Forest biomass is an essential indicator for monitoring the Earth’s ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world’s forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities.

Background: Being the product of the same environment, soil and vegetation are mutually associated with each other, but the relationships between edaphic properties and vegetation characteristics are still far from clear. Accordingly, the specific aim of this study is to identify relationships between forest site types/forest types and the fertility of soil organic horizons in northwestern Russia. The relationships were assessed at the level of three large forest regions, the northern and middle taiga of the Republic of Karelia, and the Karelian Isthmus (Leningrad region), based on 37 spruce, 66 pine, and 16 birch plots which were integrated with the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). Results: Soil forming rock and land-use history partly explain the differences in the fertility of soil organic horizons between the forest ecosystems in northwestern Russia. Climatic factors are closely correlated with plant species richness, density and the fertility of soil organic horizons. Nutrient content in the organic horizons increased from poor to rich site types identified according to composition of understory vegetation and the occurrence of certain indicator species, i.e. Cajander's forest site types. The most informative parameters in explaining differences between Cajander's types were nitrogen, carbon to nitrogen ratio, exchangeable calcium, magnesium, potassium, and base saturation. Extractable phosphorus, carbon to nitrogen ratio, exchangeable calcium, magnesium, aluminum and base saturation were the most informative parameters in explaining differences between forest types identified within the Cajander types in accordance with the tree species composition, i.e. Sukachev's forest types. The organic horizons of spruce and birch-dominated forests contained significantly more nutrients, compared to those dominated by pine. These differences were explained by differences in litter quality, and the crown shape and density of tree species, which affect the intensity of nutrient leaching. Conclusions: The study presents new findings regarding the relationships between forest sites/types and the fertility of soil organic horizons in northwestern Russia. Differences in organic horizon's fertility between the taiga subzones are explained by differences in the soil forming rock, climatic conditions, land-use history and shares of forest site types/forest types.

Research Highlights: It was found that both tree species and ground vegetation affected soil carbon stock in boreal forests. Carbon stocks in the mineral layers were related negatively to the C/N ratio in the organic horizon and pine proportion in the growing stock volume, and positively to the share of herbaceous plants and the proportion of spruce. Background and Objectives: Existing research showed the effects of tree species on soil carbon stocks in organic horizons, but these effects were less clear in mineral horizons. Little is known about the effects of ground vegetation on soil carbon stock. This study aims to identify associations between the forest vegetation composition and soil carbon stocks in northwestern Russia. Materials and Methods: Research data from 109 pine, spruce and birch forests of different Cajander’s and Sukachev’s types with different functional compositions of ground vegetation at autonomous positions are discussed in this paper. The V-test was used to assess the impact of vegetation on soil carbon stocks. Results: Variations in Carbon stocks in the mineral layers were associated with the soil types and vegetation composition. Carbic Albic Podzols accumulated the least amount of carbon in the mineral profile. Carbon stock in the mineral layers in pine forests was considerably lower than in spruce and birch forests. Spruce forests with the highest share of herbaceous plants were characterised by the highest carbon stocks in the mineral layers, while pine forests with dwarf shrubs and green mosses accumulated more carbon in the organic layers, but carbon stocks in the mineral layers here were the lowest. Conclusions: Differences in soil carbon stocks between and within northern and middle taiga in northwestern Russia were associated not only with soil types but also with the proportions of forest types dominated by different tree species and ground vegetation functional groups.

Linking vegetation, soil biota, and soil carbon stocks in forests has a high predictive value. The specific aim of this study was to identify the relationships between vegetation, earthworms, and soil carbon stocks in nine types of forests dominating autonomous landscape positions in a coniferous–broadleaf forest zone of the European part of Russia. Mountain forests were selected in the Northwest Caucasus, while plain forests were selected in Bryansk Polesie and on the Moskva-Oka plain. One-way analysis of variance (ANOVA) and v-tests were used to assess the impact of different factors on soil C stocks. To assess the contribution of vegetation, litter quality, and earthworms to variation of carbon stocks in organic (FH-layer) and mineral layer (0–50 cm), the method of hierarchical partitioning was performed. The highest C stocks in the organic horizons were associated with the low-quality litter, i.e., with a low base saturation, high acidity, and wide C/N ratio. The highest soil C stocks in the mineral layers were found in mixed forests with the highest richness of plant species, producing litterfall of different quality. The С stock in the organic horizon was negatively related to the biomass of worms that process the litter, while the carbon stock in the mineral layers was positively related to the biomass of worms whose life activity is related to the mineral layers. These findings demonstrated the substantial influence of plants producing a litter of different quality, and of earthworms, belonging to different functional groups, on soil С stocks in coniferous–broadleaf forests.

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