Potential use of seasonal forecasts for operational planning of north European forest management

Weather and climate conditions can have large impacts on the outcome of forest management operations: Suboptimal conditions can increase the amount of driving damage to forest ground caused by the heavy machines used for harvesting, forwarding and soil scarification. Planting of tree seedlings is commonly practised after clear cutting, and drought in summer or soil frost uplifting in autumn reduces the likelihood of successful plant establishment. Weather and climate also influence the risk of forest fires and the occurrence and development of pest and pathogens, and thereby the timing suitable for surveillance and countermeasures. In this study, the potential use of seasonal forecasts to support the operational planning of forest management in northern Europe was assessed. The analysis was based on temperature and precipitation data from WFDEI System 4 with 15 ensemble members representing seasonal hindcasts (retrospective predictions) for the period of 1981-2010. The data was used directly and as input to a soil model from which monthly indices of frozen soil and plant water stress were calculated. Relatively low skills were found for most months, and in particular for longer lead times. Highest skill was found for bias corrected temperature of January to March, with one month lead time. The skill was higher for the soil model indices, in particular those related to soil frost, as they are influenced by cumulative processes and the initial model conditions contribute to the skill. Probabilistic forecasts on frozen soil can thus be valuable for planning of which areas to harvest, taking the risk of driving damage to forest soils and forest roads into account.