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Understanding the comprehensive impacts of environmental factors on soil organic carbon (SOC) and soil inorganic carbon (SIC) in different land use types is of great significance for sustainable soil management. Least absolute shrinkage and selection operator (LASSO) and structural equation modelling were applied to reveal the driving mechanism of SOC, SIC and the ratio between SOC to SIC (SOC/SIC) in three major land use types (forest, grassland and farmland) in a forest-grassland ecotone (FGE) of Inner Mongolia, Northeast China. Mean annual temperature (MAT), mean annual temperature (MAP) and Enhanced Vegetation Index (EVI) were selected by LASSO as the three most important environmental factors affecting SOC, SIC and SOC/SIC in all land use types. MAT had the strongest direct effects on SOC in forest and grassland among all the environmental factors, suggesting temperature was the most important control factor of SOC in forest and grassland. EVI had relatively strong indirect effects on SOC by influencing total nitrogen and total phosphorus in grassland and farmland, respectively. MAT and MAP had significantly direct effects on SIC in all land use types, demonstrating the balance between precipitation and evapotranspiration affected by temperature were the major control factors of SIC. In addition, MAT had significantly positive direct effects (>42%) on SOC/SIC in all land use types, suggesting climate warming can have positive feedbacks on the proportion of SOC in the soil carbon pool in FGE. This study provides a comprehensive understanding of the driving mechanism of SOC, SIC and SOC/SIC in FGE of Northeast China. • MAT, MAP, and EVI were the main factors affecting SOC, SIC and SOC/SIC of FGE. • Temperature was the most important factor of SOC in forest and grassland of FGE. • MAT and MAP had significantly direct effects on SIC in all land use types of FGE. • Climate warming can increase the proportion of SOC in the soil carbon pool of FGE. [ABSTRACT FROM AUTHOR]

This study aimed to explore the ecological stoichiometric characteristics of soil carbon ( C ), nitrogen ( N), and phosphorus( P) in a northern forest-grass ecotone and evaluate its response to influencing factors to reveal the limiting factors of soil nutrients and the driving mechanism of ecosystem evolution in the region. Sampling points were set up at an interval of 25 km from north to south in the study area for field investigation and soil sample collection. The soil ecological stoichiometric characteristics and their relationship with environmental factors were analyzed using statistics and redundancy analysis( RDA). The results showed that: the average concentration of soil organic carbon( SOC), total nitrogen( TN), and total phosphorus( TP) in the 0-20 cm soil layer was 36.76, 2.65, and 0.60 g • kg-1, respectively, and the C N P ratio was 61:4:1. In the 20-30 cm soil layer, the contents of SOC, TN, and TP decreased, they were 27.95, 2.30, and 0.55 g•kg-1, respectively, and the C: N: P ratio was 51:4:1. The region was characterized by N deficiency. For different vegetation types, the contents of SOC, TN, and TP were in the following order: forest>forest and sandy grassland>sandy grassland, and there were significant differences among the three vegetation areas( P<0.05). The contents of SOC, TN, and TP increased with an increase in precipitation, altitude, and temperature. In the 0-20 cm soil layer, the C: N, C: P, and N: P ratios increased with an increase in precipitation and altitude, but decreased with an increase in temperature. In the 20-30 cm soil layer, C: P and N: P ratios increased with an increase in precipitation and altitude but did not change significantly with temperature. C: N ratio increased with an increase altitude but did not change significantly with precipitation and temperature. RDA indicated that the main driving factor of soil ecological stoichiometry in the area was vegetation, followed by soil, terrain, and climate. The results revealed the response mechanism of soil ecological stoichiometry to influencing factors, and this is an important guide to ecological restoration and soil quality health development in forest-grassland ecotones in northern China. [ABSTRACT FROM AUTHOR]

