160,990 research outputs found
Influence of gap size on wind damage variables in a forest
No full textWindstorms are the major disturbance factor in tropical and European forest ecosystems. An airflow model can provide the basis to interpret spatial patterns of wind damage on trees, and guide strategies with respect to that concern. In contrast to recent advances on modelling of perturbed canopy flows, few studies have considered the effects of canopy inhomogeneity on the pattern of flow statistics, which in its turn describes the relative risk of wind damage on trees. An atmospheric boundary-layer two-equation closure model SCADIS based on transport equations for turbulent kinetic energy (E) and specific dissipation (omega = epsilon/E, where E is the dissipation of E) (E-omega model), which accounts for the flow dynamics within a plant canopy [Sogachev, A., Panferov, O., 2006. Modification of two-equation models to account for plant drag. Bound. Lay. Meteorol. 121, 229-266] was used to carry out a series of numerical experiments with gap sizes from 3 to 75 tree heights, h, in a modelled forest. Spatial variations of integral wind loading presented as a sum of static and dynamic (gust) components on trees around the gaps were estimated from modelled data. To quantify the changes of wind load characteristics due to gap growth relatively to the undisturbed forest they were normalized by the correspondent values for that forest. The results show that for round gaps the maximal static wind loading on trees surrounding the gap as large as 75h increases up to 14 times of that for undisturbed forest. The maximal static load is located on the exposed (or downwind) gap edge independently of gap size. The maximal value of the gust component increases with the gap diameter up to the gap size of 20h only, where it is 2.6-3.0 times higher than for undisturbed forest, and remains constant for larger gaps. With the growth of gap size the area of maximal values of E shifts from downwind gap edge to the lateral borders of the gap increasing the contribution of gust loading there. Thus, the integral wind loading increases nonlinearly with gap size and for the gap size of 75h it can be up to seven times higher than that for undisturbed forest. The spatial distribution of maximal values of integral loading is similar to that of static loading up to gap size of 20h. For larger gaps the location of integral loading maximum shifts gradually towards lateral borders with increasing of gap diameter. (c) 2008 Elsevier B.V. All rights reserved
Changes of forest stands vulnerability to future wind damage resulting from different management methods
No full textThe structure of forests stands changes continuously as a result of forest growth and both natural and anthropogenic disturbances like windthrow or management activities – planting/cutting of trees. These structure changes can stabilize or destabilize forest stands in terms of their resistance to wind damage. The driving force behind the damage is the climate, but the magnitude and sign of resulting effect depend on tree species, management method and soil conditions. The projected increasing frequency of weather extremes in the whole and severe storms in particular might produce wide area damage in European forest ecosystems during the 21st century. To assess the possible wind damage and stabilization/destabilization effects of forest management a number of numeric experiments are carried out for the region of Solling, Germany. The coupled small-scale process-based model combining Brook90 [1] and SCAlar DIStribuiton turbulence model [2-4] is implemented. The SRES climate scenarios A1B and B1 dynamically downscaled by Climate Local Model CLM [5] are used to project the future climate conditions in the area. The experiments are performed for two tree species (spruce and beech) and a mixed stand and for two target diameter harvesting scenarios. The results show considerable increment of wind damage risks towards 2100 compared to “present climate conditions”, caused by the combination of weak increase of wind speed and precipitation and strong increase of air and soil temperature. The effect is stronger for coniferous species than for deciduous ones. It is shown that management activities have a strong destabilizing effect on forests due to joint influence of climatic factors and decrease of stand density
Impact of Target Diameter Harvesting on Spatial and Temporal Pattern of Drought Risk in Forest Ecosystems Under Climate Change Conditions
No full textForests are influenced by many disturbances, especially drought, windthrow, pest attacks, air pollution, and forest management. The climate change results in increasing frequency of weather extremes which will probably cause drought stresses in European forest ecosystems. By integrating several new features within the BROOK90 model, smallscale coupled process-based modeling was carried out for different climate and target diameter harvesting scenarios in the region of Solling, Germany. The results show considerable increment of drought risks towards 2100 compared to “present climate conditions”, caused by changes in precipitation and increase of mean air temperature. Beyond this it is shown that for the Solling site the changes of structure and microclimate produced by target diameter harvesting result in a decrease of drought stress and could be implemented to mitigate drought events
Radiation and Temperature Responses to a Small Clear-Cut in a Spruce Forest
No full textEffects of a small clear-cutting on solar radiation, soil and air temperature regimes were investigated by continuous field measurements in a spruce forest in Solling, Central Germany, during vegetation period of 2005. Five meteorological stations, installed in central part of a small clear-cut area (2.5 ha) and close to edges of a surrounding forest, allowed to quantify the spatial variability of meteorological parameters within the clear-cut and to describe the impacts of the forest on clear-cut microclimate. The differences of microclimatic conditions between the clear-cut and the surrounding forest were derived using an additional station installed inside the forest about 150 m from the clear-cut. Results showed that clear-cutting leads to significant changes of spatial and temporal patterns of solar radiation and soil temperature. Solar radiation at the clear-cut was very heterogeneously distributed and about 5-11 times higher than inside the forest. It reached maximum at northeastern part and minimum at southwestern part of the clear-cut. The daily maximal soil temperature at 10 cm depth was measured at northern parts of the clear-cut and it was by up to 6°C higher than in the forest. Daily minimal soil temperature at the clear-cut was about 1-3°C higher than in the forest, too. The main factors influencing the soil temperature patterns were seasonally changed incoming solar radiation, ground vegetation and its phenology, as well as soil moisture. The mean daily maximal air temperature measured at the clear-cut was by up to 2.5°C higher and the mean daily minimal temperature by up to 0.5°C lower than in the surrounded forest
