Why are some plants evergreen while others are deciduous?

 By Richard B. Primack

 

"Between every two pines is a doorway to a new world." John Muir.

 

A question that has puzzled generations of scientists and naturalists is, why are some plant species evergreen, while other species are deciduous and drop their leaves in the autumn? In a recent article, I report on the results of a three-year experiment making evergreen white pine saplings drop their leaves each year, effectively making them deciduous. I found that holding onto their leaves for several years helps the pines survive and grow more quickly.

 

Photo 1: At the field site in winter with an abundance of healthy pine saplings.

 

The results of the experiment were strikingly apparent after just one growing season—pine saplings forced to become deciduous grew only 20% as much as the control plants. 

 

Photo 2: A control sapling in winter showing leaves from the previous two years. Two-year-old leaves are present below the 1-year-old lateral shoots. 

 

Photo 3: Sapling in winter with all leaves from previous two years removed. It will make new leaves in the coming spring.

 

An even bigger surprise was in store the following year. By the end of the second year, 75% of the “deciduous” pine saplings had died, in contrast to the evergreen saplings that were all still alive. And by the end of the third year, all the deciduous pine saplings were dead. 

 

This experiment involves a very simple design, going out in the late fall or winter and removing leaves to simulate the life cycle of a deciduous plant species. Despite this simplicity, as far as I know, no one has ever done this type of experiment before.   

 

Publication LINK -- Richard Primack (2025). Later Year Retention of Evergreen Leaves Is Important to Plant Growth and Survival in Eastern White Pine. Northeast Naturalist.

 

 

Flowers and Trees are Blooming Earlier: Is it because of Climate Change?

  By Richard B. Primack 

 

“This world is but a canvas to our imagination.”  Henry David Thoreau in A Week on the Concord and Merrimack Rivers.

 

This week, our research about climate change in Concord combining Thoreau’s records and modern observations was featured the Short Wave program on National Public Radio. This was the first episode of Nature Quest, a monthly Short Wave segment that answers listener questions about their local environment. 

 

Our Concord research highlighted that wildflowers are now blooming earlier and trees are leafing out earlier than in the past, and that these changes are due to a warming climate.  

 

I want to again thank Phil Cafaro, Professor of Environmental Philosophy (recently retired from Colorado State University), for directing us to Thoreau’s records of flowering times. So much of our research over the last 23 years followed from his initial suggestion. 

Here is a link to the story transcript: LINK

Visiting Scholar in Copenhagen Part 5: University of Copenhagen Geology Museum

 By Richard B. Primack

 

“Only that traveling is good which reveals to me the value of home and enables me to enjoy it better.” Henry David Thoreau in his Journal.

 

The University of Copenhagen Geology Museum contains many remarkable historic collections, along with many vibrant new exhibits. The Museum is also grappling with its colonial past, an issue which is linked to many of the collections.

 

Photo 1: This replica of the Ote Worm Museum from the 17^th century represents the origins of the current museum. 

 

Photo 2: The museum has a large collection of polar bears and skulls from Greenland, Denmark’s former colony, which have been used to demonstrate the declining bone mass of polar bears likely due to pesticides and other pollutants.

 

Photo 3: Old seed collections from the colonial past have proved useful for genetic studies; some of the old seeds have even been germinated.

 

Photo 4: The winning photos of the international “Wildlife Photographer of the Year” contest are on display at the museum.  

 

Photo 5: A photograph shows tadpoles migrating in a pond in Canada.

  

Photo 6: A photo of elephants wandering through a village in India.

 

 

 

Visiting Scholar in Copenhagen Part 4: Spring comes to the Botanical Garden

 By Richard B. Primack

 

“Only that traveling is good which reveals to me the value of home and enables me to enjoy it better.” Henry David Thoreau in his Journal.

 

When we arrived in Copenhagen on March 3, the University of Copenhagen Botanical Garden showed only early signs of spring, such as crocuses and snow drops. But by our last day on March 28, many more signs of spring were evident, especially in the rock garden area. 

 

Photo 1: The main rock garden is dotted with color from early spring flowers.

 

Photo 2: Primula vulgaris has one of the most dramatic flower displays.

 

Photo 3: Saxifraga sancta produces a mass of vibrant yellow blossoms.

  

Photo 4: Mukdenia rossii is another saxifrage distinguished by blackened surface rhizomes. 

 

Photo 5: A few early Rhododendrons are putting on a dramatic display of large colorful flowers.

 

 

Visiting Scholar in Copenhagen Part 3: City Hall

 By Richard B. Primack

 

“Only that traveling is good which reveals to me the value of home and enables me to enjoy it better.” Henry David Thoreau in his Journal.

 

Copenhagen has many remarkable historical buildings such as the City Hall, or Radhus, which dominates the main city square. 

 

Photo 1: The City Hall is a dark imposing brick building built in 1905.

  

Photo 2: A statue in front depicts a bull killing a dragon.

 

Photo 3: There is a large interior space, illuminated by a skylight, often used for public purposes, such as the current high school art exhibit on the theme - The Pulse of Denmark.

 

Photo 4: One entry in the exhibit is a diorama of husband and wife fighting while their daughter cries in another room.

  

Photo 5: Numerous artistic flourishes provide beauty, such as this stylized display of seaweed. 

 

Photo 6: A sculpted display of flowers embedded in the wall enriches the experience.

Photo 7: Besides magnificent architecture, the City Hall is also a functional space, with offices arranged along corridors, all illuminated by a skylight.