Preprints
https://doi.org/10.5194/soil-2020-75
https://doi.org/10.5194/soil-2020-75

  15 Dec 2020

15 Dec 2020

Review status: a revised version of this preprint is currently under review for the journal SOIL.

Predicting the spatial distribution of soil organic carbon stock in Swedish forests using remotely sensed and site-specific variables

Kpade O. L. Hounkpatin, Johan Stendahl, Mattias Lundblad, and Erik Karltun Kpade O. L. Hounkpatin et al.
  • Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, SE-75007, Uppsala, Sweden

Abstract. The status of the SOC stock at any position in the landscape is subject to a complex interplay of soil-state factors operating at different scales and regulating multiple processes resulting either in soils acting as a net sink or net source of carbon. Forest landscapes are characterized by high spatial variability and key drivers of SOC stock might be specific for subareas compared to those influencing the whole landscape. Consequently, separately calibrating models for subareas (local models) that collectively cover a target area can result in different prediction accuracy and SOC stock drivers compared to a single model (global model) that covers the whole area. The goal of this study was therefore to (1) assess how global and local models differ in predicting the humus layer, mineral soil and total SOC stock in Swedish forests, (2) identify the key factors for SOC stock prediction and their scale of influence.

We use the Swedish National Forest Soil Inventory (NFSI) database and a digital soil mapping approach to evaluate the prediction performance using Random Forest modelling calibrated locally for the northern, central and southern Sweden (local models) and for the whole Sweden (global model). Models were built by considering (1) only site characteristics which are recorded on the plot during NFSI, (2) remotely sensed variables and (3) both site characteristics and remotely sensed variables.

Local models are generally more effective for predicting SOC stock after testing on independent validation data. Using remotely sensed variables together with NFSI data indicates that such covariates have limited predictive strength but that site specific variables from the NFSI covariates show better explanatory strength for SOC stocks. The most important covariates that influence the humus layer, mineral soil and total SOC stock were related to the site characteristic covariates and include the soil moisture class, vegetation type, soil type and soil texture. Future studies could focus in mapping these influential site covariates which have potential for future SOC stock prediction models.

Kpade O. L. Hounkpatin et al.

 
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Kpade O. L. Hounkpatin et al.

Kpade O. L. Hounkpatin et al.

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Short summary
Forests store large amounts of carbon in soils. Implementing suitable measures to improve the sink potential of forest soils would require accurate data on the carbon stored in forest soils as well as better understanding of factors affecting this storage. This study showed that the prediction of soil carbon stock in Swedish forests soils can gain in accuracy when one divides a big region into smaller areas in combination with information collected locally and those derived from satellites.