Study On Canopy Interception Characteristics And Model Simulation Of Subtropical Secondary Forest

Forests are a major component of the Earth,s ecosystem,and canopy interception plays a key role in forest hydrological processes and forest ecosystem services.The branches and leaves of forest canopy interception of precipitation,reduced rainfall directly landing on soil erosion,thus reducing the loss of nutrients in the soil,in addition to the forest is the effective measure to protect the soil,forest also has a positive hydrological and chemical effects,such as the regulation of water storage,water flow and water quality,flood and flood prevention.During the whole year from May 2017 to April 2018,this paper studied three typical secondary forests in the subtropical region:Coniferous and deciduous mixed forest(Pinus.massoniana-Lithocarpus.glaber),Deciduous broad leaved forest(Choeros-pondias.axillaris)and evergreen broad leaved forest(Lithocarpus.glaber-Cyclobalanopsis.glauca)as the research object,the aim was to compare the differences between the three kinds of secondary forest canopy intercept and variation characteristics,and discusses characteristics of atmospheric precipitation effect on regulating the interception by canopy and canopy structure,and the interception by canopy model simulation,for quantitative evaluation of subtropical forest water conservation and provide a scientific basis for ecological benefits.The main results are as follows:(1)The rainfall intensity increased and the frequency of rainfall outside the forest decreased.There was a negative correlation between the two.The rainfall outside the forest was positively correlated with the rainfall intensity.The higher the rainfall intensity,the greater the rainfall outside the forest.The higher the rainfall level,the rain outside the forest.The frequency of occurrence decreases,and the two are negatively correlated.During the study period,a total of 132 rainfall events were recorded with a cumulative rainfall of 1398.5 mm.The rainfall is mainly concentrated in May-June,with a cumulative rainfall of 733 mm,accounting for 52.75%of the annual rainfall.The annual rainfall events were mainly light rain(<10 mm),accounting for 74%of the annual rainfall events,and the cumulative rainfall was only 15%of the total annual rainfall.The rainfall intensity<0.5 mm/h occurred 77 times,the highest frequency,accounting for 58.33%of the total number of times in the year.The accumulated rainfall was only 137.4 mm,accounting for 9.82%of the annual rainfall.(2)There was a significant positive correlation between the penetrating rainfall of the three secondary forests and the rainfall outside the forest,which increased with the increase of rainfall outside the forest.The stemflow amount and stemflow rate were also significantly positively correlated with the rainfall outside the forest,and increased with the increase of rainfall.The penetrating rainfall was recorded as 845.725 mm for Pinus.massoniana-Lithocarpus.glaber,790.825 mm for Choeros-pondias.axillaris and 624.58 mm for Lithocarpus.glaber-Cyclobalanopsis.glauca,and the annual penetration rain rate was 60.47.%,56.55%and 44.66%.The annual stemflow rates were:9.71 mm,22.01 mm,and 15.99 mm,accounting for 0.69%,1.57%,and 1.14%of the annual rainfall.(3)There is a very significant linear relationship between the canopy interception of three secondary forests and the rainfall outside the forest.The canopy interception rate and atmospheric rainfall are a power function relationship.The accumulated forest canopy interception in the whole year is 575.97 mm for Pinus.massoniana-Lithocarpus.glaber,597.408 mm for Choeros-pondias.axillaris,and 764.19 mm for Lithocarpus.glaber-Cyclobalanopsis.glaucay accounting for 41.18%of the annual rainfall,42.72%,54.64%.There were significant differences in canopy interception rates among the three secondary forests.(4)There are obvious seasonal differences in the rainfall distribution of the three secondary forests.In summer,the amount of penetrating rainfall,stem flow and canopy interception are higher than other seasons.(5)There is a positive correlation between the canopy interception rate and the leaf area index of Pinus.massoniana-Lithocarpus.glaber and Lithocarpus.glaber-Cyclobalanopsis.glauca.The R2 is>0.9,and the fitting correlation is high.The canopy of the two stands The rejection rate increases as the leaf area index increases.(6)Gash model to simulate the three kinds of secondary forest were higher than in the amount of interception by canopy interception by canopy quantity actual value.Because the Gash model has certain assumptions,the results obtained from the simulation are generally higher than the actual canopy interception.Gash model is mainly affected by the parameters E and S,Pt and St affected the result of the simulation interception by canopy.