts in a multicentennial perspective. We find that variations in streamflow have been much greater in the past than in the original study. There was higher variability in the mid to late 1700s, ranging from severe and extended drought conditions from 1723 to 1739 and again in 1768–1778 to two decadal length episodes of very wet conditions in the mid 1700s and late 1700s. Reduced amplitude is seen in the mid-1800s, and several pluvial events are reconstructed for the 1900s. Although recent droughts are severe and disturbing economic and ecological systems in Mongolia and it appears that eastern Mongolia is drying, the drying trend since the late 1900s might in fact be accentuated by a change from a particularly wet era in Mongolia. The recent drought might be a return to more characteristic hydroclimatic conditions of the past four centuries in Mongolia

The contribution of insects to global forest deadwood decomposition

The amount of carbon stored in deadwood is equivalent to about 8 per cent of the global forest carbon stocks. The decomposition of deadwood is largely governed by climate with decomposer groups—such as microorganisms and insects—contributing to variations in the decomposition rates. At the global scale, the contribution of insects to the decomposition of deadwood and carbon release remains poorly understood. Here we present a field experiment of wood decomposition across 55 forest sites and 6 continents. We find that the deadwood decomposition rates increase with temperature, and the strongest temperature effect is found at high precipitation levels. Precipitation affects the decomposition rates negatively at low temperatures and positively at high temperatures. As a net effect—including the direct consumption by insects and indirect effects through interactions with microorganisms—insects accelerate the decomposition in tropical forests (3.9% median mass loss per year). In temperate and boreal forests, we find weak positive and negative effects with a median mass loss of 0.9 per cent and −0.1 per cent per year, respectively. Furthermore, we apply the experimentally derived decomposition function to a global map of deadwood carbon synthesized from empirical and remote-sensing data, obtaining an estimate of 10.9 ± 3.2 petagram of carbon per year released from deadwood globally, with 93 per cent originating from tropical forests. Globally, the net effect of insects may account for 29 per cent of the carbon flux from deadwood, which suggests a functional importance of insects in the decomposition of deadwood and the carbon cycle

Reconstruction of defoliating insects outbreak frequency in Bogd Khan Mountain, Mongolia by dendroecological method

