Spatial distribution of soil organic carbon along topographic gradients in the Ejido Adolfo Ruiz Cortines, Durango, Mexico

Temperate forests are key to regulating climate and biogeochemical cycles. Specifically, forest management in these ecosystems favors the fixation and storage of carbon in the soil, reducing the concentration of atmospheric carbon dioxide (CO₂). The objective of this research was to analyze the distribution of soil organic carbon stored along a slope in different orientations in a temperate forest under management in the Ejido Adolfo Ruiz Cortines de Durango, Mexico. The factor analyzed was the orientation and position of the slopes. For orientation, slopes with North, South, East, and West orientations were selected, the position of each slope was divided into three sections: low, medium, and high slope, and a zenith area. On each slope, humus and leaf litter stocks were measured, and soil samples were collected to determine bulk density (Bd), soil porosity (P), soil moisture content (M), soil organic matter (SOM), and soil organic carbon (SOC). The carbon storage capacity was significantly influenced by slope orientation. In this sense, the SOC had the following trend: South (73.70 Mg ha^-1) >North (73.12 Mg ha^-1) >East (67.23 Mg ha^-1) >West (54.09 Mg ha^-1) >Zenith (47.75 Mg ha^-1). Regarding the position, the upper part of the slope had the highest content (83.66 Mg ha^-1), while the middle and lower parts had the lowest accumulation with 57.31 Mg ha^-1 and 60.13 Mg ha^-1, respectively. The orientation and position directly influenced the SOC reservoirs, being key to the productivity of the ecosystem, benefiting local producers.

1. INTRODUCTION

Temperate forests are important since they provide multiple goods and services essential for human beings and life on the planet in general; particularly, they are key in the regulation of climate and biogeochemical cycles. Specifically, forest management in these ecosystems favors the fixation and storage of carbon in the soil, reducing the concentration of atmospheric carbon dioxide (CO2) due to changes in environmental conditions, vegetation structure, and composition(Terrer et al., 2021). The importance of carbon in the soil results in the fact that it improves the availability of nutrients and improves soil fertility and structure, being key to the productivity of forest ecosystems(Gerke, 2022).

Soil stores a greater amount of carbon (1500 pg); Buczko et al. (2023) indicate that one square meter of forest land stores about 15 kg of C. In particular, soil humidity and temperature, leaf litter, root distribution, and soil microbiology can be modified depending on the intensity and the felling or practice carried out on the forest mass(Buraka et al., 2022); which directly impacts soil carbon stocks(Mushinski et al., 2017). However, this sequestration capacity can also vary due to various factors such as climate, precipitation, temperature, and solar energy, as well as species composition and site-specific conditions(Buczko et al., 2023).

Reed et al. (2021) point out that soil can be a sink or a source of carbon; this is a function of perturbation and changes in land use that break the carbon cycle. Therefore, it is important to analyze what factors are responsible for storage, allowing global climate change to be mitigated. In this sense, Lefèvre et al. (2017) point out that the factors that control the decomposition of SOM are soil temperature and water content, which significantly influence the storage of C in the soil due to their effect on microbial activity, and in turn the microbiological composition. The amount of SOC stored in the soil depends on the balance between the amount of C entering the soil and leaving the soil as gases. From microbial mineralization, C can also be lost or gained through soil erosion or deposition, leading to the redistribution of C from the soil on a local, landscape, and regional scale.

In Mexico, there is a great variability of climatic, geomorphological, and edaphological conditions, resulting in a wide diversity of habitats and species(Herrera-Romero et al., 2020). The quantity, quality, and distribution of organic carbon in the soil depend on the interaction of climatic, edaphic, topographic, and biological factors. Specifically, topography plays an important role in defining soil properties with respect to temperature and moisture regimes and is considered to be one of the main soil-forming factors since hillside position, slope, and orientation are important factors in soil formation and can affect soil moisture content. plant growth and distribution of SOC(Jakšić et al., 2021)(Zhang et al., 2023).

On the slopes, sequences of soils are formed with different characteristics between depth and texture. In the upper part of the slope, shallow soils of coarse texture are formed due to the erosive processes of the surface soil. The low slopes are characterized by the formation of deeper soils with fine textures and differentiated profiles. This is associated with higher concentrations of SOC on lower slopes due to soil deposition from the dragging of dead plant material (branches and leaves) from the upper part. On the other hand, orientation plays an important role on slopes Jakšić et al. (2021) and Maheshwori et al. (2025) point out that north-facing slopes receive less direct sunlight, storing more SOC in the soil, unlike south-facing slopes that are warmer and drier and present more sparse vegetation. and therefore, the accumulation of SOC in minor. However, it has been documented that the East orientation stores a greater amount of SOC compared to the North and West orientations(Niu et al., 2022).

Understanding the spatial dynamics of the SOC on a slope is important to identify areas of vulnerability to climate change, which are more prone to erosion and soil degradation due to their relief. Most research assesses slopes as a whole(Buraka et al., 2022)(Jakšić et al., 2021)(Maheshwori et al., 2025)(Niu et al., 2022), however, the dynamics within a slope change in the areas that make it up, for example: the upper areas of the slopes are more vulnerable to losing SOC due to sediment dragging, the lower part is benefited by the accumulation of organic matter, this is very common in agricultural areas, But in a poorly managed forest ecosystem, the dynamics could change by implementing proper management practices. According to Jakšić et al. (2021) and Leal et al. (2023), areas under forest management reduce cover by modifying soil properties depending on the intensity of management practices. Therefore, the objective was to analyze the distribution of soil organic carbon stored along a slope in different orientations in a temperate forest under management in the Ejido Adolfo Ruiz Cortines in Northwest Mexico, belonging to the mountain massif of the Sierra Madre Occidental.

2. MATERIAL AND METHODS

2.1. Description of the study area

The experiment was conducted in May 2025 in an area located southwest of Durango, Mexico, in the Sierra Madre Occidental. Specifically, in the ejido Adolfo Ruiz Cortines, between coordinates 23°44'48.43" N and 105°18′17.03^′′W, presenting a temperate subhumid and semi-cold subhumid climate, with rainfall in

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