LOOK: An archive of pressed flowers (and weeds) at the Denver Botanic Gardens reflects changing temperatures

Underneath the Denver Botanic Gardens’ greenhouse, you’ll find the herbarium, a massive library of pressed plants collected over the course of a century.

Erigeron eximius, a wild daisy variety, found near Empire, CO on Aug. 22, 1999. (Kevin J. Beaty/Denverite)research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Erigeron eximius, a wild daisy variety, found near Empire, CO on Aug. 22, 1999. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Erigeron eximius, a wild daisy variety, found near Empire Aug. 22, 1999. (Kevin J. Beaty/Denverite)

Most people think of the Denver Botanic Gardens merely as a pretty weekend activity. While that’s true, there’s more to it beneath the surface, in this case, literally.

Take a flight of stairs down below DBG’s greenhouse and you’ll find the herbarium, a massive library of pressed plants collected over the course of a century. And most of the archive’s accessions, or entries, have been collected in Colorado.

Aquilegia correa, AKA Columbine, plucked from Park County Aug. 9, 1995. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Aquilegia correa, AKA Columbine, plucked from Park County Aug. 9, 1995. (Kevin J. Beaty/Denverite)

Using the data associated with these pressed accessions, a team of scientists working at the Gardens were able to show how plant life cycles have shifted since the 1950s.

Qualitative ecologist Michelle DePrenger-Levin, conservation botanist Rebecca Huft, database associate Richard Levy and systematist Melissa Islam collaborated on a study that, according to Huft, shows a number of Colorado’s alpine plants have bloomed earlier and earlier over the last 60 years.

Achillea lanulosa, AKA western yarrow, picked from Grand County, Aug. 29, 2004. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Achillea lanulosa, AKA western yarrow, picked from Grand County Aug. 29, 2004. (Kevin J. Beaty/Denverite)

Each plant in the collection is noted with a collection date which points to the time of year that it bloomed. Stacking all these various collection dates together reveals a pattern of change.

Arnica mollis, a member of the sunflower family, discovered Aug. 16, 1957 near Rocky Mountian National Park. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Arnica mollis, a member of the sunflower family, discovered Aug. 16, 1957, near Rocky Mountain National Park. (Kevin J. Beaty/Denverite)

The most surprising result,” Huft told Denverite, is that “the changes are strong enough to still show a significant trend toward earlier flowering times when all species are analyzed together.”

According to their data-crunching, an average of 57 species bloomed an average of 33 days earlier today than they did in 1955. This change in life cycle, or phenology, is an indication of changing climate in Colorado.

Advancing bloom dates over 61 years of select species. (Courtesy Denver Botanic Gardens)
The graph on the left shows trend lines for 57 species’ collection dates over 61 years; the species’ collection dates advanced an average of 33 days. The graph on the right shows how one species’ collection date was 53 days later over 61 years, demonstrating how different species respond differently to similar changing conditions. (Courtesy Denver Botanic Gardens)

While Huft says they can’t say for sure if globally-rising temperatures are the culprit, she says “these results provide strong support for plant changes in response to climate change.

The study also helps to identify species to keep an eye on in the future.

Potentilla ovina, or tundra cinquefoil, found in Clear Creek Jul. 19, 1977. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Potentilla ovina, or tundra cinquefoil, found in Clear Creek July 19, 1977. (Kevin J. Beaty/Denverite)

Overall, the team concluded that all 468 species’ bloom times advanced an average 3.4 days per degree that average high temperatures increased. Of those species studied, 67 showed an average 10.6-day increase per degree.

Not all of the species show earlier bloom times, said Huft, but while some plants are blooming sooner due to higher average temperatures others are changing their range, moving higher up mountainsides, or else becoming less dense in other areas.

The study is set to be published this summer. Findings were presented in October at the Natural Areas Conference in Davis, California. The charts on this page come from a powerpoint presented at the conference.

Changes in bloom date of select species as it relates to annual average high temperatures. (Courtesy Denver Botanic Gardens)
The chart on the left shows how 67 species’ collection dates correspond to increases in average high temperatures; these species’ were collected an average of 10 days later per degree increase. The chart on the right shows how two species’ collection date were delayed an average 8.9 days per temperature increase, showing how different species respond differently to similar changes in conditions. (Courtesy Denver Botanic Gardens)

While the Denver Botanic Gardens’ study pulls data from all over the state, Colorado is also home to a plot that’s been observed since 1973. Dr. David Inouye has kept up continuous monitoring of plant and animal life cycles at the Rocky Mountain Biological Laboratory in Gothic that’s become the gold standard for such research.

In a 2009 analysis of four species over 39 years, Inouye and his team found that “plants are leafing out and flowering earlier in many locations as a response to warmer temperatures and earlier snowmelt.”