In Waldbeständen der Bogd Khan Bergen, Ulaanbaatar, Mongolei, wurden Bohrkernproben aus dem Stammholz gezogen, um die Häufigkeit von Schadinsektenkalamitäten zu rekonstruieren. Die Korrelation der Larix sibirica, Pinus sibirica, Pinus sylvestris and Picea obovata Chronologien auf Monatsmittelwerte der Temperatur sowie der Niederschlagsmengen zeigte, dass der jährliche Durchmesserzuwachs wesentlich von der Menge der Frühjahrsniederschläge bestimmt wird und von heißen Sommern negativ beeinflusst wird. Darüber hinaus waren während des Zeitraumes von 1800 bis 1900 bei den vier untersuchten Baumarten Wuchsstörungen erkennbar, die hypothetisch durch Klimaschwankungen oder Insektenkalamitäten verursacht sein könnten. Die rekonstrierten Daten aus dem 19 Jahrhundert wurden mit den im zwanzigsten Jahrhundert beobachteten und dokumentierten Massenvermehrungen des Sibirischen Arvenspinners (Dendrolimus sibiricus Tschetw) zwischen 1925-1929 und 1955-1957, des Schlehen-Bürstenspinners (Orgyia antiqua Linn) in 1941-1944, sowie des Sibirischen Arvenspinners und des Spanners Erannis Jacobsoni Djak in 1971-1972 und des Sibirischen Arvenspinners und von E. Jacobsoni im Jahr 1989 in den Bogd Khan Bergen verglichen. Die jüngsten Massenvermehrungen des Sibirischen Arvenspinners, des Schlehen-Bürstenspinners und des Schwammspinners (Ocneria dispar Linn) traten in den Jahren 2000, 2003 and 2005 in dieser Region auf. Alle Massenvermehrungen waren an den Bohrkernen als verminderte Radialzuwächse erkennbar. Die Bohrkerne ließen auch drastische Zuwachseinbrüche in den Jahren 1902-1903, 1879 - 1880, 1847-1849 and 1825-1829 erkennen, die insgesamt einen annähernd dreißigjährigen Zyklus der Massenvermehrungen erkennen lassen.Tree-ring cores (samples) were collected to reconstruct frequency of insect outbreaks in the larch forest of eastern part of Bogd Khan Mountain, Ulaanbaatar, Mongolia. Using tree ring measurements, master chronologies of four conifer species were built. The response functions of Larix sibirica, Pinus sibirica, Pinus sylvestris and Picea obovata chronologies with monthly mean temperature and monthly total precipitation for the interval from 1940 to 2000 showed that their radial growth are mainly controlled by spring precipitation and negatively affected by high summer temperatures. Comparisons of the tree ring chronologies among the four species showed growth suppressions which climate variations and the probable occurrence of insect outbreaks from 1800 to 1900. According the recorded outbreaks, Siberian moth (Dendrolimus sibiricus Tschetw) invasion noted in 1925-1929 and in 1955-1957, vapourer moth (Orgyia antiqua Linn) in 1941-1944, Siberian moth, Jacobsons geometrid moth (Erannis Jacobsoni Djak) in 1971-1972 and Siberian moth and geometrid moths were infested in 1989 in Bogd Khan Mountain, Ulaanbaatar. Recently Siberian moth, vapourer moth and gypsy moth (Ocneria dispar Linn) attacks occurred in 2000, 2003 and 2005 in this region. All these outbreaks reduced radial growth of trees in this region, which were confirmed by this study. Moreover, we identified major disturbances which are most probably linked to insect outbreaks for the years 1902-1903, 1879 - 1880, 1847-1849 and 1825-1829 which may could indicate a roughly 30 year frequency.submitted by Byambagerel SuranWien, Univ. für Bodenkultur, Masterarb., 2009(VLID)103654

Effects of Scots Pine (Pinus sylvestris L.) plantations on plant diversity in Northern Mongolia

This study was carried out in Scots pine (Pinus sylvestris L.) plantations that were previously established in West Khentii Mountains of Northern Mongolia. In this study, species composition, richness, diversity and plant cover changes among planted forests with different plantation ages were analyzed. We found an obvious difference of species composition between natural stands and plantations. Our findings revealed continuous changes in vascular plant composition among plantations by increasing light-demanding species. A number of species from forest and forest-meadow mesophytes were replaced with xerophytes from forest-steppe and steppe. Current profound changes in species composition and a stable existence of invasive plant species from different ecological groups have a tendency to be stored during the initial stage of forest plantation establishment. The strong effect of planted trees on the growing environment appeared rather late, and has intensified since 15 years after the plantation establishment

Approaching a thermal tipping point in the Eurasian boreal forest at its southern margin

Climate change is increasing the intensity and frequency of extreme heat events. Ecological responses to extreme heat will depend on vegetation physiology and thermal tolerance. Here we report that Larix sibirica, a foundation species across boreal Eurasia, is vulnerable to extreme heat at its southern range margin due to its low thermal tolerance (Tcrit of photosynthesis: ~ 37–48 °C). Projections from CMIP6 Earth System Models (ESMs) suggest that leaf temperatures might exceed the 25th percentile of Larix sibirica’s Tcrit by two to three days per year within the next two to three decades (by 2050) under high emission scenarios (SSP3-7.0 and SSP5-8.5). This degree of warming will threaten the biome’s continued ability to assimilate and sequester carbon. This work highlights that under high emission trajectories we may approach an abrupt ecological tipping point in southern boreal Eurasian forests substantially sooner than ESM estimates that do not consider plant thermal tolerance traits