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Abstract The vegetation restoration experiment was carried out by selecting the arborshrubgrass plants with strong stress resistances in the drawdown area of the reservoir of Chongqing Bashan Lake National Wetland Park. The results showed that the survival rate of Taxodium distichum was only 33% in August since the completion of the planting in May 2017， while the survival rates of other plant species were all 100%. After the rising and falling of water levels from September 2017 to February 2018， the investigations conducted in April 2018 showed that the flooding lasted for 130 d at the altitude of 668-672 m， where the preserving rate of Betula nigra was very low of only 25%. The flooding lasted for 120 d at the altitude of 672-675 m， where B. nigra， Pontederia cordata， and Thalia dealbata showed good preserving conditions with the preserving rates over 55%， while Canna indica， Cyperus alternifolius and Iris tectorum had poor preserving conditions with the rates below 50%. The drawdown area with the altitude of 675-678 m had the flooding lasted for 84 d， and good preserving conditions were found in B. nigra， T. distichum， Pterocarya stenoptera， Distylium chinense， Rosa multiflora， P. cordata， T. dealbata and Iris tectorum， which had the preserving rates reach up to 65%， and the preserving rate of B. nigra was as high as 76.2%， but the preserving rates of C. indica and C. alternifolius were low.
Key words Bashan Lake; Drawdown area; Ecological restoration; Plant configuration
Located in Chengkou County of Chongqing Municipality in the south of Daba Mountains， Chongqing Bashan Lake National Wetland Park mainly includes Bashan Reservoir and the Ren River， Qian River lying within Chengkou County as well as the surrounding buffer areas. The area is dominated with rivers， low mountains and valleys， and tidal flats. The drawdown area of the reservoir has a sparse vegetation coverage， single landscape， poor soil and water conservation capacity， and a gully of mountain streams and slight human disturbance. This study was aimed to carry out vegetation restoration in the drawdown area of Chongqing Bashan Lake National Wetland Park through the selection of plants which had good soil and water conservation capacities and could adapt to local growth environment.
Materials and Methods
Test site selection
The test area was the drawdown area of the reservoir with an altitude of 668-678 m located in Xinling Village， Bashan Town， Chengkou County of Chongqing Bashan Lake National Wetland Park， with a total length of 700 m. The test area was covered with farmland or cultivated land before the construction of the reservoir. Test design
The selected plants and specific configuration were as shown in Table 1. All plant species were planted in May 2017， and the survival rates were analyzed after 3 months with the growth conditions recorded. After the inundation from the reservoir storage filling in September to April 2018， the survival rates and growth conditions of the plants were observed and recorded.
Results and Analysis
Water level fluctuations
According to the specific situation of water level fluctuation， the water level monitoring time was from September 2017 to February 2018. In September 2017， the water level rose to the afforestation area. In February 2018， the water level dropped below 668 m， and the monitoring stopped. As shown in Table 2， the area with the altitude of 668-672 m had the longest flooding time of 130 d， and the water flooded to the water level of 678m or more for 36 d. From October to December 2017， the area with the altitude of 670-672 m was totally in submerged state. The highest water level in September and October was above 680 m， and the water level in November was 668-675 m， while in January 2018， the water level dropped to the lower part of the afforestation area with the lowest water level of 656.43 m.
Survival and growth of arbors and shrubs
As shown in Table 3， before the flooding， the survival rate of T. distichum was only 33% due to drought， while all other species survived. After flooding， the preserving rates of different tree species were different in different planting areas. In the planting area with an altitude of 675-678 m， the preserving rate of survived T. distichum was 75%， and the preserving rates for Salix babylonica and Pterocarya stenoptera were more than 60%. D. chinense and R. multiflora grew at the altitude of 678 m， and during the flooding period， the preserving rate for each was 80% and 90%， respectively. R. multiflora bloomed in April. The preserving rate of B. nigra varied greatly in different planting areas. The preserving rate was 76.2% in the planting area with an altitude of 675-678 m， while it dropped to 25% in the planting area with an altitude of 668-672 m. The preserved seedlings had new shoots emerged in April， all of which showed good growth vigor. The growth conditions of B. nigra， D. chinense and R. multiflora were shown in Fig.1， 2， 3 and 4， respectively.
