Play it safe with tree seeds
Written by Eve Beaury, edited by Grace Gutierrez
Summary
Due to climate change, invasions, and other disturbances, many tree species in the Eastern United States are suffering from increased mortality and/or lower recruitment rates. Planting seeds sourced from warmer climates (termed ‘climate-adjusted provenancing’; Prober et al. 2016) could be a viable strategy for preserving long-lived forest species. At the same time, trees often grow best in local or slightly warmer climates, so sourcing seed/plant material from too far away could harm populations. To support science-based decision-making on seed selection, U.S. Forest Service researchers developed a guide to inform safe seed transfer distances for eastern forest species. The guide synthesizes the best known information on the adaptability, genetic diversity, and dispersal capacity of 14 major and 12 minor tree species in east coast forests, including Acer, Betula, Picea, Pinus, and Quercus species. Synthesized data sources include common garden and genetic studies, literature reviews, and tree planter’s notes.
For most tree species, plant performance will be maintained or increased if seeds are collected within 200-300 miles (322-483 km) of a planting site. In particular, seeds collected within this distance from regions further south are likely to perform better under changing climate conditions. However, some species with low gene flow may be less tolerant to long distance transfer; low gene flow may increase local adaptation and differentiation between populations, such that individuals may not breed well when mixed together (e.g., outbreeding depression, Gann et al. 2019). Because of this risk, Pike & Haase (2024) recommend collecting seeds of species such as sugar maple (Acer saccharum), jack pine (Pinus banksiana), and white spruce (Picea glauca) from distances closer to 70 miles (113 km). For each species, the guide provides a table summarizing key information on adaptability and sources to further support safe transfer distances and science-based decision-making.
Take home points
Most tree species in the eastern United States have a recommended transfer distance between 200 and 300 miles (322-483 km), where seeds collected within this distance from regions further south are likely to perform similarly, if not better under changing climate conditions.
Sugar maple, white spruce, and jack pine may be less tolerant to long distance transfer, with recommended distances closer to 70 miles/113 km.
Management implications
The guidebook summarizes the following information: genetics, cone and seed traits, insects and disease, known palatability to browse (white-tailed deer), recommended transfer distances, and range expansion potential
For species with high gene flow and high genetic diversity, sampling many individuals from a local population (a large stand) will capture a large amount of genetic diversity
For species with moderate/low gene flow and moderate/high genetic diversity, sampling individuals from several local populations (stands) and pooling is recommended.
For species with moderate/low gene flow and low genetic diversity, obtaining a sample with high genetic diversity will be difficult and unlikely to affect successful outcomes
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Keywords: Climate-smart restoration, assisted migration, assisted gene flow, climate adjusted provenancing, forest, managed relocation, plants, restoration