Productivity and land degradation dynamics in Mexico | Dinámica en la productividad y degradación de tierras en México

إنجليزي. Land productivity (LP) is considered a fundamental indicator to measure land degradation and desertification. Frequently, TP is quantified in terms of Net Primary Productivity (NPP) in order to determine land productivity dynamics (LDP) by estimating three dimensionless metrics: trend, status and yield. In Mexico, there is still no nationwide study that quantifies and analyzes the PT indicator in areas with similar conditions (land cover and bioclimatic characteristics). The objective of this research was to quantify the TP indicator on a national scale, by determining the dynamics of land productivity (DPT) in the period 2000-2019. The analysis was based on eight dominant climatic regions with similar vegetation cover where Net Primary Productivity (NPP) was calculated by incident photosynthetically active radiation (MJm-2 yr-1), the fraction of photosynthetically active radiation intercepted by green tissues and solar radiation use efficiency (gMS MJ-1). Subsequently, TP was determined through a multitemporal analysis of PPN to calculate three metrics: trend, state and yield. Land productivity dynamics (LPD) was evaluated with the combination of the above three metrics and five classes were obtained: improving, stable, stressed, moderately degraded and degraded. Finally, 20 land and vegetation uses were identified according to the dynamics and degradation of TP in the eight climatic regions. Data analysis was performed using the R language (v4.2.3) integrated in the QGIS geographic information system (v3.28). Average annual PPN varied across the country, ranging from less than 500 g m-2 yr-1 in the arid climate region to just over 3,000 g m-2 yr-1 in the very humid region of the country. The lowest PPN value was located in the very arid climatic region (31 g m-2 yr-1) and the highest value (4,366 g m-2 yr-1) was observed in the very humid region of the country. The stable trend metric was found in 86% of the national territory, improvement in 9.6% and decrease in 3.9% of the total national territory. The PT status metric presented stable condition in almost 88% of the territory, improvement in 10.9% and decrease in 1.3%. While the TP yield metric had a degraded condition in 53.2% of the country's surface and 46.7% was classified as non-degraded. The TPD was stable in 78% of the national territory, improvement was observed in 11.78%, degradation in 4.26%, moderate degradation in 5.3% and stressed condition in 0.56% of the national territory. In slightly more than 70% of the area occupied by type of land use and vegetation, there were no changes in TPD. However, it was found that the 20 classes of land use and vegetation were exposed to degradation and moderate degradation of TP dynamics. The most exposed vegetation was identified in coniferous forests (humid climatic regions), coastal vegetation (sub-humid and semi-arid climatic regions), human settlements (sub-humid climatic region), secondary vegetation of arid climates and other wooded areas (mainly in semi-arid climatic regions). Although all 20 land use and vegetation classes were exposed to degradation and moderate degradation of TP dynamics, it was observed that, in all of them, the class of improvement of TP dynamics was present, mainly in areas without apparent vegetation and other wooded surfaces. According to the results obtained, it is clear that land productivity varies from one climatic region to another, and that it is dynamic through the years, so the use of multitemporal analysis is required to monitor land productivity through time. This allows having solid information necessary in decision making for the conservation and improvement of land productivity and reduction of land degradation and desertification in Mexico. The results obtained in this study contribute to have quantitative information of the land productivity indicator, which can be useful for future research measuring land degradation and desertification in Mexico.

الأسبانية؛ قشتالية. La productividad de la tierra (PT) es un indicador fundamental para medir la degradación y desertificación de este recurso. En México aún no se cuenta con un estudio a escala nacional que cuantifique y analice el indicador PT en áreas con condiciones similares (cobertura de la tierra y características bioclimáticas). El objetivo de esta investigación es cuantificar el indicador de PT a escala nacional mediante la determinación de la dinámica de la productividad de la tierra (DPT) para el periodo 2000-2019. El análisis tomó como base ocho regiones climáticas dominantes con cobertura vegetal similar donde se calculó la productividad primaria neta (PPN) mediante la radiación fotosintéticamente activa incidente (MJm-2 año-1), la fracción de la radiación fotosintéticamente activa interceptada por los tejidos verdes y la eficiencia en el uso de la radiación solar (gMS MJ-1). Posteriormente se determinó la PT a través de un análisis multitemporal de la PPN para calcular tres métricas: tendencia, estado y rendimiento. Se evaluó la dinámica de la productividad de la tierra (DPT) con la combinación de las tres métricas anteriores y se obtuvieron cinco clases: mejora, estable, estresado, moderadamente degradado y degradado. Por último, se identificaron los usos de suelo y vegetación según la dinámica y degradación de la PT en las ocho regiones climáticas. El análisis de datos se realizó utilizando el lenguaje R (v4.2.3) integrado en el sistema de información geográfica QGIS (v3.28). La PPN promedio anual varió en todo el país, desde menos de 500 g m-2 año-1 en la región climática árida, hasta poco más de 3000 g m-2 año-1 en la región muy húmeda del país. La métrica de tendencia estable se encontró en 86% del territorio nacional. La métrica de estado de PT presentó condición estable en casi 88% del territorio, mientras que la métrica de rendimiento de PT tuvo una condición degradada en 53.2% de la superficie del país. La DPT fue estable en 78% del territorio nacional. En poco más de 70% de la superficie ocupada por tipo de uso de suelo y vegetación no hubo cambios de la DPT. Los resultados obtenidos en este estudio contribuyen a tener información cuantitativa del indicador de productividad de la tierra que puede ser de utilidad para futuras investigaciones que midan la degradación y desertificación de tierras en México.