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Taking the Pulse of Our Planet

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Herbarium records provide insight to flowering phenology in the Southeast U.S.

Photo: Jason Hollinger via Wikimedia CommonsIn a nutshell

When it comes to studying the influence of climate on flowering phenology, plants in temperate or tropical areas are often the focus. In temperate regions, flowering phenology is linked to temperatures in the 1-3 months prior to flowering; in tropical regions, precipitation influences flowering. Sub-tropical regions contain plants with various flowering times throughout the spring and summer. Flowering in these regions is thought to be more sensitive to temperature than precipitation, though this has not been widely studied.

To address this gap in knowledge regarding cues to flowering in plants of the subtropics, the authors of this study looked at herbarium records of over 1700 native herbaceous flowering plant species from South Carolina from 1951 to 2009. They found plants that flowered in early and late spring and summer were al influenced by March temperatures; February temperatures also appear to be important to plants that flowered late in the season.

What is special about this study?

The authors focus on the humid, subtropical ecosystem of the southeast, which has not been extensively studied. This region is an important transitional zone in between tropical and temperate regions, but little is known about the phenology of the flowering plants in this region.

Many universities, museums, and botanical gardens keep herbarium records, but they are an underappreciated resource. Previous studies that used herbarium records focused on a small set of highly collected species, limited to a localized area. These authors used records from a large suite of species from across the state. This broader focus gives general estimates of how flowering varies from year to year across the entire community.

What does this mean for YOU?

Studies like this fill in the gaps in our knowledge of what causes plants to leaf out, flower, and fruit at different times. We can then better understand how changes in climate will impact these communities in the future. This study is also an important validation of the use of herbarium records to show yearly and long-term patterns of variation in flowering phenology. These records are critical when other types of records are not available.


Citation:  Park, I.W. and Schwartz, M.D. 2015 Long-term herbarium records reveal temperature-dependent changes in flowering phenology in the southeastern USA. International Journal of Biometeorology 59:347-355. 


Learn what your 2014 observations reveal, and the ways scientists are using your observations. We cover results from the 2014 Campaigns, as well as a range of other results from observers across the country. 

Dogwood Campaign Results

Volunteers have been tracking cloned lilacs for over 50 years, and these observations have been invaluable for documenting how plants are responding to a variable and changing climate. However, lilacs don't grow very well in the southernmost parts of the US. A dogwood was recently cloned for distribution in southeastern states to address part of this data gap, and Nature's Notebookparticipants began submitting observations in 2013.

2015 Results:

Our 2015 Year End Summary webinar explains some of the patterns that were seen in observations of dogwoods and lilacs submitted to Nature's Notebook.


2014 Results:

Cloned Dogwoods:

The graph below shows the timing of breaking leaf buds, flowers or flower buds, and open flowers for all cloned dogwoods monitored through Nature's Notebook in 2013 and 2014. Breaking leaf buds and open flowers occurred slightly later in 2014, and for a longer period of time. Observers reported flowers or flower buds slightly earlier than last year, and for a much longer period of time. 

This may be attributed to the cold winter across most of the country, which likely affected the onset of leaf bud break and also may have caused aborted buds to remain on the tree for a long period of time. The flowers that did survive opened their petals later this year than last year. 

Cloned dogwood phenophases 2013 and 2014


The map below shows that  leaf-out and flowering were reported earlier in southern states than in northern states. Leaf-out in deciduous plants in temperate regions is very often cued by spring temperature, and as you know, we experienced warm temperatures much sooner in the South than in the North and Midwest this year. 

Cloned dogwood 2014 map

2013 Results:

Cloned Dogwoods:

The graph below shows the duration of 3 phenophases: breaking leaf buds, flowers/flower buds, and open flowers in 2013. 

cloned dogwood phenophase duration 2013

The map below shows the sites at which observers reported observations of breaking leaf bud in cloned and flowering dogwoods in 2013. The color gradient indicates the range for first reported date for breaking leaf bud at each site. 

Onset of breaking leaf bud in dogwoods 2013

The graphs below show the number of records reported for breaking leaf buds and open flowers among registered cloned dogwood plants from January to June in 2013. In the top graph you can see that the proportion of breaking leaf buds peaked in March and then decreased in May and June. Open flowers were observed on dogwoods in March and April. 

 number of records dogwood 2013

Nature's Notebook results webinar 2013: Why do scientists care so much about what's happening in your yard?

Nature's Notebook results webinar 2013: Why do scientists care so much about what's happening in your yard?

Spring of 2012 arrived remarkably early in much of the U.S... but what about 2013? What do those observations that you've been diligently collecting and reporting in your yard say about this year? How are scientists and decision-makers using these observations? View our 2013 results webinar video below to learn more or download the slides

Green Wave Southeast - Maples, Oaks, Poplars

laurel oakWe invite you to join us in tracking the “green wave”—the flush of green that accompanies leaf-out–-over the course of the spring season, as well as the spread of seasonal color across the country in the autumn.



New USA National Phenology Network information sheets synthesize recent changes in climate and phenology in eight U.S. regions. Find out what changes have been observed in salamanders in the Southeast, caribou in Alaska, ragweed in the Great Plains and more.