Do Plants use the Summer Solstice for Growth Strategies?

 By Richard B. Primack 

 

“Summer passes into autumn in some unimaginable point of time, like the turning of a leaf..” Henry David Thoreau in A Week on the Concord and Merrimack Rivers.

 

A recent high-profile article in the Proceedings of the National Academy of Sciences by Victor Van der Meerschvandermer and E. M. Wolkovich suggests that trees use the time of the summer solstice, the longest day of the year, to determine when to start the process of bud dormancy and leaf senescence that will end the growing season. Trees might even use the summer solstice to gauge how many flower buds will be set for the following year.  

 

Figure 1: The summer solstice is the longest day of the year.

 

I was asked to comment on the article for the Canadian newspaper Globe and Mail, and wrote the following:

 

The study is valuable in showing the potential of the summer solstice in determining major plant process. However, as the authors point out, because the summer solstice also occurs at the time of maximum temperatures, it remains unclear if plants are using day length or temperature to undergo transitions in growth. To disentangle these two factors requires further research with plants in the field and the lab.  

 

Photo 1: Trees may be responsive to the summer solstice.

 

Also, this study considers the general case of all plants, but it is almost certain that different tree species, such as beeches, pines, oaks and maples, will each have their own combinations of environmental cues and ways of responding to future climate change. This question needs to be investigated.

 

And further, we have strong evidence that later in the summer, plants use temperature (both high temperatures and low temperatures), precipitation and soil moisture, and photoperiod to determine the start of bud dormancy and leaf senescence. So perhaps we do not need to hypothesize the addition of another factor, such as summer solstice, especially since it occurs months before the end of the growing season.

 

Photo 2: Is autumn leaf color change triggered by the summer solstice months earlier? 

 

Here is a link to the scientific article: LINK

 

Here are links to two popular articles on this topic: LINK 1 and LINK 2

 

 

Seattle Woody Plants: Trees not Typically Grown in Boston

 By Richard B. Primack 

 

“I suspect that the child plucks its first flower with an insight into its beauty & significance which the subsequent botanist never retains.” Henry David Thoreau in his Journal.

 

 

On a recent spring trip to Seattle, Washington, I encountered many novel woody plants. The wetter and milder climate of the area provides welcoming conditions for many plants which can’t be found, or only found rarely, in Boston.

 

Here are some examples of these trees:

 

Photo 1: Giant redwoods (Sequoiadendron giganteum) are grown as street trees. 

 

Photo 2A: Laurel cherries (Prunus laurocerasus) are commonly grown as hedges. 

 

Photo 2B: Small plants being used to start a hedge.

 

Photo 2C: Open flowers.

 

Photo 3: Chusan palm (Trachycarpus fortunei) growing in a yard.

 

 

 

Seattle Woody Plants: Shrubs and Small Trees

 By Richard B. Primack 

 

“I suspect that the child plucks its first flower with an insight into its beauty & significance which the subsequent botanist never retains.” Henry David Thoreau in his Journal.

 

 

On a recent spring-time trip to Seattle, Washington, I encountered many novel woody plants. The wetter and milder climate of Seattle provides conditions that are amenable to many plants which are not found in Boston, or can only be found there rarely.

 

Photo 1A: Blue blossoms (Ceanothus thyrsiflorus) is a shrub with masses of soft blue flowers.

 

Photo 1B: Close-up of the blue blossoms flowers. 

 

Photo 2A: A variety of flowering dogwood tree (Cornus florida?) that has unusually wide and large bracts.

 

Photo 2B: Close-up of the bracts.

 

Photo 3A: Red claw (Escallonia rubra) is a small shrub with dramatic red flowers. 

 

Photo 3B: Close-up of the Red claw flowers. 

 

Photo 4A: Boxleaf hebe (Hebe buxifolia) is a small shrub with small, symmetrically arranged leaves and an abundance of small white flowers.

 

Photo 4B: Close-up of the Boxleaf hebe flowers. 

 

Photo 5A: Rock rose (Cistus sp.) is a small shrub with large poppy-like flowers.

 

Photo 5B: Close-up of a Rock rose flower.