Survival and growth conditions of aquatic plants
As shown in Table 4， all aquatic plants survived after planting. In the planting area with the altitude of 672-675 m， the water was flooded for 120 d. C.indica and C. alternifolius were in pool preservation conditions with the preserving rates below 20%， the preserving rates of P. cordata， T.dealbata and I.tectorum reached over 50%， in which the preserving rate of T.dealbata was as high as 80%， showing good growth conditions. The water flooding lasted for 84 d in the area with the altitude of 675-678 m. The preserving rates of C.indica and C. alternifolius were low of below 4f5%， while the preserving rates of P. cordata and T.dealbata reache up to 98%. All preserved plants had new shoots emerged from the aboveground parts， showing good growth conditions. Conclusion
The planting was completed in May 2017， and the survival rate of T. distichum was only 33% by August， while the survival rates of other plant species were all 100%.
After the rising and falling of water levels from September 2017 to February 2018， the investigations conducted in April 2018 showed that the flooding lasted for 130 d at the altitude of 668-672 m， where the preserving rate of B. nigra was very low of only 25%. The flooding lasted for 120 d at the altitude of 672-675 m， where B. nigra， P. cordata， and T. dealbata showed good preserving conditions with the preserving rates over 55%， while Canna indica， Cyperus alternifolius and Iris tectorum had poor preserving conditions with the rates below 50%. The drawdown area with the altitude of 675-678 m had the flooding lasted for 84 d， and good preserving conditions were found in B. nigra， T. distichum， P. stenoptera， D. chinense， R. multiflora， P. cordata， T. dealbata and I. tectorum， which had the preserving rates reach up to 65%， and the preserving rate of B. nigra was as high as 76.2%， but the preserving rates of C. indica and C. alternifolius were low.
Most of the configured plants in the drawdown area of Bashan Lake Reservoir grow well， and B. nigra， T. distichum， D. chinense and I. tectorum can be used as the main vegetation for vegetation restoration in the drawdown area of Bashan Lake Reservoir.
Vegetation restoration in the drawdown area is a long process. The plants in the drawdown area of the Bashan Lake Reservoir have to undergo longterm tests. The lodged and tilted plants should be erected and earthed up， and the exposed roots should be ridged and consolidated， which require further tests in production.
References
[1] The Overall Planning of Bashan Lake National Wetland Park[R]. 2017.
[2] QIN HW， LIU ZX， ZHOU DX， et al. Physiological responses of Distylium chinense （Fr.） Diels to antiseason submergence[J]. Journal of Henan Agricultural Sciences， 2012， 41（11）： 126-128.
[3] GAO L， WU JC， XIONG XZ， et al. The seed germination and growth characteristics of introduced plant Betula nigra in hydrofluctuation belt of Three Gorges Reservoir area[J]. Journal of Chongqing Normal University （Natural Science Edition）， 2017， 34（4）： 40-47.
Key words Bashan Lake; Drawdown area; Ecological restoration; Plant configuration
Located in Chengkou County of Chongqing Municipality in the south of Daba Mountains， Chongqing Bashan Lake National Wetland Park mainly includes Bashan Reservoir and the Ren River， Qian River lying within Chengkou County as well as the surrounding buffer areas. The area is dominated with rivers， low mountains and valleys， and tidal flats. The drawdown area of the reservoir has a sparse vegetation coverage， single landscape， poor soil and water conservation capacity， and a gully of mountain streams and slight human disturbance. This study was aimed to carry out vegetation restoration in the drawdown area of Chongqing Bashan Lake National Wetland Park through the selection of plants which had good soil and water conservation capacities and could adapt to local growth environment.
Materials and Methods
Test site selection
The test area was the drawdown area of the reservoir with an altitude of 668-678 m located in Xinling Village， Bashan Town， Chengkou County of Chongqing Bashan Lake National Wetland Park， with a total length of 700 m. The test area was covered with farmland or cultivated land before the construction of the reservoir. Test design
The selected plants and specific configuration were as shown in Table 1. All plant species were planted in May 2017， and the survival rates were analyzed after 3 months with the growth conditions recorded. After the inundation from the reservoir storage filling in September to April 2018， the survival rates and growth conditions of the plants were observed and recorded.
