:Yes, it's larger than just the northern side of Borišov but the largest part of the reserve is on the northern side nonetheless (and extending further). If you feel the expression pristine is awkward, can you find a better one? The reserve consists of more types of well-preserved forests, that's the reason for its protection. One of the meanings of the word pristine is original, not affected by humans. I don't think the presumed awkwardness is a reason to delete the fact (http://www.sopsr.sk/velkafatra/sk/opk.htm, both sources). Primeval forest might be a better expression.  

 :There is board under the Borišov and Ploská mountain that says it's one of the largest (by area) avalanche slopes in Slovakia, the book and the map in resources say the same.  

 :As for deforestation, it is indeed deforested as well as all summits of "Holna Fatra". The natural upper tree limit was lowered by humans by some 200-250m (this figure varies from source to source). All books say so, as well as here: http://www.sopsr.sk/velkafatra/sk/vu2.htm. You can even see it on Borišov, where the trees reach almost the summit on the northern side, while the southern slope was stripped of trees. Naturally, the trees should be missing rather on the nortern side where the climate is harsher. 

 :Please, correct the language or punctuation if you find it faulty but do not remove the substantial  information. There are two sources listed on the bottom and they agree on all these facts (as well as any other articles or sources I have). Separate sources should be in places where there's some ambiguous information which is not the case here.