Editorial: Remembering Natalya Nikolaevna Vygodskaya

As the Guest Editor I want to dedicate this Special Issue in memory of my university professor Natalya Nikolaevna Vygodskaya (Figure 1) [...

Comparing Forest Measurements from Tree Rings and a Space-Based Index of Vegetation Activity in Siberia

Different methods have been developed for measuring carbon stocks and fluxes in the northern high latitudes, ranging from intensively measured small plots to space-based methods that use reflectance data to drive production efficiency models. The field of dendroecology has used samples of tree growth from radial increments to quantify long-term variability in ecosystem productivity, but these have very limited spatial domains. Since the cambium material in tree cores is itself a product of photosynthesis in the canopy, it would be ideal to link these two approaches. We examine the associations between the normalized differenced vegetationindex (NDVI) and tree growth using 19 pairs of tree-ring widths (TRW) and maximum latewood density (MXD) across much ofSiberia. We find consistent correlations between NDVI and both measures of tree growth and no systematic difference between MXD and TRW. At the regional level we note strong correspondence between the first principal component of tree growth and NDVI for MXD and TRW in a temperature-limited bioregion, indicating that canopy reflectance and cambial production are broadly linked. Using a network of 21 TRW chronologies from south of Lake Baikal, we find a similarly strong regional correspondence with NDVI in a markedly drier region. We show that tree growth is dominated by variation at decadal and multidecadal time periods, which the satellite record is incapable of recording given its relatively short record

Northern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change in the 21st century

During the past several decades, the Earth system has changed significantly, especially across Northern Eurasia. Changes in the socio-economic conditions of the larger countries in the region have also resulted in a variety of regional environmental changes that can have global consequences. The Northern Eurasia Future Initiative (NEFI) has been designed as an essential continuation of the Northern Eurasia Earth Science Partnership Initiative (NEESPI), which was launched in 2004. NEESPI sought to elucidate all aspects of ongoing environmental change, to inform societies and, thus, to better prepare societies for future developments. A key principle of NEFI is that these developments must now be secured through science-based strategies co-designed with regional decision makers to lead their societies to prosperity in the face of environmental and institutional challenges. NEESPI scientific research, data, and models have created a solid knowledge base to support the NEFI program. This paper presents the NEFI research vision consensus based on that knowledge. It provides the reader with samples of recent accomplishments in regional studies and formulates new NEFI science questions. To address these questions, nine research foci are identified and their selections are briefly justified. These foci include: warming of the Arctic; changing frequency, pattern, and intensity of extreme and inclement environmental conditions; retreat of the cryosphere; changes in terrestrial water cycles; changes in the biosphere; pressures on land-use; changes in infrastructure; societal actions in response to environmental change; and quantification of Northern Eurasia's role in the global Earth system. Powerful feedbacks between the Earth and human systems in Northern Eurasia (e.g., mega-fires, droughts, depletion of the cryosphere essential for water supply, retreat of sea ice) result from past and current human activities (e.g., large scale water withdrawals, land use and governance change) and potentially restrict or provide new opportunities for future human activities. Therefore, we propose that Integrated Assessment Models are needed as the final stage of global change assessment. The overarching goal of this NEFI modeling effort will enable evaluation of economic decisions in response to changing environmental conditions and justification of mitigation and adaptation efforts

Radiation and Temperature Responses to a Small Clear-Cut in a Spruce Forest

Effects 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

Transpiration of a mixed forest stand: field measurements and simulation using SVAT models

Transpiration 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

Variation in photosynthetic light-use efficiency in a mountainous tropical rain forest in Indonesia

Photosynthetically active radiation (Q)-use efficiency (F) is an important parameter for deriving carbon fluxes between forest canopies and the atmosphere from meteorological ground and remote sensing data. A common approach is to assume gross primary production (P,) and net primary production (P-n) are proportional to Q absorbed by vegetation (Q(abs)) by defining the proportionality constants epsilon(Pg) and epsilon(Pn) (for P-g and P-n respectively). Although remote sensing and climate monitoring provide Q(abs) and other meteorological data at the global scale, information on c is particularly scarce in remote tropical areas. We used a 16-month continuous CO2 flux and meteorological dataset from a mountainous tropical rain forest in central Sulawesi, Indonesia to derive values of epsilon(Pg). and to investigate the relationship between P-g and Q(abs). Absorption was estimated with a 1D SVAT model from measured canopy structure and short wave radiation. The half-hourly P, data showed a saturation response to Q(abs). The amount Of Q(abs) required to saturate P-g was reduced when water vapor saturation deficit (D) was high. Light saturation of P-g was still evident when shifting from half-hourly to daily and monthly time scales. Thus, for a majority of observations, P-g was insensitive to changes in Q(abs). A large proportion of the observed seasonal variability in P-g could not be attributed to changes in Q(abs) or D. Values of epsilon(Pg) varied little around the long-term mean of 0.0179 mol CO2 (mol photon)(-1) or 0.99 g C MJ(-1) (the standard deviations were +/- 0.006 and +/- 0.0018 mol CO2 (mol photon)(-1) for daily and monthly means, respectively). In both cases, c p. values were more sensitive to Q(abs) than to daytime D. These findings show that the current epsilon-approaches fail to predict P-g at our tropical rain forest site for two reasons: (1) they neglect saturation of P-g when Q(abs), is high; and (2) they do not include factors, other than Q(abs) and D, that determine seasonality and annual sums of P-g

A comparative analysis of simulated and observed photosynthetic CO2 uptake in two coniferous forest canopies

Gross canopy photosynthesis (Pg) can be simulated with canopy models or retrieved from turbulent carbon dioxide (CO2) flux measurements above the forest canopy. We compare the two estimates and illustrate our findings with two case studies. We used the three-dimensional canopy model MAESTRA to simulate Pg of two spruce forests differing in age and structure. Model parameter acquisition and model sensitivity to selected model parameters are described, and modeled results are compared with independent flux estimates. Despite higher photon fluxes at the site, an older German Norway spruce (Picea abies L. (Karst.)) canopy took up 25% less CO2 from the atmosphere than a young Scottish Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation. The average magnitudes of Pg and the differences between the two canopies were satisfactorily represented by the model. The main reasons for the different uptake rates were a slightly smaller quantum yield and lower absorptance of the Norway spruce stand because of a more clumped canopy structure. The model did not represent the scatter in the turbulent CO2 flux densities, which was of the same order of magnitude as the non-photosynthetically-active-radiation-induced biophysical variability in the simulated Pg. Analysis of residuals identified only small systematic differences between the modeled flux estimates and turbulent flux measurements at high vapor pressure saturation deficits. The merits and limitations of comparative analysis for quality evaluation of both methods are discussed. From this analysis, we recommend use of both parameter sets and model structure as a basis for future applications and model development.20 page(s