Intergroup Discussion
Dynamic Factor and Fatiguing of Root/Soil System

Fatiguing

• Add fatiguing rates to model to account for soil and root damage during storm. Based on Galway artificial tree swaying experiments
• Add fatiguing over winter to account for repeated storm effects. Based on provisional Galway measurements on forces required to displace test trees. Needs further experimental work.
• Currently mechanistic wind damage models do not have dynamic component but rely on empirically derived gust factors. Integration of Galway work on relationship between tree dynamic and static behaviour dependent on improvements to Joensuu and FC models.
• For fatiguing require temporal element in models
• Suggestion that coupling of tree resonance to gust frequency important and affected by changes in tree characteristics such as MoE, dbh, height etc. Needs more work before this can be incorporated in models.
• Trees may be able to take very high wind loads for short periods. Destruction may well be accumulation of damage over considerable period (years). For example breakage depends on energy input in discrete packets. This will be true of both stem and root breakage and soil failure.
• Test whether gust factor function of windspeed and/or time of year using existing forestry commission data gathered continuously over last 2 years.