1-20 von 476 Publikationen

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      Gene flow of common ash (Fraxinus excelsior L.) in a fragmented landscape. 

      Semizer-Cuming, Devrim; Kjær, Erik Dahl; Finkeldey, Reiner
      PloS one 2017; 12(10): Art. e0186757
      Gene flow dynamics of common ash (Fraxinus excelsior L.) is affected by several human activities in Central Europe, including habitat fragmentation, agroforestry expansion, controlled and uncontrolled transfer of reproductive material, and a recently introduced emerging infectious disease, ash dieback, caused by Hymenoscyphus fraxineus. Habitat fragmentation may alter genetic connectivity and effective population size, leading to loss of genetic diversity and increased inbreeding in ash populations. Gene flow from cultivated trees in landscapes close to their native counterparts may also influence the adaptability of future generations. The devastating effects of ash dieback have already been observed in both natural and managed populations in continental Europe. However, potential long-term effects of genetic bottlenecks depend on gene flow across fragmented landscapes. For this reason, we studied the genetic connectivity of ash trees in an isolated forest patch of a fragmented landscape in Rösenbeck, Germany. We applied two approaches to parentage analysis to estimate gene flow patterns at the study site. We specifically investigated the presence of background pollination at the landscape level and the degree of genetic isolation between native and cultivated trees. Local meteorological data was utilized to understand the effect of wind on the pollen and seed dispersal patterns. Gender information of the adult trees was considered for calculating the dispersal distances. We found that the majority of the studied seeds (55-64%) and seedlings (75-98%) in the forest patch were fathered and mothered by the trees within the same patch. However, we determined a considerable amount of pollen flow (26-45%) from outside of the study site, representing background pollination at the landscape level. Limited pollen flow was observed from neighbouring cultivated trees (2%). Both pollen and seeds were dispersed in all directions in accordance with the local wind directions. Whereas there was no positive correlation between pollen dispersal distance and wind speed, the correlation between seed dispersal distance and wind speed was significant (0.71, p < 0.001), indicating that strong wind favours long-distance dispersal of ash seeds. Finally, we discussed the implications of establishing gene conservation stands and the use of enrichment planting in the face of ash dieback.
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      Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia 

      Sabajo, Clifton R.; le Maire, Guerric; June, Tania; Meijide, Ana; Roupsard, Olivier; Knohl, Alexander
      Biogeosciences 2017; 14(20) p.4619-4635
      Indonesia is currently one of the regions with the highest transformation rate of land surface worldwide related to the expansion of oil palm plantations and other cash crops replacing forests on large scales. Land cover changes, which modify land surface properties, have a direct effect on the land surface temperature (LST), a key driver for many ecological functions. Despite the large historic land transformation in Indonesia toward oil palm and other cash crops and governmental plans for future expansion, this is the first study so far to quantify the impacts of land transformation on the LST in Indonesia. We analyze LST from the thermal band of a Landsat image and produce a highresolution surface temperature map (30 m) for the lowlands of the Jambi province in Sumatra (Indonesia), a region which suffered large land transformation towards oil palm and other cash crops over the past decades. The comparison of LST, albedo, normalized differenced vegetation index (NDVI) and evapotranspiration (ET) between seven different land cover types (forest, urban areas, clear-cut land, young and mature oil palm plantations, acacia and rubber plantations) shows that forests have lower surface temperatures than the other land cover types, indicating a local warming effect after forest conversion. LST differences were up to 10.1 2.6 C (mean SD) between forest and clear-cut land. The differences in surface temperatures are explained by an evaporative cooling effect, which offsets the albedo warming effect. Our analysis of the LST trend of the past 16 years based on MODIS data shows that the average daytime surface temperature in the Jambi province increased by 1.05 C, which followed the trend of observed land cover changes and exceeded the effects of climate warming. This study provides evidence that the expansion of oil palm plantations and other cash crops leads to changes in biophysical variables, warming the land surface and thus enhancing the increase of the air temperature because of climate change.
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      Soil trace gas fluxes along orthogonal precipitation and soil fertility gradients in tropical lowland forests of Panama 