Results and Analysis
Water level fluctuations
According to the specific situation of water level fluctuation， the water level monitoring time was from September 2017 to February 2018. In September 2017， the water level rose to the afforestation area. In February 2018， the water level dropped below 668 m， and the monitoring stopped. As shown in Table 2， the area with the altitude of 668-672 m had the longest flooding time of 130 d， and the water flooded to the water level of 678m or more for 36 d. From October to December 2017， the area with the altitude of 670-672 m was totally in submerged state. The highest water level in September and October was above 680 m， and the water level in November was 668-675 m， while in January 2018， the water level dropped to the lower part of the afforestation area with the lowest water level of 656.43 m.
Survival and growth of arbors and shrubs
As shown in Table 3， before the flooding， the survival rate of T. distichum was only 33% due to drought， while all other species survived. After flooding， the preserving rates of different tree species were different in different planting areas. In the planting area with an altitude of 675-678 m， the preserving rate of survived T. distichum was 75%， and the preserving rates for Salix babylonica and Pterocarya stenoptera were more than 60%. D. chinense and R. multiflora grew at the altitude of 678 m， and during the flooding period， the preserving rate for each was 80% and 90%， respectively. R. multiflora bloomed in April. The preserving rate of B. nigra varied greatly in different planting areas. The preserving rate was 76.2% in the planting area with an altitude of 675-678 m， while it dropped to 25% in the planting area with an altitude of 668-672 m. The preserved seedlings had new shoots emerged in April， all of which showed good growth vigor. The growth conditions of B. nigra， D. chinense and R. multiflora were shown in Fig.1， 2， 3 and 4， respectively.
Survival and growth conditions of aquatic plants
As shown in Table 4， all aquatic plants survived after planting. In the planting area with the altitude of 672-675 m， the water was flooded for 120 d. C.indica and C. alternifolius were in pool preservation conditions with the preserving rates below 20%， the preserving rates of P. cordata， T.dealbata and I.tectorum reached over 50%， in which the preserving rate of T.dealbata was as high as 80%， showing good growth conditions. The water flooding lasted for 84 d in the area with the altitude of 675-678 m. The preserving rates of C.indica and C. alternifolius were low of below 4f5%， while the preserving rates of P. cordata and T.dealbata reache up to 98%. All preserved plants had new shoots emerged from the aboveground parts， showing good growth conditions. Conclusion
The planting was completed in May 2017， and the survival rate of T. distichum was only 33% by August， while the survival rates of other plant species were all 100%.
After the rising and falling of water levels from September 2017 to February 2018， the investigations conducted in April 2018 showed that the flooding lasted for 130 d at the altitude of 668-672 m， where the preserving rate of B. nigra was very low of only 25%. The flooding lasted for 120 d at the altitude of 672-675 m， where B. nigra， P. cordata， and T. dealbata showed good preserving conditions with the preserving rates over 55%， while Canna indica， Cyperus alternifolius and Iris tectorum had poor preserving conditions with the rates below 50%. The drawdown area with the altitude of 675-678 m had the flooding lasted for 84 d， and good preserving conditions were found in B. nigra， T. distichum， P. stenoptera， D. chinense， R. multiflora， P. cordata， T. dealbata and I. tectorum， which had the preserving rates reach up to 65%， and the preserving rate of B. nigra was as high as 76.2%， but the preserving rates of C. indica and C. alternifolius were low.
Most of the configured plants in the drawdown area of Bashan Lake Reservoir grow well， and B. nigra， T. distichum， D. chinense and I. tectorum can be used as the main vegetation for vegetation restoration in the drawdown area of Bashan Lake Reservoir.
Vegetation restoration in the drawdown area is a long process. The plants in the drawdown area of the Bashan Lake Reservoir have to undergo longterm tests. The lodged and tilted plants should be erected and earthed up， and the exposed roots should be ridged and consolidated， which require further tests in production.
References
[1] The Overall Planning of Bashan Lake National Wetland Park[R]. 2017.
[2] QIN HW， LIU ZX， ZHOU DX， et al. Physiological responses of Distylium chinense （Fr.） Diels to antiseason submergence[J]. Journal of Henan Agricultural Sciences， 2012， 41（11）： 126-128.
[3] GAO L， WU JC， XIONG XZ， et al. The seed germination and growth characteristics of introduced plant Betula nigra in hydrofluctuation belt of Three Gorges Reservoir area[J]. Journal of Chongqing Normal University （Natural Science Edition）， 2017， 34（4）： 40-47.