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Can we help? Assisted migration in an age of global warming

As the planet warms, species are on the move. The phenomenon has been observed in oceans, with fish populations shifting to the poles, and on land, with creatures moving to higher elevations in search of cool. Many species are struggling for survival in shrinking habitats.

And here in Ontario, higher temperatures are taking a toll of an iconic northern bird. The Gray Jay – the friendly Whiskey Jack of the boreal forest – has undergone a 50 per cent population drop in Algonquin Park over the past 25 years. The decline has been linked to spoilage of its perishable winter food caches, once kept reliably refrigerated by cold winters. Areas that in the past supported the Gray Jay are now abandoned.

The plight of some species – the American pika, the Edith’s checkerspot butterfly, the California newt – is so critical that the question being posed is whether they need assisted migration, which means being moved by us to locations where we deem the climate to be suitable for them, now and 50 to 100 years from now.

It’s a controversial idea on many fronts. Do we know enough about these species, about their resilience or their vulnerability? Will the relocated species bring disease or become invasive? Will the practice undercut attempts to reduce and mitigate climate change? Will it undermine existing protection for species at risk?

But we have lost Costa Rica's Golden Toad and Australia's White Lemuroid Possum, both species that resided in high-altitude tropical forests, and both believed to have gone extinct because of higher temperatures. Extinction is happening. 

As for the Gray Jay, if it is to move north, its habitat – forests of black and white spruce and jack pine - has to expand northward as well. And that takes time. Most tree species can migrate naturally up to a few hundred metres a year through seed dispersal. What we are seeing now are climatic conditions that may move north by several thousand metres a year, according to a recent Forest Ministers’ report on Canadian trees’ vulnerability to climate change.

It’s unlikely most tree species can move fast enough to keep pace with changes accompanying a warming planet. So the report considers assisted migration – giving cautious approval to movement of populations within a species’ range, but expressing reservations about range expansion or translocation of exotics (moving a species to a location where it has not occurred before).

The Torreya Guardians offer one of the best online documentations of citizens’ efforts at assisted migration. Torreya taxifolia is a yew that is only found along a 65-kilometre stretch of the Apalachicola River in northen Florida. In recent years it has been attacked by a variety of fungal pathogens that make it die back cyclically at the sapling stage. No adult specimens survive in the wild.

The Torreya Guardians rallied in 2004 to grow seedlings and cuttings, and in 2008 “rewilded” T. Tax at several locations on private property in North Carolina. The young plants appear to be thriving and the good news is that it appears the new plantings do not suffer from fungal disease.

While forestry and conservation managers have to exercise caution about what species they introduce onto the landscape, assisted migration seems to me to be a good use of garden space. Here in Simcoe County we are in the fortunate position of being at the upper range for many Carolinian species – the Carolinian forest being an area that stretches from the Carolinas to the northern shore of Lake Erie. These mixed deciduous forests are rich in beautiful plants. Among them:

Trees: Tulip Tree (Liriodendron tulipifera), Hop Tree (Ptelea trifoliata), Eastern Redbud or Judas Tree (Cercis Canadensis), Flowering Dogwood (Cornus florida), Red Mulberrry (Morus rubra), Hackberry (Celtis occidentalis), Honey Locust (Gleditsia triacanthos), Black Walnut (Juglans nigra), Ohio Buckeye (Aesculus glabra).

Shrubs: Spicebush (Lindera benzoin), Prickly Ash (Xanthoxylum americanum), Bladdernut (Staphylea trifolia), Dwarf Hackberry (Celtis tenuifolia), Witch Hazel (Hamamelis virginiana), Burning Bush (Euonymus atropupurea), Fly Honeysuckle (Lonicera Canadensis), Carolina Rose (Rosa Carolina), Swamp Rose (Rosa palustris).

Perennials: Butterfly Weed (Asclepias tuberosa), Harbinger of Spring (Erigenia bulbosa), Bloodroot (Sanguinera Canadensis).

Link to Torreya Guardians
- 3 March 2013 at 09:44pm

"Here in Simcoe County we are in the fortunate position of being at the upper range for many Carolinian species – the Carolinian forest being an area that stretches from the Carolinas to the northern shore of Lake Erie. "

All the more reason for treating the MInesing Swamp and the Nottawasaga river with a little respect, rather than abandoning them to the crass experimentation of the speculators.
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