Aspen ( Populus tremuloides ) germination is dependent on seed ripeness at collection and not seed age: A 12-y study of aspen seeds in long-term storage

Abstract Trembling aspen (Populus tremuloides Michx. [Salicaceae]) is an important early successional reclamation species with small, wind-dispersed seeds that have short viability once released. Seeds can be placed into freezers to maintain viability, but information regarding the viability of aspen seeds in long-term storage is limited. Furthermore, seed ripeness at the time of collection may also impact the germination and longevity of seeds in storage. In this study, we collected aspen seeds in 2012, 2013, 2015, and 2016 within the Peace Region of Alberta. Seedlots were categorized into 3 ripeness categories, based on color, and tested for germination. Seeds were subsequently stored at –20 °C (–4 °F) at a moisture content of 6% on average. Germination tests were repeated on seedlots over several years, with the most recent tests occurring in 2024. Germination was significantly higher in the ripest seeds (85 ± 4.8%) relative to less ripe seeds (61.5 ± 8.9%). Seed age did not significantly affect germination, demonstrating that aspen seeds can be stored for more than a decade without losing viability. We recommend collecting ripe seeds with a brown seedcoat as they maintained the highest germination. The ability to maintain aspen seedlots for 10+ y will be beneficial for ecological restoration, particularly in regions where local populations are fragmented by industrial activity.