Month: May 2024

We are entering the hottest time of the year for most of our readers except for those who live in the Southern Hemisphere or in tropical locations where there is not a big seasonal cycle. Heat can have a big impact on both gardens and gardeners, so this is a great time to look at a new product that is now available from the National Weather Service to alert people who spend time outside to the dangers of high temperatures. This new HeatRisk product will help you use the 7-day forecast to identify times when the heat will be the most severe—which will allow you to plan your outdoor work accordingly to avoid the worst dates and times of dangerous heat conditions. I will also provide some resources for how heat affects plants from The Garden Professors and briefly talk about one potential consequence of high temperatures on the upcoming Atlantic tropical season, which starts June 1 in the United States.

How does high heat affect gardeners?

Usually when we talk about heat, we are talking about high temperatures. But as they say, “it’s not (just) the heat, it’s the humidity.” High temperatures alone can cause problems for humans and animals because our bodies are built to work best in a narrow range of temperatures. If the temperature goes above that range (or below it), our physical systems experience distress and eventually will shut down. High humidity makes it worse because it makes our natural ability to cool off by sweating less effective because the water on the skin from sweat does not evaporate readily when the water content of the air is high. Many indices for the heat index factor in both temperature and humidity, and the wet bulb globe temperature (WBGT–more on this in a minute) includes temperature, humidity, wind speed, and solar radiation because all of these factors can affect the body’s ability to cool off.

If you are outdoors for a long time and start to experience dizziness or nausea or even worse become unconscious, then you are likely experiencing a heat-related illness and you need to get to a cooler area where you can recover right away. In the worst cases, a trip to the hospital may be needed when the body temperature is elevated above the safe range for human life. You can learn more about protecting yourself from high heat at Heat.gov.

What is the NWS HeatRisk map?

Fortunately, there are number of online tools available that can help identify days and times when the danger from high heat is most likely. The National Weather Service has just released a new experimental product called HeatRisk, which provides an interactive map that shows where the heat will be the most dangerous over the next few days. An example of the map is shown below. You can either zoom in on the map or click on your location to get a specific temperature forecast for that spot.

Another tool that may be useful is available across the United States from the Southeast Regional Climate Center at https://convergence.unc.edu/tools/wbgt/. Their tool produces hourly forecasts of WBGT based on National Weather Service forecasts for several days ahead at whatever US location you choose (not just the Southeast) that can determine when conditions are most dangerous for working or playing outside. The WBGT is often used by sports teams to determine if it is safe for players to practice outdoors and how often they need to take a break. The tool gives you the choice of several state regulations for threshold values for WBGT that should determine whether football or other practice is safe. The same information can be used to decide if outdoor workers need extra water breaks in the shade or when gardeners should come in, cool down, and rehydrate.

How does high heat affect plants and gardens?

Plants respond differently to heat than humans and other animals do because they don’t sweat. High heat can cause the plants to close the stomas in their leaves to retain moisture but a long enough period of high temperatures and dry conditions with little soil moisture leads to wilting and eventually, death of the plants. I am not an expert on this, but fortunately Jim Downer and other GP authors have written several blog posts in the past that address the effects of heat stress on plants. John Porter has also written on the effects of high temperatures on pollination and ripening. Check out some of these posts, especially Jim’s post on abiotic disorders, to see what effects high temperatures may have on your garden.

What do we expect from this year’s Atlantic tropical season and how is it related to high temperatures?

This year we have seen a lot of record high temperatures across the globe due in part to greenhouse warming. Sea surface temperatures in the northern Atlantic Ocean have been especially high, most likely due to a combination of greenhouse warming and the absence of aerosol particles in the atmosphere due to the switch to cleaner fuel for ocean vessels a couple of years ago. This change allowed more sunlight to heat up the ocean surface. These ocean temperatures are so much higher than normal that the temperatures are closer to August values than what we usually expect in late May. Since hurricanes feed and grow over water than is warmer than 80 F, it means that the atmosphere over the main development region for Atlantic tropical storms is stoked and could contribute to both a larger number of storms than usual and more rapid development for any storms that do develop. It’s no wonder that the forecasts for the number of named storms in the Atlantic this year is one of the highest ever predicted. So if you are anywhere within reach of an Atlantic storm (which is most of the eastern US but also includes most of the Caribbean, Mexico, and potentially even Central or northern South America and parts of Europe), you should be prepared for tropical activity well in advance of any storms that might come your way this year.

Enjoy the hot weather but treat it with respect

If you like hot weather as much as I do, you are looking forward to the warmer weather we will see over the next few months. But if the weather gets too hot, as it is now in India, Mexico, and other places, heat-related illnesses and even deaths will become more likely. In 2023, the United States set a new record for the number of heat-related deaths. Climate change will make devastating heat waves more likely in the future, so make sure you are prepared. If you understand how heat affects your bodies, pets, and gardens and know how to take care of yourself, you will be better equipped to enjoy the dog days of summer this year and in the future as the earth’s temperature continues to rise. Be safe and enjoy the summer heat!

It’s time for our Spring edition of People and Plants. This time we’ll be taking a look at the life and accomplishments of Asa Gray.

