Evergreen Leaf Adaptation
Date: Around 1999
How are the leaves/needles of coniferous trees adapted to
their environment (vs. broadleaf, deciduous trees)?
Needles, with smaller surface and fewer pores, lose water much less rapidly
than broad leaves, which helps them adapt to winter's drying. Lack of
available water in winter is as much a factor in leaf function as is cold.
Any decent botany book will explain further.
A general answer would be that conifer needles, in comparison to broadleaf
leaves, are thicker, tend to have waxy coatings, and are more numerous.
These qualities enable the tree to hold them for several seasons, in
comparison to deciduous trees regular leaf loss. The waxy coatings promote
water conservation and enable the trees again to hold a canopy during dry
periods of the year when water might not be available. The small size and
number of needles provides a mechanism by which a tree can effective capture
a great percentage of incident sunlight. (This can be seen in the (general)
lack of light under such general as spruce, fir, or hemlock.) This
capability can reduce plant competition for nutrients with those species
which are shade-intolerant.
It should be noted that evergreen trees do in fact lose a percentage of
their needles during the year, but the investment of the entire canopy does
not have to be replaced yearly, as occurs with deciduous trees. One noted
exception, the larch, is a deciduous conifer; because of this, the species
is a poor choice for a holiday tree.
Thanks for using NEWTON!
Conifers go beyond deciduous angiosperms in showing adaptations to cold
climates, with spire shapes to shed snow. Because of the slow nutrient
release in the soil, it may be too expensive to replace leaves each year,
so conifer leaves are evergreen.
Anthony R. Brach, Ph.D.
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Update: June 2012