south faces of the mountain range. In mid-latitudes in the Northern Hemisphere, northern-facing slopes are cooler than south-facing slopes because they receive less direct solar radiation. R. B. Livingston found that slope variation on the range exerts marked influence on all environmental factors (Livingston 1982). The upper, north-facing slopes are steep and abrupt (35„a to 40„a), while the south-facing slopes are more moderate (20„a). Accordingly, the angle of mid-day insolation is typically 55„a to 60„a greater on the south slopes than on the north slopes, except in late fall and winter when no direct light strikes the steep north-facing hill (Livingston 1982). Even though the area this experiment took place in does not exactly exhibit the same temperature variations discussed by Livingston, this can be still be used as a representation of north-facing slopes being warmer than south-facing slopes around the world.
             On the Holyoke Range there are various species of Betula that have similar areas of optimal growth. The cherry birch, Betula lenta, can be found both in woods and in open and uplands on moist, protected, north-or east-facing slopes (Elias 1980). The yellow birch, Betula lutea, can also be found among cherry birch, but in the south
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