In what ways is soil pH and light the two critical factors for plant growth in the Boreal Forest?

Since this is not my area of expertise, I searched Google under the key words "ph light 'Boreal Forest'" to get these possible sources:

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http://66.102.7.104/search?q=cache:oesmr3d2NdgJ:maine.washcoll.edu/04/Lab%2520Reports/Bradley_Western_Mts.pdf+ph+light+%22Boreal+forest%22&hl=en&gl=us&ct=clnk&cd=4&client=safari
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I hope this helps. Thanks for asking.