Conserving Southern Ontario’s Eastern Hemlock Forests Opportunities to Save a Foundation Tree Species Research Report No. 38 Ancient Forest Exploration & Research www.ancientforest.org [email protected] BY MICHAEL HENRY AND PETER QUINBY 2019 Table of Contents EXECUTIVE SUMMARY ................................................................................................................................. 4 INTRODUCTION ............................................................................................................................................ 4 THE VALUE OF EASTERN HEMLOCK ............................................................................................................. 5 A Long-lived Climax Species ......................................................................................................................... 5 Old Growth ................................................................................................................................................... 5 A Foundation Species ................................................................................................................................... 6 INVASION OF HEMLOCK WOOLLY ADELGID ................................................................................................ 7 History and Biology ...................................................................................................................................... 7 Rates and Patterns of Spread ...................................................................................................................... 7 Cold Tolerance .............................................................................................................................................. 9 Status and Risk Factors in Ontario ............................................................................................................. 10 Long-distance Dispersal by Birds ............................................................................................................... 12 HWA MANAGEMENT.................................................................................................................................. 13 Current Management Practices in the Northeast, USA ............................................................................ 13 Silvicultural Management .......................................................................................................................... 15 Host Resistance .......................................................................................................................................... 15 Importance of Early Detection Surveys ..................................................................................................... 16 Strategies from Other U.S. Jurisdictions.................................................................................................... 16 Strategies Identified in the Management Plan for Canada ...................................................................... 17 Improving Management Strategies ........................................................................................................... 17 Phase out the removal of infested trees in the short term .................................................................. 17 Do-nothing option .................................................................................................................................. 18 Prioritize development of field insectaries ........................................................................................... 18 Keep invasive species watch lists up to date ........................................................................................ 18 HEMLOCK DISTRIBUTION IN ONTARIO ...................................................................................................... 18 Existing Mapping ........................................................................................................................................ 18 Topographic Predictors .............................................................................................................................. 22 Identifying Priority Stands for Conservation ............................................................................................. 22 Introduction ............................................................................................................................................ 22 Methods .................................................................................................................................................. 22 Results..................................................................................................................................................... 23 Setting Priorities for Monitoring ................................................................................................................ 26 HWA DETECTION ........................................................................................................................................ 26 2 Detection Methods .................................................................................................................................... 26 Visual inspections of branches .............................................................................................................. 26 Ball sampling .......................................................................................................................................... 27 Crawler sampling .................................................................................................................................... 27 Citizen Monitoring ...................................................................................................................................... 27 Season (when to look) ............................................................................................................................ 27 Monitoring priorities (where to look) ................................................................................................... 27 Promoting awareness and starting monitoring early ........................................................................... 28 Workshops .............................................................................................................................................. 28 Survey protocols ..................................................................................................................................... 28 Other awareness efforts ........................................................................................................................ 29 Reporting HWA in Ontario ..................................................................................................................... 30 The Larger Context of Invasive Species ..................................................................................................... 30 Opportunities for Increased Stakeholder Involvement ............................................................................ 31 ACKNOWLEDGEMENTS .............................................................................................................................. 32 AFER’s MISSION AND GUIDING PRINCIPLES .............................................................................................. 32 REFERENCES ................................................................................................................................................ 32 APPENDIX 1a - Hemlock and Adelgid Biology APPENDIX 1b - Citizen's Guide to Adelgid Detection APPENDIX 2 - Table of Hemlock Forest Sites 3 EXECUTIVE SUMMARY This document was developed to help inform a citizen-science approach to hemlock woolly adelgid (HWA) detection and is complementary to the HWA Plan for Canada that was released in 2018. HWA attacks and kills eastern hemlock (Tsuga canadensis), a long-lived shade-tolerant species that is commonly a dominant tree in old-growth forests of southern and central Ontario. The hemlock is considered a “foundation species” because of its strong influence on the environment and on other species including understory plants, forest animals, and aquatic organisms found in associated streams. In addition to a detailed literature review, this report provides a map and descriptions of 94 high- conservation value forests in southern Ontario that should be part of a network to monitor the health of eastern hemlock. HWA has spread through more than half the entire North American range of eastern hemlock and can cause very high mortality, threatening the existence of many hemlock forests in the long-term. HWA colonizes new areas primarily by wind, birds, and humans, at an average rate of roughly 8.1 km/yr in the northern part of its range. Biocontrol of HWA using a suite of predators remains the best hope for conserving eastern hemlock populations. If biocontrol fails, the principal sources of protection are host resistance, which is likely very rare; or climatic refugia, which are likely to continue to shrink in the face of climate change. Chemical treatments will also be important in some situations, but associated environmental impacts need further research. The effectiveness of silvicultural management (e.g., thinning, logging) is currently unknown, as are the ecological costs. Further research should include an evaluation of the ecosystem impacts of management. Best management