Enhancing subtropical monsoon grassland management: Investigating mowing and nutrient input effects on initiation of grazing lawns

Abstract

Subtropical monsoon grasslands in Asia are commonly in a fire-dominated state with tall grasses (> 2 m) that provide poor-quality forage for mammalian herbivores. In contrast, small patches of grazing lawns with short, nutritious grasses are sparsely distributed within these subtropical monsoon grasslands. Despite the importance of grazing lawns in providing high-quality forage for mammalian herbivores, the process of formation and maintenance of grazing lawns has not been studied in the monsoon grasslands of subtropical Asia. We conducted a large-scale multi-year experiment in subtropical monsoon grasslands within a protected area in Nepal to examine whether mowing tall grasses at different frequencies and spatial scales, along with the application of chemical fertilisers (urea or single superphosphate), could change tall grasslands into grazing lawns. We found that nitrogen and phosphorus concentrations in grasses increased to levels exceeding the minimum maintenance requirements for ruminants in 3600 m2 plots that were mown four times and fertilised. The concentrations of nitrogen and phosphorus remained below the minimum maintenance level for ruminants in unfertilised and unmown plots and in small plots that were four-time mown and fertilised. The frequently mown plots exhibited a significant increase in the proportion of ground cover of lawn grass, from 1% to 3%, and a corresponding decrease in the proportion of ground cover of tall grasses, from 24% to 1%. These results supported our hypothesis that frequent mowing at a larger spatial scale with the addition of chemical fertilisers and grazing leads to the inception of grazing lawns that are favourable for wild herbivores. However, the persistence of the grazing lawns presents challenges due to the highly productive monsoon season and the functional extinction of large bulk grazers. To our knowledge, this is the first empirical study conducted in the subtropical monsoon grasslands of Asia to experimentally demonstrate the importance of active management for the initiation of grazing lawns. Our findings have important implications for the management of subtropical monsoon grasslands.