Study On The Typhoon Impact On Natural Rubber Forest Yield And Risk Assessment Model In Hainan

Typhoon is a major meteorological hazard that damages rubber forests and affects dry rubber production.It is an urgent scientific issue to reveal the mechanism of typhoons impacting rubber tree yield,and to evaluate the influence of typhoons on rubber yield and typhoon disaster risk.In this study,typhoon"Rammasun","Kujira"and rubber forests affected by typhoons from 2017 to 2019 were taken as the main research objects.The biological mechanism of rubber production process affected by typhoon was revealed,and the model of rubber tree timber volume and dry rubber yield forecast was constructed.On the basis of remote sensing technology,a damage assessment model of rubber yield was established.On this basis,a comprehensive evaluation index system for typhoon disaster risk in rubber forests was improved,a risk assessment model for typhoon disaster was constructed,and risk assessment of typhoon disaster in rubber forests was conducted.The main results of the study are as follows:(1)The relationship between the rubber production period and typhoon impact patterns in Hainan Province.In the last 40 years(1980-2019),Hainan Island has been affected by typhoons all year round(no impact in 2004).The average number of impacts per year is about5 to 6,with typhoon impacts recorded from April to December.The average number of landfalls per year is 2 to 3,with typhoons recorded from April to November.July to October are the months with the most typhoons affecting and landing on Hainan Island,especially in July,August and September.The months when typhoons affect and land on Hainan Island often coincide with the rubber tree's rubber production period,thus causing serious damage.In particular,nearly 50%of the typhoons that land on the eastern coast have winds of 11 or more,which can cause significant harm to rubber planting and production.(2)Changes in the characteristics of rubber stands and the microclimate of the forest after typhoon damage.After being affected by the typhoon,the branches and trunks of rubber trees were broken,resulting in obvious changes in the microclimate within the forest.The water content of the soil at different depths in the rubber forest was increased by the typhoon precipitation,with the 60cm depth being more obvious.The destruction of the rubber tree canopy after the typhoon impact caused an increase in the light transmission of the rubber forest and a significant increase in solar radiation within the forest,thus changing the temperature distribution at different heights within the rubber forest and reducing the difference in temperature gradients at different heights.The variability in relative humidity across heights was not significant.(3)Patterns of changes in photosynthetic properties and chlorophyll fluorescence parameters of rubber tree leaves after typhoon damage.The artificial mechanical damage test was employed to simulate the breakage damage of rubber tree canopies during the typhoon impact.It was shown that after 2 d of mechanical damage stress,the net photosynthetic rate and stomatal conductance,intercellular CO₂ concentration and transpiration rate of rubber tree leaves all decreased significantly,indicating that the stomatal factor was the main factor in the decrease of net photosynthetic rate under mechanical damage.After different mechanical damage stresses,leaf photosynthetic rate gradually reached the control level within 11-19 d.The kinetic curve of rapid chlorophyll fluorescence induction in leaves changed significantly after mechanical damage.Initial fluorescence(O phase),was higher in all rubber trees under different stresses compared to the control.The maximum fluorescence intensity(P-phase)also decreased significantly compared to the control,with the O-J-I-P phase of the curve still having a relatively clear inflection point.The PIabs and PItotal of the 80%damage treatment were 2.589 and 1.371 respectively,a decrease of 63.01%and 59.17%respectively compared to CK.It indicated that both photosystem I(PS?)and photosystem II(PS?)activities of rubber tree leaves were severely damaged after mechanical damage,and the stability of photosynthetic performance was reduced.The Malondialdehyde(MDA)content and antioxidant protective enzymes(CAT and SOD,POD)activities increased in rubber tree leaves after mechanical damage stress following typhoon damage.(4)Changes in physiological parameters of rubber tree rubber production and rubber excretion after typhoon damage.Latex and dry rubber yield decreased significantly and dry rubber content(DRC)was significantly higher than in the control after typhoon damage.In terms of the monthly changes in the initial rate of rubber discharge and the latex tube blockage index,the two typhoons in June and July affected the initial rate of rubber discharge mainly in August,September and October,with some recovery in November,and the changes in the dry rubber content and latex tube blockage index were consistent with each other,in contrast to the changes in yield and initial rate of rubber discharge.Rubber trees,affected by wind,have lower latex thiol(R-SH)and inorganic phosphorus(Pi)content than rubber trees unaffected by wind in September-November,with lower yield due to blocked rubber discharge.(5)A model was constructed to assess the impact of typhoon disasters on the dry rubber yield of rubber trees.On the basis of the rubber stand characteristics data,a simulation model of rubber established wood volume based on diameter at breast height,tree height and canopy area was developed.Compared to the RMSE of the binary timber volume model with diameter at breast height and tree height as variables,the values were reduced by 4.5%and the R2 was increased by 4.3%.The RMSE and R2 of the predicted and measured values based on a 1:1 line for the dry gum yield forecasting model based on climatic elements,stand growth and hazard indices were 0.0354 kg/plant and 0.986 respectively.The improved dry gum yield forecasting model showed a 32.6%reduction in RMSE and a 17.4%increase in R2in comparison to the traditional yield forecasting model.The mean absolute error in the calculated damage assessment of this model for different stand sections was 20.3 kg/hm².Based on FY-3C and contemporaneous ground meteorological observations,the CASA(Carnegie-Ames-Stanford approach)model was utilized to develop a model for estimating the net primary productivity of natural rubber and the rubber production potential of natural rubber in Hainan.As a result,NDVI-based disaster loss rating criteria were developed,and dynamic assessment of potential yield changes and disaster losses in rubber forests before and after typhoon impacts was conducted.(6)Disaster risk assessment of the impact of typhoons on rubber plantations in Hainan.The typhoon risk of rubber plantations was assessed in terms of both hazard and vulnerability.Hierarchical analysis and the TOPSIS model were adopted to obtain the rubber typhoon risk assessment results,and multi-year rubber yield data were also employed to analytically corroborate the assessment results.The ranking of typhoon hazard risk for rubber cultivation in Hainan province was most in line with the typhoon hazard assessment.Typhoon risk is a dominant factor in risk,but not a single determinant.Planting technology,variety improvement and other measures have played a better role in contributing to vulnerability reduction.The results of this study provide a core model for dynamic assessment of rubber yield,typhoon risk,typhoon disaster damage and post-disaster recovery,as well as a scientific basis for the layout and production of rubber production areas.