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

Abstract

Climate change is amplifying forest disturbances, especially those by insect pests. In addition to native species, biological invasions by 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, efficient, 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 a range of spatial and temporal scales. Rapid development of methods for general forest inventory also support development of forest health monitoring and management. The continuously developing field of remote sensing and geographical information systems provide new means for various forest monitoring tasks. However, disturbance monitoring, especially by insect pests, gives an extra challenge and increased uncertainties compared to other forest monitoring tasks. With new approaches, however, valuable information on disturbances can be derived for evaluation of insect-induced forest disturbance at reasonable high accuracy and reduced amount of needed fieldwork. This dissertation aims towards improved forest health monitoring, particularly disturbances by defoliating insect pests. Insect-induced disturbances from single tree level to larger areas in Fennoscandia and eastern USA were evaluated in five sub-studies. The sixth and final sub-study comprises continental scale species distribution models in North America and East Asia. In these sub-studies, different remote sensing sensors and approaches, and ecological niche modeling for species potential distributions were employed in disturbance evaluation. Study species include native insect pests and an invasive alien species. In context of recent research and the included sub-studies, issues specific to insect disturbance monitoring are discussed. Pattern, frequency, scale, and intensity of insect infestations vary depending on the insect pest and forested 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 control or 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 depending on the region affecting further selection of usable data sets and methods. Information on potential ranges of insect pests and, to some extent, on future impacts of infestations can be obtained employing spatial modeling techniques, such as ecological niche modeling. These models are more frequently used at the regional and continental levels, however, smaller scale can be applied. Various modeling approaches can also be applied in