Indicator 1.3.1 - Genetic diversity of reforestation seed lots
core indicator


Reforestation after harvesting is mandatory on crown land across Canada. Most harvested areas regenerate naturally from seed that blows into the area from trees left behind in the harvest blocks or from trees in neighboring forest stands. However, to ensure complete reforestation, jurisdictions often plant seedlings or seed areas that have not regenerated sufficiently by natural means.

The genetic diversity of planted seedlings or seed must be sufficiently robust to support the genetic adaptation required to respond to potential risks due to disturbance and changing environmental conditions. Low genetic diversity could potentially reduce the overall genetic diversity of the species in the forest, reducing the ability of species to respond to environmental change. Low genetic diversity among seedlings could arise if the seedlings are derived from clones or from only a few parents of superior growing ability. This indicator provides a simple description of the genetic diversity of seedlings and seed used in reforestation across Canada by examining the number of parents from which seedlings and seed are derived. Efforts underway to monitor genetic diversity are also described.

Planting and seeding account for about 15% of the forest land successfully regenerated in Canada (Indicator 2.5). The genetic diversity of seed used for reforestation is a result of both the number of areas where seed is collected and the parental composition of those areas. Most of the seed used in reforestation programs across Canada is collected from natural stands where the number of parent trees is typically in the hundreds, if not thousands. This seed likely has all the genetic variation present in the natural population where it was collected. In addition, seed is collected from thousands of different areas across the country. In some jurisdictions, a significant portion of the seed for reforestation also comes from seed orchards (plantations consisting of fewer parent trees specifically chosen for desirable characteristics, such as fast growth rates or potential disease resistance). In British Columbia in 2003-2004, for example, 40% of reforestation seedlings were produced from 195 unique orchard seed lots. Still, despite the smaller number of parent trees in orchards, recent genetic research on white spruce and jack pine has indicated that there is no significant difference in genetic variation between orchard and wild (natural) stand seed lots (Stoehr and El-Kassaby 1997, Godt et al. 2001). Given these results, combined with the relatively small proportion of the total harvest area reforested through planting and seeding and the fact that most seed comes from a large number of natural stands, the impact of planting and seeding on the overall genetic diversity of Canada's forest is probably minimal.

Continued monitoring of genetic diversity across the landscape is key to meeting biological diversity objectives that are sustainable over the long term. To aid in the management of genetic resources, jurisdictions are taking several steps to monitor the genetic diversity of seed lots and develop gene resource information programs.

British Columbia, for example, is developing gene resource data sets to track information related to the genetic diversity of seed lots. The province has also established legally enforceable technical standards for all seed lots used for reforestation, including standards for how the seed is collected, the physical quality of seed, the minimum effective population size, and parent tree identification. In addition, the province is realigning the boundaries of its Seed Planning Zones and Units, where seed is collected, with more ecologically meaningful boundaries on the basis of geography and climate. It also carefully regulates the storage, selection, use, and transfer of seed used for crown land reforestation. These initiatives, allow British Columbia to manage the genetic diversity of seedlings and seed it uses for reforestation.

In Ontario, several collection and storage measures are in place to protect its genetic resource base. While the province has seed lots resulting from treebreeding programs, tree seed also continues to be collected from general populations in all species ensuring a very deep and diversified genetic pool. At the same time, a substantial seed bank exists at the Ontario Tree Seed Plant where portions of these general collections are frozen and stored for future use.

Ironically, the genetic diversity of some orchard seed lots can be greater than the local natural population. In Prince Edward Island, for example, the forests have been severely degraded due to selective harvesting over the past 250+ years. The approach of taking the best and leaving the rest has resulted in regeneration in some areas being dependent on seed sources from a very small population-in some cases a single tree. Results from Prince Edward Island's tree improvement program have shown significant increases in growth beyond that expected from most treebreeding programs, likely due to the reduction in inbreeding.