Understanding how global change affects ecosystem is a momentous challenge for ecology. Interactions between climate, land use and other environmental drivers are often assumed but not so frequently tested when addressing how ecosystem functions and services are affected by those factors. Due to their extension (more than 20% of terrestrial land) and the amount of functions and services they provide, grasslands are an excellent ecosystem for tackling this issue. Here, we analyze plant diversity and soil organic carbon (SOC) distribution in mountain grasslands under a wide span of environmental conditions, and assess expected responses to global environmental changes. Plant diversity and SOC are proxies for many ecosystem functions and have relevance in biodiversity conservation and palliation of climate change. Due to the wide climate, topography, management and soil variability in mountain grasslands, our data encompass an extensive range of environmental conditions. We use a linear modelling approach respecting the original source of variation of response variables with the support of machine-learning techniques. We aimed to answer two main questions: 1) How do interactions between global change factors –changes in climate and livestock management- shape plant species richness and SOC distribution patterns in mountain grassland communities? 2) Is there a relationship between plant diversity and SOC stocks beyond climate and management factors/drivers?
Results/Conclusions
Stressful climatic conditions enhanced the negative effects of grassland fragmentation and patch disaggregation on plant species richness. Additionally, livestock management modified the impact of patch disaggregation and fragmentation. Moderate grazing intensity increased species richness in poorly connected grassland patches, and cattle grazing enhanced species richness in lowly fragmented areas, whereas sheep grazing partially compensated species impoverishment due to fragmentation.
Temperature seasonality was the most important geophysical factor driving SOC stocks. It was positively related to SOC but only under certain conditions: exposed hillsides, steep slopes and relatively intensively grazed areas. We obtained some unexpected interaction effects between grazer type, soil nutrients and herbage quality. Soil N was a crucial factor modulating effects of livestock species and vegetation´s neutral detergent fiber content; herbage recalcitrance effects varied depending on grazer species.
Temperature seasonality modulated the relationship between species richness and SOC. Nonetheless, using a diversity interaction modeling framework we illustrate how plant guilds, especially legumes, played a crucial role on SOC stocks. SOC stocks increased with legume proportion, but this relationship decreased at high legume proportions. Additionally, legume effects were enhanced when grasses were the main companions compared to non-legume forbs.