Integrating the risk of natural disturbances into forest management in Norway

Abstract

Natural disturbances can rapidly change the structure and species composition of forests. Their effects can also compromise the provision of services and products from forest ecosystems. Therefore, it is very relevant that the risk of natural disturbances is considered when planning forest management prescriptions. This study presents a general framework for integrating risk into long-term forest management, via two main steps: 1) risk assessment (damage characterisation and modelling); and 2) risk management (simulation and optimisation). This research characterises the primary natural disturbances in Norway, and presents occurrence and damage models for the most relevant of these. The results show that the main natural disturbances in Norway are snow, wind and browsing from ungulates. The models identify which stand and site variables are more influential when predicting a forest's vulnerability to damage. The browsing occurrence models show that the most relevant variables to explain stand vulnerability are stand age, size and density. The model predicting snow and wind damage occurrence highlights the importance of the stand density, structure, mean diameter and height, but also site-related variables, such as latitude or altitude. The models predicting the damage rate for snow and wind damage, use covariates, such as stand basal area, height, diameter and slenderness. Snow and wind damage models are used in a stand dynamic simulation to optimise management prescriptions for considering risk. The optimal management schedules for a spruce dominated stand leave lower volumes towards the end of the rotation and shorten the rotation length. This thesis provides relevant information that can be used by managers in considering the risk of natural disturbances in forest management and planning.