| Turnover rate of forest community is an important indicator of measuring forest dynamics,which is defined as the relative ratio between changes in a variable such as species richness or stem abundance and the total amount of the variable in the community in certain period.Analyzing community turnover dynamics can help us in understanding community assembly process and further elucidating the dynamics of forest ecosystems.Bawangling national nature reserve is one of the regions with the rich tropical forest vegetation types in China.There still remain various tropical old-growth forest vegetation types and the natural secondary forests that are recovering after disturbances of different manners and intensities experienced by the old growth in the nature reserve.It is an appropriate place to study forest biodiversity and community dynamics.In the past,chronosequence(i.e.space for time substitutions)has been the only indirect approach in researches on forest community dynamics in Bawangling nature reserve.No results have been issued on basis of direct monitoring the dynamic changes of communities with time.In this thesis,woody plant turnover dynamics were examined based on censuses of thirty one 1-ha forest dynamics plots(FDPs)distributed across five typical old-growth forests and the tropical lowland and montane secondary rainforest forests recovered after anthropogenic disturbances such as shifting cultivation(slash and burn),clear cutting,and selective logging in the nature reseve.Data of species richness,stem abundance and basal area of woodyplants in each forest dynamics plot before and after the census interval of 5 years were compared tp assesss their turnover dynamics with the recovery stages,the manners and intensities of disturbances,vegetation types,and species functional traits.Finally,factors influencing the turnover dynamics were explored by correlation analysis.The main results of the studyare as follows:1.By comparing and analyzing the turnover dynamics of woody plants in tropical lowland secondary rainforest at different recovery stages,we found that individual abundance turnover rate in early,middle and late recovery stages was 8.43%,5.02% and 3.28%,respectively.Species richness turnover rate was 4.47%,2.49% and 1.65%,respectively.Basal area turnover rate was 9.17%,5.35% and 2.99%,respectively.Individual mortality made most contribution to individual turnover dynamics,species recruitment made most contribution to species richness dynamics,the relative growth rate of basal area made the main contributions to turnover dynamics of basal area in the process of community recovery,respectively.The change trend of turnover dynamics of woody plants with recovery process was mainly dependent on the dynamic change of saplings(1?DBH<5cm).The turnover rates of woody plants were significantly related to recovery time,illumination,elevation and soil organic matter content.2.By comparing and analyzing the turnover dynamics of woody plants in tropical lowland secondary rainforest recovered after disturbances of different manners(shifting cultivation and clear logging),we found that: individual abundance turnover rate in the secondary forests after shifting cultivation,clear logging and old-growth forest was 5.02%,3.82% and 3.31%,respectively,species richness recruitment rate was 2.46%,1.25% and 1.45% respectively,basal area turnover rate was 5.24%,3.74% and 2.81%,respectively.Community turnover dynamics of shifting cultivation secondary forest was significantly higher than that of clear-logging forest and old forest,while there was little difference between clear-logging forest and old forest.Individual mortality made most contribution to individual turnover dynamics,species recruitment made most contribution to species richness dynamics,the relative growth rate of basal area made the main contributions to basal area turnover dynamics of woody plants.Individual abundance and basal area turnover dynamics of woody plants were mainly affected by the dynamics of saplings(1?DBH<5cm),while species richness turnover dynamics was mainly affected by the dynamics of grown up plants(DBH?5cm).Illumination,soil water content,disturbance intensity(slash-and-burn>logging>old-growth)were positively correlated with the turnover rates of woody plants,while soil available nitrogen,soil available potassium content and elevation were negatively correlated with the turnover rates of woody plants.3.The turnover dynamics of woody plants in the secondary forests which have recovered after different cutting intensities(clear cutting and selective logging)were analyzed and compared with those of the old-growth tropical montane rainforest.We found that the individual abundance turnover rate of woody plants in the secondary forests after clear cutting and selective logging,and the old-growth tropical montane rainforest was 3.44%,3.77% and3.93% respectively.The turnover rate of species richness was 1.51%,1.30% and 1.57%respectively.The turnover rate of basal area was 3.33%,2.90% and 3.13% respectively.The comparative analysis showed that the individual