The Study Of Forest Canopy Structure And Photosynthesis In Subtropical Evergreen Broad-leaved Forest Communities

There are almost 40% of all terrestrial species lives in the forest canopy layer. The study of forest canopy is of great significance for global atmospheric CO2 increasing, global warming, global land use change, terrestrial carbon sequestration and biodiversity conservation. The structure and function of forest canopy is essential and also is important to forest ecosystem study. Most of the world's subtropical evergreen broad-leaved forest (EBLF) is distributed in China. As the typical zonal vegetation type, it is also one of the largest vegetation types in China. In this thesis, field experiments and one-year in situ observations were done in different evergreen broad-leaved forest community in various successional stage in Tiantong National Forest Park to quantitatively describe the canopy structure, micrometeorological factors dynamic and photosynthesis. The main findings are as followed:(1). In the typical growing season of July and August, the canopy layer openness is between 11.5% and 13.5%, the mean leaf angle (MLA) ranges from 14.5 to 16.0 for different successional communities. The leaf area index (LAI) of arbor canopy layer is increased with the successional progress, but there are no significant differences between them. The LAI is 2.2 - 2.5. The LAI of the understory shrub layer, which is opposite to that of the arbor layer, is less than 1.5 except that of the LAI is about 2.8 in shrub community, an earlier successional stage.(2). The canopy layer LAI increases with the time in growing season and reaches the maximum value in the summer. The value of LAI reanges from 1.9 to 2.5 but with no significant seasonal difference for each successional stage. The seasonal change of the canopy layer openness which is opposite to that trend of canopy layer LAI, is very significant. The value changes from 10% to 15%.(3). The [CO2] of shrub layer in each successional community is 370-380μmol/mol in Tiantong evergreen broad-leaved forest; The photosynthetically active radiation (PAR) and relative humidity (RH) of shrub layer are less than that of the over canopy in each community, but a little increase for the temperature. The PAR of shrub layer is less than 14% of that over forest canopy for all the year The temperature below canopy layer increases from 0.1 to 0.3℃than that of over canopy. The RH below canopy layer is just 1.5% less than that of RH over canopy layer.(4). There is negative correlation between the openness and the canopy layer LAI and temperature in C. fargesii community. While the canopy layer LAI is positively correlated with temperature below canopy and PAR. But there is no significant correlationship between RH below canopy and canopy structure. In sunny and cloudless conditions, the accuracy of simulated PAR over canopy by ground-based optical instrument can reach upto 98%, the accurate simulation of seasonal PAR still need to adjust with in situ meteorological data. But the accuracy of simulated PAR under canopy is still inaccurate and need further improvement(5). The net photosynthetic rate (Pn) of shrub canopy layer in each successional community is between 1.4 and 5.0μmol CO2 /m2 s. The Pn in arboreal canopy layer is less than 1.0μmol CO2 /m2 s in the Secondary Shrub community; the Pn for the other communities are all can reach 7.0μmol CO2 /m2 s. The Pn of arboreal canopy layer increased gradually with the successional progress and eventually tend to stable condition. The Pn of shrub canopy layer increased first, then decreased and finally increased again. The Pn of shrub canopy layer and arbor canopy layer in each community are significantly correlated with the micrometeorological factor such as T, [CO2], RH and PAR respectively.