      Matson, Amanda L.; Corre, Marife D.; Langs, Kerstin; Veldkamp, Edzo
      Biogeosciences 2017; 14(14) p.3509-3524
      Tropical lowland forest soils are significant sources and sinks of trace gases. In order to model soil trace gas flux for future climate scenarios, it is necessary to be able to predict changes in soil trace gas fluxes along natural gradients of soil fertility and climatic characteristics. We quantified trace gas fluxes in lowland forest soils at five locations in Panama, which encompassed orthogonal precipitation and soil fertility gradients. Soil trace gas fluxes were measured monthly for 1 (NO) or 2 (CO2, CH4, N2O) years (2010–2012) using vented dynamic (for NO only) or static chambers with permanent bases. Across the five sites, annual fluxes ranged from 8.0 to 10.2 Mg CO2-C, −2.0 to −0.3 kg CH4-C, 0.4 to 1.3 kg N2O-N and −0.82 to −0.03 kg NO-N ha−1 yr−1. Soil CO2 emissions did not differ across sites, but they did exhibit clear seasonal differences and a parabolic pattern with soil moisture across sites. All sites were CH4 sinks; within-site fluxes were largely controlled by soil moisture, whereas fluxes across sites were positively correlated with an integrated index of soil fertility. Soil N2O fluxes were low throughout the measurement years, but the highest emissions occurred at a mid-precipitation site with high soil N availability. Net negative NO fluxes at the soil surface occurred at all sites, with the most negative fluxes at the low-precipitation site closest to Panama City; this was likely due to high ambient NO concentrations from anthropogenic sources. Our study highlights the importance of both short-term (climatic) and long-term (soil and site characteristics) factors in predicting soil trace gas fluxes.
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      Tree Growth Rings in Tropical Peat Swamp Forests of Kalimantan, Indonesia 

      Worbes, Martin; Herawati, Hety; Martius, Christopher
      Forests 2017; 8(9): Art. 336
      Tree growth rings are signs of the seasonality of tree growth and indicate how tree productivity relates to environmental factors. We studied the periodicity of tree growth ring formation in seasonally inundated peatlands of Central Kalimantan (southern Borneo), Indonesia. We collected samples from 47 individuals encompassing 27 tree species. About 40% of these species form distinct growth zones, 30% form indistinct ones, and the others were classified as in between. Radiocarbon age datings of single distinct growth zones (or “rings”) of two species showing very distinct rings, Horsfieldia crassifolia and Diospyros evena, confirm annual growth periodicity for the former; the latter forms rings in intervals of more than one year. The differences can be explained with species-specific sensitivity to the variable intensity of dry periods. The anatomical feature behind annual rings in Horsfieldia is the formation of marginal parenchyma bands. Tree ring curves of other investigated species with the same anatomical feature from the site show a good congruence with the curves from H. crassifolia. They can therefore be used as indicator species for growth rate estimations in environments with weak seasonality. The investigated peatland species show low annual growth increments compared to other tropical forests.
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      Leaf-IT: An Android application for measuring leaf area 

