Zone limitations for Douglas Fir.

I'm a tree farmer in Alberta.
I have an opportunity to pick up a box of doug fir labeled as grown for SBS the Sub-boreal spruce zone. -- Area around Prince George down toward Clearwater. Bit cooler than the Interior Doug Fir zone.

The climate data for the BC BGC subzones is here:

http://cfcg.forestry.ubc.ca/resources/cataloguing-in-situ-genetic-resources/subzonevariant-climate-data/

Now I'm puzzled.
The second lower case letter is for temperature (generally. some exceptions for coastal...) going h, w, m, k, c for hot, warm, moderate, kool, and cold.
Yet the average for the warms is higher than the average for the hots.

But the differences in all the characteristics are pretty small.

So now I go to

http://www.for.gov.bc.ca/hre/becweb/resources/classificationreports/subzones/index.html


And download the chunk for SBF Now on page 214 of that document doug fir has the dominant or subdominant bar for dh, dw, mh, and mw, and NO other appearance at all. Not even the tiny .1 -1% category. Temperature differences between subzones is about half a degree C.

Given the tiny temperature differences between subzones, there would seem to be either:

* A factor that the climate data doesn't capture about the differences between SBS subzones
* Some tipping point factor for either the survival or propagation of doug fir.

Can anyone tell me:
A: Why does douglas fir grow so well in 'h' zones, nearly as well in 'w' zones, and not at all in 'm' and 'k' zones. (A link to a relevant web page would be fine)
B: Is attempting to grow douglas fir near Edmonton a waste of my time and money? At first blush my climate norms are close to those of SDF, but the firs seem to thing that there is a big difference chunks that have tiny differences.

 

I can address question two a little bit. Should be possible to grow var. glauca (Rocky Mountain Douglas-fir), as it is listed as hardy to Zone 3b (which is what Edmonton seems to be). Prince George is perhaps Zone 3, so these should be among the most cold-resistant genetic lines. I notice some Manitoba nurseries are stocking the tree.