A Dynamic Global Vegetation Model (DGVM) is a computer program that simulates shifts in potential vegetation and its associated biogeochemical and hydrological cycles as a response to shifts in climate. DGVMs use time series of climate data and, given constraints of latitude, topography, and soil characteristics, simulate monthly or daily dynamics of ecosystem processes. DGVMs are used most often to simulate the effects of future climate change on natural vegetation and its carbon and water cycles.
DGVMs generally combine biogeochemistry, biogeography, and disturbance submodels. Disturbance is often limited to wildfires, but in principle could include any of: forest/land management decisions, windthrow, insect damage, ozone damage etc. DGVMs usually "spin up" their simulations from bare ground to "equilibrium" vegetation to establish realistic initial values for their various "pools": carbon and nitrogen in live and dead vegetation, soil organic matter, etc. corresponding to a documented historical vegetation cover.
DGVMs are usually run in a spatially distributed mode, with simulations carried out for thousands of "cells", geographic points which are assumed to have homogeneous conditions within each cell. Simulations are carried out across a range of spatial scales, from global to landscape. Cells are usually arranged as lattice points; the distance between adjacent lattice points may be as coarse as a few degrees of latitude or longitude, or as fine as 30 arc-seconds. Simulations of the conterminous United States in the first DGVM comparison exercise (LPJ and MC1) called the VEMAP project in the 1990s used a lattice grain of one-half degree. Global simulations by the PIK group and collaborators using 6 different DGVMs (HYBRID, IBIS, LPJ, SDGVM, TRIFFID, and VECODE) used the same resolution as the general circulation model (GCM) that provided the climate data, 3.75 deg longitude x 2.5 deg latitude, a total of 1631 land grid cells. Sometimes lattice distances are specified in kilometers rather than angular measure, especially for finer grains, so a project like VEMAP is often referred to as 50 km grain.
Several DGVMs appeared in the middle 1990s. The first was apparently IBIS (Foley et al., 1996), VECODE (Brovkin et al., 1997), followed by several others described below:
Several DGVMs have been developed by various research groups around the world:
- LPJ - Germany, Sweden
- IBIS - Integrated Biosphere Simulator - U.S.
- MC1 - U.S.
- HYBRID - U.K.
- SDGVM - U.K.
- SEIB-DGVM - Japan
- TRIFFID - U.K.
- VECODE - Germany
- CLM-DVGM - U.S.
- LANDIS II - U.S.
The next generation of models - earth system models (ex. CCSM, ORCHIDEE, JULES, CTEM ) - now includes the important feedbacks from the biosphere to the atmosphere so that vegetation shifts and changes in the carbon and hydrological cycles affect the climate.
LANDIS II, Forest LANdscape DIsturbance and Succession (LANDIS) -II (Scheller et al. 2007) simulates forest succession and disturbances. LANDIS-II builds upon and preserves the functionality of previous LANDIS forest landscape simulation models. LANDIS-II is distinguished by the inclusion of variable time steps for different ecological processes; use of a rigorous development and testing process used by software engineers; including a flexible, open architecture.
DGVMs commonly simulate a variety of plant and soil physiological processes. The processes simulated by various DGVMs are summarized in the table below. Abbreviations are: NPP, net primary production; PFT, plant functional type; SAW, soil available water; LAI, leaf area index; I, solar radiation; T, air temperature; Wr, root zone water supply; PET, potential evapotranspiration; vegc, total live vegetation carbon.
| process/attribute | formulation/value | DGVMs |
|---|---|---|
| shortest time step | 1 hour | IBIS |
| 2 hours | TRIFFID | |
| 12 hours | HYBRID | |
| 1 day | LPJ, LANDIS II, SDGVM, SEIB-DGVM, MC1 fire submodel | |
| 1 month | MC1 except fire submodel | |
| 1 year | VECODE | |
| photosynthesis | Farquhar et al. (1980) | HYBRID |
| Farquhar et al. (1980) Collatz et al. (1992) |
IBIS, LPJ, SDGVM | |
| Collatz et al. (1991) Collatz et al. (1992) |
TRIFFID | |
| stomatal conductance | Jarvis (1976) Stewart (1988) |
HYBRID |
| Leuning (1995) | IBIS, SDGVM, SEIB-DGVM | |
| Haxeltine & Prentice (1996) | LPJ | |
| Cox et al. (1998) | TRIFFID | |
| production | forest NPP = f(PFT, vegc, T, SAW, P, ...) grass NPP = f(PFT, vegc, T, SAW, P, light competition, ...) |
MC1 |
| GPP = f(I, LAI, T, Wr, PET, CO2) | LPJ | |
| competition | for light, water, and N | MC1, HYBRID |
| for light and water | LPJ, IBIS, SDGVM, SEIB-DGVM | |
| Lotka-Volterra in fractional cover | TRIFFID | |
| Climate-dependent | VECODE, LANDIS II | |
| establishment | All PFTs establish uniformly as small individuals | HYBRID |
| Climatically favored PFTs establish uniformly, as small individuals | SEIB-DGVM | |
| Climatically favored PFTs establish uniformly, as small LAI increment | IBIS | |
| Climatically favored PFTs establish in proportion to area available, as small individuals | LPJ, SDGVM | |
| Minimum 'seed' fraction for all PFTs | TRIFFID | |
| mortality | Dependent on carbon pools | HYBRID |
| Deterministic baseline, wind throw, fire, extreme temperatures | IBIS, LANDIS II | |
| Deterministic baseline, self-thinning, carbon balance, fire, extreme temperatures | LPJ, SEIB-DGVM, LANDIS II | |
| Carbon balance, wind throw, fire, extreme temperatures | SDGVM, LANDIS II | |
| Prescribed disturbance rate for each PFT | TRIFFID | |
| Climate-dependent, based on carbon balance | VECODE, LANDIS II | |
| Self-thinning, fire, extreme temperatures, drought | MC1, LANDIS II |
References:
Famous quotes containing the words dynamic, global, vegetation and/or model:
“We Americans have the chance to become someday a nation in which all radical stocks and classes can exist in their own selfhoods, but meet on a basis of respect and equality and live together, socially, economically, and politically. We can become a dynamic equilibrium, a harmony of many different elements, in which the whole will be greater than all its parts and greater than any society the world has seen before. It can still happen.”
—Shirley Chisholm (b. 1924)
“However global I strove to become in my thinking over the past twenty years, my sons kept me rooted to an utterly pedestrian view, intimately involved with the most inspiring and fractious passages in human development. However unconsciously by now, motherhood informs every thought I have, influencing everything I do. More than any other part of my life, being a mother taught me what it means to be human.”
—Mary Kay Blakely (20th century)
“We love to see any redness in the vegetation of the temperate zone. It is the color of colors. This plant speaks to our blood.... What a perfect maturity it arrives at! It is the emblem of a successful life concluded by a death not premature, which is an ornament to Nature. What if we were to mature as perfectly, root and branch, glowing in the midst of our decay, like the poke!”
—Henry David Thoreau (1817–1862)
“...that absolutely everything beloved and cherished of the bourgeoisie, the conservative, the cowardly, and the impotent—the State, family life, secular art and science—was consciously or unconsciously hostile to the religious idea, to the Church, whose innate tendency and permanent aim was the dissolution of all existing worldly orders, and the reconstitution of society after the model of the ideal, the communistic City of God.”
—Thomas Mann (1875–1955)