Raíces pequeñas del dosel del pinabete (Picea abies): distribución e influencia en el crecimiento de hayas

The horizontal and vertical distribution of live fine roots (diameter < 2 mm) of overstory Norway spruce [Picea abies (L.) Karst.] and their influence on diameter and height growth of underplanted beech (Fagus sylvatica L.) and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) saplings were studied on experimental plots in the Solling Mountains (Germany). The aims of this study were to investigate how overstory fine root density varies with stand density, and how it influences growth of the underplanted saplings to changes in belowground resources availability in connection with simultaneously changing light availability. Most fine roots were concentrated in the humus layer (more than 45%) and in the top mineral soil (0-5 cm, about 15%). Fine root biomass increases with overstory basal area and decreases with rising distance from the nearest overstory tree, reaching about zero within ca. 8 m distance. Over the whole two-year study period, light availability alone was the decisive factor for growth of the beech saplings (5 resp. 6 years of age) while growth of the Douglas-fir saplings in the first study year (6 years of age) was additionally affected by a shortage of belowground resources due to root competition in a season with less than average rainfall. This species-specific response of underplanted saplings to changes in above and belowground resources is of silvicultural importance for the establishment of a mixed stand beneath a mature canopy: the more sensitive Douglasfir should be planted on the central parts of openings with little or none belowground competition while the less sensitive beech can be placed below the denser parts of the overstory.Se estudia la distribución horizontal y vertical de las raíces finas (diámetro < 2 mm) vivas del dosel de pinabete y su influencia en el diámetro y el crecimiento en altura de hayas plantadas y en brinzales de abeto Douglas en parcelas experimentales en las montes de Solling (Alemania). Los objetivos de este estudio es analizar cómo la densidad de raíces finas del dosel varía con la densidad del rodal, y cómo influye en el crecimiento de los árboles jóvenes del subpiso debido a los cambios en la disponibilidad de recursos en el suelo, en relación con el cambio al mismo tiempo en la disponibilidad de luz. Las raíces más finas se concentra en la capa de humus (más del 45%) y en la parte mineral superior del suelo (0-5 cm, aproximadamente el 15%). La biomasa de raíces finas aumenta con el área bisimétrica del dosel y disminuye con la distancia creciente al árbol más cercano del dosel, hasta llegar a cero dentro de ca. 8 m de distancia. Durante el periodo de estudio de dos años, la disponibilidad de luz era el único factor decisivo para el crecimiento de los plantones de haya (5 resp. 6 años de edad) mientras que el crecimiento de las plántulas de pino de Douglas en el primer año de estudio (6 años de edad) se vio afectado adicionalmente por la escasez de recursos en el suelo debido a la competencia de las raíces en una temporada con una precipitación menor del promedio. Esta respuesta especie-especifica de los árboles del subpiso a los cambios en los recursos por encima y por debajo del suelo es de importancia silvícola para la creación de una masa mixta bajo un dosel maduro: la especie más sensible, pino de Douglas, se debe plantar en las partes centrales de las aberturas con poca o ninguna competencia bajo tierra, mientras que el haya, menos sensible, se puede colocar debajo de las partes más densas del estrato superior

Symmetry superposition studied by surface second-harmonic generation.

The components of a third-rank χ(2) tensor have been split into contributions due to 1-fold, 2-fold, 3-fold, and ∞-fold or isotropic rotation axes for a surface of Cs symmetry. Theoretical analysis of the rotation patterns obtained by the surface second-harmonic (SH) generation indicates that a complete symmetry analysis cannot be performed without knowledge of the relevant distribution functions. Rotation axes of lower symmetry create via ‘‘overtones’’ or ‘‘harmonics’’ contributions apparent in the analysis of the rotation axes of higher symmetry. An experimental example is the observation of structural changes of Au(111) surfaces in an aqueous electrolytic environment. Potential-dependent buildup and removal of a Au(111)-(1×23) surface could be monitored in situ and in real time. Symmetry analysis of the SH rotation patterns reveals both contributions due to a 3-fold axis due to the regular (1×1) structure and simultaneously a 1-fold and a 2-fold axis due to the (1×23) reconstruction

Factors promoting larch dominance in central Siberia: fire versus growth performance and implications for carbon dynamics at the boundary of evergreen and deciduous conifers

The relative roles of fire and climate in determining canopy species composition and aboveground carbon stocks were investigated. Measurements were made along a transect extending from the dark taiga zone of Central Siberia, where Picea and Abies dominate the 5 canopy, into the Larix zone of Eastern Siberia. We test the hypotheses that the change in canopy species composition is based (1) on climate-driven performance only, (2) on fire only, or (3) on fire-performance interactions. We show that the evergreen conifers Picea obovata and Abies sibirica are the natural late-successional species both in Central and Eastern Siberia, provided there has been no fire for an 10 extended period of time. There are no changes in the climate-driven performance of the observed species. Fire appears to be the main factor explaining the dominance of Larix. Of lesser influence were longitude, hydrology and active-layer thickness. Stand-replacing fires decreased from 300 to 50 yr between the Yenisei Ridge and the upper Tunguska. Repeated non-stand-replacing surface fires eliminated the regenera15 tion of Abies and Picea. With every 100 yr since the last fire, the percentage of Larix decreased by 20 %. Biomass of stems of single trees did not show signs of age-related decline. Relative diameter increment was 0.41±0.20% at breast height and stem volume increased linearly over time with a rate of about 0.36 tCha−1 yr−1 independent of age class and 20 species. Stand volumes reached about 130 tCha−1 (equivalent to about 520m3 ha−1). Individual trees of Larix were older than 600 yr. The maximum age and biomass seemed to be limited by fungal rot of heart wood. 60% of old Larix and Picea and 30% of Pinus sibirica trees were affected by stem rot. Implications for the future role of fire and of plant diseases are discussed.JRC.H.3-Forest Resources and Climat