Validation and improvement of the integrated dynamic forest ecosystem model ForSAFE at Swiss ICP-forests level II sites (LWF)

Fig. 1 Litterfall collector on the LWF-Plot in Novaggio. Photo: Peter Waldner (WSL)

Research background

European forests are exposed to a series of adverse natural and anthropogenic stresses including air pollutant deposition, climate change, and industrial harvesting as a result of increasing demands for (fuel) wood. The response of forest ecosystem components and nutrient cycle processes to the most relevant stressors is being monitored since over a decade now (i.a. LWF Programme). Biogeochemical models, on the other hand, are being used to estimate the scope of future damage, to predict the timing of ecosystem response and to evaluate effects mitigation measures. Recently, more integrated forest ecosystem response models were put to use and their functionality has to be examined using monitoring data.

Objectives

The objective of the project is

- to verify the integrated forest ecosystem response model ForSAFE at the intensively monitored LWF plots by evaluating the model results with measurements, by identifying the key-reasons for discrepancies and by revising respective elements in the procedure;

- upon revision, to model the soil chemistry of LWF plots with different scenarios of climate, N deposition and forest management practices (e.g. change in tree species, whole tree harvesting, wood ash amendment);

- and to identify requirements for the regionalization of the modelling.

Method

The model evaluation will involve the following steps:

1. Blind validation: ForSAFE will be applied to a selection of LWF plots using input data collected according to the currently used national mapping procedures and model results will be compared with the monitoring data upon availability. Within the scope of this initial comparison of the output, a common schematic conceptual view of the forest ecosystem will be established and appropriate performance measures will be selected.

2. Input data: In order to clarify whether discrepancies origin from inappropriate input or to shortcomings in model formulation, we will gradually replace national with local input derived from the monitoring data at the LWF sites and analyze the changes in the model predictions in relation to the measurements.

3. Processes: We will further analyze time series monitoring data and assess mass balances that are relevant for the model (e.g. hydrologic cycle, nutrient cycle) in view of implemented processes and process formulations to identify shortcomings or missing dynamics.

4. Model improvement: For a limited number of key problems (either shortcomings or missing dynamics) alternative solutions will be worked out, implemented and tested.

5. Scenario analysis: Upon consolidation, the model will be used for a scenario analysis at selected LWF sites to exemplify the mutual impacts of changes in atmospheric deposition, climate and management on forest ecosystems with time horizon 2100.

Expected results and relevance

The project will provide knowledge about and predictions for the long-term impacts of air pollutant, particularly N, deposition, climate change and forest management practices on the biogeochemical site conditions of the studied LWF sites: i.e. depletion of nutrients, toxicity risk for roots, decrease in biodiversity and nitrate release into groundwater resources, etc.. Furthermore, the project will elaborate an integrated forest ecosystem response model that can be used to carry out effect analyses for other sites for which the required input data is available (such as soil physico-chemical properties and stand description, etc.). This will be the basis for a national assessment of the sensitivity of forests regarding natural and anthropogenic stressors and the prerequisite for the evaluation of effects mitigation measures (planned for the second phase of the research programme 2012-2015).