large red oak in our backyard produces bushels of acorns every year,
but this year there are hardly any acorns to be found. Do you know
what might have caused this acorn shortage? We're worried our
squirrels won't have enough acorns to get them through the winter,
especially since cold weather arrived early this year.
The lack of acorns
this year is extreme and very widespread, extending from Nova Scotia
to Virginia and as far west as Kansas, according to a recent article
in the Washington Post by Brigid Schulte. It has generated an e-mail
discussion among Penn State Cooperative Extension educators in
horticulture and forestry, as well as questions from the public.
There are a number of reasons oaks fail to produce acorns, generally
a combination of environmental effects and genetics. Forest
ecologists have long noted that oaks produce an abundant acorn crop
only one out of every three or four years. But they usually produce
some acorns, even in bust years. And not all species of oaks --
there are 17 native to Pennsylvania and a few non-native species
that have naturalized here -- would have a bust year at the same
White oak is native to Pennsylvania
weather accounts for the lack of acorns in many years, but given the
differing climate and weather conditions occurring at any one time
across such a large area, it is unlikely we can blame it all on the
weather. Late frosts can kill oak flowers before they are
pollinated. Of course, 2008's spring was one of the most spectacular
in recent memory here in Pittsburgh, so we cannot blame a late
Oaks are wind pollinated, rather than insect pollinated. Although
cross-pollination -- the pollen from one tree landing on the female
flowers of another tree -- is preferred because it increases genetic
diversity, oaks are able to pollinate themselves. It is possible
that heavy spring rains at bloom time could wash the pollen out of
the air before it reaches female flowers.
But the National Weather Service records for the Pittsburgh area
show no unusual rain events when our oaks would have been in bloom.
Another theory is that the oaks are stressed by drought or gypsy
moth outbreaks. However, stressed oaks have a tendency to produce a
lot of acorns in order to keep the species going.
Red & White
Oaks are broken down into the white and red groups. The white oak
group includes white oak, swamp white oak and chestnut oak. Their
leaves do not have bristles on the lobes and their acorns mature in
one growing season. The red oak group includes northern red oak, pin
oak and black oak. Their leaves have bristles at the tips of the
lobes, and their acorns take two seasons to mature. If unfavorable
weather in the spring of 2007 interfered with flowering or
pollination, there would be few ripe red oak acorns on your tree.
Northern Red Oak foliage
fruits like acorns are known as hard mast, a critical source of
protein, carbohydrates and fats that helps wildlife survive winter
when other food sources are minimal. Fortunately, there are other
sources of hard mast, including hickory nuts, beechnuts, hazelnuts,
walnuts and pine seeds. If you want to help your local squirrels
through the winter, put food out for them. Although they love
sunflowers and unsalted peanuts, it is healthier for them if you
stick with native food sources such as hazelnuts or walnuts in the
Field biologists, naturalists and others will be watching 2009's
acorn crop with keen interest to see if this was just an abnormally
bad "bust" year or if 2008's scarce acorn crop is a harbinger of
things to come.
ACORNS OF COMMON
NORTHEASTERN U.S. OAKS
(Quercus velutina) - Acorn ½-1 inch long, ripens over
2 growing seasons, kernel yellow and bitter.
(Quercus montana) - Acorn 1-1½ inches long, ripens in
1 growing season, kernels somewhat sweet.
Oak (Quercus rubra) - Acorn ¾-1¼ inches long,
ripens over 2 growing seasons, kernel is bitter.
Pin Oak (Quercus
palustris) - Acorn ½ inch long, ripens over 2 growing
(Quercus coccinea) - Acorn 1 inch long, ripens over 2
growing seasons, kernel white and bitter.
(Quercus alba) - Acorn ¾-1 inch long,
ripens in 1
growing season, kernels were used by Indians for
Black Walnut trees
Oak Wilt disease
Black Walnut Tree poison