Anne Quillet

Toward dynamic global vegetation models for simulating vegetation-climate interactions and feedbacks: recent developments, limitations, and future challenges.

There is a lack in representation of biosphere-atmosphere interactions in current climate models. To fill this gap, one may introduce vegetation dynamics in surface transfer schemes or couple global climate models (GCMs) with vegetation dynamics models. As these vegetation dynamics models were not designed to be included in GCMs, how are the latest generation dynamic global vegetation models (DGVMs) suitable for use in global climate studies? This paper re- views the latest developments in DGVM modelling as well as the development of DGVM-GCM coupling in the frame- work of global climate studies. Limitations of DGVM and coupling are shown and the challenges of these methods are highlighted. During the last decade, DGVMs underwent major changes in the representation of physical and biogeochemi- cal mechanisms such as photosynthesis and respiration processes as well as in the representation of regional properties of vegetation. However, several limitations such as carbon and nitrogen cycles, competition, land-use and land-use changes, and disturbances have been identified. In addition, recent advances in model coupling techniques allow the simulation of the vegetation-atmosphere interactions in GCMs with the help of DGVMs. Though DGVMs represent a good alternative to investigate vegetation-atmosphere interactions at a large scale, some weaknesses in evaluation methodology and model design need to be further investigated to improve the results.

Wetland chronosequence as a model of peatland development: Vegetation succession, peat and carbon accumulation

Model validation experiments are fundamental to ensure that the peat growth models correspond with the diversity in nature. We evaluated the Holocene Peatland Model (HPM) simulation against the field observations from a chronosequence of peatlands and peat core data. The ongoing primary peatland formation on the isostatically rising coast of Finland offered us an exceptional opportunity to study the peatland succession along a spatial continuum and to compare it with the past succession revealed by vertical peat sequences. The current vegetation assemblages, from the seashore to a 3000 year old bog, formed a continuum from minerotrophic to ombrotrophic plant communities. A similar sequence of plant communities was found in the palaeovegetation. The distribution of plant functional types was related to peat thickness and water-table depth (WTD) supporting the assumptions in HPM, though there were some differences between the field data and HPM. Palaeobotanical evidence from the oldest site showed a rapid fen–bog transition, indicated by a coincidental decrease in minerotrophic plant functional types and an increase in ombrotrophic plant functional types. The long-term mean rate of carbon (C) accumulation varied from 2 to 34 g C/m2 per yr, being highest in the intermediate age cohorts. Mean nitrogen (N) accumulation varied from 0.1 to 3.9 g N/m2 per yr being highest in the youngest sites. WTD was the deepest in the oldest sites and its variation there was temporally the least but spatially the highest. Evaluation of the HPM simulations against the field observations indicated that HPM reasonably well simulates peatland development, except for very young peatlands.

The role of hydrogeological setting in two Canadian peatlands investigated through 2D steady-state groundwater flow modelling

ABSTRACT This study investigated how hydrogeological setting influences aquifer–peatland connections in slope and basin peatlands. Steady-state groundwater flow was simulated using Modflow on 2D transects for an esker slope peatland and for a basin peatland in southern Quebec (Canada). Simulations investigated how hydraulic heads and groundwater flow exported toward runoff from the peatland can be influenced by recharge, hydraulic properties, and heterogeneity. The slope peatland model was strongly dominated by horizontal flow from the esker. This suggests that slope peatlands are dependent on the hydrogeological conditions of the adjacent aquifer reservoir, but are resilient to hydrological changes. The basin peatland produced groundwater outflow to the surface aquifer. Lateral and vertical peat heterogeneity due to peat decomposition or compaction were identified as having a significant influence on fluxes. These results suggest that basin peatlands are more dependent on recharge conditions, and could be more susceptible to land use and climate changes.