title: Assessing uncertainties in a second-generation dynamic vegetation model caused by ecological scale limitations.
abstract: *Second-generation Dynamic Global Vegetation Models (DGVMs) have recently been developed that explicitly represent the ecological dynamics of disturbance, vertical competition for light, and succession. Here, we introduce a modified second-generation DGVM and examine how the representation of demographic processes operating at two-dimensional spatial scales not represented by these models can influence predicted community structure, and responses of ecosystems to climate change. *The key demographic processes we investigated were seed advection, seed mixing, sapling survival, competitive exclusion and plant mortality. We varied these parameters in the context of a simulated Amazon rainforest ecosystem containing seven plant functional types (PFTs) that varied along a trade-off surface between growth and the risk of starvation induced mortality. *Varying the five unconstrained parameters generated community structures ranging from monocultures to equal co-dominance of the seven PFTs. When exposed to a climate change scenario, the competing impacts of CO(2) fertilization and increasing plant mortality caused ecosystem biomass to diverge substantially between simulations, with mid-21st century biomass predictions ranging from 1.5 to 27.0 kg C m(-2). *Filtering the results using contemporary observation ranges of biomass, leaf area index (LAI), gross primary productivity (GPP) and net primary productivity (NPP) did not substantially constrain the potential outcomes. We conclude that demographic processes represent a large source of uncertainty in DGVM predictions.
authors.affiliation: Earth and Environmental Science Division, Los Alamos National Laboratory, Los Alamos, NM, USA. rosieafisher@gmail.com
authors.forename: Rosie
authors.initials: R
authors.lastname: Fisher
authors.forename: Nate
authors.initials: N
authors.lastname: McDowell
authors.forename: Drew
authors.initials: D
authors.lastname: Purves
authors.forename: Paul
authors.initials: P
authors.lastname: Moorcroft
authors.forename: Stephen
authors.initials: S
authors.lastname: Sitch
authors.forename: Peter
authors.initials: P
authors.lastname: Cox
authors.forename: Chris
authors.initials: C
authors.lastname: Huntingford
authors.forename: Patrick
authors.initials: P
authors.lastname: Meir
authors.forename: F Ian
authors.initials: FI
authors.lastname: Woodward
mesh_terms: D018533:Biomass; D057231:Climate Change; D003198:Computer Simulation; D017753:Ecosystem; D008954:Models, Biological; D063245:Plant Development; D018515:Plant Leaves / Q000033:anatomy & histology; D018521:Plant Physiological Phenomena; D011157:Population Dynamics; D035501:Uncertainty