The Rural Voice, 2003-10, Page 26Nature's magic
A complex chemical change helps paint the
Ontario countrgside each fall with the richest
colours in nature's paint box
By Todd Leuty
OMAF Agroforestry Specialist
22 THE RURAL VOICE
As each growing season winds
down, forest trees in Ontario
can put on spectacular shows
of fall colour.
Some seasons produce more
vibrant colours than others and the
reasons for the differences are not
fully understood. Many forests in
southern Ontario are a diverse mix of
cone -bearing conifers such as pine,
spruce and hemlock, deciduous trees
such as maple, ash, oaks and birch,
plus many smaller shrubs like
staghorn sumac that also add
brilliance to the fall colour show.
There are many complicated
interactions occurring within trees
that contribute to fall colours. These
interactions are not fully understood.
Leaf pigments, length of night, the
type of tree, genetic variation, soil
and site characteristics and the
weather all play a role.
Where do leaves get their colours?
Colour in tree and plant leaves
comes from pigments including
chlorophyll which produces green
colours, carotenoids that give yellow,
orange and brown colours and
anthocyanins that provide variations
of red and purple. Certain colours of
leaves are characteristic of particular
tree species. The timing of colour
change also varies by species.
• Sugar maple turns orange and red;
• Black maple turns a glowing yellow
• Native red maple turns brilliant
scarlet;
• Aspen, birch and yellow poplar
become golden brown;
• Beech turns a light tan;
• Oaks turns red, brown or russet;
• Hickories turn golden bronze;
• Dogwood turns purplish red;
• Elm leaves just shrivel up and fall
off.
During the spring and summer
leaves are full of chlorophyll and as a
result are green. Although other
pigments are present in the leaves
during summer they are masked by
the large quantities of chlorophyll.
Plants need lots of chlorophyll to
capture sunlight for photosynthesis,
the process that enables them to
manufacture their own food.
As the days become shorter in the
fall, chlorophyll production slows
down and eventually stops. At this
time the other carotenoid and
anthocyanin pigments become
visible. Temperature and moisture
greatly influence autumn leaf colours.
A succession of warm, sunny days