      Schrader, Julian; Pillar, Giso; Kreft, Holger
      Ecology and Evolution
      The use of plant functional traits has become increasingly popular in ecological studies because plant functional traits help to understand key ecological processes in plant species and communities. This also includes changes in diversity, inter-and intraspecific interactions, and relationships of species at different spatiotemporal scales. Leaf traits are among the most important traits as they describe key dimensions of a plant’s life history strategy. Further, leaf area is a key parameter with relevance for other traits such as specific leaf area, which in turn correlates with leaf chemical composition, photosynthetic rate, leaf longevity, and carbon investment. Measuring leaf area usually involves the use of scanners and commercial software and can be difficult under field conditions. We present Leaf-IT, a new smartphone application for measuring leaf area and other trait-related areas. Leaf-IT is free, designed for scientific purposes, and runs on Android 4 or higher. We tested the precision and accuracy using objects with standardized area and compared the area measurements of real leaves with the well-established, commercial software WinFOLIA using the Altman–Bland method. Area measurements of standardized objects show that Leaf-IT measures area with high accuracy and precision. Area measurements with Leaf-IT of real leaves are comparable to those of WinFOLIA. Leaf-IT is an easy-to- use application running on a wide range of smartphones. That increases the portability and use of Leaf-IT and makes it possible to measure leaf area under field conditions typical for remote locations. Its high accuracy and precision are similar to WinFOLIA. Currently, its main limitation is margin detection of damaged leaves or complex leaf morphologies.
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      De novo transcriptome assembly and analysis of differential gene expression in response to drought in European beech 

      Müller, Markus; Seifert, Sarah; Lübbe, Torben; Leuschner, Christoph; Finkeldey, Reiner
      PLOS ONE 2017; 12(9): Art. e0184167
      Despite the ecological and economic importance of European beech (Fagus sylvatica L.) genomic resources of this species are still limited. This hampers an understanding of the molecular basis of adaptation to stress. Since beech will most likely be threatened by the consequences of climate change, an understanding of adaptive processes to climate change-related drought stress is of major importance. Here, we used RNA-seq to provide the first drought stress-related transcriptome of beech. In a drought stress trial with beech saplings, 50 samples were taken for RNA extraction at five points in time during a soil desiccation experiment. De novo transcriptome assembly and analysis of differential gene expression revealed 44,335 contigs, and 662 differentially expressed genes between the stress and normally watered control group. Gene expression was specific to the different time points, and only five genes were significantly differentially expressed between the stress and control group on all five sampling days. GO term enrichment showed that mostly genes involved in lipid- and homeostasis-related processes were upregulated, whereas genes involved in oxidative stress response were downregulated in the stressed seedlings. This study gives first insights into the genomic drought stress response of European beech, and provides new genetic resources for adaptation research in this species.
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      Effect of climate warming on the annual terrestrial net ecosystem CO2 exchange globally in the boreal and temperate regions 

      Zhang, Zhiyuan; Zhang, Renduo; Cescatti, Alessandro; Wohlfahrt, Georg; Buchmann, Nina; Zhu, Juan; Chen, Guanhong; Moyano, Fernando; Pumpanen, Jukka; Hirano, Takashi; et al.
      Takagi, KentaroMerbold, Lutz
      Scientific Reports 2017; 7(1)
      The net ecosystem CO2 exchange is the result of the imbalance between the assimilation process (gross primary production, GPP) and ecosystem respiration (RE). The aim of this study was to investigate temperature sensitivities of these processes and the effect of climate warming on the annual terrestrial net ecosystem CO2 exchange globally in the boreal and temperate regions. A database of 403 site-years of ecosystem flux data at 101 sites in the world was collected and analyzed. Temperature sensitivities of rates of RE and GPP were quantified with Q10, defined as the increase of RE (or GPP) rates with a temperature rise of 10 °C. Results showed that on the annual time scale, the intrinsic temperature sensitivity of GPP (Q10sG ) was higher than or equivalent to the intrinsic temperature sensitivity of RE (Q10sR ). Q10sG was negatively correlated to the mean annual temperature (MAT), whereas Q10sR was independent of MAT. The analysis of the current temperature sensitivities and net ecosystem production suggested that temperature rise might enhance the CO2 sink of terrestrial ecosystems both in the boreal and temperate regions. In addition, ecosystems in these regions with different plant functional types should sequester more CO2 with climate warming.
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      Development of novel genic microsatellite markers from transcriptome sequencing in sugar maple (Acer saccharum Marsh.) 