Abstract A method for characterizing aggregate stability with repeated laser diffraction measurements was tested on soils spanning the prairie-forest ecotone in northern Minnesota, USA. These soils formed in similar parent material but display a wide range of upper horizon morphology, organic carbon content, and chemistry, allowing assessment of the method's performance over a wide range of aggregate stability and its utility in identifying factors influencing aggregate behavior. Equations representing fine material release through breakdown of two aggregate populations as first-order processes were fit to experimental data. The best-fit parameters for these equations, and an additional index of persistent water-stable aggregate content, indicated distinct differences in aggregate behavior among the major horizons of Mollisols and Alfisols. Linear models were developed to explore the relationships between these parameters and soil physicochemical characteristics for the dataset as a whole and for subsets corresponding to four zones with different vegetation history, soil orders, and major soil horizons. The relationships identified were relatively weak (R2 = 0.30 to 0.70). The best predictors for the parameters representing early disintegration of less stable aggregates were cation exchange capacity (CEC) and effective CEC (ECEC) for the whole dataset, although organic carbon and nitrogen contents also emerged as predictors for forest and Alfisol subsets. The best predictors for the index of persistent water-stable aggregate content were organic carbon content, base saturation, or exchangeable Ca/Mg ratio, depending on the particular subset and fine material size fraction used in the analysis. The relatively weak explanatory power of organic carbon content as a predictor of aggregate behavior in these experiments was somewhat surprising, given prior work on aggregate stability. Both CEC and ECEC may serve as proxies for the various combinations of organic matter and clay content that influence aggregate stability in these samples, explaining their importance as predictors. It is likely that other factors not examined in this research contributed to aggregate stability, including carbonate content, clay mineralogy, and differing frequency and types of pedoturbation under grassland and forest. The results of this study are relevant to reconstructing the development of texture-contrast profiles as forest invaded grassland over the past 4000 in the study area, as documented by paleoecological research. In particular, loss of organic matter below a thin A horizon may have facilitated initial development of an E horizon in which weak aggregation favored clay eluviation; loss of clay would then have weakened aggregate stability still further. We suggest this new method for assessing aggregate stability can also be applied to research on soil erosion and runoff potential as affected by land use and management. Highlights • Soil aggregate behavior assessed using repeated laser diffraction measurements. • Dynamics of aggregate disintegration can be modeled as first-order processes. • Method applied to comparison of aggregate behavior in grassland and forest soils. • Aggregate's stability and disintegration dynamics vary by soil order and horizon. • Disintegration rates and water-stable aggregate content related to soil properties. [ABSTRACT FROM AUTHOR]

Phytoliths are a useful tool for reconstructing paleovegetation and paleoenvironments and grass short cell phytoliths (GSCPs), in particular, can provide important paleoenvironmental information. Although herbaceous phytoliths from non-grass species in forests also provide important paleovegetation information, they have not been investigated in as much detail as GSCPs, especially in Northeast China. In this study, we examined herbaceous phytolith morphotypes and assemblages from both forested and grassland areas in NE China, comprising three vegetation types. The phytoliths in 60 herbaceous quadrats were divided into seven morphotype groups. Cross-shaped phytoliths, bilobate type-C with long shank and papillate echinate morphotypes were only observed in grassland (GRA); complex saddle and bilobate type-A were only observed in non-understory vegetation in forested areas (NON); and phytoliths with scrobiculate decoration, elongate curved, silicified stoma (F), silicified stoma (D), globular granulate and oblong ruminate were only observed in forest understory (UND). Papillate (39.7%) was the dominant phytolith type in UND assemblages, and bilobate was dominant in NON (27.2%) and GRA (55.0%). According to the results of Discriminant Analysis (DA) and Detrended Correspondence Analysis (DCA), there was no similarity between UND and GRA, while NON had similarities with both UND and GRA. We conclude that herbaceous phytolith morphotypes and assemblages from forest and grassland in NE China are substantially different, which potentially enables their use for paleovegetation reconstruction in the region. Overall, our findings provide a new approach for determining past forest–grassland boundaries in NE China. [ABSTRACT FROM AUTHOR]

Climate change and extreme events, such as drought, threaten ecosystems world-wide and in particular mountain ecosystems, where species often live at their environmental tolerance limits. In the European Alps, plant communities are also influenced by land-use abandonment leading to woody encroachment of subalpine and alpine grasslands., In this study, we explored how the forest-grassland ecotone of Alpine tree lines will respond to gradual climate warming, drought events and land-use change in terms of forest expansion rates, taxonomic diversity and functional composition. We used a previously validated dynamic vegetation model, FATE- HD, parameterized for plant communities in the Ecrins National Park in the French Alps., Our results showed that intense drought counteracted the forest expansion at higher elevations driven by land-use abandonment and climate change, especially when combined with high drought frequency (occurring every 2 or less than 2 years)., Furthermore, intense and frequent drought accelerated the rates of taxonomic change and resulted in overall higher taxonomic spatial heterogeneity of the ecotone than would be expected under gradual climate and land-use changes only., Synthesis and applications. The results from our model show that intense and frequent drought counteracts forest expansion driven by climate and land-use changes in the forest-grassland ecotone of Alpine tree lines. We argue that land-use planning must consider the effects of extreme events, such as drought, as well as climate and land-use changes, since extreme events might interfere with trends predicted under gradual climate warming and agricultural abandonment. [ABSTRACT FROM AUTHOR]