abundance turnover rate of woody plants in tropical montane rain forest increased along the disturbance intensity,the turnover rate of species richness and basal area after selective logging forest was lower than that after clear cutting and old-growth forest,but the difference was not significant.Soil available potassium content significantly promoted individual abundance turnover,altitude,soil p H value and slope significantly inhibited the turnover rate of basal area turnover rate,soil p H value and slope were also negatively correlated with individual abundance turnover rate.4.Comparing the turnover dynamics of five different types(tropical coniferous forest,tropical deciduous monsoon rainforest,tropical montane evergreen forest,tropical montane rainforest and tropical lowland rainforest)of old-growth forests,we found that:(1)The individual abundance recruitment rate,mortality rate and turnover rate of tropical coniferous forest was 2.11%,5.25% and 6.87%,respectively,and the contribution of individual mortality to turnover dynamics was greater than that of recruitment.The recruitment rate,loss rate and turnover rate of species richness was 1.35%,0.63% and 1.94%,respectively.Recruitment of species richness made more contribution to species dynamics than loss.Basal area recruitment rate,decrement rate,relative growth rate and turnover rate was 0.12%,2.78%,2.89% and5.38%,respectively.The loss and relative growth of basal area contributed significantly to the turnover dynamics.(2)The individual abundance recruitment rate,mortality rate and turnover rate in tropical deciduous monsoon rainforest was 3.09%,2.35 and 5.11%,respectively.The contribution of individual mortality to turnover dynamics was greater than that of recruitment.The recruitment rate,loss rate and turnover rate of species richness was 1.86%,0.62% and2.43%,respectively.Species recruitment made more contribution on turnover dynamics than that of loss.The basal area recruitment rate,decrement rate,relative growth rate and turnover rate was 0.25%,1.56%,3.19% and 4.74%,respectively,the relative growth of basal area made the highest contribution on basal area turnover.(3)The individual abundance recruitment rate,mortality rate and turnover rate of tropical montane evergreen forest was 1.80%,3.97% and5.41%,respectively.The contribution of individual mortality to turnover dynamics was greater than that of recruitment.Species richness recruitment rate,loss rate and turnover rate was0.79%,0.43% and 1.45%,respectively.The contribution of species recruitment to turnover dynamics was greater than that of loss.Basal area recruitment rate,decrement rate,relative growth rate and turnover rate was 0.12%,2.01%,2.05% and 3.97%,respectively.The contribution of basal area decrement and relative growth to turnover dynamics was greater than that of recruitment.(4)Individual abundance recruitment rate,mortality rate and turnover rate in montane rainforest was 1.60%,3.30% and 4.18%,respectively,and the contribution of mortality to turnover dynamics was greater than that of recruitment.Species richness recruitment rate,loss rate and turnover rate of species richness was 0.87%,0.83% and 1.66%,respectively.The contribution of recruitment to turnover dynamics was slightly greater than the loss in species.Basal area recruitment rate,decrement rate,relative growth rate and turnover rate was 0.07%,1.69%,1.76% and 3.37%,respectively.The contribution of decrement and relative growth was greater than that of recruitment.(5)Individual abundance recruitment rate,mortality rate and turnover rate in tropical lowland rainforest was 1.46%,2.00% and 3.31%,respectively,and the contribution of individual mortality to turnover dynamics was greater than that of recruitment.Species richness recruitment rate,loss rate and turnover rate was 0.82%,0.67% and 1.46%,respectively,and the contribution of species recruitment to turnover dynamics was greater than that of loss.Basal area recruitment rate,decrement rate,relative growth rate and turnover rate was 0.06%,1.00%,1.84% and 2.81%,respectively,the relative growth rate of basal area made the main contribution on the turnover dynamic indicators.Soil available potassium content,elevation and illumination were positively correlated with,while slope,soil water content and soil organic matter content were negatively correlated with the turnover rates.5.Woody plant population turnover dynamics was closely related to the variations of six key functional traits among different species in the Bawangling nature reserve on Hainan island.Specific leaf area was positively correlated with individual turnover rate,while wood density and potential maximum height(excluding woody liana)were negatively correlated with individual abundance turnover.Specific leaf area,leaf nitrogen and leaf phosphorus contents were positively correlated with the turnover rate of basal area,while leaf dry matter content and potential maximum height(excluding woody liana)were negatively correlated with the turnover rate of basal area. |
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