Tree breeding and seed source deployment under climate change (1)
Long-term strategies
Our native tree species are adapted to a combination of photoperiod and temperature, creating steep gradients of adaptation. This is an ongoing evolutionary process and, from a human-utilization perspective, the current adaptation is unlikely to be optimal. Either trees are not hardy enough to establish successfully (e.g., Scots pine in harsh localities), or stop growing too early in the fall (e.g., Norway spruce in mild localities), requiring recommendations for seed and seedling transfer to optimise value production from forests. By necessity, a meta-breeding-population must be structured in several sub-populations to fit varying conditions and avoid maladaptation. A warming climate will create novel combinations of photoperiod and temperature climate, not yet experienced in large scales. Thus, breeding populations with new climatic adaptation profiles are assembled by selecting trees that perform well at particularly warm (or cold) localities in a certain photoperiod (latitude). In addition, generalist trees with low genotype-by-environment interaction and trees with high pest and disease resistance are favoured along with traditional selection criteria (vitality, growth, stem and wood quality). For example, a seed orchard with trees from suitable breeding populations could be established today and still yield well-adapted seed for a future climate when in seed production by careful and pro-active selection of orchard clones.
Immediate actions
Breeding takes time and there is a considerable lag before actions taken in the breeding populations will affect propagation populations and operational reforestation. Silvicultural actions, such as shortening rotation age, use of species and population mixtures, change of species, etc., can be applied directly to increase preparedness and mitigate effects of climate change. Similarly, a dynamic deployment strategy based on response functions can match current reforestation material with future growth environments at a given site. Skogforsk and METLA, with input from SMHI and FMI and funding from EC FP7 and Föreningen Skogsträdsförädling, have developed new response functions for Scots pine in Sweden and Finland north of latitude 60˚ N. The functions are based on new climatic indices used in scenario and ensemble analyses in climatic research. The indices are also bias corrected towards observed climatic indices. By taking into account both the present climatic conditions, which are crucial for seedling survival and establishment, and future conditions, which determine the growing conditions during the rotation time, it is possible to optimize the deployment of reforestation stock currently available. A web-based tool for guidance, where the user decides both reforestation sites and climatic scenarios, is now under construction. A general outcome is that seed sources should be used at slightly more northern or higher altitude sites than earlier recommended to optimise per hectare production. A similar project where Sweden, Finland, Norway and the Baltic States collaborate to develop response functions for Norway spruce has recently been started within phase two of the research programme Future Forest.
Text: Bengt Andersson Gull and Mats Berlin, Skogforsk, Sweden