| The mangroves in Hainan Dongzhai harbor Mangrove National Nature Reserve suffered from degradation or even death due to the outbreak of insects of Sphaeroma sp.. Dynamic characteristics of degrading mangrove communities and soil properties were investigated to analyze the dynamic of the mangroves rapid degradation and death and variation of soil properties. Furthermore, propagules and seedlings of common mangrove species were planted in the degraded area in order to select the most suitable species for vegetation restoration. We showed that:(1)Mangrove degradation proceeded progressively from 2012 to 2014. Tree mortality increased and the number of standing trees and canopy density decreased significantly.(2)The boring of mangrove trees by Sphaeroma sp. was species selective. Different mangrove species experienced different degradation degrees along the Yanfeng East river coast, with Bruguiera gymnorrhiza experiencing the heaviest degradation degree(26.47%) followed by B.s.var.rhynochopetala(10.71%) and Bruguiera sexangula(10.42%), and Kandelia candel and Rhizophora apiculata degrading least.(3)With the progressive degradation of mangrove community, the soil physical and chemical properties also changed in the mangrove degraded area. The soil sand particles content, silt content and bulk density were significantly different between 2012 and 2014, but soil silt particles did not change. The soil p H value, total salinity, available nitrogen content, availablen phosphorus content and available potassium content were significantly different between 2012 and 2014.(4)The correlation analysis between mangrove degenerate degree and soil physical and chemical properties showed that:The mangrove degradation degree was not correlated with soil texture. There was no significant correlation between tree mortality and soil bulk density. The number of live trees and community canopy density were significantly positively correlated with the soil bulk density in mangrove degraded area. Soil bulk density and mangrove degenerate degree showed greater relevance, especially the number of live trees and community canopy density, the regression equation was:y = 0.008 x + 0.5338(R=0.524,p<0.01)y = 0.2564 x + 0.5349(R=0.576,p<0.01)Soil organic matter content was significantly correlated with the number of live trees, community canopy density and mortality. Soil available potassium content was significantly correlated with the number of live trees and community canopy density and mortality. Soil p H value, total salinity, available nitrogen and available phosphorus were not significantly correlated with the number of live trees, community canopy density nor mortality. Soil organic matter content and mangrove degenerate degree showed great relevance, especially the number of live trees, community canopy density and mortality, the regression equation was:y = 2.9234 x + 29.76(R=0.448,p<0.05)y = 105.35 x + 26.461(R=0.557,p<0.01)y =-0.7015 x + 93.385(R=-0.433,p<0.05)The regression equation of soil available potassium and the number of live trees, community canopy density and mortality respectively were:y =-19.052 x + 650.76(R=-0.455,p<0.05)y =-718.17 x + 681.86(R=-0.592,p<0.01)y = 5.2848 x + 200.64(R=0.508,p<0.05)(5) Mangrove propagules plantation was not a good idea for mangrove recovery in degraded area with low survival rate. However, when planting big seedlings(height>50cm) of Aegiceras corniculatum grown in nutrition-bags on ridges, the survival rate was higher than 95% after 1.5 years. Seedlings of were least preferred by Sphaeroma sp. with survival rate above 90% after 8 months, so Rhizophora apiculata can be choosed to be the best fit species in mangrove degraded area. Aegiceras corniculatum didn’t suffer the attack by Sphaeroma sp. so heavy, but it is subject to leaf-eating insects, so tending after planting is essential. The boring behavior of Sphaeroma sp. was the main factor leading to the seedling death of Kandelia candel,Bruguiera sexangula, so the 4 species are not suited to grow in the degraded area. |
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