Aspen (general)

USNPS photo

USNPS photo

Clonal Aspens - Lee Frelich  - May 31, 2004
Often you can see aspens that all turn color at the same time or turn all 
the same color in the fall all in one patch, and it is highly likely that 
the color patches indicate clones. Other than that you need to excavate 
the root system or do genetic sampling to see if a patch of aspens are a 
clone. For other tree species clusters are usually caused by neighborhood 
effects other than root sprout clones.

Edward Frank - June 1, 2005
Last week I posted a question concerning how to tell if an aspen grove was
clonal or grown from seed. Lee pointed out that clonal aspens will change
color all at the same time.

I have been reading on the internet from a number of sites. One key to
determining if a grove is a clone grove is that the trees are all the same
sex. Aspen is dioecious, so individual trees are either male or female.
Trees flower in March and April, before the leaves appear, with both the
male and female trees producing catkins. Male catkins produce yellow
pollen. Female catkins do not preoduce pollen. There also are
morphological differences in the catkins. See illustration from

poplar4a.gif (9190 bytes)

Here are excerpts from some of the internet sites:
European Aspen

Aspen is dioecious, so individual trees are either male or female (in
contrast to most trees, such as Scots pine, for example, where male and
female flowers occur on the same tree). Trees flower in March and April,
before the leaves appear, with both the male and female trees producing
catkins. Pollinated female catkins ripen in early summer and release tiny
seeds (each weighing about one ten-thousandth of a gram!) which are tufted
with hairs.

Aspen has an extensive root system, and ramets have been recorded growing
up to 40 metres from a parent tree. Because of their access to nutrients
through the parent tree's root system, aspen ramets can grow very quickly -
up to a metre per year for the first few years. As the ramets grow, they
remain joined through their roots, and all the interconnected trees are
called a clone. They are all the same individual organism and are therefore
all single-sexed, either male or female. Each clone exhibits synchronous
behaviour, with, for example, all the component trees coming into leaf at
the same time in the spring. A clone can also sometimes be identified by
the specific colour its leaves change to in the autumn.

Quaking Aspen

Quaking aspen forms clones connected by a common parent root system. It
is typically dieocious, with a given clone being either male or female.
Some clones produce both stamens and pistils, however. Quaking
aspen stands may consist of a single clone or aggregates of clones. 
Clones can be distinguished by differences in phenology, leaf
size and shape, branching habit, bark character, and by electrophoresis.
How to recognize male and female trees before flowering:

Here's a great suggestion from the McKinstrys in Oyen, Alberta:

  • in early spring bring a small branch from your poplar tree (label twigs
    with tape if from different trees) into the house and set in a jar of water
    soon the grey tufts (catkins) get longer, turning pinkish
  • if the branch is from a male tree the catkins then turn pale yellow as they
    shed a yellow powder (pollen) at the slightest touch. Place a dark paper or
    cloth under jar.
  • female catkins do not have pollen
  • outdoors, the wind quickly blows pollen away, so try this to be sure of
    your tree
  • if the catkins on your outdoor tree eventually turn green, the tree is
    female, and the search for male trees continues! reference - Quaking Aspen

Aspen clone takes size prize 

Quaking Aspen - Bryce Canyon National Park - 

Botanical Record Breakers - 

Devonian Botanic Garden - Aspen Poplar -