Simulating boreal forest dynamics from perspectives of ecophysiology, resource availability, and climate change

Supplementary information

Takeshi Ise and Paul R. Moorcroft

Model description

Leaf-level fluxes of carbon and water

The physiology sub-model provides values for the C flux per unit leaf area (µmol C m-2 s-1) when plants are not limited by below-ground resources, Ao(z,x,y,t), and when stomates are closed Ac(z,x,y,t), and the associated evaporative water loss per unit leaf area Ψ(z,x,y,t) in µmol H2O m-2 s-1, based on the analysis by Farquhar and Sharkey (1982). Our implementation closely follows that of Foley et al. (1996). The equation for Ao and Ac of C3 photosynthesis is:

(A1)

(A2)

where L is the absorbed photosynthetically active radiation (µmol photons m-2 s-1). Ci is the within-leaf concentration of CO2 (mol mol-1), α is the quantum efficiency (µmol photons m-2 s-1, 0.08 for C3 plants), K1 and K2 are temperature dependence factors, Vm is the maximum photosynthetic rate (µmol C m-2 s-1), and Γ is the CO2 compensation point (mol mol-1). Leaf respiration is proportional to Vm with γ = 0.02. Unless otherwise stated, we use functional forms and parameter values from Foley et al. (1996) and Moorcroft et al. (2001). Stomatal conductance cs (µmol H2O m-2 s-1) is given as:

(A3)

where M and b are the slope and intercept of the linear relation between cs and Ao (M = 8.0 for C3 plants; b = 0.01 is cuticular conductance). Ds is the difference between the model fractions of water vapor in air inside and outside the leaf and Do = 0.01 is a reference value (mol mol-1). Then, a simple one-dimensional diffusion model implies:

(A4)

Mortality

The total mortality of plants is calculated as the sum of two terms:

(A5)

The first component is an individual’s density-independent mortality rate μDI (yr-1) which is a linear function of its wood density (g/cm3):

(A6)

where is the wood density of the late successional functional type (Uhl and Jordan 1984). The second mortality component is an individual’s density-dependent mortality rate μDD (yr-1), which depends on the plant’s current net C production (NPP, kgC tree-1 month-1) relative to what it would be in full sun (NPPFS):

(A7)

Model initialization

BOREAS TE-13 (Apps and Halliwell 1999) report soil chemical compositions of 3 flux tower sites and 26 auxiliary sites in northern Manitoba. For this study, soil C and N densities of 3 representative soil types, loam, sand, and clay, are calculated to reproduce initial site-specific soil conditions. The initial soil mineralized N was 221, 106, and 70 gN m-2, respectively, and the initial soil organic C was 29.8, 5.8 and 64.0 kgC m-2, respectively.

References

Apps, M. J., & Halliwell, D. 1999. BOREAS TE-13 biometry reports. Data set (Available online [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, TN).

Farquhar, G. D., & Sharkey, T. D. 1982. Stomatal conductance and photosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology, 33, 317-345.

Foley, J. A., Prentice, I. C., Ramankutty, N., et al. 1996. An integrated biosphere model of land surface processes, terrestrial carbon balance, and vegetation dynamics. Global Biogeochemical Cycles, 10, 603-628.

Moorcroft, P.R., Hurtt, G.C., Pacala, S.W., 2001. A method for scaling vegetation dynamics: the ecosystem demography model (ED). Ecological Monographs, 71, 557-585.
Supplementary figure 2. Relative dominance of black spruce (Picea mariana) at simulation year 50. (a) 2005 condition. (b) 2100 condition. In this relatively early stage of succession, black spruce dominates wet and nutrient-poor areas. Mesic areas and sandy areas are mainly dominated by earlier successional species (i.e., trembling aspen and jack pine, respectively). The changes in temperature, precipitation, and atmospheric CO2 concentration somewhat altered the relative dominance of black spruce, especially in the western part of the study region. Due mainly to CO2 fertilization effect on nutrient-rich areas, the fast-growing, earlier successional species grew preferentially over the slow-growing black spruce.