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In the Andes of southern South America, wet meadows are much more productive than nearby arid areas. Human activities, along with climate variations may reduce the productivity of these ecosystems. However, we do not know what the relative effect of climate and human activities on their degradation status is. Here, we first quantified the degradation extent through the temporal trend of normalized difference vegetation index (NDVI), a proxy of productivity, from 1999 to 2017. We did it in 736 wet meadow areas inserted in three nearby zones with contrasting land management. Second, we analyzed the relationship between NDVI and a large-scale mode of climate variability (El Niño Southern Oscillation, ENSO) and regional climate variables (precipitation and temperature) through a structured climate model. Finally, we evaluated human activities' effects through the temporal trends in the residuals of the climate model. Independently of land management, NDVI trends were mainly negative and affected 56% of the wet meadow areas. The climate model indicated that NDVI increased under La Niña, cool and wet years. Regarding land management, the degradation level was similar across the contrasted land management. Our results suggest that climate factors rather than human activities influenced the degradation process in these areas. • Productivity during 1999–2017 decreased in 56% of the wet meadow areas. • Productivity increased under La Niña, cool and wet years. • Productivity negative trends were mainly related to climate factors rather the human activities. [ABSTRACT FROM AUTHOR]

Wet meadows are seasonally saturated wetlands that can develop in arid and semi-arid areas. In the semi-arid region of North Patagonia, Argentina wet meadows are islands of high net primary productivity surrounded by low productivity steppe vegetation. Because of this, Patagonian wet meadows have been heavily grazed by livestock for more than a century. It has been shown that overgrazed wet meadows have lower soil carbon, however, little is known about how overgrazing impacts N dynamics. To this end, we measured ammonium (NH4+), nitrate (NO3-), and total nitrogen (Nt) in paired wet meadows that varied in long-term grazing intensity (heavy vs. light). Results indicate that heavily grazed sites had on average 43% less Nt and 57% less NH4+ than lightly grazed sites. Soil NH4+ concentrations were always significantly greater than NO3- concentrations, being the later often below detection levels. In addition, NH4+ concentrations were correlated with soil moisture in lightly grazed sites, but not in heavily grazed sites. These findings indicate that implementation of better management practices are currently needed to promote more sustainable grazing in semi-arid wet meadows of North Patagonia. [ABSTRACT FROM AUTHOR]

Abstract: In extra-Andean Patagonia, wet meadows contrast with the prevailing arid steppes, and present a gradient of water availability from the periphery to the center. The objectives of this paper are to describe the spatial and temporal variation of aerial net primary production (ANPP) of Patagonian meadows, and to obtain a model for the relationship between the normalized difference vegetation index (NDVI) and ANPP. We determined ANPP in four regionally scattered meadows during 3–5 years and in three positions of the gradient of water availability. In one meadow, we correlated ANPP with NDVI during 2 years. Annual ANPP was 2–3 times larger in the center than in the periphery, and also varied 2–3 fold among the four meadows. The interannual variation of ANPP was high and similar across meadows and zones. ANPP was closely correlated with NDVI through a linear model. Within the growing season, the central zone had a more extended period of high NDVI into the summer than the peripheral and the intermediate zones. We conclude that (1) the local variation of ANPP across the gradient of water availability is strong and must be taken into account for management, and (2) the highly variable ANPP may be monitored by remote sensing. [Copyright &y& Elsevier]