Ninth International Conference on Permafrost ... - IARC Research

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The Effect of Climate and Permafrost on Tree Line Dynamics in Northwest Russia:A Preliminary AnalysisMartin WilmkingSaskia KenterJens IbendorfUniversity Greifswald, 17487 Greifswald, GermanyIntroductionTree line dynamics provide important feedbackmechanisms to the global climate system by altering albedoand carbon storage at high latitudes. A northward movementof the northern tree line is generally assumed to decreasealbedo (Chapin et al. 2005), but increase above-groundcarbon storage. However, ecosystem carbon storage mightbe reduced during tree line advance due to the respirationof (old) soil carbon and thus result in a positive feedback towarming (Wilmking et al. 2006).Establishment of trees north of tree line requires on theone hand favorable climatic conditions (climate driver) andon the other hand suitable microsite conditions (micrositedriver) (Lloyd & Fastie 2002). Suitable microsites are oftenhampered by the existence of permafrost, and thus ultimatelymay depend on permafrost degradation. Thus, one mainfactor controlling carbon storage and tree line advance inmany regions is permafrost.The EU Project “CarboNorth” aims at quantifying thecarbon budget in northwest Russia, and as part of this project,the consortium is studying tree line dynamics. This paperreports preliminary results from the dendroecological partof the investigation. Particularly, we were interested in theclimate sensitivity of established trees at tree line (climatedriver) and in the age structure of seedlings extending beyondtree line from mostly permafrost-free soils to permafrostinfluencedsoils (microsite driver).MethodsField sites were located at northern tree line in northwestRussia at 67.4°N, 62.3°E (R1), 67.2°N, 62.1°E (R2),67.1°N, 59.5°E (Kho). Each site consisted of a gradient fromtree islands on well-drained soil with permafrost pockets,through woodland to treeless tundra underlain by permafrost(conceptional permafrost degradation). Each transectconsisted of 3–4 plots (15 x 15 m): (1) forest, (2) densewoodland, (3) open woodland, and (4) tundra. Permafrostdepth was measured with a 120 cm long probe (July/August2007). We collected penetrating tree cores or disks (at rootcollar level) from every Picea obovata tree or seedlingwithin each plot in 7/2007. Samples were prepared accordingto dendrochronological standards. Age of samples wasdetermined by ring counts and adjusted for sample height.We measured ring-width (LINTAB 5, 1/1000 mm) from allR2 samples including other well-established trees close byand crossdated visually and with COFECHA. We used theprogram ARSTAN (negative exponential, straight line fits,Huggershoff) to standardize the tree ring series, to removethe biological age trend, and to build site chronologies. Wecalculated climate-growth relationships of chronologiesonly, if EPS (expressed population signal) exceeded 0.85.We used mean monthly temperature and precipitation data(1901–2002) from the closest grid point of the griddedCRU-dataset, because the temperature record correlatedvery well (r > 0.98) with the closest station (Khoseda Hard)and records of Pecora (r > 0.90) and Nar Jan Mar (r > 0.87).Correlation and response functions over time were analyzedwith the program DENDROCLIM2002 (Biondi & Waikul2004); moving window length was 50 years.ResultsMicrosite conditionsThe active layer depth was generally significantlyshallower in the tundra plots compared to woodland andforest plots, which showed similar thaw depths (Fig. 1),often exceeding the depth of the probe. While forest plotswere generally well drained, woodland and especially tundraplots were often waterlogged, and trees and seedlings hadoften established on slightly higher terrain (hummocks).Age structureThe age structure revealed a striking similarity at all plotsat all three study sites, where most individuals had establishedbetween 1950 and 1960, and none had after 1982.Climate-growth relationships at R2Only one chronology (Forest) exceeded an EPS value of0.85 during the 20 th century and, subsequently, was usedfor the calculation of climate-growth relationships. Thestandard chronology showed some significant correlationand responses to temperature, but none was very strongor stable over time. No significant correlation existed withprecipitation. The residual chronology showed significant0255075100125R1 R2 Kho TundraopenWoodlanddenseWoodlandForestFigure 1. Minimum thaw depth (in cm) across the forest–tundratransect; error bars are standard deviation.345
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tnr. individuals30201001800 1850 1900 1950 2000Figure 2. Establishment date of trees and seedlings on all plotssince 1800. Note distinct peak between 1950 and 1960.strong negative correlation and response functions toprevious July (mostly consistent over time) and also partlyto previous June and August temperatures; and significantstrong positive correlation and response functions to currentJune and July temperatures (inconsistent over time).All other chronologies did not exceed the 0.85 EPSthreshold. Preliminary analyses of individual trees andseedling groups revealed differing growth responses, withincreasing influence of precipitation closer to tundra areas.Discussion and ConclusionsTree line advance not only depends on favorable climaticconditions, but also on suitable microsites (Lloyd & Fastie2002). In northwest Russia, where recent warming has notbeen pronounced and concentrated on spring and summer,no recent establishment in forest or woodland has occurred.In fact, most seedlings established 50–60 years ago in aperiod of winters warmer than and summers slightly coolerthan today. No seedlings have established after 1982, theperiod of strongest warming in spring and summer. Whileestablished trees show positive correlations with warmersummers (growth year), they also show a drought stress-likesignal of negative correlations to previous July temperatures,as reported from boreal forest and tree line areas in Alaska(Barber et al. 2000, Wilmking et al. 2004). More analysis isnecessary to confirm these results.The possible influence of precipitation on growth ofseedlings in the woodland plots seems to point to theadditional influence of microsite conditions on growth.Active layer depth (and thus the distance to the localwater table) varies on very small scales, partly followingthe microtopography, and seedlings often establish on topof hummocks. There, soil temperatures are higher, andno waterlogging occurs. However, the top of hummocksare prone to drying. Preliminary analysis revealed strong,mostly positive correlations of seedling growth with summerprecipitation. Higher precipitation might be counteractingdrought during the warmest part of the year.Our preliminary investigation points to a complexinteraction between climate (temperature and precipitation)and microsite drivers (active layer depth) for the establishmentof trees in the tundra areas of northwest Russia, warrantingfurther investigations. Our plans include the inclusion oftwo additional sites in the calculation of the climate growthrelationships of established trees and seedlings, and a moresophisticated analysis of the actual microsite conditions ofeach sampled individual.AcknowledgmentsThis study was supported by a Sofja KovalevskajaAward from the Alexander von Humboldt Foundation (M.Wilmking), the German National Scholarship Foundation(S. Kenter), and the EU-Project CARBO-North (6 th FP,Contract No. 036993).ReferencesBarber, V., Juday, G. & Finney, B. 2000. Reduced growthof Alaska white spruce in the 20th century fromtemperature-induced drought stress. Nature 405: 668-72.Biondi, F. & Waikul, K. 2004. DENDROCLIM2002. A C++program for statistical calibration of climate signalsin tree ring chronologies. Computers & Geosciences30: 303-11.Chapin, F.S. et al. 2005. Role of land-surface changes inArctic summer warming. Science 310: 657-660.Lloyd, A.H. & Fastie, C.L. 2002. Spatial and temporalvariability in the growth and climate response oftreeline trees in Alaska, Climatic Change 52: 418-509.Wilmking, M., Juday, G.P., Barber, V.A. & Zald, H.S.J.2004. Recent climate warming forces opposite growthresponses of white spruce at treeline in Alaska throughtemperature thresholds. Global Change Biology 10:1724-36.Wilmking, M., Harden, J. & Tape, K. 2006. Effect of treeline advance on carbon storage in NW Alaska. JGR111: G02023, doi:10.1029/2005JG000074.346
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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