      Harmon, Monica; Lane, Thomas; Staton, Margaret; Coggeshall, Mark V.; Best, Teodora; Chen, Chien-Chih; Liang, Haiying; Zembower, Nicole; Drautz-Moses, Daniela I.; Hwee, Yap Zhei; et al.
      Schuster, Stephan C.Schlarbaum, Scott E.Carlson, John E.Gailing, Oliver
      BMC Research Notes 2017; 10(369)
      Sugar maple (Acer saccharum Marsh.) is a hardwood tree species native to northeastern North America and economically valued for its wood and sap. Yet, few molecular genetic resources have been developed for this species to date. Microsatellite markers have been a useful tool in population genetics, e.g., to monitor genetic variation and to analyze gene flow patterns. The objective of this study is to develop a reference transcriptome and microsatellite markers in sugar maple. A set of 117,861 putative unique transcripts were assembled using 29.2 Gb of RNA sequencing data derived from different tissues and stress treatments. From this set of sequences a total of 1068 microsatellite motifs were identified. Out of 58 genic microsatellite markers tested on a population of 47 sugar maple trees in upper Michigan, 22 amplified well, of which 16 were polymorphic and 6 were monomorphic. Values for expected heterozygosity varied from 0.224 to 0.726 for individual loci. Of the 16 polymorphic markers, 15 exhibited transferability to other Acer L. species. Genic microsatellite markers can be applied to analyze genetic variation in potentially adaptive genes relative to genomic reference markers as a basis for the management of sugar maple genetic resources in the face of climate change.
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      Plywood made from plasma-treated veneers: melamine uptake, dimensional stability, and mechanical properties 

      Wascher, Richard; Kühn, Christian; Avramidis, Georg; Bicke, Sascha; Militz, Holger; Ohms, Gisela; Viöl, Wolfgang
      Journal of Wood Science 2017; 63(4) p.338-349
      This study investigates the dimensional stability and mechanical properties of plywood boards made of thermally modified and unmodified beech veneers that have undergone plasma pre-treatment before melamine resin impregnation. The water and melamine resin uptake and resulting weight percent gain of the veneers were investigated, whereby the air plasma pre-treated veneers showed improved liquid uptake. Five-layer plywood boards were then manufactured and tested for their dimensional stability, compressive strength, bending strength, and tensile strength. Plywood boards made of thermally modified and plasma pre-treated veneers showed a significantly improved dimensional stability, along with small influences on their mechanical properties.
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      Atmospheric deposition, CO2, and change in the land carbon sink 

      Fernández-Martínez, M.; Vicca, S.; Janssens, I. A.; Ciais, P.; Obersteiner, M.; Bartrons, M.; Sardans, J.; Verger, A.; Canadell, J. G.; Chevallier, F.; et al.
      Wang, X.Bernhofer, C.Curtis, P. S.Gianelle, D.Grünwald, T.Heinesch, B.Ibrom, A.Knohl, A.Laurila, T.Law, B. E.Limousin, J. M.Longdoz, B.Loustau, D.Mammarella, I.Matteucci, G.Monson, R. K.Montagnani, L.Moors, E. J.Munger, J. W.Papale, D.Piao, S. L.Peñuelas, J.
      Scientific Reports 2017; 7(1): Art. 9632
      Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO2 was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling.
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      Estimating utilization distributions from fitted step-selection functions 

