The Research On Characteristics Of Throughfall In Subtropical Secondary Forests And The Relationship With Soil Moisture

Throughfall is one of the important processes of forest hydrology,it is the part of rainfall which falling into forest after intercepted by canopy,which plays an important role in biogeochemical cycling in forest ecosystems.Many studies have research on Cunninghamia lanceolata forests and Pinus massoniana forests,while few research for secondary forests in subtropical area of southern China.At the same time,the relationship between throughfall and leaf area index(LAI)are limited as well as the influence of throughfall on soil moisture.Therefore,in this study,three types of forest were selected:mixed coniferous broad leaved forest(Pinus massoniana-Lithocarpus glaber),broadleaved deciduous forest(Choerospondias axillaris)and evergreen broad-leaf forest(Lithocarpus glaber-Cyclobalanopsis glauca).We have established a 10 m × 20 m runoff observation plot for each forest type to measure the rainfall,throughfall and soil moisture,and then analyzed the rainfall characteristics,the differences of throughfall in different forests and the influences on soil moisture.The main research results are as follows:1.In 2016,annual rainfall is 1883.32 mm.In the P.massoniana-L.glaber forest,C.axillaris forest and L.glaber-C.glauca forest,the annual throughfall of 2016 respectively was 833.42mm,900.52mm,622.68mm;the proportion of throughfall were 45.78%,47.82%,33.07%.The highest ability of rainfall interception was the L.glaber-C.glauca forest.2.Throughfall was in a very significant linear relationship with the rainfall(P<0.001).The fitting coefficient(R2)were more than 0.90,and the minimum rainfall(TFo)of three secondary forests that forming the throughfall is C.axillaris,(0.92mm)<P.massoniana-L.glaber(1.50mm)<L.glaber-C.glauca(2.19mm).As the rainfall increases,the throughfall proportion increases exponentially.But throughfall proportion would tend to be gentle and maintain at a stable level when the rainfall continuously increase.The rainfall proportion of each forest increased with the increase of rainfall level and rainfall intensity.3.There were significant negative correlations between leaf area index,canopy coverage and throughfall(proportion).With the leaf area index and canopy coverage increasing,the throughfall(proportion)declining linearly.But the regularity of distribution of the canopy width and throughfall(proportion)is not obvious,the linear regression can not be a great description of the relationship.4.The effect of soil moisture under different rainfall class is complicated.The general regularity is that with the increase of rainfall,the soil moisture of each soil layer will increase.Comparison with the stand scale,the Soil moisture of P.massoniana-L.glaber is response more sensitive to rainfall,while L.glaber-C.glauca has the least variation in soil moisture caused by rainfall.Comparison with the longitudinal of soil depth,the response regularity of soil moisture for each layer to rainfall in L.glaber-C.glauca is significantly different from P.massoniana-L.glaber,C.axillaris.It shows that evergreen broad-leaved forest has a strong control mechanism for the conservation and utilization of water as a succession top community in subtropical regions.5.Throughfall impacted soil moisture directly.With the increase of throughfall,the soil moisture shows an increasing trend.The intensity response of soil moisture decrease gradually and maintain at a stable level when the throughfall continuously increase.In the three types of secondary forests,the largest change range of soil moisture which caused by the change of throughfall is the P.massoniana-L.glaber forest,the smallest is the C.axillaris forest.It can be concluded that the regulation ability of P.massoniana-L.glaber forest is weak,while L.glaber-C.glauca forest has better ability of water regulation and conservation.