In Ontario, there are 35 static seed zones. These were established to ensure that planting stock was climatically adapted to the region of planting. This supported the approach of ‘ local is best ‘ where locally adapted seeds would be more acclimatized to the site. Recommended distances were no more than 50 kilometers from the parent stand and, if possible, less than 30 kilometers.

What is strikingly clear is that static provenances are no longer valid with a changing climate. Climatic envelopes, areas of suitable climatic habitat for tree species, are shifting north. This change will be ongoing and unrelenting. It is this unrelenting change that has us paralyzed.

So what are some issues concerning assisted migration? It is the intent of assisted migration to push seed provenances north or even introduce new species north and accomplish climatic adaptation in 1 generation in what would have taken nature several generations to achieve. One of the biggest risks of planting stock north of its current zone, is freezing damage. Natural selection has resulted in species aligning their growing cycles to avoid damage from late spring and early fall frosts. Events such as breaking dormancy, bud burst and flowering are carefully timed for tree species adapted to a local environment.

On an even larger scale, we could be mismatching tree species to photo period. By moving seed sources north, species are no longer matched to local day length. Longer photo periods experienced at more northerly latitudes may cause trees to be more susceptible to all frosts. By mid century, it is estimated that most of Ontario’s tree species will have to move 400 to 600 kilometers north to keep withing their climatic envelopes. This will, indeed, cause mismatching of tree species to photo period.

We have decided, at Puslinch Naturally Native Trees nursery, to take the plunge. We will be launching an assisted migration program. A huge undertaking but we have always been committed to a sustainable environment and forests. Now the hard work begins where we build the program and try to introduce it to our clients and general public.



People usually do not think of trees being able to migrate. But this is untrue. If you just think back 12,000 years ago, trees migrated just ahead of the crushing forces of advancing glaciers in Canada. Trees would sexually mature, send out seed and pollen ahead of the glaciers and create an advancing line of trees, moving southward. As a matter of fact, DNA testing found that some white pine tested in the Mississippi valley had come from the Algonquin park area. Of course, migrating birds and wildlife help move seeds of trees by ingesting seeds and later fertilizing another area with droppings. The native people of various regions would plant favored shrubs and trees, such as yellow wood, on their travels. In this way, they were always assured of having this plant material available.

So what I have just described is the process of migration for plants and trees. You can imagine my level of confusion when I happened upon the new term, ‘ assisted migration ‘. So were they just renaming an old term? Turns out, No. To truly understand this terminology you must believe in climate change and its consequences.

Through industrial activity and tropical deforestation, we have set the planet on a course to warm to temperatures not seen in the past 100,000 years. Earth has seen similar warmings in the distant past but the RATE of these warmings were at a substantially slower rate. For Ontario, warming is projected to be greater in the North than the South.  Precipitation wise, Northwestern Ontario and most of Southern Ontario will see a 10% decline along with an accompanying increase in temperatures. By 2100, we should see our annual temperatures rise by 6C. Overall, at a forest level, soils are going to be drier.

So what has been the immediate impact on our forests and tree species? Basically, as the climate changes, some individual trees or even whole local populations of a species may not prove adaptable to the new conditions, nor have the capacity or time to become adapted. These trees may not be able to migrate to more favorable conditions, given that climate is changing faster than natural migration via wind, water and animals, has occurred in the past. Another negative effect, a barrier to migration, is temperature and other weather extremes affecting flowering and seed production.

When you hard boil all the scientific evidence down, the real problem is the tree migration rate needed. Historically, trees can migrate at less than 10 kilometers per 100 years. With climate change and warming happening even faster than predicted, trees will have to move 150 – 200 kilometers in the next 100 years to ensure continuation of tree species within favorable climatic conditions. Obviously, the evolutionary migration rate of trees cannot keep pace with the anticipated rates.

What to do? The choice seems to be assisted migration. It is the intentional migration or relocation of southern trees species north, by man. It is a planned relocation of species, still within its natural growth range, but at the northern extent of its current habitat. In my next article, we will look at the mechanics and controversy of assisted migration of trees.