Modeling the Vegetation Dynamics of Northern Shrubs and Mosses in the ORCHIDEE Land Surface Model

Abstract

Parameterizations of plant competition processes involving shrubs, mosses, grasses, and trees were introduced with the recently implemented shrubs and mosses plant functional types in the ORCHIDEE dynamic global vegetation model in order to improve the representation of high latitude vegetation dynamics. Competition is based on light capture for growth, net primary productivity, and survival to cold-induced mortality during winter. Trees are assumed to outcompete shrubs and grasses for light, and shrubs outcompete grasses. Shrubs are modeled to have a higher survival than trees to extremely cold winters because of thermic protection by snow. The fractional coverage of each plant type is based on their respective net primary productivity and winter mortality of trees and shrubs. Gridded simulations were carried out for the historical period and the 21st century following the RCP4.5 and 8.5 scenarios. We evaluate the simulated present-day vegetation with an observation-based distribution map and literature data of boreal shrubs. The simulation produces a realistic present-day boreal vegetation distribution, with shrubs, mosses north of trees and grasses. Nevertheless, the model underestimated local shrub expansion compared to observations from selected sites in the Arctic during the last 30 years suggesting missing processes (nutrients and microscale effects). The RCP4.5 and RCP8.5 projections show a substantial decrease of bare soil, an increase in tree and moss cover and an increase of shrub net primary productivity. Finally, the impact of new vegetation types and associated processes is discussed in the context of climate feedbacks.Plain Language Summary Changes in the northern vegetation exert feedbacks on climate through surface energy and greenhouse gas fluxes. For example, increased vegetation cover can lead to warming due to stronger absorption of shortwave radiation (through decreased albedo). In this study we developed a new version of the ORCHIDEE dynamic vegetation model, allowing us to simulate the dynamical cover of mosses and shrubs, two important types of northern vegetation, alongside with grasses and trees. The prevalence of the different forms of vegetation is ruled by light capture during the growing season, mortality during the cold conditions, and competition for space. The new model is tested for present-day land cover and used for future climate projections. We simulated a realistic vegetation map for historical simulations and a substantial decrease of bare soil with shifts of vegetation in future simulations. However, the model underestimated local shrub expansion compared to observations.

Reply to Reviewer 1

“…Understanding how ecosystem functioning interacts with changing environmental conditions is a crucial yet challenging problem of Earth system research for high latitude/altitude regions and deserves further attention. Land surface models, terrestrial biosphere models, ecohydrology models, and hydrological models have been widely utilized to enhance our knowledge in terms of land surface processes, ecohydrological processes (Fatichi et al, 2016a;Fisher et al, 2014), and freezing/thawing process (Cuntz and Haverd, 2018;Druel et al, 2019;Ekici et al, 2014;Wang and Yang, 2018;Wang et al, 2017b). For instance, Zhuang et al (2001) incorporated a permafrost model into a large scale ecosystem model to investigate soil thermal temporal dynamics.…”

On Integrating Size and Shape Distributions into a Spatio-Temporal Information Entropy Framework

“…The PsishENT framework offering a range of analyses based on entropy decomposition to highlight spatio-temporal information structuring, the purpose of this example is to show the most simple and illustrative aspects and its flexibility. The data comes from a climate simulation using a Land Surface Model (LSM) predicting the plant functional types (pfts) between 2014 and 2100 [33]. Plant functional types describe the vegetation that constitutes the land cover, e.g., boreal broadleaf shrubs, C3 grass.…”

“…So, the data used here corresponds to a compositional data. The full list of pfts used in the LSM ORCHIDEE (ORganizing Carbon and Hydrology in Dynamic EcosystEms), with the version ORCHIDEE_HLveg [33,35] is given in Appendix. Note that 'bare ground' is also taken as a pft.…”

The role of vadose zone physics in the ecohydrological response of a Tibetan meadow to freeze–thaw cycles

“…Land surface models, terrestrial biosphere models, ecohydrology models, and hydrological models have been widely utilized to enhance our knowledge in terms of land surface processes, ecohydrological processes (Fatichi and Ivanov, 2014;Fisher et al, 2014;Fatichi et al, 2016a), and freezing and thawing (FT) processes (Ekici et al, 2014;Wang et al, 2017;Cuntz and Haverd, 2018;Wang and Yang, 2018;Druel et al, 2019). By either incorporating a permafrost model into L. Yu et al: Role of vadose zone physics in cold region ecosystem functioning the ecosystem model (Zhuang et al, 2001;Wania et al, 2009;Lyu and Zhuang, 2018) or equipping the soil model with vegetation dynamics and carbon processes (Zhang et al, 2018), the temporal dynamics of soil temperature, permafrost dynamics, and vegetation and carbon dynamics can be simultaneously simulated over cold region ecosystems.…”