Forest soil carbon stock estimates in a nationwide inventory: evaluating performance of the ROMULv and Yasso07 models in Finland

Aleksi Lehtonen,Mikko Peltoniemi,Alexander Komarov,Maija Salemaa,Tapio Linkosalo,Raisa Mäkipää,Risto Sievänen,Pekka Tamminen,Boris Ťupek,Tiina Nieminen,Juha Heikkinen

doi:10.5194/gmd-9-4169-2016

Abstract

Abstract. Dynamic soil models are needed for estimating impact of weather and climate change on soil carbon stocks and fluxes. Here, we evaluate performance of Yasso07 and ROMULv models against forest soil carbon stock measurements. More specifically, we ask if litter quantity, litter quality and weather data are sufficient drivers for soil carbon stock estimation. We also test whether inclusion of soil water holding capacity improves reliability of modelled soil carbon stock estimates. Litter input of trees was estimated from stem volume maps provided by the National Forest Inventory, while understorey vegetation was estimated using new biomass models. The litter production rates of trees were based on earlier research, while for understorey biomass they were estimated from measured data. We applied Yasso07 and ROMULv models across Finland and ran those models into steady state; thereafter, measured soil carbon stocks were compared with model estimates. We found that the role of understorey litter input was underestimated when the Yasso07 model was parameterised, especially in northern Finland. We also found that the inclusion of soil water holding capacity in the ROMULv model improved predictions, especially in southern Finland. Our simulations and measurements show that models using only litter quality, litter quantity and weather data underestimate soil carbon stock in southern Finland, and this underestimation is due to omission of the impact of droughts to the decomposition of organic layers. Our results also imply that the ecosystem modelling community and greenhouse gas inventories should improve understorey litter estimation in the northern latitudes.

Highlights

Soil carbon is a significant component of terrestrial carbon stocks and understanding its dynamics under changing climate is crucial
The ROMULv model predictions generally agreed with Biosoil data when soil water holding capacity was taken into account
When the ROMULv model was driven with constant soil water holding capacity, it was unable to reproduce decreasing soil carbon stocks across Finland and the model underestimated carbon stocks, especially in the south (Fig. 2e and f)

Summary

Introduction

Soil carbon is a significant component of terrestrial carbon stocks and understanding its dynamics under changing climate is crucial. The significance and interactions of different mechanisms for long-term carbon accumulation are still unknown and are often lacking in models. If we want to understand the relationship of different abiotic and environmental factors to soil carbon stocks and their dynamics, we have to combine experimental research with process-based models. One way forward is to establish soil carbon inventories in order to quantify soil carbon stocks and their change. Conventional soil inventories measuring various nutrients, carbon contents, bulk densities and stoniness It is shown that soil carbon inventories are able to produce soil maps and covariates between soil carbon quantities and other variables, such as various nutrients, the sample size of these inventories is usually not adequate for national-level soil carbon stock change assessment, with few exceptions

Methods

Results

Conclusion