Yep, does seem an odd conclusion - even Taxus baccata can take colder than that, down to about -23° or -24°C. I have seen them killed/badly damaged in a severe winter in Denmark (zone 7) when it widely got down to -27°C. Some other species of Taxus are hardier, notably T. canadensis, which is the most likely yew to have been there (and presumably the one you're comparing?). Possible they meant average winter minimum, rather than extremes, but it seems unlikely. Also, Alnus viridis (a shrubby species) is currently native in Greenland, and pines (northern origins of P. sylvestris and P. contorta subsp. latifolia) grow well there when planted in the inner fjords close to the current ice cap (Refs: Ødum, S. 1979. Actual and potential tree line in the North Atlantic region, especially in Greenland and the Faroes. Holarctic Ecology 2: 222-227; Ødum, S. 1991. Choice of species and origins for arboriculture in Greenland and the Faroe Islands. Dansk Dendrologisk Årsskrift 9: 3-78).
My understanding is there are still forests in the southern parts of Greenland (Sorbus being the main tree). I have seen forests of Salix and birch in the Ummanaq area of the west coast of Greenland, mind you the canopy is two feet tall there.
Yep. Mostly Betula pubescens subsp. tortuosa, though, up to about 5-6m tall. There used to be more, but the Vikings cut a lot down for fuel and to increase grazing for their sheep (and the sheep prevented regeneration).
