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Effects of natural afforestation of grasslands in northern Italy on stocks and fractions of soil organic carbon
Full text linkLand-use change is considered one of the major driving forces of global carbon fluxes; moreover it can induce significant alteration of soil carbon stocks. In the Italian pre-alps socio-economic structural changes have led in the last decades to a process of reduced management intensity/abandonment of grasslands characterized by low fertility or located in unfavorable areas. These areas are usually colonized by seedlings of the tree species growing in the surrounding areas. The net effect of grassland afforestation on soil carbon is not completely clear, due to the
differences in management intensities and different turnover times of aboveground and
belowground carbon stocks. The aim of the project is to study the effects of abandonment of grassland on soil carbon stocks, along a land-use management intensity gradient in Trentino region (northern Italy). Four different contrasting land uses were considered: I) managed
grassland; II) abandoned grassland; III) natural afforested area abandoned after 1973; IV) reference forest (older than 1861). The study area has an elevation of about 1150 m, with south aspect and gentle slope. Both the afforested area and the reference forest are mixed forests, dominated by Norway spruce and beech. Each sampling point consisted of eight soil cores
collected according to a systematic sampling scheme to a depth of 30 cm. After dividing the cores into four depth increments, carbon and nitrogen content were determined with an elemental analyzer. SOM fractionation by size and density will be performed in order to detect carbon changes in functionally homogeneous SOM fraction
Changes in soil organic carbon and nitrogen following forest expansion on grassland in the Southern Alps
No full textThe dominant land-use change in the Southern Alps is grassland abandonment, followed by forest expansion. Forest expansion is commonly thought to increase ecosystem C sequestration, but contradictory results have been reported. Our objective was to investigate soil organic carbon (SOC) and nitrogen (N) changes after forest expansion on abandoned grasslands. A land use and management gradient was identified in a subalpine area of Trentino (Italy) comprising four successional stages: (i) managed grassland (manG), mown and manured annually for more than 100 years; (ii) grassland abandoned 10 years ago (abanG), with shrubs and Picea abies saplings; (iii) early-stage forest (earlyF), dominated by P. abies established on grassland abandoned around 1970; and (iv) old forest (oldF), dominated by Fagus sylvatica and P. abies, representing a reference for long-term forest land use. Organic and mineral soil layers were collected down to 30 cm at eight points within three plots for each successional stage.
Significantly more SOC was stored in organic layers of oldF compared with other successional stages and the organic layer N stocks were higher in oldF compared with manG and abanG. The SOC and N concentrations were higher in the top 10 cm mineral soil of grassland plots compared with forest. The earlyF and oldF stored, on average, 28–35% less SOC in top 10 cm mineral soil compared with manG and abanG when stocks were calculated using equivalent soil mass (ESM) and equivalent soil depth (ESD) approaches respectively. SOC stocks in mineral soil (0–30 cm) calculated with ESD decreased from manG to oldF; when accounting for total stone content, SOC stocks in earlyF and oldF were 40% and 50% lower than in manG, respectively. The inclusion of organic layers offset mineral SOC stock differences when only stones <5 cm were accounted for, but when considering the total stone content, SOC stocks in earlyF remained significantly lower (−31%) than in manG. Tree biomass contributed to higher ecosystem C stocks in oldF, which stored 82–93 Mg ha−1 of C more than grasslands.
Our study revealed a decrease in total SOC stocks after forest expansion on abandoned subalpine grasslands. Tree biomass development contributed to increasing C storage, especially in a long-term forest land use. Forest management should consider that tree biomass and organic layer development require a minimum time period following grassland abandonment to compensate for the decrease in mineral SOC stocks and contribute positively to climate change mitigatio
Soil organic carbon changes following abandonment and natural afforestation of grasslands in the southern Alps
No full textChanges in soil organic carbon stocks and fractions following forest expansion on subalpine grasslands
Full text linkThe abandonment of grasslands represents the dominant land-use change (LUC) and the main driver for the establishment of new forest areas in many regions of the European Alps. Fractions sensitive to LUC can be indicative of changes in soil organic carbon (SOC) and they can allow a better understanding of OC stabilization processes. Despite the key role played by physical OC fractions, it is still unclear how they respond to forest
expansion on abandoned grasslands. Our aim was therefore to explore the impact of LUC on SOC storage, focusing on the effect of grassland abandonment and forest expansion on physical OC fractions.
In a subalpine area of the Trentino region, Italy, four land use types were investigated: i) managed grassland, mown and fertilized for more than 100 years; ii) grassland abandoned around 10 years ago, with shrubs and Picea abies saplings; iii) early-stage forest, dominated by P. abies and established on a grassland abandoned
around 1970; iv) old forest, dominated by Fagus sylvatica and P. abies. For each land use type, three subplots were sampled with eight soil cores to 30 cm depth. SOC stocks were calculated after determination of bulk density, stoniness, root biomass and organic carbon content. Aggregate size fractions were obtained through wet-sieving using a series of sieves (2000, 250, 53 mm mesh size). In size-density fractionation, a silt and clay fraction 50 mm, after physical dispersion of aggregates. The fraction >50 mm was further separated at a density of 1.6 g cm-3 in sodium polytungstate, for the estimation of particulate organic matter (POM) and stable aggregates.
