Birches of Sandy Lake & Environs (Bedford, NS)

I have been having difficulty distinguishing with confidence between Yellow Birch and Paper Birch for some individual specimens in old mixed and hardwood forest at Sandy Lake and Environs (Bedford, Nova Scotia); most are very large trees. I suspect some of these are hybrids. So this project is set up to collate observations on birches generally in the area with a focus on the large birches. I will tag* some others for reference (*i.e. identify an observation as part of this project). It can be difficult to get twigs, leaves, catkins etc from the big trees (too high up), but I try at least to get good photos of the leaves, will add photos of other features as I can get them.

According to USDA Plant profiles, Betula papyrifera Marshall var. cordifolia (Regel) Fernald (Mountain Paper Birch) occurs in NS. (https://plants.usda.gov/core/profile?symbol=BEPAC2).

** Note added, Sep 29, 2019I have been keeping an eye out for this species; on Sep 22, 2019 I observed a pretty clear case, see https://www.inaturalist.org/observations/33579965

From Nova Scotia Plants (https://ojs.library.dal.ca/NSM/pages/view/Plants) under Betula papyrifera Marshall: "Betula cordifolia is now considered to be a variety, as var. cordifolia (Regel.) Fern. The leaves are heart-shaped in outline abruptly tapering to a point."

I am somewhat confused about the status of Betula papyrifera var. cordifolia, as Betula cordifolia is a recognized species but says FNA: "In recent years Betula cordifolia has usually been treated as a variety of B . papyrifera , and perhaps it should be considered an ecological race of that species. It differs from B . papyrifera in polyploid level (diploid and tetraploid in B . cordifolia versus tetraploid, pentaploid, and hexaploid in B . papyrifera ) and in vegetative characters, including the number of lateral veins of leaves and the color of bark (W. H. Brittain and W. F. Grant 1967; P. E. DeHond and C. S. Campbell 1989)."

ACCDC lists Betula papyrifera var. cordifolia (Heart-leaved Birch) for NS, not the species: http://accdc.com//webranks/NSVASC.htm

Trees in Canada (Farrar, 1996) p 287 provides a detailed description for "Mountain Paper Birch, Betula cordiflora [syn. B.papyrifera var.cordifolora (Regel) Fern.]".

Hybridization does occur between yB and wB (yellow and white or paper birch).So are the "odd" trees I observe at Sandy Lake hybrids of yB and wB, or the separate species?

...I hope to sort it all out for the birches of Sandy Lake & Environs as I make more observations and read more lit. Preliminary observations suggest there is some pattern to where the problematical ID trees occur.

Good discussion and pics here:

http://northernforestatlas.org/2016/10/16/notes-on-the-white-birches/ less ↑