Asa Gray (November 18, 1810 – January 30, 1888), now considered the most important American botanist of the 19th century, had very humble beginnings. He was born in the back of his father’s tannery in Sauquoit, New York, the eldest of eight children. From childhood Asa was an avid reader. After completing grammar school in 1825 he attended the Fairfield Academy in Herkimer Co., New York and then went on to the Fairfield Medical College in 1826. It was then he began mounting botanical specimens. He got his medical degree and did eventually open a practise in Bridgewater, New York but never really “made a go of it”, he enjoyed botany much more. So much more that in the fall of 1831 he basically gave up his medical practise to devote more time to the study of plants.

By 1832 he was trading specimens with botanists not only in America but also in the Pacific Islands, Asia and Europe.
In early 1836 he became curator and librarian at the Lyceum of Natural History in New York, now called the New York Academy of Sciences, he resigned in 1837. In 1838 he took a position at the newly established University of Michigan as the Appointed Professor of Botany and Zoology. This position was the first devoted solely to botany at any educational institution in America. He was soon dispatched to Europe to purchase books to start the university’s library and for equipment, such as microscopes, to aid research. He spent a year traveling around Europe, visiting gardens and meeting important botanists of the day including William Hooker in Glasgow, Jospeh Descaisne in Paris, Stephan Endlicher in Vienna, and Augustin Pyramus de Candolle in Geneva. He returned to the USA in 1841.
Some trip, eh?

While he was in Paris at the Jardin des Plantes Gray came across an unnamed dried specimen, collected by André Michaux, and named it Shortia galacifolia. Over the next 38 years he spent considerable effort looking for a specimen in the wild. The first expedition in the summer of 1841 to an area in Ashe Co., North Carolina was unsuccessful. Further expeditions yielded the same negative results. In May 1877 a North Carolina herb collector found a plant he couldn’t identify. It was collected and sent to Joseph Whipple Congdon who contacted Gray telling him that he felt he’d found Shortia. Gray was thrilled to confirm this when he saw the specimen in October 1878. In spring 1879 Gray led an expedition to the spot where S. galacifolia had been found. Unfortunately, and much to his disappointment, Gray never saw the wild species in bloom.

In 1841 Gray was elected to the American Academy of Arts and Sciences. In 1842 he accepted the offer of a position at Harvard University. It included a salary of $1,000/year, teaching only botany, and being the superintendent of Harvard’s botanic garden. Though the salary was low the position allowed him plenty of time to do research and work in the garden. He was only 32.
At the time he had a priceless collection of more than 200,000 preserved plants, many of which he named as new species, and 2,000 botanical texts, which he donated to Harvard to found its botany department.

In the summer of 1844 Gray moved into what became known as the Asa Gray House in the Botanic Garden. As an academic, Gray was considered a weak lecturer but was highly regarded by his peers for his expert knowledge. He was better suited to teaching advanced rather than introductory classes, which he found tedious.
He eventually became well known by the outside of academia for his prolific writings and textbooks.

His first book, The Elements of Botany was published in 1836. In it Gray championed the idea that botany was useful not only to medicine, but also for farmers. His next work Flora of North America, co-authored with John Torrey, was published in 1938.
By the mid-1850s he had become so well-known that he wrote two high school-level texts in the late 1850s: First Lessons in Botany and Vegetable Physiology (1857) and How Plants Grow: A Simple Introduction to Structural Botany (1858). The publishers pressured Gray to make these two books non-technical enough so high school students and non-scientists could understand them.
A prolific writer, he was instrumental in unifying the taxonomy of North American plants. The most popular book was his Manual of the Botany of the Northern United States, from New England to Wisconsin and South to Ohio and Pennsylvania Inclusive, known today simply as Gray’s Manual. Gray was the sole author of the first five editions of the book and co-author of the sixth, with botanical illustrations by Isaac Sprague. Many editions have been published and it remains a standard in the field. 

Gray also worked extensively on a phenomenon called the “Asa Gray disjunction” which is the surprising morphological similarities between many eastern Asian and eastern North American plants.

Before 1840 Gray’s knowledge of Western US plants was limited to specimens sent him by collectors and colleagues working in the field. He worked with George Engelmann, Ferdinand Lindheimer, and Charles Wright who all collected widely in the Southwest including Texas, New Mexico, and parts of northern Mexico.
Accompanied by his wife, Gray finally traveled to the American West on two separate occasions, the first by train in 1872  and then again in 1877. Both times his goal was botanical research and sample collection to take back to Harvard. His collecting companion on these trips was Jospeh Dalton Hooker, son of William Hooker whom Gray had met in Glasgow on his first trip to Europe in 1838. Gray’s and Hooker’s research was reported in their joint 1880 publication, “The Vegetation of the Rocky Mountain Region and a Comparison with that of Other Parts of the World,” which appeared in volume six of Hayden’s Bulletin of the United States Geological and Geophysical Survey of the Territories.

Asa died in January of 1888 after suffering a stroke two months prior.

We’ve just skipped a stone across the pond of Asa Gray’s life. Here are some links if you’d like to learn more.
Asa at 200 –https://huh.harvard.edu/book/asa-gray-200
The Asa Gray Bulletin – https://www.jstor.org/journal/asagraybull
Asa Gray: Faith and Evolution – https://sciencemeetsfaith.wordpress.com/2020/11/17/asa-gray-bridging-faith-and-evolution/
Asa Gray online papers – https://onlinebooks.library.upenn.edu/webbin/book/lookupname?key=Gray%2C%20Asa%2C%201810%2D1888
Asa Gray Award – https://www.aspt.net/asa-gray-award