Ecological Risk And Countermeasures Of The Expressway Crossing Section In The National Park Of Hainan Tropical Rainforest

Hainan Island in south China harbours vast areas of natural forests with rich biodiversity,which is one of the globally important Indo-Burma biodiversity hotspot.Recently,National Park of Hainan Tropical Rainforest,includes seven mountains areas and covering an area of 4269 km²,was established on the island to better conserve its ecosystem integrity and authenticity.National Park of Hainan Tropical Rainforest is the only national park with expressways in China.The habitat isolation and fragmentation caused by the expressway probably affect the landscape pattern and ecosystem integrity and functions,and possess negative ecological effects in future.In this study,we first quantitatively evaluated their landscape patterns before,under and completed the expressway construction,by choosing the regions within 3 km at two sides of the expressway as the study area,based on GIS,Fragstats and landscape ecology theories.And we measured the heavy metal concentrations in soil by choosing the regions within 100 m along the expressway.Finally,we analyzed the possible isolation effects of human interference such as expressway and dam and geographical barriers（islands,rivers,etc.）on the gene flow of plant populations,based on molecular data of Primulina heterotricha and Conandron ramondioides.Aim to determine the importance of each of the ecosystem services,we quantified five ecosystem services,such as water conservation,soil retention,carbon storage,oxygen release,biodiversity maintenance,by using an integrated valuation of ecosystem services and tradeoffs（In VEST）model,a revised universal soil loss equation（RUSLE）,a net primary production transformation formula,and the maximum entropy（Max Ent）model,which is better for the conservation of rare and endangered plants,and optimization and improvement of ecosystem services of in National Park of Hainan Tropical Rainforest.The results showed below:1 Landscape dynamics and ecological risk of the expressway crossing sectionWe found that,the area of expressway（includes construction areas）in 2016 was325.51 hm²,forest cover decreased slightly but forest patch density increased.Farmland dominance decreased as a result of increased farmland fragmentation,although its area increased slightly.In 2019,when the expressway completed,the expressway area decreased slightly and forests area increased,due to afforesting along the expressway.However,the cohesion index of forest and farmland decreased in 2019,which indicated a lower connection degree and a higher landscape fragmentation.The moderate and high ecological risk area along the expressway had been increasing year by year.Nevertheless,the landscape along the expressway remained unchanged and showed slight effects on the ecosystem integrity and functioning.The habitat isolation and fragmentation caused by the expressway probably possess negative ecological effects in future.Thus,it is necessary to build overpass woodlands to increase ecosystem connectivity,and build the constructed wetlands to purify runoffs from the expressway,and establish long-term monitoring sites for enhancing ecosystem functions,such as water supply and conserving potential and water purifying ability.2 Distribution of heavy metals in soil of the expressway crossing sectionThe heavy metal Cr of soil on both sides of the expressway crossing section in Zayun and Fanyang town was higher than the background values.The whole geo-accumulation index of Cr was higher than 0,corresponding to unpolluted to moderately polluted environment.The potential ecological risk on both sides of the expressway was low,mainly due to the human community activities.The content of heavy metals of soil mainly decreased and first decreased and then increased with distance to the road,and the highest value distributed within the range of 10 m from the expressway.Heavy metals in the soil of the study area came from traffic sources and natural sources.3 Effects of expressway and geographical isolation on plant population distribution and genetic diversityThe population of P.heterotricha had obvious genetic boundaries in upstream and downstream of the Changhua River,with the F_stwas mostly higher than 0.9,and the gene flow N_mwas lower than 1.After the construction of the expressway,the population differentiation of P.heterotricha intensified,and the gene flow weakened.Based on the isolation of Changhua River,the human interference,includes expressway and Dagaungba Dam may form a greater isolation effect in affecting the ecological integrity and ecosystem services in the National Park of Hainan Tropical Rainforest.We further tested the role of such geographical isolation in species genetic diversity at a larger scale,with the Conandron ramondioides（Gesneriaceae）as an example.Pairwise F_stand N_mvalues among C.ramondioides populations from mainland China,Taiwan Island,and Japan were ranged from 0.136 to 0.561 and 0.196 to 1.592.A very high degree of genetic differentiation among three regions were found,with very limited gene flow and a clear isolation by islands.4 Spatial differentiation of ecosystem services of the National Park of Hainan Tropical Rainforest and expressway crossing sectionOver 75%area of this park exhibited dominant ecosystem services,such as water conservation,carbon storage and oxygen release.Soil retention was balanced in seven mountains,whereas the water conservation was concentrated in the eastern part of this park,i.e.Mt.Yinggeling,Mt.Limu,Mt.Wuzhi,Mt.Diaoluo.Carbon storage and oxygen release services were highest at the central part of this park,including Mt.Wuzhi,Mt.Diaoluo,Mt.Yinggeling,Mt.Bawang,and Maorui Forest Farm,while biodiversity maintenance was the most important ecosystem service in Mt.Wuzhi,Mt.Diaoluo,Mt.Bawang and Maorui Forest Farm.The total and average volumes of five ecosystem services in this park had declined slowly in 2010 but were increased quickly in 2019.The ecosystem services of the expressway crossing section were lower than other regions of the National Park.These results are helpful for formulation of effective management strategy of this national park.