Evaluating CENTURY and Yasso soil carbon models for CO₂ emissions and organic carbon stocks of boreal forest soil with Bayesian multi‐model inference

Abstract

We can curb climate change by improved management decisions for the most important terrestrial carbon pool, soil organic carbon stock (SOC). However, we need to be confident we can obtain the correct representation of the simultanous effect of the input of plant litter, soil temperature and water (which could be altered by climate or management) on the decomposition of soil organic matter. In this research, we used regression and Bayesian statistics for testing process‐based models (Yasso07, Yasso15 and CENTURY) with soil heterotrophic respiration (Rh) and SOC, measured at four sites in Finland during 2015 and 2016. We extracted climate modifiers for calibration with Rh. The Rh values of Yasso07, Yasso15 and CENTURY models estimated with default parameterization correlated with measured monthly heterotrophic respiration. Despite a significant correlation, models on average underestimated measured soil respiration by 43%. After the Bayesian calibration, the fitted climate modifier of the Yasso07 model outperformed the Yasso15 and CENTURY models. The Yasso07 model had smaller residual mean square errors and temperature and water functions with fewer, thus more efficient, parameters than the other models. After calibration, there was a small overestimate of Rh by the models that used monotonic moisture functions and a small generic underestimate in autumn. The mismatch between measured and modelled Rh indicates that the Yasso and CENTURY models should be improved by adjusting climate modifiers of decomposition or by accounting for missing controls in, for example, microbial growth. Highlights We tested soil carbon models against monthly soil Rh fluxes and amounts of SOC stock. The models accurately reproduced most of the seasonal Rh trends and amounts of SOC. Under autumn temperature and moisture, Rh was mismatched before and even after the parameterization. The seasonality of the temperature and water functions should be adjusted in models.

Carbon forestry compensation on estate level

“…Many of the quantitative results in this paper depend on the market prices of roundwood assortments, bare land, silviculturar and harvesting expenses, carbon emission, as well as the discount rate applied in Eqs. (10) and (11). Considering eventual changes of the latter two is straightforward in terms of Eqs.…”

“…In the occurrence of clearcutting and soil preparation, net release of carbon from the soil to the atmosphere begins [7,8,9,10]. Correspondingly, maintenance of canopy cover possibly is essential in carbon sequestration.…”

KEYLINK: towards a more integrative soil representation for inclusion in ecosystem scale models. I. review and model concept

“…Essentially, most models describe the soil as consisting of homogeneous horizons, where SOM transformation occurs in a cascade from easily degradable to passive or stable SOM based on its chemical complexity/degradability. Equations are based on first-order kinetics (depending on pool size) where decay-rate constants are controlled by the initial litter quality (mostly represented as CN ratio or recalcitrance) and modified by temperature (t) and humidity (h) ( Liski et al, 2005 ; Parton et al, 1987 ; Tupek et al, 2019 ). This representation can adequately be parameterised to simulate a stable soil under unchanging conditions, but cannot explain differences in functioning between soils concerning C and nutrient cycling, plant nutrition and hydrological processes, nor represent changes due to climate, management or pollution ( Vereecken et al, 2016 ).…”

Calculating the Additional Carbon Sequestration of Finnish Forestry

“…The earlier models for DOM (Pukkala, 2014) are based on simulations with the Yasso07 decomposition model (Tuomi et al, 2011). This model has been updated based on additional data, resulting in the Yasso15 model (Akujärvi et al, 2019;Didion et al, 2016;Ťupek et al, 2019). Also, the models for simulating the uses of harvested timber and the life cycles of wood-based products have been fine-tuned in recent research (Hurmekoski et al, 2020;Pukkala, 2020).…”