Centennial-to-millennial fluctuations in July temperatures in North Finland as recorded by timberline tree rings of Scots pine

A tree-ring proxy of summer temperature anomalies for northern Finland for the past 7500 yr was analyzed using Fourier spectrum and wavelet approaches. Multicentennial (250-450 yr) variability is present in the proxy record during most of the time range. This variability is suggested to reflect low-frequency variability in the North Atlantic Oscillation. Century-scale (90-130 yr) variation is another important feature of the tree-ring proxy data during the Holocene and may be attributed to Glessberg solar activity variations. In addition, an approximately 2000-yr quasi-period is found in this temperature proxy data, similar to the millennial-scale variability, present in many climate records from the North Atlantic region. The results point to the importance of multiple forcings underlying significant Holocene climatic fluctuations.     

Using phytogeomorphology, cartography and GIS to explain forest site productivity expressed as tree height in southern and central Finland

Using geomorphological knowledge, spatial data and GIS methods, one can obtain phytogeomorphological site variables describing interactions between landforms and vegetation. We used 15 site variables derived from maps to explain forest site productivity in southern and central Finland expressed as dominant height of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) with ages of 30–110 years. These site variables were grouped into two: Group 1 with seven variables describing geographical conditions of sites including climate, and Group 2 with eight variables describing local morphometric and soil properties. We calculated slope and aspect from a 25 × 25 m DEM. The catchment area, calcium content in soil, length of the growing season, radiation index, sea index, lake index, past highest shoreline and total annual temperature sum with threshold + 5 °C were also obtained. Then we classified the landforms of 688 sample plots into four major types and 15 sub-types. We applied regression analysis to explain the tree height as a function of the tree age and the phytogeomorphological site variables. When the tree height was explained with the tree age and the Group 1 variables, the remaining standard error of the model was 16.6–17.9%. When the Group 2 variables were added to the analysis, the standard error decreased slightly. The most significant variables were the temperature sum, latitude coordinate and length of the growing season. Other significant variables were elevation, slope and aspect. The major landform types, sub-types and watershed area did not explain the tree height. Furthermore, if the forest site types determined in the field were included, the remaining standard error decreased by ca. 2%, showing the importance of field information.     

Fire Danger Monitoring Using ERS-1 SAR Images in the Case of Northern Boreal Forests

Research was carried out to assess the potential of imaging radar systems formonitoring forest fire danger. In Canada, daily forest fire danger ratings are generated by the Canadian ForestFire Danger Rating System (CFFDRS), based on estimates of fire weather indices (FWI) and measured foliar moisturecontent (FMC). To evaluate the potential of imaging radar, an experiment was conducted using test sitesconsisting of jack pine, black spruce and white spruce stands located in the MacKenzie river basin, NorthwestTerritories, Canada. Radar image intensity values from ERS-1 SAR imagery collected over these stands in 1994 werecompared to FWI indices and FMC data. FWI indices were calculated using data from local weather stations.Seasonal trends in radar backscatter (⁰) were shown to correlate with temperature and precipitation. Significant relationships were found between ⁰ and FWI codes and indices, particularly in thecase of the black spruce stands, with slow-drying fuels, like duff moisture code (DMC), drought code (DC), and build-upindex (BUI). Rates of changes in ⁰were related to rates of changes in FMC, particularly in the case ofthe jack pine stands for old FMC and in the case of white spruce stands for composite FMC.     

Dating prehistoric bog-fires in northern England to calendar years by long-distance cross-matching of pine chronologies

The ages of prehistoric fires can be approximated by radiocarbon dating of charcoal or associated material, but such dating is often inaccurate and at best imprecise. Pine trunks preserved in British and Irish peats occasionally show firescars, which might be dated through dendrochronology to yield calendar-year dates. However, unlike oak, there is no master pine chronology to provide absolute dates, so dating is dependent on interspecies cross-matching; for sites in the British Isles with no dated oaks, calendar-year dating of prehistoric pines has hitherto proved impossible. We present a first success in dating, accurately and precisely, prehistoric fire events recorded in subfossil bog-pine trunks, using long-distance cross-matching of pine chronologies between White Moss, Cheshire, and the Humberhead Levels, England. Results demonstrate a bog-fire in Cheshire in spring 2800 BC, and again in 2710 BC, between spring and summer. Further successful long-distance cross-matching of pine would permit international climatological comparisons. © 1997 John Wiley & Sons, Ltd.     

Performance of GNSS-R GLORI data for biomass estimation over the Landes forest

The Above-Ground Biomass (AGB) is a key parameter used for the modeling of the carbon cycle. The aim of this study is to make an experimental assessment of the sensitivity of Global Navigation Satellite System (GNSS) reflected signals to forest AGB. This is based on the analysis of the data recorded during several GLORI airborne campaigns in June and July 2015, over the Landes Forest (France). Ground truth measurements of tree height, density and diameter at breast height (DBH), as well as AGB, were carried out for 100 maritime pine forest plots of various ages. The GNSS-R data were used to obtain the right-left (Γ_RL) and right-right (Γ_RR) reflectivity observables, which are geo-referenced in accordance with the known positions of relevant GPS satellites and the airborne receiver. The correlations between forest AGB and the GNSS-R observables yield the highest sensitivity at high elevation angles (70°-90°). In this case, for (Γ_RL) and the reflectivity polarization ratio (PR = Γ_RL/Γ_RR) estimated with a coherent integration time Tc = 20 ms, the coefficients of determination R² are equal to 0.67 and 0.51, with a sensitivity of −0.051 dB/[10⁶g (Mg) ha⁻¹], and −0.053 dB/[Mg ha⁻¹], respectively. The relationships between AGB and the observables are confirmed through the use of a 5-fold cross validation approach, with several different coherent integration times.     

