Forest health monitoring in transition: Evaluating insect-induced disturbances in forested landscapes at varying spatial scales

Climate change is amplifying forest disturbances, especially those by insect pests. In addition to native species, alien insects are threatening forest health, ecosystem sustainability, and economic return. Uncertainties related to insect pest infestations are increasing along the risk of high impacts. There is a high demand of accurate and cost-effective methods for forest health monitoring to prevent, control, and mitigate the various negative impacts, as well as to support decision-making. Current needs for information for efficient forest 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 spatial and temporal scales. The developing field of remote sensing and geographical information systems provide new means for various forest monitoring. However, disturbance monitoring, especially by insect pests, gives an extra challenge and increased uncertainties compared to other forest monitoring tasks. With new approaches, valuable information on disturbances can be derived for evaluation of insect-induced forest disturbance at reasonable high accuracy and reduced amount of fieldwork. This dissertation aims towards improved forest health monitoring. Insect-induced disturbances from tree level to larger areas were evaluated in six sub-studies. Different remote sensing sensors and approaches, and ecological niche modeling were employed in disturbance evaluation. Study species include native and invasive insect pests. In context of recent research, issues specific to insect disturbance monitoring are discussed. Pattern, frequency, scale, and intensity of insect infestations vary depending on the pest and landscapes in question affecting disturbance detection and impact evaluation. Sensors, platform, and/or modeling methods have to be chosen accordingly. Environmental features, such as topography, and level of landscape fragmentation give restrictions to the method selection, as well as to the appropriate spatial resolution. Importance of varying information is also affected by the scale and resolution of investigation. Timing of data acquisition is crucial. Early detection and timely management operations are often the only way to mitigate insect outbreaks. Moreover, amount and accuracy of auxiliary information, including forest inventory data, and disturbance history, differ between countries and continents. Forest policies and practices differ between regions affecting selection of usable data sets and methods. Forest health monitoring should be included into forest monitoring systems for timely disturbance detection, accurate monitoring, and impact evaluation. Higher and lower spatial resolution remote sensing should be combined over varying spatial ranges and 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. Plenty of valuable research on forest health monitoring exist. However, considerably more research is still needed before comprehensive monitoring systems can be adopted at the operational level. Development of remote sensing and modeling techniques, as well as improving computational power and databases facilitate continuous improvement of forest health management practices