      Signer, Johannes; Fieberg, John; Avgar, Tal
      Ecosphere 2017; 8(4): Art. e01771
      Habitat-selection analyses are often used to link environmental covariates, measured within some spatial domain of assumed availability, to animal location data that are assumed to be independent. Step-selection functions (SSFs) relax this independence assumption, by using a conditional model that explicitly acknowledges the spatiotemporal dynamics of the availability domain and hence the temporal dependence among successive locations. However, it is not clear how to produce an SSF-based map of the expected utilization distribution. Here, we used SSFs to analyze virtual animal movement data generated at a fine spatiotemporal scale and then rarefied to emulate realistic telemetry data. We then compared two different approaches for generating maps from the estimated regression coefficients. First, we considered a na€ıve approach that used the coefficients as if they were obtained by fitting an unconditional model. Second, we explored a simulation-based approach, where maps were generated using stochastic simulations of the parameterized step-selection process. We found that the simulation-based approach always outperformed the na€ıve mapping approach and that the latter overestimated home-range size and underestimated local space-use variability. Differences between the approaches were greatest for complex landscapes and high sampling rates, suggesting that the simulation-based approach, despite its added complexity, is likely to offer significant advantages when applying SSFs to real data.
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      Soil nitrogen oxide fluxes from lowland forests converted to smallholder rubber and oil palm plantations in Sumatra, Indonesia 

      Hassler, Evelyn; Corre, Marife D.; Kurniawan, Syahrul; Veldkamp, Edzo
      Biogeosciences 2017; 14(11) p.2781-2798
      Oil palm (Elaeis guineensis) and rubber (Hevea brasiliensis) plantations cover large areas of former rainforest in Sumatra, Indonesia, supplying the global demand for these crops. Although forest conversion is known to influence soil nitrous oxide (N2O) and nitric oxide (NO) fluxes, measurements from oil palm and rubber plantations are scarce (for N2O) or nonexistent (for NO). Our study aimed to (1) quantify changes in soil–atmosphere fluxes of N oxides with forest conversion to rubber and oil palm plantations and (2) determine their controlling factors. In Jambi, Sumatra, we selected two landscapes that mainly differed in texture but were both on heavily weathered soils: loam and clay Acrisol soils. Within each landscape, we investigated lowland forests, rubber trees interspersed in secondary forest (termed as "jungle rubber"), both as reference land uses and smallholder rubber and oil palm plantations as converted land uses. In the loam Acrisol landscape, we conducted a follow-on study in a large-scale oil palm plantation (called PTPN VI) for comparison of soil N2O fluxes with smallholder oil palm plantations. Land-use conversion to smallholder plantations had no effect on soil N-oxide fluxes (P = 0. 58 to 0.76) due to the generally low soil N availability in the reference land uses that further decreased with land-use conversion. Soil N2O fluxes from the large-scale oil palm plantation did not differ with those from smallholder plantations (P = 0. 15). Over 1-year measurements, the temporal patterns of soil N-oxide fluxes were influenced by soil mineral N and water contents. Across landscapes, annual soil N2O emissions were controlled by gross nitrification and sand content, which also suggest the influence of soil N and water availability. Soil N2O fluxes (µg N m−2 h−1) were 7 ± 2 to 14 ± 7 (reference land uses), 6 ± 3 to 9 ± 2 (rubber), 12 ± 3 to 12 ± 6 (smallholder oil palm) and 42 ± 24 (large-scale oil palm). Soil NO fluxes (µg N m−2 h−1) were −0.6 ± 0.7 to 5.7 ± 5.8 (reference land uses), −1.2 ± 0.5 to −1.0 ± 0.2 (rubber) and −0.2 ± 1.2 to 0.7 ± 0.7 (smallholder oil palm). To improve the estimate of soil N-oxide fluxes from oil palm plantations in this region, studies should focus on large-scale plantations (which usually have 2 to 4 times higher N fertilization rates than smallholders) with frequent measurements following fertilizer application.
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      Rhizosphere hydrophobicity: A positive trait in the competition for water. 

