Figure 1.
Conceptual scheme of the functional-structural tree model coupled with soil water balance for Mongolian Scots pines: the seed gives the initial pool of biomass, which is used to build organs (internodes, leaves) and thus the plant architecture.
The seedlings take up water from soil for leaf transpiration and biomass production during each growth cycle. The biomass produced is a product of the amount of water transpired by plant and water-use efficiency (WUE). The biomass is stored in the common pool of reserves and is then distributed among organs, which ends the growth cycle. The plant topology, which deals with the physical connections between plant components, is constructed based on automaton rules at the organ scale. Plant architecture can be constructed by topological and geometric information, which includes the shape, size, orientation and spatial location of the components.
Figure 2.
Flowchart for the functional-structural tree model coupled with soil water balance for Mongolian Scots pines.
The fluxes of the model are computed on two time scales: daily for the plant transpiration and yearly for the processes of biomass production and 3D canopy development. There are interactions and feedbacks between the plant architecture (shoots) and transpiration and water absorption through leaf area index (LAI).
Table 1.
Symbols and description of the main parameters and variables used in the model for Mongolian Scots pine trees growth. Values are given only for parameters. (GU: Growth Unit, PA: Physiological Age).
Figure 3.
Simulation of soil water dynamic in a plot of six-year-old Mongolian Scots pines in 2007.
The growth season for Mongolian Scots pine in 2007 is from 100th to the 280th day. Rainfall, Ks, ETa and Ta represent, respectively, daily precipitation, the simulated values of water-stress coefficient, actual evapotranspiration and actual transpiration. The soil texture is 93.98%±6.00% sand, 5.49%±5.46% silt, and 0.52%±0.55% clay and is uniform through the whole profile (0–300 cm). Maximum effective rooting depth Zr is 1 m, soil water content at field capacity θF is 0.12 m3 m−3 and soil water content at wilting point θW is 0.07 m3 m−3. Trees were planted in 1 m (between-row)×1 m (within-row) spacing in the plot.
Figure 4.
Comparisons between measured and fitted results at organ scale for six-year-old Mongolian Scots pines measured in 2007.
(a) Internode fresh biomass, with RMSE = 3.72 g; (b) Internode length, with RMSE = 6.65 cm; (c) Internode diameter, with RMSE = 0.38 cm; (d) Needle biomass, with RMSE = 0.47 g; (e) Total fresh biomass of different PA (including internodes and needles), with RMSE = 10.80 g. PA1, PA2, PA3 and PA4 represent, respectively, trunk, first-order branch, second-order branch and third-order branch; (f) Linear regression between aboveground dry biomass and sum of transpiration estimated (y = 0.48x, R2 = 0.93, p = 0.0001).
Figure 5.
Comparisons between measured and fitted fresh biomass at plant scale for Mongolian Scots pines from one- to six-year old measured in 2007.
(a) Aboveground fresh biomass, with RMSE of 26.8 g; (b) Internodes fresh biomass, with RMSE of 13.0 g; (c) Needles fresh biomass, with RMSE of 18.6 g; (d) Total fresh biomass of different PA(including internodes and needles), with RMSE = 9.4 g. PA1, PA2, PA3 and PA4, represent, respectively, trunk, first-order branch, second-order branch and third-order branch.
Table 2.
Meteorological conditions from 2001 to 2007.
Figure 6.
Comparison of fresh biomass, length, diameter between prediction and observation of three six-year-old pines measured in 2006.
The regression equations between observations and predictions and statistical tests for each indicator are listed as following: (a) Internodes biomass, y = 1.01+0.96x, (R2 = 0.93, p<0.0001, n = 15); (b) Internodes length, y = −4.64+1.20x, (R2 = 0.91, p<0.0001, n = 15); (c) Internodes diameter, y = −0.06+0.94x, (R2 = 0.99, p<0.0001, n = 15); (d) Needles biomass, y = 0.57+1.07x, (R2 = 0.99, p<0.0001, n = 8); (e) Trunk and branches fresh biomass, y = −64.84+1.11x, (R2 = 0.97, p = 0.0168, n = 4); (f) Total fresh biomass, y = 54.46+0.89x, (R2 = 0.86, p = 0.0235, n = 6).
Figure 7.
Comparison between simulated images and taken photo for Mongolian Scots pine.
(a) Visualization of the 3D architecture of a Mongolian Scots pine simulated from one- to six-year old, according to local soil data and meteorological data recorded from 2001 to 2006; (b) A photo of 5-year-old Mongolian Scots pine taken in Nov, 2006.
Figure 8.
Sensitivity analysis of biomass, height and diameter for a six-year-old Mongolian Scots pine when precipitation changes from 50% less than actual to 50% more than actual in 5% steps.
Figure 9.
The simulated 3D canopy architecture of six-year-old trees under three precipitation regimes of 50%, 100% and 150% of actual precipitation.