Feedbacks of windthrow for Norway spruce and Scots pine stands under changing climate
No full textWind damage is one of the major natural disturbances that can occur worldwide in most types of forests. Enhanced management using adequate decision support systems (DSS) can considerably reduce the risk of windthrow. The decision support system 'Forest and Climate Change' (DSS-WuK) which is currently being developed at Gottingen University aims at providing a tool for the quantitative assessment of biotic and abiotic risks for forest ecosystems under the conditions of changing climate. In order to assess the future risks of wind damage the system employs a coupled modelling approach combining the turbulence model SCAlar DIStribution (SCADIS) with the soil-vegetation-atmosphere-transfer (SVAT) model BROOK 90. The present study investigates projections of wind damage in Solling, Germany under climate scenarios A1B and B1, taking into account the windthrow feedbacks-changes of microclimate as a result of tree fall and consequent stabilization or destabilization of a forest stand. The results of the study indicate that in Solling the risk of windthrow for spruce and pine forest stands is likely to increase considerably during the 21st century. The general tendencies indicate that under A1B the probability of damage would be higher than under B1 and that under the same climate and soil conditions the risk for spruce stands would be higher than for pine stands of equal age. The degree of damage and feedback contribution as well as a sign of feedback in each particular case will strongly depend on the particular local or regional combination of climatic and soil factors with tree species, age and structure. For Solling the positive feedback to local climatic forcing is found. The feedback contributes considerably (up to 6% under given conditions) to the projected forest damage and cannot be neglected. Therefore, the adequate projection of future damage probabilities can be performed only with a process-based coupled soil-atmosphere model with corresponding high spatial and temporal resolution
Application of a three-dimensional model for assessing effects of small clear-cuttings on radiation and soil temperature
No full textA three-dimensional model Mixfor-3D of soil–vegetation–atmosphere transfer (SVAT) was developed and applied to estimate possible effects of tree clear-cutting on radiation and soil temperature regimes of a forest ecosystem. The Mixfor-3D model consists of several closely coupled 3D sub-models describing: forest stand structure; radiative transfer in a forest canopy; turbulent transfer of sensible heat, H2O and CO2 between ground surface and the atmospheric surface layer; evapotranspiration of ground surface vegetation and soil; heat and moisture transfer in soil. The model operates with the horizontal grid resolution, 2 m × 2 m; vertical resolution, 1 m and primary time step, 1 h. The model was tested against meteorological data obtained at a small clear-cutting area in Otterbach in central Germany during summer 2005. The meteorological data including air temperature and humidity, precipitation, solar radiation, wind speed and direction, soil temperatures at 10 and 20 cm depth were measured by five automatic stations within the clear-cut area. One reference station was placed about 100 m from the clear-cut inside the forest stand. Comparisons of modelled and measured solar radiation fluxes and soil temperature profiles showed that the model adequately describes the spatial heterogeneity and dynamics of these variables under different weather conditions. The model can be used to explore solar radiation and soil temperature patterns within heterogeneous forest plots, with applications to various silvicultural tasks
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
Water supply patterns over Germany under climate change conditions
Full text linkA large ensemble of 24 bias-corrected and uncorrected regional climate model (RCM) simulations is used to investigate climate change impacts on water supply patterns over Germany using the seasonal winter and summer Standardized Precipitation Index (SPI) based on 6-month precipitation sums. The climate change signal is studied comparing SPI characteristics for the reference period 1971–2000 with those of the "near" (2036–2065) and the "far" (2071–2100) future. The spread of the climate change signal within the simulation ensemble of bias-corrected versus non-corrected data is discussed. Ensemble scenarios are evaluated against available observation-based data over the reference period 1971–2000. After correcting the model biases, the model ensemble underestimates the variability of the precipitation climatology in the reference period, but replicates the mean characteristics. Projections of water supply patterns based on the SPI for the time periods 2036–2065 and 2071–2100 show wetter winter months during both future time periods. As a result soil drying may be delayed to late spring extending into the summer period, which could have an important effect on sensible heat fluxes. While projections indicate wetting in summer during 2036–2065, drier summers are estimated towards the south-west of Germany for the end of the 21st century. The use of the bias correction intensifies the signal to wetter conditions for both seasons and time periods. The spread in the projection of future water supply patterns between the ensemble members is explored, resulting in high spatial differences that suggest a higher uncertainty of the climate change signal in the southern part of Germany. It is shown that the spread of the climate change signals between SPIs based on single ensemble members is twice as large as the difference between the mean climate change signal of SPIs based on bias-corrected and uncorrected precipitation. This implies that the sensitivity of the SPI to the modelled precipitation bias is small compared to the range of the climate change signals within our ensemble. Therefore, the SPI is a very useful tool for climate change studies allowing us to avoid the additional uncertainties caused by bias corrections
Measured PAR-use efficiencies of photosynthesis in a mountainous tropical rain forest in Indonesia
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