Hysteresis resulting in forestry heat storage underestimation: A case study of plantation forestry in northern China

Abstract Heat storage (Q) is an important component of the near-surface energy balance, and has been increasingly considered in recent energy balance studies. Studies have revealed that the hysteresis of heat storage was always been ignored, which leaded to the underestimation of heat storage proportion in energy balance. So, for further understanding the role of hysteresis effect in forestry heat storage, an observation experiment of heat storage in forestry of Pinus sylvestris var. mongolica Litv forestry - a common species in northern China - was conducted. Heat storage in the atmosphere beneath canopy, in the canopy biomass, and in the soil above a soil heat-flow plate were monitored continuously, to determine the distribution of stored heat, and solar radiation was simultaneously monitored to verify the hysteresis of heat storage versus radiation. Seasonal variations were separately analyzed to further clarify phenological effect on hysteresis. Correlation relationship was tested of lag time and underestimated energy versus climatic factors and physiological characteristics, for clarifying the reasons that resulting in hysteresis differences under different experimental day. The main results were as follows: (1) Hysteresis exists in heat storage and the lag time was 3.79 h in our study area; (2) The evaluation of hysteresis is crucial to avoid an underestimation of heat storage. Correction of lag time increases the heat storage proportion in R from 3.78% to 8.48%; (3) Increasing of air temperature and humility daily differences will enhance the underestimated energy. High radiation condition will weak the underestimation on heat storage and short the lag time. Soil moisture and leaf area index were not effect energy hysteresis significantly in sandy vegetation. Climatic factors were the main reason that resulting in the differences of hysteresis. This study helps to improve understanding energy transmitting in canopy and offering a new view in solving surface energy imbalance.