Light environment simulation and biomass estimation of Cunninghamia lanceolata stand canopy

The study aimed to investigate the light interception of Chinese fir (Cunninghamia lanceolata) stands under different density patterns, and further estimate their biomass accumulation, so as to provide scientific references for the design and management of C. lanceolata plantation.

The plant modeling method and virtual geographic environment technology were used to construct the 3D stand scene, and stand density was applied as the indicator to design different stand models. The photosynthetically active radiation and shadow area of each stand were simulated and calculated by the astronomical algorithm and radiosity model to evaluate the shade of the stand. Then the average net photosynthetic rate was estimated using the non-rectangular hyperbolic photosynthetic model and converted to biomass accumulation to evaluate the productive potential of each stand mode.

1) The light interception of stands with different densities increased with the increase of light intensity. The maximum PAR of the 1.5 m×1.5 m, 2.0 m×2.0 m and 2.5 m×2.5 m stands was 1 577.52, 1 568.68 and 1 546.08 μmol·m^-2·s^-1, respectively. 2) Under the 2.5 m×2.5 m stand pattern, the proportion of sunshine leaf area at each time was the largest, with an average value of 0.92. 3) In the horizontal structure, the radiation intensity increased from northwest to southeast. In the vertical structure, with the decrease of stand density, the proportion of sunshine leaf area of each layer increased gradually. 4) The photosynthetic rate of the sunshine leaves was much higher than that of the shaded leaves, with a maximum value of 9.79 μmol·m^-2·s^-1, while the shaded leaves were all less than 0.7 μmol·m^-2·s^-1. 5) Based on the net photosynthetic rate, the biomass production of different stand modes at each time was estimated. The daily biomass accumulation of each stand mode was 17.54, 17.10 and 15.93 kg, respectively.

According to the light interception and distribution of the stands under each planting mode, it can be seen that stands with high LAI have a stronger light interception ability, but the distribution is more clustered, causing relatively fewer actual sunshine leaf areas. When the stand density is low, the light environment within the stand canopy is improved. According to the proportion of sunshine leaf area and biomass accumulation of each stand mode, 2.0 m×2.0 m was considered to be the optimal planting mode. The research results can provide some scientific references for the planting management of C. lanceolata stands.