Mountain ecosystems play an essential role in sustainable mountain development, providing benefits and values to humanity not only for the rich biodiversity they contain, but also because of their important role in climate regulation, water cycle, provisioning of recreation, tourism, cultural or spiritual values. The high biodiversity of the mountain areas allow the provision of a wide range of ecosystem services. However, different impacts to the environment threaten the delivery of these services and, consequently, the quality of life of people, both living in the mountains and outside the mountains. Recognizing, demonstrating and capturing the value of ecosystem services can play an important role in setting policy directions for ecosystem management and conservation and, thus, in increasing the provision of ecosystem services and their contributions to human well-being. Quantifying and mapping of these benefits can also help managers and decision makers to realize the importance of these sites for conservation and to allow the proper understandings of the impacts of mountain forest ecosystems on territorial development and welfare of local populations. The paper aims to outline the relevance and applicability of the ecosystem services approach for the assessment of the condition of mountain ecosystems and the services, they provide, for better understanding by the scientific community and to support decision makers in sustainable management of mountain regions.

Forest soils are a key element of the forest ecosystems which could contribute to carbon storage and climate change mitigation. The carbon sequestration and storage potential of the forest soils, however, depends to a great extent on the forestry operations and forest management activities carried out in the forest. There is a widely accepted assumption that under a set of climate and management conditions the carbon content in the forest soils is at equilibrium. However, different factors like management activities, productivity, decay rates and/or natural disturbances could alter the carbon dynamics of forest soils. The aim of the current study was to assess the carbon stock and the carbon stock changes in mineral forest soils in Bulgaria based on the forest soil monitoring information gathered under the ICP Forest Programme. For that purpose, a dataset from the programme on mineral forest soils from 1998 was processed and analysed. The carbon stock for each sample plot was estimated for the 0-30 cm layer. The carbon stock change was calculated for all the sample plots with repeated measurements over the study period. The results were further analysed with parametric and non-parametric statistical tests to assess whether the carbon stock changes are significant. However, the lack of other relevant observations within the monitoring implementation such as litter decomposition, turnover rates, climatic conditions, etc., hinder the application of dynamic soil carbon models in assessing and predicting the current and the future rate of the soil carbon in forests in Bulgaria. 

The aim of this study is to test the suitability of the SoilGrids system for ecosystem reporting, research and monitoring. The study is conducted in the Rila Mountains in Bulgaria, an area characterised by diverse ecological factors. We propose a methodological approach to compare SoilGrids predictions with independent point observations, addressing issues of inconsistency across survey layers when combining data from different sources. The comparative analysis is discussed in respect to point data, soil type, altitude and climate. The results show that the SoilGrids represents the main soil parameters well in terms of their dynamics over the altitudinal range. There is a good agreement between the observed and predicted values for the averages of the parameters - bulk density, coarse fraction, soil organic carbon (SOC) content and SOC stock. The average measured SOC stock (0-30 cm) is 58.54 t/ha, while the average predicted SOC stock (0-30 cm) is 55.38 t/ha. However, the study also showed that the predicted values for nitrogen content are almost two times higher than the observed figures and the pH values from the SoilGrids are less acidic than those measured in the field.

Litter decomposition regulates carbon and nutrient cycling in forest ecosystems, yet its response to interacting effects of seasonality, elevation, and microclimate remains poorly understood, especially in mountain forests experiencing climate change (Panayotov and Tsvetanov (2023), Ma et al. (2024)). Slope aspect can generate strong microclimatic contrasts over short distances and may therefore outweigh elevation as a driver of decomposition. We tested this in the Rila Mountains, Bulgaria, across an altitudinal gradient of 1500–1800 m a.s.l. on north- and south-facing slopes during spring, summer, and autumn. Eight permanent plots were established, with four plots per slope aspect. North-facing plots supported mixed montane forest dominated by Norway spruce ( Picea abies Karst.) and European beech ( Fagus sylvatica L.), whereas south-facing plots were characterized by Norway spruce ( Picea abies Karst.) and Scots pine ( Pinus sylvestris L.) stands. Litter decomposition was measured using the Tea Bag Index 3.0 protocol (Middelanis et al. 2023), with green tea and rooibos buried at 8 cm depth and excavated at days 20, 40 and 90 per season. Decomposition rate ( k , d⁻¹) and labile fraction ( a , g g⁻¹) were estimated by nonlinear least squares fitting. Soil moisture, pH, and β-glucosidase activity were measured at each retrieval, while static soil properties, stand mensuration, and species composition were recorded for each plot. Meteorological variables, including air temperature and precipitation, were used to characterize regional conditions during the study period. Environmental controls on decomposition were assessed using Wilcoxon tests, Pearson correlations, season-specific Principal Component Analysis with TBI parameters as supplementary variables and Spearman correlations. North- and south-facing slopes differed significantly in CN ratio, soil texture, moisture, β-glucosidase activity, species composition, and stand basal area (Wilcoxon tests, p < 0.05). Multivariate analyses revealed consistent seasonal patterns in the environmental controls of tea decomposition. PCA showed that the main ordination axis (Dim1, ~60% variance) reflected a soil-microclimate gradient driven by moisture, temperature, silt content, basal area, and enzyme activity. North‑ and south‑facing slopes separated clearly in spring and autumn, when microclimatic contrasts were strongest, but converged in summer. The supplementary TBI variables aligned with distinct parts of this gradient: decomposition rate ( k ) consistently associated with warmer, drier, more exposed conditions, whereas the stabilization factor ( a ) aligned with moister, finer‑textured soils and higher enzymatic activity. Spearman correlations supported these patterns. Moisture was negatively related to k but positively to a , while basal area and enzyme efficiency were strong predictors of stabilization. Silt and temperature-precipitation interactions further modulated decomposition responses. Together, the results indicate that short‑term microclimate controls early mass loss, whereas soil properties and microbial functioning govern stabilization, with exposure acting as a seasonal modifier of these relationships. Long-term microclimate and soil monitoring is essential for understanding how future climate change may affect decomposition processes and forest carbon balance. Because these findings are based on a single field experiment, broader observations across seasons, sites, and forest types are needed to confirm the patterns observed here and strengthen their general applicability.

