Cross
the stream using the new bridge which leads to the north-facing slope. This part of the trail receives
considerably less direct sunlight than the more southerly exposed sections on
which we have been hiking. The effects of this reduced incoming light differ
from season to season and also from year to year. In the winter, snow melts more
slowly on this slope and often persists on into the early spring. In the spring,
soil temperatures rise more slowly and fern fiddleheads emerge and wildflowers
bloom often weeks later than on the warmer, sunnier parts of the trail. In the summer,
the impact of this shading depends upon the
season's rainfall. In years in which rainfall is average or above average you
will see less dense vegetation on these shady slopes because of the reduced
incoming sunlight. In
years of below average rainfall, we are likely to see denser vegetation on this slope due to the
water conserving influence of the shade. These observations are consistent with
the ecological "law" called the Law of Limiting Factors. When rainfall is
limiting anything that slows evaporative water loss from the soil (like shading)
will favor overall plant growth. When rainfall is not limiting, soil moisture
will remain high even on the sunnier slopes so the stimulatory effect of
sunlight on photosynthesis will be the driving "limiting" factor.
Cross
the stream using the new bridge which leads to the north-facing slope. This part of the trail receives
considerably less direct sunlight than the more southerly exposed sections on
which we have been hiking. The effects of this reduced incoming light differ
from season to season and also from year to year. In the winter, snow melts more
slowly on this slope and often persists on into the early spring. In the spring,
soil temperatures rise more slowly and fern fiddleheads emerge and wildflowers
bloom often weeks later than on the warmer, sunnier parts of the trail. In the summer,
the impact of this shading depends upon the
season's rainfall. In years in which rainfall is average or above average you
will see less dense vegetation on these shady slopes because of the reduced
incoming sunlight. In
years of below average rainfall, we are likely to see denser vegetation on this slope due to the
water conserving influence of the shade. These observations are consistent with
the ecological "law" called the Law of Limiting Factors. When rainfall is
limiting anything that slows evaporative water loss from the soil (like shading)
will favor overall plant growth. When rainfall is not limiting, soil moisture
will remain high even on the sunnier slopes so the stimulatory effect of
sunlight on photosynthesis will be the driving "limiting" factor. 
