(1) MODEL AND VERSION
Full model name
a) PnET v3.0
A unified model consolidating three earlier models, PnET-II, PnET-Day and PnET-CN, which function as nested modules. (Note: Only PnET-II was used in this study)
Host institution
Complex Systems Research Center, University of New Hampshire
Key references
a) PnET (original):
Aber JD, Federer CA (1992) A generalized, lumped-parameter model of photosynthesis, evapotranspiration and net primary production in temperate and boreal forest ecosystems. Oecologia 92: 463-474
b) PnET-II:
Aber JD, Ollinger SV, Federer CA, et al. (1995) Predicting the effects of climate change on water yield and forest production in the northeastern U.S. Climate Res. 5: 207-222
c) PnET-Day:
Aber JD, Reich PB, Goulden ML (1996) Extrapolating leaf CO2 exchange to the canopy: a generalized model of forest photosynthesis compared with measurements by eddy correlation. Oecologia 106: 257-265
d) PnET-CN:
Aber JD, Ollinger SV, Driscoll CT (1996) Modeling nitrogen saturation in forest ecosystems in response to land use and atmospheric deposition. Ecological Modeling 101: 61-78
(2) MODEL TYPE (E.G. ECOSYSTEM, BIOGEOGRAPHY, DGVM)
Ecosystem (biogeochemical)
(3) PRIMARY MODEL PURPOSE
Daily and monthly time-step modeling of carbon, nitrogen and water balances in forest ecosystems.
(4) MODELING APPROACH
The lumped-parameter model is built on two principle relationships:
(1) Maximum photosynthetic rate is a function of foliar N concentration.
(2) Stomatal conductance is a function of realized photosynthetic rate.
Leaf area display and C, N, O3 and H2O are predicted by combining the above relationships with standard equations describing light attenuation in canopies and photosynthetic response to diminishing radiation intensity, along with the effects of soil water stress and vapor pressure deficit.
PnET is designed to require no calibrated parameters.
(5) RESOLUTION (SPACIA, TEMORAL)
Spatial: Plot to regional scale. No adjacency effects (ie. runs an isolated instance for every pixel).
Temporal: Daily or monthly time steps.
(6) SPATIAL AND TEMPORAL SCALE(S) AT WHICH THE MODEL RESULTS SHOULD BE CONSIDERED
Same as above.
(7)PROCESSES AND PROCESS COMPONENTS SIMULATED (E.G. CARBON: GPP, NPP, NEP)
Carbon:
Gross photosynthesis, net photosynthesis, net primary productivity (for foliage, wood and roots), litter pool, soil organic matter (for one 15 yr compartment).
Water:
a) Soils (simple bucket, saturated/unsaturated flow, controls on water movement through the profile, etc.): Simple bucket
b) Energy balance: (e.g. latent, sensible heat, aet, pet): AET and PET calculated from biologic controls.
c) Snow: Snow melt and partial precipitation.
d) 'Order' of water balance: (e.g. incoming water is first evaporated from plant/soil surface, then infiltration, transpiration, runoff) PnET uses the above ordering exactly.
Nitrogen:
Complete N cycle: N included in every biomass pool and tied to hydrologic flux (ie. N leaching is calculated), mineralization and nitrification, N deposition.
(8) SIMULATED RESERVOIR
Carbon:
a) Vegetation: Foliage, wood and roots.
b) Litter: Combined with soil organic matter pool.
c) SOC: Combined with soil organic matter pool.
Nitrogen:
a) Vegetation: Foliage, wood and roots.
b) Litter:Combined with soil organic matter pool.
c) SON: Combined with soil organic matter pool.
Soil water: Single reservoir.
(9) CALIBRATION VARIABLE(S) AND METHOD:
None.
(10) SCALING OF THE PROCESSES TO THE GRID CELL
Grid cell aggregated parameters are used. If there is are mixed vegetation types within the grid cell a weighted average of the parameters are used.
(11) DISTURBANCE: (FIRE, GRAZING, HARVEST, TREE REMOVAL, ETC.)
All of the above and additionally N deposition, agriculture and fertilization.
(12) VEGETATION I/O: (E.G. POTENTIAL, ACTUAL)
Both potential and actual vegetation but as input only.
(13) INPUT DRIVERS (CLIMATE, SITE, VEG, SOILS) AND RESOLUTION (E.G. DAILY, MONTHLY) REQUIRED FOR MODEL INITIALIZATION:
Climate (daily or monthly): Maximum temperature, minimum temperature, precipitation, and radiation.
Site: Water holding capacity and latitude.
Vegetation: Physiologic group (deciduous, coniferous, grassland, etc.)
Soils: Water holding capacity.
(14) ADDITIONAL COMMENTS:
Nitrogen cycling module (PnET-CN) requires disturbance history.