Dissertationes Forestales 278 Forest health monitoring in transition: Evaluating insect- induced disturbances in forested landscapes at varying spatial scales Tuula Kantola Department of Forest Sciences Faculty of Agriculture and Forestry University of Helsinki Academic dissertation To be presented with the permission of the Faculty of Agriculture and Forestry, University of Helsinki, for public criticism in Auditorium 105 (B6) of the B-building (Viikki Campus, Latokartanonkaari 7, Helsinki) on June 14th 2019, at 12 o’clock noon. 2 Title of dissertation: Forest health monitoring in transition: Evaluating insect-induced disturbances in forested landscapes at varying spatial scales Author: Tuula Kantola Dissertationes Forestales 278 https://doi.org/10.14214/df.278 Use licence CC BY-NC-ND 4.0 Thesis supervisors: Adjunct professor Päivi Lyytikäinen-Saarenmaa Department of Forest Sciences, University of Helsinki, Finland Professor Markus Holopainen Department of Forest Sciences, University of Helsinki, Finland Pre-examiners: Professor Olle Anderbrant Department of Biology, Lund University, Sweden Associate professor Tuuli Toivonen Department of Geography and Geosciences, University of Helsinki, Finland Opponent: Dr. (Docent) Tarmo Virtanen Department of Environmental Sciences, University of Helsinki, Finland ISSN 1795-7389 (online) ISBN 978-951-651-646-5 (pdf) ISSN 2323-9220 (print) ISBN 978-951-651-647-2 (paperback) Publishers: Finnish Society of Forest Science Faculty of Agriculture and Forestry of the University of Helsinki School of Forest Sciences of the University of Eastern Finland Editorial Office: The Finnish Society of Forest Science Viikinkaari 6, FI-00790 Helsinki, Finland http://www.dissertationesforestales.fi 3 Kantola T. (2019). Forest health monitoring in transition: Evaluating insect-induced disturbances in forested landscapes at varying spatial scales. Dissertationes Forestales 278. 146 p. https://doi.org/10.14214/df.278 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 4 risk assessment, providing information for decision-making and forest health management operations. Models can be coupled with other techniques, including remote sensing. The feasibility of modeling is emphasized when predicting and projecting future events, especially those connected to the climate change related changes in insect population dynamics or adaptation to various forest management operations. 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 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. Keywords: Ecological niche modeling, Forest disturbances, Forest health monitoring, Insect pests, Invasive species, Remote sensing 5 PREFACE My journey towards completing this dissertation has been long and colorful with many twists. The stepping-stones during the journey have been washed with tears and colored with laughter and joy. It has not been the easiest of the journeys, or the most straightforward, but surely worth of it, every single day. These years have been rich in so many ways. They have included work and living in Finland and Texas, various forest insect pests and forest environments, collaboration with a range of different people, teaching, and thesis supervision, travelling, fieldwork, etc. I have been blessed with so many great people beside me during this part of my life. I have also gain new friendships along the route, in Finland and abroad. I want to express my most sincere gratitude to my supervisors Adjunct prof. Päivi Lyytikäinen-Saaremaa and Prof. Markus Holopainen. This exiting part of my life started on the hallways of the Department of Forest Sciences. I met Päivi after a long while and we started a friendly chat. She suddenly dropped a straight question if I would like to start a dissertation under her supervision on monitoring insect pest disturbances. That just felt right; I didn’t even need time for consideration. Since then, a beautiful and complex world of insect pests on the forest environments have opened in front of me. Markus already had a big role during my master’s studies. He trusted me a lot in teaching. He enabled, e.g., several unforgettable summers in Hyytiälä field station as an assistant and later as a responsible teacher. My supervisors have provided me good working conditions facilitating independent work, development of my own ideas, and given me plenty of responsibilities from the start. They have been compassionate and understanding through the rough patches and encouraging during the whole journey. Further, it has always been so much fun to brainstorm and plan for the future! I spent over four years at the Knowledge Engineering Laboratory, in Texas A&M University. I am extremely grateful to Prof. Robert N. Coulson for enabling these experiences and kindly supervising me throughout these years and beyond. In addition to providing me an opportunity to learn about insect outbreaks in the landscape context, he also gave me an opportunity to see the world outside the much-loved forests inviting me later to work in the project on the amazing monarch butterfly. I can also attribute my immensely improved English skills to these time periods in Texas and to Prof. Coulson’s untiring