121,834 research outputs found
Variability with xylem depth in sap flow in trunks and branches of mature olive trees
No full textKnowledge of sap flow variability in tree trunks is important for up-scaling transpiration from the measuring point to the whole-tree and stand levels. Natural variability in sap flow, both radial and circumferential, was studied in the trunks and branches of mature olive trees (Olea europea L., cv Coratina) by the heat field deformation method using multi-point sensors. Sapwood depth ranged from 22 to 55 mm with greater variability in trunks than in branches. Two asymmetric types of sap flow radial patterns were observed: Type 1, rising to a maximum near the mid-point of the sapwood; and Type 2, falling continuously from a maximum just below cambium to zero at the inner boundary of the sapwood. The Type 1 pattern was recorded more often in branches and smaller trees. Both types of sap flow radial patterns were observed in trunks of the sample trees. Sap flow radial patterns were rather stable during the day, but varied with soil water changes. A decrease in sap flow in the outermost xylem was related to water depletion in the topsoil. We hypothesized that the variations in sap flow radial pattern in a tree trunk reflects a vertical distribution of water uptake that varies with water availability in different soil layers
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
Erratum to: Absorptive root area and stem resistivity in whole trees of contrasting structure and size – improvement of methods(Plant and Soil, (2014),383, 257, 273, DOI 10.1007/s11104-014-2126-5)
No full textTranspiration 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
Branch sap flow in a mature olive tree: dynamics and relation to architectural traits
No full textThis study examined how sap flow in shoots and branches of a mature olive tree (Olea europaea ‘Coratina’) related to morphological traits which are linked to tree hydraulic architecture. Spatial and temporal variations of sap flow within the tree canopy were investigated; they were analyzed with respect to the ratio between sapwood area and leaf area (SA/LA), and in relation to evaporation demand. The work was carried out on distinct sets of sap flow data, collected using different thermal methods (Heat Field Deformation - HFD and Stem Heat Balance with external heating – SHB). Sap flow density (q) appeared to be governed largely by the ratio SA/LA, irrespective of the strength and heterogeneity of the evaporation demand that affected the tree water loss. The relationship between q and SA/LA suggested a higher efficiency of the water supply pathway when SA/LA was lower, i.e. in smaller (and more distal) branches
Absorptive root area and stem resistivity in whole trees of contrasting structure and size - improvement of methods
No full textAims
The study was focused on comparing the results of the three instrumental methods applied simultaneously for root studies in several tree species representing contrasting situations: root systems of different structure and stems of a wide range of diameters (especially when considering their resistivity). We want to learn properties of the methods, make some improvements and test their validity, before they will be applied to a large series of trees at the stand level.
Material and methods
Douglas fir (Pseudotsuga menziessii (Mirbel) Franco) with very asymmetric root system and Blue spruce (Picea pungens Engelm.) with homogeneous root system growing in the Mendel University Training Forest Enterprise in Křtiny, were selected as the main sample trees. Three variants of stem impedance measurements needed for absorptive root area estimates were applied to an additional series of over 20 trees. In order to characterize vertical and circumferential (around stem) root distribution we applied (1) the sap flow radial patterns measured by the multi-point sensors based on the heat field deformation (HFD) method, and (2) a modified earth impedance (MEI) method from the group of thermodynamic and electric measuring methods and finally we (3) almost harmlessly excavated the whole root system by supersonic air stream. Three steps of absorptive root area measurements were improved: (a) Impact of stem impedance was almost eliminated, (b) Excessive variation of stem impedance values measured too close to stems (in a place with the most heterogeneous materials) was compensated by extrapolation of several close points, (c) Impact of high curvature of small stems was determined and eliminated by an equation.
Results
All the methods gave similar results when considering differences between individual trees as well as between stem sides. Sap flow density was interesting when expressed per measured absorptive root area and leaf area. Experimental data of main and additional sample trees confirmed validity of relationship, which can be applied to improve stem resistivity especially in small trees.
Conclusions
Results indicated, that all the instrumental methods are field applicable and suitable for quantitative measurements, when specific properties of the methods and stem macrostructure are taken into account. Soil electric parameters characterize the important properties related to presence of cracks, water content, and ion concentration, which are being analyzed now
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
The vanishing author in computer-generated works: a critical analysis of recent Australian case law
Get PDFAbstract
The use of software is ubiquitous in the creation of many copyright works, yet the requirement in copyright law that every work have a human author who engages in independent intellectual effort means that its use may prevent copyright subsistence. Several recent Australian cases have refocused attention on authorship as an essential criterion of copyright subsistence, and these cases suggest that much computer-produced output may be authorless and thus lack copyright protection. This article, the first in a two-part series, analyses how each case deals with the question of authorship of computer-produced works and why the use of software diminishes copyright protection for a significant number of computer-generated works. The article critiques the application of conventional notions of human authorship developed in the pre-computer age to modern productions and suggests alternative approaches to authorship that satisfy both the major objectives of copyright policy and the need to adapt to the computer age. The article argues that, without a broader judicial approach to authorship of computer-generated works, Parliament must remedy the lacuna in protection for these ‘authorless’ works. Possible solutions for reform are suggested. In a forthcoming article, the author comprehensively examines those reform proposals
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