Especially in the top 10 cm, mineral soil OC stocks were lower in early-stage and old forest (-28%) than in managed and abandoned grasslands. Despite a tendency toward increasing mean size of aggregates according
to aggregate size fractionation, size-density fractionation revealed a significant decline in OC allocation to stable aggregates from grassland to forest. In 0-10 cm, the fraction of SOC stored in stable aggregates shifted from 78% in managed grassland to 59% in the old forest. Size-density fractionation also showed that a greater fraction of SOC was stored in POM in the old forest (18% of SOC stock) compared with the managed grassland (5%), but it
did not compensate for the decreased OC accumulation in stable aggregates. The OC allocation to silt and clay fractions remained unchanged, thus showing lower response to LUC. The decline in SOC storage in stable aggregate fractions was indicative of the decreasing total mineral SOC stocks after forest expansion on subalpine grasslands. Higher OC allocation to POM fraction in the mineral soil and changed carbon distribution between mineral and organic soil layers suggest an overall decrease in SOC stability and a concomitant shift to more labile OC fraction
Changes in SOC stocks and fractions after natural afforestation of alpine grasslands
No full textLand use changes are considered one of the major driving forces of global carbon fluxes and can induce significant alterations of soil organic carbon stocks. In the European Alps, the dominant form of land use change is represented by the abandonment of marginal mountain grasslands and their invasion by tree species, i.e. a transition from grassland to forest. While an increase in live and dead aboveground biomass is commonly reported, the impact on soil organic carbon (SOC) is still unclear. The main objective of the current study was to quantify the effect of abandonment and forest regrowth of mountain grassland on SOC, considering both SOC stocks and its physically separated fractions.
The study area is located in a pre-alpine area of the Trentino region (Italy), with an elevation of about 1150 m. We compared four land uses representing a transition from grassland to forest: I) managed grassland; II) grassland abandoned 10 years ago; III) natural afforested grassland abandoned after 1973; IV) reference forest, already present in 1861. The afforested area and the reference forest are both dominated by Norway spruce (Picea abies) and beech (Fagus sylvatica). For each land use intensity three sampling areas were selected. In each area we collected eight soil cores to a depth of 30 cm, dividing the soil core in 4 depth increments. To assess changes in SOC stocks, we measured bulk density, stoniness, root biomass and organic carbon content. Mineral SOC stocks were calculated using both an equivalent depth and an equivalent mass approach. Changes in SOC fractions were assessed using aggregate size fractionation (Cambardella and Elliott, 1993) and size-density fractionation procedures.
Preliminary results show higher soil C concentrations in forest sites compared to grassland. This can be attributed to higher C inputs and lower mineralization rates due to a higher degree of soil aggregation and protection of soil organic matter, but also to the higher stoniness registered in forest sites which can lead to a concentration of C inputs in a smaller volume of soil. If C stocks are computed using an equivalent soil depth approach, mineral SOC stocks are lower in forest land uses compared to grassland while no significant difference emerges if an equivalent soil mass approach is used. The aggregate size fractionation highlighted an increase in C stored in large macroaggregates following afforestation and a decrease in silt and clay size fraction (<53 μm). The strongest change shown through the size-density fractionation procedure is a three-fold increase in C stored in free organic matter (POM) from grassland to forest. Intriguingly, we found a decreasing trend in the microaggregate (53-250 μm) fraction as well as for the mineral-associated heavy fraction following afforestation, suggesting a decrease in the more stable SOC fraction, while the labile fractions increase
Effects of forest expansion on mountain grassland: changes within soil organic carbon fractions
No full textBackground and Aims Grassland abandonment followed by forest succession is the dominant land-use change in the European Alps. We studied the impact of current forest expansion on mountain grassland on changes in physical soil organic carbon (SOC) fractions along a land- use and management gradient, focusing on changes in aggregate stability and particulate organic matter (POM).
Methods Four successional stages were investigated: managed grassland, two transitional phases in which grassland abandonment led to colonization by Picea abies (L.) Karst., and old mixed forest dominated by Fagus sylvatica L. and P. abies. Soil samples collected from the mineral soil (0-5 cm, 5-10 cm, 10-20 cm0-20 cm) were fractionated following two procedures: 1) aggregate size fractionation, separating aggregates based on their dimension, and 2) size-density fractionation, separating stable aggregates from non-occluded POM.
Results The dimension of aggregates assessed by aggregate -size fractionation tended to increase, whereas SOC allocation to stable aggregates assessed by size-density fractionation decreased following conversion of grassland to forest (e.g from 81 to 59% in the 0-5 cm layer). The amount of SOC stored in POM increased by 3.8 Mg ha-1 in the integrated 0-20 cm layer from managed grassland to old forest.
Conclusions The combination of two physical SOC fractionation procedures revealed that natural fForest succession on abandoned grasslands led to a decline in physical SOC stability in the mineral soil, suggesting that SOC can become more susceptible to management and environmental modifications as indicated by decreased amounts of stable aggregate C and increased amounts of POM-C
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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
Quantification, distribution and major predictors of soil N content along a range of forest ecosystems and climatic conditions in Italy
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