Abstract

The re-measurement of permanent forest inventories offers a unique opportunity to assess the occurrence and impact of forest disturbances. The present study aims at exploring the main forest damages in Norway based on the extensive data of several consecutive national forest inventories during the period 1995–2014. Five of the most common disturbance agents in Norway are selected for analysis: wind, snow, browsing, fungus and insect damage. The analyses focuses on the frequency and variation along time, the average damage at stand level and the spatial patterns of damage occurrence, resulting in a characterization of the damage produced by disturbances in Norway. The highest damage occurrences by disturbance agent are due to browsing, snow and wind. Snow presents a decreasing temporally trend in damage frequency in the studied period. By forest type, mature and intermediate birch forest are found to be more affected by snow damage, whereas mature spruce forest is by wind damage. The results from this study provide support to the hypothesis that damages by autumnal moth (Epirrita autumnata) on birch are more common in mature stands. No major attacks from bark beetle (Ips typographus) are found, probably related to the lack of major storm damages in the period. Forest types susceptibility to fungus has no apparent variation over time except in the last years, as increased occurrence is observed on mature spruce stands probably correlated with warmer than average periods. Browsing damage causes the most severe losses, as expected, in young stands, and is allocated mainly on the most productive forests. Although some of the disturbances present locally moderate effects, the results show no major disturbances threatening Norwegian forests in the studied period. Finally, the Norwegian national forest inventory demonstrates its reliability as a basis to understand the occurrence and effects of major natural disturbances.

Highlights

  • Natural disturbances are a key factor in forest dynamics [1], and a reason for the potential distribution of terrestrial vegetation [2]

  • Long-term damage analysis enhances the understanding of natural disturbances in forest areas [30] and it can help forecast the probability of damage given different timeframes

  • Previous studies have demonstrated the reliability of National Forest Inventories (NFIs) data to assess the occurrence of the most doi:10.1371/journal.pone.0161361.g004

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Summary

Introduction

Natural disturbances are a key factor in forest dynamics [1], and a reason for the potential distribution of terrestrial vegetation [2]. Understanding e.g. the establishment of a stand after a severe disturbance, or the diversification of species and structure coming from a frequent but mild disturbance, provides the forester with information that can be included in management plans and objectives. This assertion can be applied either, if the objective is to emulate through management the evolution pathways of a natural forest [5,6], account for expected losses when defining a management plan [7], or combine economic and risk mitigation objectives [8]

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