Carina A. Ortiz

A multi-model comparison of soil carbon assessment of a coniferous forest stand

We simulated soil carbon stock dynamics of an Austrian coniferous forest stand with five soil-only models (Q, ROMUL, RothC, SoilCO2/RothC and Yasso07) and three plant-soil models (CENTURY, CoupModel and Forest-DNDC) for an 18-year period and the decomposition of a litter pulse over a 100-year period. The objectives of the study were to assess the consistency in soil carbon estimates applying a multi-model comparison and to present and discuss the sources of uncertainties that create the differences in model results. Additionally, we discuss the applicability of different modelling approaches from the view point of large-scale carbon assessments.Our simulation results showed a wide range in soil carbon stocks and stock change estimates reflecting substantial uncertainties in model estimates. The measured stock change estimate decreased much more than the model predictions. Model results varied not only due to the model structure and applied parameters, but also due to different input information and assumptions applied during the modelling processes. Initialization procedures applied with the models induced large differences among the modelled soil carbon stocks and stock change estimates. Decomposition estimates of the litter pulse driven by model structures and parameters also varied considerably.Our results support the use of relatively simple soil-only models with low data requirements in inventory type of large-scale carbon assessments. It is important that the modelling processes within the national inventories are transparently reported and special emphasis is put on how the models are used, which assumptions are applied and what is the quality of data used both as input and to calibrate the models.

Transient trade-off between climate benefit and biodiversity loss of harvesting stumps for bioenergy

To replace fossil fuel and thereby mitigate climate change, harvesting of wood such as stumps for bioenergy will likely increase. Coarse deadwood is an important resource for biodiversity and stumps comprise the main part of the coarse deadwood in managed forests. We provide the first integrated analysis of the long‐term climate and biodiversity impacts of a whole landscape. We simultaneously project climate and biodiversity impacts of harvesting stumps to substitute for fossil coal, assuming scenarios with different proportions of the landscape with stump harvest (10, 50, 80%) the coming 50 years. A life cycle approach was used to calculate future global temperature changes and future metapopulation changes in six epixylic lichens. Metapopulation dynamics were projected using colonization and extinction models based on times series data. Harvesting stumps from ≥50% of the clear‐cut forest land benefits climate with a net global temperature reduction >0.5·10−9 K ha−1 after 50 years if assuming substitution of fossil coal. For all scenarios, using stump bioenergy leads to immediate (within 1 year) reductions in temperature of 50% compared to using fossil coal, increasing to 70% reduction after 50 years. However, large‐scale stump harvest inflicted substantial metapopulation declines for five of six lichens. High stump harvest levels (≥50%) put common lichens at risk of becoming red‐listed following the IUCN criteria. The net temperature reduction (cooling effect) from substituting fossil coal with stumps harvested for bioenergy increased over time, while lichen metapopulations stabilized at lower equilibria after two to three decades. This indicates that trade‐offs between climate and metapopulations of commons species are transient, where climate benefits become more prevalent in the long term. As both objectives are important for meeting (inter‐)national climate and biodiversity targets, integrated analyses such as this should be encouraged and urged to guide policymaking about large‐scale implementation of stump harvest.