What is an “improved” tree?

Planting trees is a rite of spring for many people in Minnesota.  But a lot can go wrong, and the success of your tree planting hinges on many factors.  One that is often overlooked is the seed source.  The quality of seed and seedlings used for reforestation can impact the long-term success of your planting.   Many of the future traits of a tree are locked in the young seedling’s DNA — qualities related to its appearance as a mature tree are not visible in the seedling itself.  When you plant a tree seedling you can only hope that it will resemble the species as you know it.

One option is to plant improved seedlings, where parentage is known and parent trees are selected for their ability to produce seed with above-average growth rates and other qualities.  A forest grown from improved seed will produce between 8 – 30% more volume per acre than a stand grown from local sources, depending on the species.  (Think of volume either in terms of cords of wood per acre, or wood per tree.)  Improved white spruce may produce up to 30% more wood than a local source.  Red pine and jack pine may demonstrate growth rates that exceed local sources by 12-20% respectively.  For jack pine, improved seedlings are also characterized by straighter stems and wider branch angles to reduce knot size.  Eventually white pine with improved resistance to blister rust disease will be available as well.

In Minnesota, all improved evergreen seedlings are produced by natural wind-pollination and are not genetically modified, so an improved white spruce seedling does not contain DNA from another organism such as a frog or a strawberry plant.  Improved seed is not produced “clonally,” so no two improved seedlings are genetically identical.   Seedlings from a wild collection are demarcated either by their seed zone (MN DNR seed zones, USDA plant hardiness zones, or County), depending on the grower and the information they retain on the seed they purchased and grew.

Improved seedlings might be a little taller than locally-sourced seedlings, but otherwise should be similar in appearance to others of its species, subject to the treatments received in the nursery where they were grown.  Differences between improved and local sources generally aren’t apparent until several years of growth have elapsed.  If a tree is planted on the wrong site then it may never thrive, and the increases in growth that you anticipated (and paid for) might not be realized.  Remember that improved seedlings are not a silver bullet — using improved seedlings will not make up for errors caused by lousy planting habits, incorrect site selection, or inadequate site preparation!  The same principals for a successful tree planting still apply whether you’re planting improved or local sources.

Where should you plant improved seedlings?  For red pine and white spruce improved seedlings are appropriate to plant anywhere the species occurs in Minnesota.  Improved sources tend to “behave” more like southern sources, so avoid frost pockets (low-areas on a site where cold air may pool), and in northern parts of the state favor south-facing sloped areas where conditions are slightly warmer.  Improved sources might not be best for all sites – if you’re uncertain, rely on local sources.

Improved seedlings are used primarily for commercial reforestation but are available in limited supply to purchase from select private growers and the MN DNR State Nursery program.  Expect to pay more for an improved seedling than for a bulked seed source – improved seed is more expensive to produce because of the costs incurred to manage the seed orchard and the seed source trials that accompany them.  Orchards are produced and managed by members of the Minnesota Tree Improvement Cooperative; they are the sole proprietors of improved seed in Minnesota.  For more information visit our website.  Remember, your future forest is only as good as the tree seed used to grow it.

Photos: a seedling-seed orchard and a grafted orchard. A seed source trial.
-Carrie Pike, Research Fellow
Department of Forest Resources

Carrie Pike directs the Minnesota Tree Improvement Cooperative, based at the University of Minnesota’s Cloquet Forestry Center.

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3 Comments

  1. “What is an “improved” tree?

    In Minnesota, all improved evergreen seedlings are produced by natural wind-pollination and are not genetically modified,…”

    If “improved tree seeds” are produced by natural pollination, what makes them improved. Especially when compared to “local” trees. What is going on in the forest management to produce “improved” trees?

  2. Jan, The trees in the orchard are selected because they consistently produce offspring with higher-than average growth rates, regardless of the pollen parent. So we can increase the growth rates just by selecting trees for their “maternal” qualities. Sometimes, tree improvement programs need to control the pollen parent as well but in Minnesota we can increase growth rates for white spruce, black spruce, jack pine, white pine, and red pine just through maternal selections.

  3. Seed orchards with improved trees for production of improved seeds are usually naturally wind-pollinated. But the pollen-parent to the seed is often an improved seed orchard tree. Dad is as important as Mum.

    Still pollen flies widely and in many seed orchards a considerable part of the pollen parents are trees outside the orchard. In such cases you may claim that “maternal qualities” are more important than paternal. The seed orchard should be localized and utilized with the provenance of this “contaminating” pollen in mind. Out-side pollen widens genetic diversity. Sufficient outside pollen of right provenance means that the seed orchard seeds can be harvested earlier in the life of the seed orchard, before it is sufficient pollen production of the orchard trees.