1,721,098 research outputs found
Effect of contrasting water supply on the diameter growth of Norway spruce and aspen in mixed stands: a case study from the southern Russian taiga
No full textStem radial growth of Norway spruce (Picea abies (L.) Karst.), aspen (Populus tremula L.), birch (Betula alba L.), alder (Alnus incana (L.) Moench) and mountain ash (Sorbus aucuparia L.) was measured in an unmanaged mixed uneven-aged tree stand in the southern taiga of European Russia by band dendrometers during the growing seasons of 2000–2001. In addition woody cores were taken from sample spruce and aspen trees using increment borers for dendrochronological analysis. Analysis of the tree rings was made for period from 1999 to 2002, the period while daily meteorological data were available. Spruce and aspen represented 40 and 44% of the entire stand basal area, respectively. However, basal area has grown over 60% of the total in spruce and less than 15% in aspen for each year during the period of 1999–2002. These results indicate the transformation processes of secondary aspen-spruce stands of the Southern European Taiga into a mixed spruce-aspen-birch stands. The most intensive radial growth of the spruce trees was observed in 2000 with high over-watering conditions in summer, whereas the highest radial growth in aspen was observed during the extremely dry growing season of 2002. The basal area growth for entire forest stand ranged from 5.3 m2 ha–1 in 1999 to 11.4 m2 ha–1 in 2000. Annual increments of radial growth measured by dendrometers and by microscopic evaluation of woody cores were quite similar in spruce. In contrast, this comparison was poor for aspen trees because zero growth in some of aspen trees (measured by dendrometers) was occurred.Effets d’une alimentation en eau variée sur la croissance en diamètre de l’épicéa et du tremble dans des peuplements mélangés étudiés dans le sud de la taïga russe. La croissance radiale saisonnière de l’épicéa (Picea abies (L.) Karst.), du tremble (Populus tremula L.), du bouleau (Betula alba L.), de l’aulne (Alnus incana (L.) Moench) et du sorbier (Sorbus aucuparia L.) a été mesurée, dans une forêt mixte non gérée dominée par l’épicéa et le tremble, et située dans la taïga du sud en Russie d’Europe. Les mesures ont été effectuées à l’aide de dendromètres à ruban pendant les saisons 2000–2001 en parallèle avec les données météorologiques. En plus des carottes de bois ont été prélevées sur tous les épicéas et trembles mesurés pour faire une analyse dendrochronologique. L’épicéa et le tremble représentaient 40 et 44 % de la surface terrière du peuplement. Néanmoins, annuellement dans la période 1999–2002, la croissance de la surface terrière de l’épicéa représentait plus de 60 % de la croissance totale de la surface terrière contre moins de 15 % pour le tremble. Ces résultats révèlent la transformation de la forêt secondaire de trembles en forêt mixte à dominance d’épicéa. La croissance la plus forte de l’épicéa été observée pendant la saison 2000, caractérisée par une surabondance de l’eau dans le sol pendant l’été, tandis que la croissance maximale du tremble a été observée pendant la saison extrêmement sèche du 2002. La croissance totale de la surface terrière du peuplement variait de 5.3 m2 ha–1 en 1999 jusqu’à 11.4 m2 ha–1 en 2000. La croissance annuelle radiale mesurée par les dendromètres et par la mesure des accroissements annuels sur les carottes de sondage était similaire chez l’épicéa. En contraste chez le tremble, cette concordance était faible à cause de l’absence de croissance radiale d’une partie des trembles mesurés par les dendromètres
Transpiration of a mixed forest stand: field measurements and simulation using SVAT models
No full textTranspiration of a mixed spruce-aspen-birch forest at the Valday Hills in Russia was determined using sap flow measurements and two different SVAT (Soil-Vegetation-Atmosphere-Transfer) models. The more sophisticated Mixed Forest multi-layer SVAT model (MF-SVAT) considers water uptake and transpiration of each tree species individually, and the simple Multi-Layer (ML-SVAT) describes the forest stand using averaged effective parameters of canopy structure and tree physiology. Comparisons of modelled and measured transpiration rates under sufficient soil moisture conditions did not show any significant differences between two models. Under limited soil moisture conditions MF-SVAT described forest transpiration still realistically whereas ML-SVAT overestimated it by up to 50%. Drought in the upper soil layers reduced transpiration of spruces more than of deciduous trees due to differences in physiological properties and vertical root distribution. Individual regulation of the transpiration of different tree species is typical for mixed forests and cannot be accurately described with averaged parameterisation such as used in ML-SVAT
Spruce roots under heavy machinery loading in two different soil types
No full textWe studied the influence of soil compaction by heavy machinery (two-wheeled trailer with 0.2 MPa pressure) on spruce roots at two sites in the Moravian Highlands with different soil properties to determine whether soil compaction by loading affects root water uptake. We also analysed the effects of the soil type and water-holding capacity with regards to root structure development. Site Jedovnice has a loamy to sandy-loamy soil texture with a shallow groundwater table at approximately 1 m in depth. The roots are mostly distributed in deeper layers. Site Mraveniste has shallow, sandy-loamy soil overlying a granodiorite. This site has no access to groundwater and a higher proportion of shallow roots. To evaluate the effect of soil compaction, we installed heat-field-deformation sap flow sensors in the superficial roots and stem bases of trees close to machinery trails. Our results showed that loading mainly affected soils with a high proportion of shallow roots (33% of shallow roots at site Mraveniste; 22% at site Jedovnice). The number of roots treated by loading, verified after root opening with an air spade, depended on root positioning in soil. Acropetal sap flow occurred in roots in soil layers with sufficient available soil water. Some of the sampled trees exhibited decreased daytime sap flow after loading. In the shallower site Mraveniste the root responses to loading were also accompanied by water redistribution among the roots and between the roots and soil. Basipetal (reverse) flow was recorded in roots in dryer soil layers. Soil compaction due to loading substantially increased the magnitude and duration of redistributed flow between soil layers with different water contents. Determining the soil type and soil water content is recommended before choosing the machinery type for a given forest because the predicted tree root structure can be used to assess possible damage due to loading. (C) 2012 Elsevier B.V. All rights reserved.TIP [FRTI4/139]; IGA LDF [12/2010
Transpiration of a mixed forest stand: field measurements and simulation using SVAT models
No full textTranspiration of a mixed spruce-aspen-birch forest at the Valday Hills in Russia was determined using sap flow measurements and two different SVAT (Soil-Vegetation-Atmosphere-Transfer) models. The more sophisticated Mixed Forest multi-layer SVAT model (MF-SVAT) considers water uptake and transpiration of each tree species individually, and the simple Multi-Layer (ML-SVAT) describes the forest stand using averaged effective parameters of canopy structure and tree physiology. Comparisons of modelled and measured transpiration rates under sufficient soil moisture conditions did not show any significant differences between two models. Under limited soil moisture conditions MF-SVAT described forest transpiration still realistically whereas ML-SVAT overestimated it by up to 50%. Drought in the upper soil layers reduced transpiration of spruces more than of deciduous trees due to differences in physiological properties and vertical root distribution. Individual regulation of the transpiration of different tree species is typical for mixed forests and cannot be accurately described with averaged parameterisation such as used in ML-SVAT
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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