Distinct guidelines have been proposed in Romania and Switzerland for the management of pasture-woodlands that either focused on the regulation of grazing pressure (Romanian production perspective) or overall tree cover (Swiss conservation perspective). However, the landscape structural diversity and the cover of forest-grassland ecotones, which are both crucial for nature conservation value, were not explicitly considered. We aimed to compare the country-specific management guidelines regarding their efficiency for the conservation of the structurally diverse forest-grassland mosaics in the light of recent land-use and climate change. In strategic simulation experiments using the process-based model of pasture-woodland ecosystems WoodPaM, we analyzed the relationships among drivers for the formation of mosaic patterns (grazing intensity, climate change) and the resulting landscape properties (tree cover, forest-grassland ecotones, mosaic structure) during the past until today (2000 AD). The results showed that tree canopy densification following recent climate warming is likely to trigger landscape structural shifts. Medium grazing pressure promoted the development of the full range of pasture-woodland habitats and is therefore confirmed as a management strategy that balances agronomic demands and nature conservation value. Tree cover is rejected as a criteria to monitor pasture-woodland conservation status, because its relationship to landscape structural diversity and to the cover of forest-grassland ecotones did not hold for changing climate. Our results suggest “experimental-retrospective” analysis as a useful tool to test conclusions from expert knowledge. [ABSTRACT FROM AUTHOR]

Ecotones are frequently associated with habitat fragmentation, one of the main causes of biodiversity loss. Conifer reforestations are assumed to enhance connectivity between forest remnants, buffering negative effects of fragmentation (edge effect). Conversion of agricultural lands into conifer plantations is commonly considered a good practice, although its implications on biodiversity are still unclear., We compare effects of two matrices (non-native conifer reforestations and semi-natural grasslands) on epigeic centipedes of native forests in central Italy. Assemblages were sampled at progressive distances from the edge, both in the matrix and the native forest. Basing on habitat-matrix similarity, reforestations should show lower edge effects compared to grasslands. Consequently reforestations could act as secondary habitat, while grasslands as barrier or semipermeable matrix., Several species occurred in both native forest and matrix: 47% of species at the forest-reforestation ecotone, 16% at the forest-grassland ecotone. Both reforestation and grasslands affected forest indicators ( Lithobius castaneus and L. tylopus). L. castaneus showed reforestations had a lower magnitude (0.95) and a greater depth of edge effect (53 m into the forest). Conversely, grasslands had a higher magnitude (1.00) and a lower depth of edge effect (17 m)., Our findings show reforestations can act as secondary habitat, while grasslands as semipermeable matrix. Secondly, grasslands mainly threat forest species by isolation, while conifer reforestations by edge-effect penetration. In conclusion, the establishment of non-native conifer reforestation, although enhances connectivity, is not risk free and further comparative studies are due to evaluate positive and negative effects on biodiversity. [ABSTRACT FROM AUTHOR]

• Pixels with greater subpixel percent tree cover generally had earlier greenup dates (GUDs). • A large area of significantly earlier GUD was observed across the Hulunbuir forest-grassland ecotone. • Increases in spring temperature and percent tree cover contributed to the earlier trends in GUD. Changes in climate and land cover are potential drivers of land surface phenology changes. Here, we investigate whether subpixel percent tree cover (PTC) change is an important driver of trends in satellite derived vegetation spring greenup date (GUD) across the Hulunbuir temperate forest-grassland ecotone in northeastern China. GUD was estimated using the MODIS-derived enhanced vegetation index time series during 2001–2020 with a spatial resolution of 500 m. To understand the influential mechanisms of PTC on GUD, we examined relationships between the spatial variations in GUD and PTC at multiple spatio-temporal extents. Forested pixels with greater PTC were found to have generally earlier GUDs for all forest types. The GUD of forests was also generally earlier than that of grassland. On the other hand, we observed approximately 23.7% and 1.2% significantly earlier and later trends in GUD across the region, respectively. Meanwhile, widespread increases in preseason land surface temperature (LST) and PTC were detected. Both increases in LST and PTC contributed to the earlier GUD in the forested region. Specifically, we found negative correlations (Spearman correlation coefficient -0.17 to -0.55) between the change slopes of GUD and PTC in every forest and grassland type. The results highlight the important impacts of subpixel PTC on GUD variations, and improve the understanding of ecosystem changes under the effects of climate and human activities (e.g., afforestation) over the Hulunbuir temperate forest-grassland ecotone. [ABSTRACT FROM AUTHOR]

Questions: What is the structure of the anthropogenic upper forest-grassland ecotone and are there differences in the spatial relationships between the tree species involved? Location: Valfurva Valley, Italian central Alps. Methods: We conducted a spatial distribution and structure analysis in three 1-ha permanent plots along an altitudinal gradient, from the treeline to the sub-alpine forest. We reconstructed the age structure from cores from each individual with diameter > 4 cm at 50 cm height. Results: All tree species and age classes examined had a clumped structure. The cluster tendency was more evident at the treeline where the environmental conditions are more severe. In the sub-alpine forest there was a repulsion between Pinus cembra and Pious mugo but at the treeline P. cembra was frequently found downslope from P. mugo. Conclusions: Although human influence has been the main driving force in shaping the present forest structure, in the last few decades natural dynamics have become the predominant force acting on forest structure and processes, showing a higher magnitude as altitude increases. Our results emphasize the existence of facilitating and interfering mechanisms between different species. P. cembra seems to be favoured compared to the other tree species. [ABSTRACT FROM AUTHOR]