      Zeppenfeld, Thorsten; Balkenhol, Niko; Kóvacs, Kristóf; Carminati, Andrea
      PloS one 2017; 12(7): Art. e0182188
      The ability to acquire water from the soil is a major driver in interspecific plant competition and it depends on several root functional traits. One of these traits is the excretion of gel-like compounds (mucilage) that modify physical soil properties. Mucilage secreted by roots becomes hydrophobic upon drying, impedes the rewetting of the soil close to the root, the so called rhizosphere, and reduces water availability to plants. The function of rhizosphere hydrophobicity is not easily understandable when looking at a single plant, but it may constitute a competitive advantage at the ecosystem level. We hypothesize that by making the top soil hydrophobic, deep-rooted plants avoid competititon with shallow-rooted plants. To test this hypothesis we used an individual-based model to simulate water uptake and growth of two virtual plant species, one deep-rooted plant capable of making the soil hydrophobic and a shallow-rooted plant. We ran scenarios with different precipitation regimes ranging from dry to wet (350, 700, and 1400 mm total annual precipitation) and from high to low precipitation frequencies (1, 7, and 14 days). Plant species abundance and biomass were chosen as indicators for competitiveness of plant species. At constant precipitation frequency mucilage hydrophobicity lead to a benefit in biomass and abundance of the tap-rooted population. Under wet conditions this effect diminished and tap-rooted plants were less productive. Without this trait both species coexisted. The effect of root exudation trait remained constant under different precipitation frequencies. This study shows that mucilage secretion is a competitive trait for the acquisition of water. This advantage is achieved by the modification of the soil hydraulic properties and specifically by inducing water repellency in soil regions which are shared with other species.
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      On the Effect of Thinning on Tree Growth and Stand Structure of White Birch (Betula platyphylla Sukaczev) and Siberian Larch (Larix sibirica Ledeb.) in Mongolia 

      Gradel, Alexander; Ammer, Christian; Ganbaatar, Batsaikhan; Nadaldorj, Ochirrragchaa; Dovdondemberel, Batdorj; Wagner, Sven
      Forests 2017; 8(4): Art. 105
      The forests of North Mongolia are largely dominated either by larch (Larix sibirica Ledeb.) or birch (Betula platyphylla Sukaczev). The increasing demand for timber and firewood is currently met by removal of wood from these forest stands. Therefore, silvicultural approaches that account for both utilization and protection are needed. Thinning trials were established in the research area Altansumber, in the mountain forest steppe west of the town of Darkhan. We analyzed the response of non-spatial and spatial structure and growth of birch and larch stands on thinning. Before thinning, spatial tree distribution was largely clumped. Thinning promoted regular tree distribution. Ingrowth of new stems after thinning tended to redirect stand structure towards clumping. Both relative and absolute tree growth and competition were evaluated before, directly after, and three years after the thinning. Competition played a significant role in tree growth before thinning. A reduction in competition after thinning triggered significantly increased growth of both birch and larch. The observed positive growth response was valid in absolute and relative terms. A methodically based forest management strategy, including thinning operations and selective cuttings, could be established, even under the harsh Mongolian conditions. Our findings could initiate the development of broader forest management guidelines for the light-taiga dominated stands.
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      Oil Palm and Rubber Tree Water Use Patterns: Effects of Topography and Flooding 

