This Month’s Ask An Expert Question Is: What are Seed Zones and why are they important?
Seed Zones are biogeographic regions, created to help track and promote the use of locally-sourced tree seed for reforestation. Not to be confused with ‘Plant Hardiness Zones’, a ‘Seed Zone’ tells you the region where the seeds that’s your native plants were grown from was collected. Our system of Seed Zones, created by the Ministry of Natural Resources and Forestry, group together watersheds with similar climates, based on the Ontario Climate Model (OMNRF, 1997).
Seed Zones are important for tracking where seed comes from and also for deciding where the best locations to plant them are. Some species can be locally adapted, meaning they tend to perform best in the environmental conditions of their parents. In the absence of additional, species specific data, the general recommendation then is that you should plant trees derived from as close to your seed zone as possible, because they will be adapted to local conditions and perform better than an individual of the same species grow from seed far from your home Seed Zone.
Some populations may be locally adapted, some may not be. Though they may seem like hard-and-fast rules, Seed Zones were not created to restrict the movement of seed, only to have a unified tracking system, to better inform our decisions. In fact, there may be microclimates beyond an individual’s Seed Zone or adjacent zone that provides the optimal growing conditions. This is because local adaptation is not as generalizable as geographic climate data, and because each species will be locally adapted to different conditions, and to different degrees.
There are no strict rules on Seed Zones in Ontario, they are offered simply as a guiding principle. Allowing seed and plants to be transferred between zones actually encourages gene-flow which promotes adaptation to future environmental changes. It may also be practical in order to make up for stock limitations within a given zone.
It’s also important to note that Seed Zones were created for trees, and extended later to grasses, shrubs, and wildflowers. We can expect that trees can adapt to long-term climate patterns, whereas shorter-lived herbaceous species—grasses and wildflowers—are less likely to be adapted to long-term climate patterns, and mores so to small-scale environmental differences like soil type, or moisture level, disturbance regime, or community of competitors. There have been numerous studies on the assisted migration of native trees in Ontario, however, very few studies have been conducted on the level and scale of local adaptation in native herbaceous species, and best practices for their assisted migration and restoration in the face of climate change.