Stand Biomass at Treeline Ecotone in Russian Subarctic Mountains Is Primarily Related to Species Composition but Its Dynamics Driven by Improvement of Climatic Conditions

Plant-soil interactions alter nitrogen and phosphorus dynamics in an advancing subarctic treeline

Treelines advance due to climate warming. The impacts of this vegetation shift on plant-soil nutrient cycling are still uncertain, yet highly relevant as nutrient availability stimulates tree growth. Here, we investigated nitrogen (N) and phosphorus (P) in plant and soil pools along two tundra-forest transects on Kola Peninsula, Russia, with a documented elevation shift of birch-dominated treeline by 70 m during the last 50 years. Results show that although total N and P stocks in the soil-plant system did not change with elevation, their distribution was significantly altered. With the transition from high-elevation tundra to low-elevation forest, P stocks in stones decreased, possibly reflecting enhanced weathering. In contrast, N and P stocks in plant biomass approximately tripled and available P and N in the soil increased fivefold toward the forest. This was paralleled by decreasing carbon (C)-to-nutrient ratios in foliage and litter, smaller C:N:P ratios in microbial biomass, and lower enzymatic activities related to N and P acquisition in forest soils. An incubation experiment further demonstrated manifold higher N and P net mineralization rates in litter and soil in forest compared to tundra, likely due to smaller C:N:P ratios in decomposing organic matter. Overall, our results show that forest expansion increases the mobilization of available nutrients through enhanced weathering and positive plant-soil feedback, with nutrient-rich forest litter releasing greater amounts of N and P upon decomposition. While the low N and P availability in tundra may retard treeline advances, its improvement toward the forest likely promotes tree growth and forest development.

Trends and driving forces of agricultural carbon emissions: A case study of Anhui, China

To facilitate accurate prediction and empirical research on regional agricultural carbon emissions, this paper uses the LLE-PSO-XGBoost carbon emission model, which combines the Local Linear Embedding (LLE), Particle Swarm Algorithm (PSO) and Extreme Gradient Boosting Algorithm (XGBoost), to forecast regional agricultural carbon emissions in Anhui Province under different scenarios. The results show that the regional agricultural carbon emissions in Anhui Province generally show an upward and then downward trend during 2000-2021, and the regional agricultural carbon emissions in Anhui Province in 2030 are expected to fluctuate between 11,342,100 tones and 14,445,700 tones under five different set scenarios. The projections of regional agricultural carbon emissions can play an important role in supporting the development of local regional agriculture, helping to guide the input and policy guidance of local rural low-carbon agriculture and promoting the development of rural areas towards a resource-saving and environment-friendly society.

Long-term spatiotemporal dynamics in a mountain birch (Betula pubescens ssp. czerepanovii) forest in south-east Norway

Mountain birch forest covers large areas in Eurasia, and their ecological resilience provides important ecosystem services to human societies. This study describes long-term stand dynamics based on permanent plots in the upper mountain birch belt in SE Norway. We also present forest line changes over a period of 70 years. Inventories were conducted in 1931, 1953, and 2007. Overall, there were small changes from 1931 up to 1953 followed by a marked increase in biomass and dominant height of mountain birch throughout the period from 1953 to 2007. In addition, the biomass of spruce (Picea abies) and the number of plots with spruce present doubled. The high mortality rate of larger birch stems and large recruitment by sprouting since the 1960s reveal recurrent rejuvenation events after the earlier outbreak of the autumnal moth (Epirrita autumnata). Our results demonstrate both a high stem turnover in mountain birch and a great ability to recover after disturbances. This trend is interpreted as regrowth after a moth attack, but also long-term and time-lagged responses due to slightly improved growth conditions. An advance of the mountain birch forest line by 0.71 m year-1 from 1937 to 2007 was documented, resulting in a total reduction of the alpine area by 12%. Most of the changes in the forest line seem to have taken place after 1960. Regarding silviculture methods in mountain birch, a dimension cutting of larger birch trees with a cutting interval of c. 60 years seems to be a sustainable alternative for mimicking natural processes.

Regeneration of Pinus sibirica Du Tour in the Mountain Tundra of the Northern Urals against the Background of Climate Warming

Climate is one of the key drivers of the plant community’s structure and trends. However, the regional vegetation-climate features in the ecotone have not yet been sufficiently studied. The aim of the research is to study features of Pinus sibirica Du Tour germination, survival, and growth in the mountain tundra of the Northern Urals against the background of a changing climate. The following research objectives were set: To determine the abundance and age structure of P. sibirica undergrowth on the mountain tundra plateau, identify the features of P. sibirica growth in the mountain tundra, and examine the correlation between the multi-year air temperature pattern, precipitation, and P. sibirica seedling emergence. A detailed study of the Pinus sibirica natural regeneration in the mountain stony shrub-moss-lichen tundra area at an altitude of 1010–1040 m above sea level on the Tri Bugra mountain massif plateau (59°30′ N, 59°15′ E) in the Northern Urals (Russia) has been conducted. The research involved the period between 1965 and 2017. Woody plant undergrowth was considered in 30 plots, 5 × 5 m in size. The first generations were recorded from 1967–1969. The regeneration has become regular since 1978 and its intensity has been increasing since then. Climate warming is driving these processes. Correlation analysis revealed significant relationships between the number of Pinus sibirica seedlings and the minimum temperature in August and September of the current year, the minimum temperatures in May, June, and November of the previous year, the maximum temperatures in May and August of the current year, and precipitation in March of both the current and previous years. However, the young tree growth rate remains low to date (the height at an age of 45–50 years is approximately 114 ± 8.8 cm). At the same time, its open crowns are rare single lateral shoots. The length of the side shoots exceeds its height by 4–5 times, and the length of the lateral roots exceeds its height by 1.2–1.5 times. This is an indicator of the extreme conditions for this tree species. With the current rates of climate warming and the Pinus sibirica tree growth trends, the revealed relationships allow for the prediction that in 20–25 years, the mountain tundra in the studied Northern Urals plateau could develop underground-closed forest communities with a certain forest relationship. The research results are of theoretical importance for clarifying the forest-tundra ecotone concept. From a practical point of view, the revealed relationship can be used to predict the trend in forest ecosystem formation in the mountain forest-tundra ecotone.