Elevation gradients provide a natural framework for studying environmental change over short geographical distances. As the altitude increases, the temperature declines, the variability in air humidity increases, and the growing season shortens. Furthermore, even under otherwise comparable environmental conditions, the slope aspect affects the microclimate of the ecosystems. These combined factors strongly influence ecosystem processes, including microbial activity and the rate of litter decomposition in mountainous forest ecosystems and thus affecting carbon and nutrient cycling.To test the hypothesis on the relative roles of seasonality, elevation, and microclimate in controlling litter decomposition rates in forest ecosystems, we conducted a field experiment in Rila Mountains (Bulgaria) along an altitudinal gradient, throughout different stages of the vegetation period, and across contrasting slope exposures. We applied an updated Tea Bag Index (3.0) protocol as described in Middelanis et al. (2023) ensuring a time-series mass loss data by excavating the buried tea bags three times within a 90-days field experiment per season. The study was set along 100 m altitudinal gradients between 1500-1800 m a.s.l on north-facing and south-dominated slopes during three biologically active seasons – from early spring to late autumn. Enzyme activities and soil pH were measured at each sampling event (i.e., tea-bag incubation and excavation), thus providing repeated measurements that captured seasonal and microclimatic variation. In addition, soil physicochemical properties (soil organic carbon, total nitrogen, texture, bulk density, skeleton content, and ICP-based geochemistry) and stand mensuration were obtained to provide the sampling plots' characterization. Meteorological data, including air temperature and precipitation variables, were analyzed to characterize the regional meteorological conditions during the studied period. This integrated approach facilitated the analysis of the effects of multiple factors influencing litter decomposition in mountain forests. The study found that the labial fraction and the decomposition constant differed notably between tea types, with consistently higher decomposition rates and decomposable fractions for green tea compared to rooibos tea across all sites and seasons, reflecting differences in substrate quality. The decomposition rate varied between sampling plots, exposure sites, and seasons. No clear pattern in decay rate was identified across the elevation gradient during the study period, with the exception of the spring season, when a decline in decomposition rate was observed with increasing elevation. Strong seasonal patterns were exhibited, with maximum decomposition rates occurring in summer at south-facing sites, whereas north-facing sites demonstrated equal or higher decomposition rates in autumn. These trends are further supported by statistically significant variations in the seasonal activity of microorganisms observed between the two surveyed areas with contrasting slope aspects, as well as by significant disparities in enzyme activity across seasons. The study demonstrated that litter decomposition in mountain forests is shaped by multiple interacting factors. It provided a good basis for comparing the relative influence of seasonality, elevation, and microclimatic conditions, highlighting the importance of their combined effects. However, further long-term experiments are needed to refine these insights and better capture the temporal variability of decomposition processes.

This study quantifies how different land-use types influence surface soil characteristics (0–5 cm) and the dynamics of soil organic carbon (SOC) and nitrogen in the mountainous ecosystems of the Rila Mountains. Across 54 forest and agricultural plots, pH, bulk density, coarse fraction, C:N ratio, SOC, total nitrogen (TN), and their respective stocks were assessed using standard analytical methods and statistical tests (Shapiro–Wilk, ANOVA, Kruskal–Wallis, correlation and regression analysis). Land use significantly affected all soil parameters except pH. Forest soil showed lower bulk density and lower SOC stocks compared with grasslands. Unmown meadows exhibited the highest SOC and TN concentrations and stocks, while potato fields recorded the highest bulk density and elevated TN stocks, reflecting intensive management impacts on surface soil properties. Forest soils displayed species-specific patterns, with Scots pine and Silver fir showing comparatively lower SOC and TN stocks attributable to historical degradation and site limitations. As the study focused on the uppermost soil layer (0–5 cm), the results should be interpreted more as indicators of surface soil dynamics rather than as estimates of total topsoil carbon and nutrient storage. Correlation analysis revealed strong positive relationships among SOC, TN, and the C:N ratio, and strong negative relationships between SOC and both bulk density and coarse fraction in managed agricultural lands. The findings demonstrate that minimizing soil disturbance and maintaining permanent vegetation cover—particularly through conservation of unmanaged grasslands—offer great capacity for enhancing the soil organic matter accumulation in mountainous ecosystems.