Abstract:In order to solve the problem of freezethaw disasters caused by low temperatures that living standing wod were vulnerable during the overwintering period. A method for freeze-thaw detection was proposed based on the sequence envelope analysis of stem moisture of living standing wood during the overwintering period by analyzing the change of stem moisture and environmental temperature data. Firstly, based on the use of a freeze-thaw detection sensor with independent intellectual property rights,the real-time information on the stem moisture and environmental temperature of living standing wood was obtained, and the changes of stem moisture and environmental temperature data of living standing wood during the overwintering period were clarified through pre-tests by the research team of Beijing Forestry University and the research team. However, ambient temperature was indirectly related to the physiological state of the living standing wood and cannot be used alone as a basis for determining freeze-thaw conditions, and the change of stem moisture of standing trees during the winter due to water-ice interactions in the stem can reflect the freeze-thaw conditions of the living standing wood. Secondly, a method of freeze-thaw condition detection based on the envelope analysis of stem moisture series was proposed. And 1320 min was selected as the signal sampling interval for the envelope analysis to obtain the extreme values of the data for quantitative representation of the freeze-thaw condition of living standing wood. The mean values of the upper and lower lines of the stem moisture envelope and the lower line of the envelope in combination with the ambient temperature were used to establish a normalised calculation model of the freeze-thaw condition assessment index. Finally, three broad-leaved tree species (Violet, Begonia and Balsam Poplar) were chosen as representatives to verify the generalisability of the method based on the sequence envelope analysis of stem moisture in standing wood during freeze-thaw. The experimental site of Violet was located at Sanqingyuan Nursery of Beijing Forestry University, Haidian District, Beijing (116°21′14″E, 40°0′54″N), for the period of November 1st, 2018—April 1st, 2019.The experimental site of Begonia was located at the nursery of Hesheng Institute of Ecological Science and Technology, Horinger County, Huhhot City District, Inner Mongolia (111°50′28″E, 40°32′33″N), for the period September 1st, 2018—June 1st,2019.The experimental site of Balsam Poplar was located at the experimental forestry farm under Northeast Forestry University in MaorMountain, Harbin City, Heilongjiang Province (127°34′48″E, 45°16′12″N), for the period October 1st,2018May 1st,2019. The freeze-thaw condition of the Violet was slight throughout the wintering period, with a maximum freezethaw index of 0.004, much less than 1.0. The freeze-thaw condition of the Begonia tree was more variable, with a fluctuating index between 0.1 and 0.7. The freeze-thaw condition of the Balsam Poplar was relatively severe, with a maximum freeze-thaw index of 0.9. The tests results showed that the proposed principle and the self-developed freeze-thaw detection sensor were accurate and reliable, and can be used as an effective means to detect the freeze-thaw condition of living standing wood, which can provide theoretical and data support for early warning of plant frost damage.
