Changes in grassland phenology and growth rate, rather than diversity, drive biomass production after fire

Abstract

Plant phenology and growth rate are sensitive bio-indicators of climate change and anthropogenic disturbances. Fire is widespread in many ecosystems worldwide. Understanding how plant growth varies in its response to fire disturbance is critical for fire management. Despite the effects of fire on various aspects of plant ecology, such as the composition and growth of vegetation, little is known about the impact of fire on biomass production resulting from changes in functional group composition, plant phenology, and growth rate. Prescribed-burning of three types of grassland along an aridity gradient in Inner Mongolia, China, did not significantly affect species richness or the relative abundance of various functional groups across the three grasslands. Fire-induced advancement (∼3 weeks) and elongation (∼2 weeks) of growing periods increased perennial grass and community production in the low aridity grassland (aridity index, AI = 0.38). In contrast, marginal changes in phenology did not influence production in the moderate aridity grassland (AI = 0.27). Post-fire delayed and shortened growing period by ∼5 and 4 weeks respectively and thus reduced community production in the high aridity grassland (AI = 0.20). Post-fire plant growth rate was reduced by ∼44% in the low aridity grassland but was enhanced by 20–100% in the moderate and high aridity grasslands. The opposing effects of fire on growth rate vs. phenological responses largely negated any overall effect on community production. Our results indicate that phenology and growth rate rather than diversity were the primary contributors to the variation in production after fire. We provide new empirical evidence that prescribed-burning would not be a suitable management tool in extremely arid grasslands because it delays growing period and reduces production, both of which may influence grazing time and intensity. Our findings highlight the compensatory effects of plant phenology and growth rate on the regulation of biomass production.