Promoting and maintaining diversity in contemporary hardwood forests: Confronting contemporary drivers of change and the loss of ecological memory

Declines in the diversity of herbaceous and woody plant species in the understory of eastern North American hardwood forests are increasingly common. Forest managers are tasked with maintaining and/or promoting species diversity and resilience; however, the success of these efforts depends on a robust understanding of past and future system dynamics and identification and application of appropriate silvicultural interventions. We review how historical timber harvesting and land use, increases in deer population sizes, invasive species, and contemporary forest management practices interact to erode ecological memory and increase resilience debt of hardwood forests of eastern North America. The erosion of ecological memory and growing resilience debt in these forests pose significant challenges for forest managers because they alter the response of forests to management from the understory to overstory. Differences in how much ecological memory these systems retain, as well as the mosaic of interacting factors influencing contemporary dynamics, preclude a one size fits all management approach. That being said, our review has identified a host of common factors and pathways that can be manipulated. The approach we propose requires a more thoughtful understanding of the forest understory as the foundation upon which resilient systems are built. Which silvicultural levers will have the greatest utility clearly depend on the ecological context of the forest, and a willingness to experiment and adapt. We offer a conceptual model and recommendations for managers confronting novel plant communities and uncertain system dynamics.