RED DGVM: simple approach to modelling vegetation with novel implications.

Arthur Argles,Peter Cox,Jonathan Moore

doi:10.5194/egusphere-egu2020-16276

Abstract

&lt;p&gt;The modelled global vegetation for the end of the 21st century is currently is insufficiently constrained&lt;br&gt;by climate models. A significant proportion of that uncertainty has been attributed to the limitations&lt;br&gt;of current Dynamic Global Vegetation Models (DGVMs), and the misrepresentation of mortality, dis-&lt;br&gt;turbance and regrowth within forests. Improving the simulation of the underlying processes of de-&lt;br&gt;mographic change is of primary importance in the development of predictors of future climate.&lt;/p&gt;&lt;p&gt;Here we present the Robust Ecosystem Demography (RED), a new dynamical vegetation model which&lt;br&gt;simulates the size-structure of forests by partitioning the population of a Plant Functional Type (PFT)&lt;br&gt;into mass classes. Allometric scaling of mortality and growth across mass classes allows for a variety&lt;br&gt;of complex demographic processes to be captured, such as disturbances and regrowth. Competition&lt;br&gt;among PFTs is done purely through restricting the recruitment of new vegetation to unshaded space.&lt;br&gt;RED represents a reduction of complexity from more numerically unwieldy cohort DGVMs which&lt;br&gt;simulate both size and patch dimensions. The limited number of dimensions and simple competitive&lt;br&gt;regime allows the equilibrium state to be solved for analytically, providing two potential functions - (i)&lt;br&gt;Avoiding-spinning up by providing an equilibrium state for intilisation. (ii) Insights into the demog-&lt;br&gt;raphy of vegetated areas, arising from parameter tuning to fit observation, such as coverage or carbon&lt;br&gt;mass. When paired with a rate of mortality or carbon assimilate rate gives, respectfully, required as-&lt;br&gt;similate or mortality rates.&lt;br&gt;We demonstrate the model functionality using offline UKESM PFT carbon assimilate rates, paired&lt;br&gt;with observed vegetation cover from the ESA LC_CCI datasets for the 9 different PFTs. From this&lt;br&gt;dataset we calibrate a novel global equilibrium mortality map for each PFT and show the competitive&lt;br&gt;and successional behaviour of dynamical runs with convergence to the fitted equilibrium. Finally, we&lt;br&gt;explore underlying ecological questions that emerge from the equilibrium solutions.&lt;/p&gt;

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