Long-Term Dynamic Of Biomass And Its Response To Temperature In Tropical Montane Rainforest Of Jianfengling,Hainan Island

Since the period of industrialization(1850-1900),the earth’s climate system and surface structure are undergoing tremendous changes at an unprecedented rate.The impact of global climate change on the structure,function,and diversity of ecosystems is becoming more and more significant.Tropical forests are the most important "carbon sinks" on the planet,and their dynamic changes are of great significance for maintaining the global carbon balance and slowing the increase of greenhouse gases.At present,a large number of studies have proved that tropical forests are sensitive to climate change,but due to the lack of long-term fixed plot observation data,there is still a lack of clear understanding of how tropical forests respond to and adapt to global warming.Therefore,this article takes the tropical mountain rainforest primordial forest and secondary forest in the Jianfengling area of Hainan Island as the research object,combined with the temperature data of the meteorological observation field of the Jianfengling forest ecosystem in Hainan from 1984 to 2017,and obtains data through field sample surveys and analyzes the time of temperature.Sequence changes,Jianfengling tropical montane rain forest biomass and its components,and the effects of temperature on biomass and its components,explore the response and adaptation mechanisms of tropical montane rain forests to temperature changes.The main findings are as follows:(1)From 1984 to 2017,all temperature factors showed an obvious upward trend,but the trend of climate warming did not conform to a linear correlation.Among the various temperature factors,the lowest extreme temperature has the largest climate tendency rate,which is 0.63 ℃/10.0 a.Time series analysis showed that with 2003 as the mutation point,the average temperature increase rate increased after 2003,and the average difference between before and after the mutation was 0.69 ℃.The annual precipitation in Jianfengling showed a slow upward trend as a whole(z>0),the annual precipitation increased insignificantly,and showed a weak upward trend,with a certain periodicity.The abnormal or near-abnormal climate in Jianfengling mountain rain forest often accompanies the occurrence of ENSO events.(2)From 1984 to 2017,the biomass of the virgin forest and the secondary forest of the Jianfengling tropical mountain rain forest and the change trend of the biomass over time showed a quadratic curve and a cubic curve,respectively.The biomass of the primary forest was significantly higher than that of the secondary forest.The annual net changes in biomass of the two forest types were basically positive,first increasing and then decreasing with time.In the same year,the change range of the biomass and its components of the mountain rain forest primary forest was lower than that of the secondary forest.During the study period,the number of trees in the secondary forest of Jianfengling mountain rainforest decreased significantly with time.The biomass of dead individuals and the biomass of new individuals showed a significant increase,but the biomass of dead individuals was always greater than the biomass of new individuals.The significant increase in new biomass(P<0.01)is mainly related to the significant increase in the number of new individuals,and is combined with the number of new individual plants and the new individual biomass per plant.(3)Within a certain temperature range,the increase in temperature has a certain promotion effect on the forest biomass.However,with the intensification of global warming,the degree of driving of the positive and negative effects of rising temperature on forests has changed,resulting in a slowdown in biomass growth.It is mainly manifested in the significant negative correlation between the net change in biomass and the average temperature(P<0.001).The four indicators of new individual biomass,dead individual biomass,number of new individual plants,and number of dead individual plants in tropical mountain rainforest all showed a significant quadratic curve relationship with the average temperature(P<0.05).The biomass of newly-increased individuals and the biomass of dead individuals increase with the increase of temperature,and when the temperature reaches 20.3℃,the biomass of newly-increased individuals and the biomass of dead individuals decrease with the increase of temperature.The primary forest biomass of tropical mountain rain forest showed a significant negative correlation with the extreme maximum temperature,and the secondary forest biomass showed a significant negative correlation with the average minimum temperature.