Abstract
Abstract. Leaf area index (LAI) and its seasonal dynamics are key determinants of vegetation productivity in nature and as represented in terrestrial biosphere models seeking to understand land surface atmosphere flux dynamics and its response to climate change. Non-structural carbohydrates (NSCs) and their seasonal variability are known to play a crucial role in seasonal variation in leaf phenology and growth and functioning of plants. The carbon stored in NSC pools provides a buffer during times when supply and demand of carbon are asynchronous. An example of this role is illustrated when NSCs from previous years are used to initiate leaf onset at the arrival of favourable weather conditions. In this study, we incorporate NSC pools and associated parameterizations of new processes in the modelling framework of the Canadian Land Surface Scheme-Canadian Terrestrial Ecosystem Model (CLASS–CTEM) with an aim to improve the seasonality of simulated LAI. The performance of these new parameterizations is evaluated by comparing simulated LAI and atmosphere–land CO2 fluxes to their observation-based estimates, at three sites characterized by broadleaf cold deciduous trees selected from the FLUXNET database. Results show an improvement in leaf onset and offset times with about 2 weeks shift towards earlier times during the year in better agreement with observations. These improvements in simulated LAI help to improve the simulated seasonal cycle of gross primary productivity (GPP) and as a result simulated net ecosystem productivity (NEP) as well.
Highlights
Biosphere–atmosphere interactions constitute a complex system which plays an important role in the regulation of the climate
We evaluate the performance of the original and modified versions of the CLASS–CTEM framework in simulating leaf phenology at three well-studied sites in the eastern United States, which are selected from the FLUXNET network: (1) Harvard Forest (US-Ha1) located at 42.53◦ N and 72.17◦ W, (2) Morgan–Monroe State Forest (US-MMS) at 39.32◦ N and 86.41◦ W, and (3) the University of Michigan Biological Station (US-UMB) at 45.55◦ N and 84.71◦ W
The CLASS–CTEM model, similar to other land surface schemes implemented in other Earth system models, is not tuned for any specific location but is expected to behave realistically at all locations
Summary
Biosphere–atmosphere interactions constitute a complex system which plays an important role in the regulation of the climate. These interactions are important determinants governing the physical and chemical properties of the atmosphere as well as the growth of plants and result in the biosphere and atmosphere behaving as a coupled system (Pilegaard et al, 2003) Understanding this coupled behaviour is a key research priority due to the important role that terrestrial ecosystems play in modulating the global carbon cycle and to the significance of land surface characteristics for local and regional climate through biogeophysical effects (Cox et al, 2000; Prentice et al, 2001; Bonan, 2008; Franklin et al, 2016).
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