松粉热模拟产物中饱和烃生物标志物分布

松粉和高岭土混合样品热模拟残渣氯仿抽提物和烃饱馏份中的生物标志物主要是正构烷烃系列化合物,其次是类异戊二烯烷烃、甾族系列、三环二萜烷和系列化合物,检测出少量量烷基环己烷系列,异构烷烃系列和类胡萝卜烷系列生物标志物。各类地球化学指标显示松粉热解排烃呈现１５０￣２５０℃和３００￣４００℃两个高峰期,前期生烃物质可能来地孢粉抽粉壁中的类脂物,后期主要来泊于分外壁中的孢粉素,后斯的排烃量大于前期。正构烷烷     

基于遥感的漳平市杉松林地表可燃物负荷量估测

 杉木林和马尾松是分布于漳平市的两种易燃的可燃物类型。其可燃物负荷量的多少决定着林火行为。在利用ASTER计算杉木林小班平均植被覆盖度的基础上估算其郁闭度,通过与地面调查结果比较分析,校正已发生明显变化的小班郁闭度。根据已有估测方程,结合小班数据中的年龄、胸径和树高等因子对杉木地表可燃物负荷量进行了估测,据此对各杉木小班的燃烧性、燃烧强度及火险等级等因素进行初步评价。最后对漳平市另一易燃的可燃物马尾松类型开展地表可燃物负荷量估测及分析。     

Mapping Paleo‐Fire Boundaries from Binary Point Data: Comparing Interpolation Methods

Fire history studies have traditionally emphasized temporal rather than spatial properties of paleo‐fire regimes. In this study we compare four methods of mapping paleo‐fires in central Washington from binary point data: indicator kriging, inverse distance weighting, Thiessen polygons, and an expert approach. We evaluate the results of each mapping method using a test (validation) dataset and receiver operating characteristic plots. Interpolation methods perform well, but results vary with fire size and spatial pattern of points. Though all methods involve some subjectivity, automated interpolation methods perform well, are replicable, and can be applied across varying landscapes.     

Bristlecone pine tree rings and volcanic eruptions over the last 5000 yr

Many years of low growth identified in a western USA regional chronology of upper forest border bristlecone pine (Pinus longaeva and Pinus aristata) over the last 5000 yr coincide with known large explosive volcanic eruptions and/or ice core signals of past eruptions. Over the last millennium the agreement between the tree-ring data and volcano/ice-core data is high: years of ring-width minima can be matched with known volcanic eruptions or ice-core volcanic signals in 86% of cases. In previous millennia, while there is substantial concurrence, the agreement decreases with increasing antiquity. Many of the bristlecone pine ring-width minima occurred at the same time as ring-width minima in high latitude trees from northwestern Siberia and/or northern Finland over the past 4000-5000 yr, suggesting climatically-effective events of at least hemispheric scale. In contrast with the ice-core records, the agreement between widely separated tree-ring records does not decrease with increasing antiquity. These data suggest specific intervals when the climate system was or was not particularly sensitive enough to volcanic forcing to affect the trees, and they augment the ice core record in a number of ways: by providing confirmation from an alternative proxy record for volcanic signals, by suggesting alternative dates for eruptions, and by adding to the list of years when volcanic events of global significance were likely, including the mid-2nd-millennium BC eruption of Thera.     

A record of Holocene environmental and ecological changes from Wildwood Lake,Long Island,New York

Analyses of pollen, charcoal and organic content in a lake sediment core from Wildwood Lake, Long Island, New York, provide insights into the ecological and environmental history of this region. The early Holocene interval of the record (ca. 9800–8800 cal. a BP) indicates the presence of Pinus rigida–Quercus ilicifolia woodlands with high fire activity. A layer of sandy sediment dating to 9200 cal. a BP may reflect a brief period of reduced water depth, consistent with widespread evidence for cold, dry conditions at that time. Two other sandy layers, bracketed by ¹⁴C dates, represent a sedimentary hiatus from ca. 8800 to 4500 cal. a BP. This discontinuity may reflect the removal of some sediment during brief periods of reduced water depth at 5300 and 4600 cal. a BP. In the upper portion of the record (<4500 cal. a BP), subtle changes at ca. 3000 cal. a BP indicate declining prevalence of Quercus–Fagus–Carya forests and increasing abundance of Pinus rigida, perhaps due to reduced summer precipitation. Elevated percentages of herbaceous taxa in the uppermost sediments represent European agricultural activities. However, unlike charcoal records from southern New England, fire activity does not increase dramatically with European settlement. These findings indicate that present‐day Pinus rigida–Quercus ilicifolia woodlands on eastern Long Island are not a legacy of recent, anthropogenic disturbances. Copyright © 2010 John Wiley & Sons, Ltd.