Soil productivity does not always equate to more deer. Look at our MDC harvest map and you will see the counties with highest harvest generally are timbered more and have more cover. Best soil productivity is along the river and NW Missouri. But, due to loss of CRP and loss of other cover there are no longer the numbers of deer like there was 5 years ago.
A few years ago I lived in North Dakota and the soil was higher in organic carbon than I have ever seen in Missouri even along the Malta Bend farms and due to lack of cover - there was no where for a deer to hide....now I will say with healthier soil usually equates a fatter, larger framed deer. There are quite a few Whitetail strains and generally the principle is the farther north you travel the larger the frame. Same thing with furbearers.....a coon trapper from Georgia or Texas should travel up and catch a northern MN or Canada coon - they will be in for a shock. I kept one of my 49" coons I caught from North Dakota - I had never seen such a mammoth.
Good job on the doe - looks like nice eating....I get tired of cleaning deer after a while.
I agree with most of your post but soil fertility is the base for better quality habitat...and ultimately better populations. But, there are for sure other factors at play. Critters need food, water, cover, and space in an optimum arrangement. Other factors include things such as hunting pressure and diseases such as EHD/CWD.
Also, some good deer populations exist in prairie type habitat in states such as Kansas, Nebraska, and the Dakota's. Not much timber there?
Bergman's Rule is farther north - bigger body concept you referenced.