      Hardanto, Afik; Röll, Alexander; Niu, Furong; Meijide, Ana; Hendrayanto; Hölscher, Dirk
      Frontiers in Plant Science 2017; 8: Art. 452
      Oil palm and rubber plantations extend over large areas and encompass heterogeneous site conditions. In periods of high rainfall, plants in valleys and at riparian sites are more prone to flooding than plants at elevated topographic positions. We asked to what extent topographic position and flooding affect oil palm and rubber tree water use patterns and thereby influence spatial and temporal heterogeneity of transpiration. In an undulating terrain in the lowlands of Jambi, Indonesia, plantations of the two species were studied in plot pairs consisting of upland and adjacent valley plots. All upland plots were non-flooded, whereas the corresponding valley plots included non-flooded, longterm flooded, and short-term flooded conditions. Within each plot pair, sap flux densities in palms or trees were monitored simultaneously with thermal dissipation probes. In plot pairs with non-flooded valleys, sap flux densities of oil palms were only slightly different between the topographic positions, whereas sap flux densities of rubber trees were higher in the valley than at the according upland site. In pairs with long-term flooded valleys, sap flux densities in valleys were lower than at upland plots for both species, but the reduction was far less pronounced in oil palms than in rubber trees (􀀀22 and 􀀀45% in maximum sap flux density, respectively). At these long-term flooded valley plots palm and tree water use also responded less sensitively to fluctuations in micrometeorological variables than at upland plots. In short-term flooded valley plots, sap flux densities of oil palm were hardly affected by flooding, but sap flux densities of rubber trees were reduced considerably. Topographic position and flooding thus affected water use patterns in both oil palms and rubber trees, but the changes in rubber trees were much more pronounced: compared to non-flooded upland sites, the different flooding conditions at valley sites amplified the observed heterogeneity of plot mean water use by a factor of 2.4 in oil palm and by a factor of 4.2 in rubber plantations. Such strong differences between species as well as the pronounced heterogeneity of water use across space and time may be of relevance for eco-hydrological assessments of tropical plantation landscapes.
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      Seed dispersal at alpine treeline: an assessment of seed movement within the alpine treeline ecotone 

      Johnson, Jeremy S.; Gaddis, Keith D.; Cairns, David M.; Krutovsky, Konstantin V.
      Ecosphere 2017; 8(1): Art. e01649
      Alpine treelines are expected to advance to higher elevations in conjunction with global warming. Nevertheless, the importance of treeline reproductive patterns and seed dispersal within the alpine treeline ecotone remains unresolved. In this study, we address two research questions at mountain hemlock treelines on the Kenai Peninsula, Alaska: (1) What is the primary mode of reproduction and (2) are seeds leading to recruitment derived from within the local treeline populations or are they arriving from more distant seed sources? To answer these questions, we exhaustively sampled mountain hemlock individuals along a single mountain slope, and genotyped single nucleotide polymorphisms using doubledigest restriction site-associated DNA sequencing. First, we assessed mode of reproduction by determining the proportion of sampled individuals with identical multilocus genotypes that are the product of clonal reproduction. Second, we used a categorical parentage analysis to identify parent–offspring pairs, so that the proportion of treeline reproduction events could be spatially quantified and dispersal distance measured. We identified sexual reproduction as the primary mode of reproduction at our study site. Seedling establishment was characterized by extensive seed immigration and gene flow into the ecotone. The average dispersal distance was 73 m with long-distance dispersal identified as dispersal occurring at distances greater than 450 m. We found that production of seeds within the alpine treeline ecotone is not necessarily a requirement for treelines to advance to higher elevations in response to climate change. The extensive seed dispersal and gene flow into the alpine treeline ecotone is likely sufficient to propel the ecotone higher under more favorable climate.
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      Improving Execution Speed of Models Implemented in NetLogo 

      Railsback, Steven; Ayllón, Daniel; Berger, Uta; Grimm, Volker; Lytinen, Steven; Sheppard, Colin; Thiele, Jan
      Journal of Artificial Societies and Social Simulation 2017; 20(1)
      NetLogo has become a standard platform for agent-based simulation, yet there appears to be widespread belief that it is not suitable for large and complex models due to slow execution. Our experience does not support that belief. NetLogo programs o en do run very slowly when written to minimize code length and maximize clarity, but relatively simple and easily tested changes can almost always produce major increases in execution speed. We recommend a five-step process for quantifying execution speed, identifying slow parts of code, and writing faster code. Avoiding or improving agent filtering statements can o en produce dramatic speed improvements. For models with extensive initialization methods, reorganizing the setup procedure can reduce the initialization e ort in simulation experiments. Programming the same behavior in a di erent way can sometimes provide order-of-magnitude speed increases. For models in which most agents do nothing on most time steps, discrete event simulation – facilitated by the time extension to NetLogo – can dramatically increase speed. NetLogo’s BehaviorSpace tool makes it very easy to conduct multiple-model-run experiments in parallel on either desktop or high performance cluster computers, so even quite slow models can be executed thousands of times. NetLogo also is supported by e icient analysis tools, such as BehaviorSearch and RNetLogo, that can reduce the number of model runs and the e ort to set them up for (e.g.) parameterization and sensitivity analysis.
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      Thermal stability of processed PVC/bamboo blends: effect of compounding procedures 

