Effects of Burning Severity and Root System on Herb Land Surface Evapotranspiration: A Study Based on Prescribed Fire in Southwest China

ABSTRACT Post‐fire evapotranspiration (ET) exerts a significant influence on soil moisture dynamics and thus vegetation recovery in, particularly, karst ecosystems in southwest China. Despite the widespread use of remote sensing and mathematical modelling to estimate large‐scale land surface post‐fire ET, few studies directly examine how burn severity and vegetation species affect small‐scale ET. This study bridges the gap by conducting two experiments. In the first experiment, lysimeters containing Artemisia Iavandulifolia and Miscanthus sinensis (with tap and fibrous root systems, respectively) were grown for 2.5 years, followed by prescribed burning with varying severities (low, moderate and high). Post‐fire ET was monitored over 1‐year period, with unburned control for comparison. In the second experiment, the soil surface burns were carried out to assess ET under three surface conditions: burned surface with ash cover (BSA), burned surface without ash cover (BO) and unburned surface with ash cover (UA). The ET was measured using the mass change method, and atmospheric and soil moisture were also collected. Results indicated that prescribed fire reduced post‐fire post‐fire ET by up to 46%–62%, depending on both fire severity and herb species. On low and moderate burning severities surfaces, ET from Miscanthus sinensis was greater than that with Artemisia Iavandulifolia . But, in high‐burning severity conditions, the opposite was true. This shift was due to varying heating depth of burn and root distribution of the two herbs. ET varied depending on atmosphere conditions. The dependence declined with the fire severity. The biomass and ash coverage were not significantly related to ET. However, decreasing evaporation was detected as the burning severity increased for the BSA and BO. These results suggested that the post‐fire changes in soil properties were a key driver of ET dynamics.