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catkins / 20 April 2019 / Bailey, Colorado

Living at 8,750′ elevation in the mountains of Colorado, Spring is here for Jean and I, finally! (Although, it’s May 10th, and it has been snowing for two days.)

We saw our first aspen tree catkins of the year on Saturday, April 20. Above is a photo I took of them on April 27. We have quaking aspens, by the way, as opposed to the other two mentioned in the below article.

We heard hummingbirds for the first time and saw one briefly on the feeder, also on April 27. We always see the Broad-tailed Hummingbirds first, pictured below: “Migratory hummingbirds usually in [their] breeding territory about mid-April. They breed across mountain forests and meadows throughout the Western United States from eastern California and northern Wyoming south through Great Basin and Rocky Mountain states to southern Arizona and western Texas. In September, they generally move south to winter in Mexico, Guatemala and, occasionally, El Salvador.” Soon afterwards, the Rufous species of hummingbird shows up here, at our elevation, in Bailey.

Broad-tailed Hummingbird with snowfall / 10 May 2019 / Bailey, Colorado

As far as Maibocks, I love good beer. These beauties “are brewed in winter and released in late April and May. They are rich yet not overbearing, and are enjoyed before the searing throes of summer.” Aside from that, they are very good to my taste buds at just this time, when the aspen catkins grow, then fall away, after which little green aspen buds appear. Those buds then transform into the quaking, green aspen leaves that most people associate with aspen trees.

But, what of the too-often overlooked, too-little-reflected-upon catkins? The following article, hopefully, will nurture such reflection.

The Aspen Catkin: What will become of this fuzzy little thing?

Kara Rogers – April 13, 2011

Aspens, of which there are three species—the American quaking aspen (Populus tremuloides), the American big-tooth aspen (P. grandidentata), and the European aspen (P. tremula)—exhibit several curious traits when it comes to reproduction. For example, each tree is either male or female, a condition known as dioecism, and while both male and female aspens produce catkins, only the male catkin has pollen, which is transferred to a female by the wind. And when the right breeze comes along in early summer, the pollinated female will release her seeds, which parachute along through the air, swept away to some distant place.

Aspens have a low rate of reproductive success. Indeed, it takes trillions of seeds being dispersed on the wind each year to ensure that a percentage sufficient for species propagation happens to parachute into a suitable environment, where they can germinate and sprout. Reproductive success is limited in part because aspens have strict germination constraints. For example, aspens are shade-intolerant, and therefore a seed needs a sunny spot to grow. That spot also must be free from seed-eating animals and able to retain moisture.

Another constraint on reproduction actually is imposed prior to pollination and has to do with the distance between male and female trees. Each aspen grove is a clone, meaning that all the trees in a grove are identical to the founder sapling. Hence, if a female sapling happened to give rise to the grove, all the individual trees in the grove will be female. This means that pollination can occur only if groves of the opposite sex are relatively close to one another. If they are separated by too great a distance, pollination between them is unlikely.

The future of each species of aspen hinges on its tufted catkin seeds, new generations of which face the perilous wind-borne journey every spring. Most do not make it. The ones that do, however, spawn entire groves of aspens—stands of trees that may survive for hundreds or possibly thousands of years.

This post was originally published in NaturePhiles on TalkingScience.org.

top photo by: s.a. bort / 27 April 2019 / Bailey, CO.

second photo by: s.a. bort / 10 May 2019 / Bailey, CO.