Quaking aspen (Populus tremuloides) reproduces both by seeds and root sprouts.
This Willow Family (Salicaceae) member is dioecious, having male and female flowers on different plants. These unisexual, densely clustered, hairy, pendant catkins produce capsules, fruits that split open at maturity releasing numerous tufted seeds to be scattered by the wind. The small seeds have very short viability and must germinate within a week or two after release. A lack of moisture during seed dispersal often results in few seeds germinating. And of those that do, even fewer survive because of fungi, unfavorable soil conditions and adverse temperature changes between day and night temperatures.
Rather than via seeds, the primary reproductive strategy of quaking aspen is through shoots and suckers that sprout along the tree’s long, lateral roots. The group or colony of trees produced from a single aspen via sprouting stems/suckers is a clone. Once established this clone is genetically identical to the original tree and the entire clone is the same sex as the original tree. Individual clones can be distinguished by slight differences in leaf size and shape, bark character, branching habit, resistance to disease and air pollution, sex, autumn leaf color and time of flushing (leaf opening).
Any single stem in a clone rarely lives more than 100 years. However, when the stem dies it is replaced by new stems from the same parent root system. Thus quaking aspen clones can cover many acres and can perpetuate themselves for centuries or even millennia.
In Fishlake National Forest (Utah) there is a male quaking aspen clone named Pando (“I spread out” in Latin) considered to be the largest living single organism by total biomass. This clone, or “single” tree, is estimated to be 80,000 years old and weigh over 14,000,000 pounds. Unfortunately scientists believe Pando is dying. The exact reason is unknown but drought, grazing (deer and livestock) or fire suppression (allowing succession to a conifer forest) are possible reasons.
These quaking aspen clones were photographed in October on Wheeler Mountain in Great Basin National Park (Nevada). From a distance, the individual clumps of yellow leaves amid the conifers identify separate quaking aspen clones.