Because this study worked with live plants, the research team could also see beyond first bloom times to other effects that point to a changing environment. “Climate change,” says the study, “is also influencing the reproduction, growth and other important traits of many species.”

Salix brachyacarpa, known as the shortfruit willow, collected Aug. 3, 2012 from Arapahoe National Forest. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Salix brachyacarpa, known as the shortfruit willow, collected Aug. 3, 2012, from Arapahoe National Forest. (Kevin J. Beaty/Denverite)

It’s proof that foresight is crucial to effective science. The Botanic Gardens’ study was only made possible through the diligent collections made by naturalists that began more than 100 years ago. In fact, the herbarium contains plants going back as far as 1821, though the very old accessions tend not to come from Colorado.

The herbarium itself predates the Botanic Gardens, founded by George Kelly and Kathryn Kalmbach in 1947. According to Melissa Islam, the current head curator, Kalmbach was the first to manage the collection until she died in 1962.

The Denver Botanic Gardens Kathryn Kalmbach Herbarium. (Courtesy Scott Dressel-Martin/Denver Botanic Gardens)
The Denver Botanic Gardens Kathryn Kalmbach Herbarium. (Courtesy Scott Dressel-Martin/Denver Botanic Gardens)

The library has since been named the “Kathryn Kalmbach Herbarium” in her honor. It contains about 60,000 specimens and adds about 1,700 each year.

Tonestus Pygmaeus, known as the pygmy goldenweed, collected on Mt. Goliath Aug. 18, 1982. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Tonestus Pygmaeus, known as the pygmy goldenweed, collected on Mt. Goliath Aug. 18, 1982. (Kevin J. Beaty/Denverite)

And you too can feast your eyes on the collection. Islam says curious parties are “welcome to visit Monday-Thursday, 9 to 2 p.m. We encourage visitors to make an appointment.” To do that, you can call 720-865-3593 or email research@botanicgardens.org.”

You can also participate in ongoing phenological studies through Nature’s Notebook, a citizen science program that tracks plant stages and played a part in DGB’s study. All you need to do is sign up and then take simple notes while you’re out enjoying the Colorado wilderness.

Antennaria Rosea, known as rosy pussytoes, collected near Gothic, CO, Jul. 5, 1948. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Antennaria Rosea, known as rosy pussytoes, collected near Gothic, July 5, 1948. (Kevin J. Beaty/Denverite)
Erigeron Coulteri, known as Coulter's daisy, plucked from Pueblo County Sept. 2, 1931. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Erigeron Coulteri, known as Coulter’s daisy, plucked from Pueblo County Sept. 2, 1931. (Kevin J. Beaty/Denverite)
Aquilegia correa, AKA Columbine, plucked from Park County Aug. 9, 1995. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Aquilegia correa, AKA Columbine, plucked from Park County Aug. 9, 1995. (Kevin J. Beaty/Denverite)
Trifolium nanum, known as the dwarf clover, found in Park County, Jul 22, 1995. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Trifolium nanum, known as the dwarf clover, found in Park County, Jul 22, 1995. (Kevin J. Beaty/Denverite)
Castilleja miniata, known as the "giant red Indian paintbrush," found in Jackson, CO, Aug. 3, 2002. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Castilleja miniata, known as the “giant red Indian paintbrush,” found in Jackson Aug. 3, 2002. (Kevin J. Beaty/Denverite)
Antennaria Rosea, known as rosy pussytoes, collected from Jefferson County, Jul. 4, 1937. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Antennaria Rosea, known as rosy pussytoes, collected from Jefferson County July 4, 1937. (Kevin J. Beaty/Denverite)
Erigeron ursinus, a wild daisy variety, found on Mt. Parnassus Jul. 5, 1997. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Erigeron ursinus, a wild daisy variety, found on Mt. Parnassus July 5, 1997. (Kevin J. Beaty/Denverite)
Achillea lanulosa, AKA western yarrow, picked from Grand County, Aug. 29, 2004. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Achillea lanulosa, AKA western yarrow, picked from Grand County Aug. 29, 2004. (Kevin J. Beaty/Denverite)
Erigeron Coulteri, known as Coulter's daisy, plucked from Pueblo County Sept. 2, 1931. (Kevin J. Beaty/Denverite) research; science; botany; flowers; archive; denver botanic gardens; dbg; climate change; kevinjbeaty; denver; denverite; colorado;
Erigeron Coulteri, known as Coulter’s daisy, plucked from Pueblo County Sept. 2, 1931. (Kevin J. Beaty/Denverite)

Kevin Beaty

Author: Kevin Beaty

Kevin Beaty is a media producer with experience in a variety of settings spanning Hollywood film sets to international backpack journalism expeditions. He is on a never-ending quest to meld artful imagery, functional design and intimate storytelling. His biggest struggle in any given moment is whether to shoot stills or video.