Climate change is amplifying forest disturbances, especially those by insect pests. Invasions by alien insects are also threatening forest health. Uncertainties related to insect pest infestations are increasing along the risk of high impacts. There is a demand of accurate and cost-efficient methods for forest health monitoring to prevent, control, and mitigate the negative impacts. Current needs for information for efficient forest health management are complex and extensive. The required quality cannot be met with traditional forest inventory methods. Forest information should be up-to-date and available across a range of spatial and temporal scales. Rapid development of remote sensing and spatial modeling could also support forest health monitoring and management; however, an extra challenge with increased uncertainties are encountered.
The dissertation aims towards improved forest health monitoring, particularly disturbances by defoliating insect pests. Insect-induced disturbances were evaluated in six sub-studies. Different remote sensing sensors and modeling approaches were employed for disturbance evaluation in Fennoscandia and North America. Pattern, frequency, scale, and intensity of insect infestations vary depending on pest and forested landscapes in question, affecting the applied methodology. Sensors, platforms, and modeling methods have to be chosen accordingly. Timing of data acquisition is crucial; early detection and timely management operations are often the only way to mitigate insect outbreaks. Importance of varying information is also affected by the scale and resolution of investigation.
Forest health monitoring should be included into forest monitoring systems, including accurate and timely disturbance detection, monitoring of infestations, and impact evaluation. Higher and lower spatial resolution remote sensing should be combined and spatial modeling techniques incorporated for flexible and cost-efficient monitoring over a gradient of different forest ecosystems, climatic conditions, and forest inventory and management practices. Open access remote sensing archives with high temporal resolution could facilitate continuous monitoring of wide forest areas. Developing satellite technology may respond to these needs. However, more research is needed before these systems can be adopted at the managing level.