Page 23 - Forest Trees of Maine

The relationship between tree age and size can be very deceptive. Many tree
species can survive in a shaded understory for years, with nearly microscopic growth
rings. These tree species are called shade tolerant. When the canopy is partially or
wholly removed by harvest, mortality or weather, increased available sunlight allows
accelerated growth. This process is known as release. Some long-lived species, such
as red spruce, can survive for decades in the understory, then for centuries in the
overstory. Others are shade tolerant but short lived; for example, balsam fir rarely
exceeds 100 years in total age. Still other species such as quaking aspen and paper
birch are intolerant of shade and relatively short-lived. An observer with knowledge
of tree species and growth characteristics can deduce the history of a forest without
cutting or boring holes in stems to count rings.
TR E E P AR TS AND F UNCT IONS 21