      Bahari, Shahril Anuar; Grigsby, Warren; Krause, Andreas
      European Journal of Wood and Wood Products 2017; 75(2) p.147-159
      Polyvinyl chloride (PVC) was mixed with bamboo (Bambusa vulgaris) particle and additives by using PVC composite manufacturing system including initial dry blending with hot-cool mixing, followed by granulation via counter-rotating extrusion, and then consolidation by compression moulding to produce compression moulded board (CMB). The effects of different bamboo particle size (75 µm and 1 mm), bamboo particle loading (25 and 50% loading ratio), and differing processing lubricants content level (compositions 1 and 2) on the thermal stability of the composites were determined. Results show no significant trends in glass transition temperature (Tg) between dry blends, granules, and CMB, and between B. vulgaris particle loading at the respective processing steps. For samples with higher lubricant contents, the PVC Tg was observed to decrease up to 5 °C, possibly due to the reduced melt viscosity. The thermal decomposition temperature at 5% mass loss (T−5%) appeared to decrease from dry blend to CMB due to sample degradation on further processing at higher temperatures. The use of 50% B. vulgaris particle loading also reduced the T−5% values, assignable to bamboo particle degradation caused by the high processing temperatures. For oxidative induction time (OIT) testing, only granules and CMB from pure PVC composites system showed measurable oxidative times compared with OIT profiles of PVC/B. vulgaris composites system, suggestive of comparatively stabilized thermoplastic composites. This revealed that processing with bamboo particles does not contribute to degradation of PVC composites.
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      Species proportions by area in mixtures of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) 

      Dirnberger, Gerald; Sterba, Hubert; Condés, Sonia; Ammer, Christian; Annighöfer, Peter; Avdagić, Admir; Bielak, Kamil; Brazaitis, Gediminas; Coll, Lluís; Heym, Michael; et al.
      Hurt, VáclavKurylyak, ViktorMotta, RenzoPach, MaciejPonette, QuentinRuiz-Peinado, RicardoSkrzyszewski, JerzyŠrámek, Vítde Streel, GéraudSvoboda, MiroslavZlatanov, TzvetanPretzsch, Hans
      European Journal of Forest Research 2016; 136(1) p.1-13
      Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species’ proportions estimated with this method are best approximated by the proportions of the species’ leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach.
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    • Zeitschriftenartikel

      The macroecology of island floras 

      Weigelt, Patrick
      Frontiers of Biogeography 2015; 7(3)
      Islands are key model systems in biogeography and ecology. However, standardized data on environmental characteristics of the large number of islands worldwide have so far been lacking, and the effects of these characteristics on island ecology and biodiversity remain insufficiently understood. In my PhD thesis, I presented the first comprehensive environmental characterization of the world’s islands, covering past and present bioclimatic and physical island characteristics (including the spatial setting of islands and archipelagos). I used these data to investigate how island characteristics influence the diversity and assembly of island floras at different spatial scales and across major plant groups. To this end, I assembled a global database of vascular plant species composition including 45,000 species and covering 1,070 islands. I showed that different aspects of island environments affect different facets of insular diversity (species richness, turnover, phylogenetic diversity) across scales and major plant groups, in accordance with their predominant dispersal- and speciation-related traits and adaptations to climate. The results contribute to a better understanding of the environmental and evolutionary drivers of plant assemblage composition, on islands as well as on mainlands.
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