Soil and Plant Nutrients Are Maintained-and Can Be Enhanced-by Long-Term Frequent Fire in an Afromontane Grassland

Abstract

Questions Fire is a key ecological and evolutionary force in many grassy biomes, including the Afromontane region of South Africa, where it supports critical ecosystem processes such as nutrient cycling. Anthropogenic activities are expected to alter fire regimes, with consequences for grassland nutrient dynamics and, by extension, species composition and productivity. We asked how long-term variation in fire frequency and season of burn influences nutrient concentrations in soils and plant communities, and whether responses differ among plant functional types.Location uKhahlamba-Drakensberg montane grasslands, South Africa.Methods We assessed the effects of fire frequency and season on soil and plant nutrient dynamics using a subset of five treatments from a 40-year burning trial. Soil samples were collected to 15 cm depth and composited per plot for analysis of total carbon, nitrogen, phosphorus and potassium. Aboveground biomass was harvested from four quadrats per plot and living material analysed by functional type for nitrogen, phosphorus and potassium.Results Annual burning significantly affected soil carbon, nitrogen, phosphorus and potassium concentrations; however, frequent fire did not lead to long-term nutrient depletion. Plant nutrient concentrations were generally not correlated with soil nutrient levels and were largely insensitive to fire regime. Grasses displayed a modest positive nutrient response to frequent burning, while forbs showed no response.Conclusions Our findings suggest that these montane grasslands are resilient within a range of fire regimes, maintaining nutrient stocks and functional integrity even under frequent burning. These results challenge the assumption that repeated fire necessarily depletes soil nutrients and highlights the importance of long-term experiments in understanding ecosystem responses to fire.