Returning to the Jackson Laboratory

Posted by Richard Primack

“Practically, the old have no very important advice to give the young. I have lived some thirty years on this planet, and I have yet to hear the first syllable of valuable or even earnest advice from my seniors."  
-Thoreau, Walden

In 1967, I was a high school student off for a summer of research on mouse genetics at the Jackson Laboratory in idyllic Bar Harbor, Maine. The most amazing part of the program was the chance to meet and interact with intellectually motivated students from around the United States.

Recently, I was invited back to the Jackson Lab after 49 years to talk with a new crop of high school students about my memories of the program, what I have done and am currently doing in my research, and what I had learned over the course of my career and life. Above is a 3 minute version of my talk; keep in the mind the above quote from Thoreau that the wisdom of seniors has little value.

Low Water at Walden Pond

Posted by Richard B. Primack

“The Pond rises and falls, but whether regularly or not, and within what period, nobody knows, though, as usual, many pretend to know.”  -Thoreau, Walden

As Henry David Thoreau noted 160 years ago, Walden goes through multi-year cycles changing water level. This spring Walden Pond is exceptionally low, with a broad expanse of sandy margins around much of the pond, and contrasts with the pond’s recent high in the spring of 2010, when water entered the forest around the pond and even flooded the p

aths.

Low water at Walden this year means a large sandy margin all around the pond

The past few years of low water have allowed alder and birch saplings and wildflowers, such as lance-leaved violets and yellow wood sorrel, to establish on the sandy beaches below the forest margin. When the water rises again in coming years, this invading edge of plants will be drowned.

Lance-leaved violets have established along the beach

Young alder plants at the forest edge will likely drown in future years when the water rises again

The water has fallen so low this year that part of a submerged sand bar—one that Thoreau described in his survey of Walden Pond—is now exposed. In Thoreau’s 1846 survey, he noted that the sandbar across the mouth of what is now known as Thoreau’s Cove on the northwest corner of the pond (the cove closest to the site of Thoreau’s cabin) was 7 feet below the water’s surface.

Thoreau's Cove, a sandbar on the northwest corner of Walden Pond

Also related the low water level, the large vernal pool near Thoreau’s cabin site, known as Wyman’s Meadow, has no standing water. In typical years, the meadow fills with water in the late winter and spring, and mole salamanders, American toads, and other amphibians lay their egg masses in the water; later in early summer the pool is alive with tadpoles and juvenile amphibians. By the summer’s end, the pool dries out and the meadow becomes a carpet of colorful flowers. But this year, without any standing water, the amphibians have no place to breed—and children visiting Walden will have no tadpoles to catch.

Dr. Les Kaufman walks across Wyman's Meadow, which is uncharacteristically dry in 2016

The extreme low water and wide beaches that we are seeing this year—an extreme that Thoreau noted too—is a part of what makes Walden Pond so endlessly fascinating. Something to consider next time you take a stroll around the pond.

You can read my full article on this topic in the Concord Journal by clicking HERE.

Late spring frost damages flowers and young leaves!

Posted by Amanda Gallinat

One feature of climate change that's of interest to our lab is the increasing likelihood of frost damage to flowers and young leaves in the spring. Warm temperatures cause plants to flower and leaf-out earlier, and increasing variability in spring temperatures, including late-spring frost events, is leading to a greater likelihood that vulnerable flowers and young leaves will be damaged by frost. This spring, we have seen this phenomenon in action in the Boston area! 

Following a record-breaking warm winter and warm spring, plants at the Arnold Arboretum started leafing out and flowering at the end of February!

These photos of Hamamelis mollis (top left), Lonicera korolkowii (top right), Lonicera tatarica (bottom left), and Cornus officinalis (bottom right) were taken at the Arboretum on February 28, 2016. 

In early April (4-6), after several hundred species of plants had leafed out and/or flowered at the Arboretum, freezing nighttime temperatures (between 22 and 25 degrees F) hit the Boston area. The results varied among species in the days and weeks that followed. Some species' flowers and flower buds never recovered, and this was particularly striking in the collection of cherry trees at the Arboretum:

Sargent's cherry (Prunus sargentii) during peak flowering in 2015 (left) and 2016 (right). The inset photo shows heavy frost damage to flower buds and light frost damage to young leaves.

Other plants like Forsythia sp. had flowers that were also badly damaged by frost. For wild plants, frost damage to flowers can have dramatic consequences for reproduction.

Forsythia flowers at the Arboretum, typically healthy and bright yellow, are now mostly drooping and golden-brown

In addition to frost damage to flowers and flower buds, we observed that many young leaves were killed or damaged by the frost. We have recently conducted experiments on the frost tolerance of young leaves in the laboratory, so we were particularly interested in seeing the effects of a natural frost on leaves at the Arboretum. In some cases, such as many of the Berberis species, leaves showed almost no damage following the natural frost. In other species, leaves that looked heavily damaged in the days following frost events were able to mostly recover, such as in Prinsepia sinensis, while some species appear to have sustained permanent frost damage. It is unclear whether heavily damaged plants will re-flush new leaves or simply undergo limited photosynthesis during this growing season.  

Prinsepia sinensis just after a frost (April 5th, left) and a few days later (April 7th, right)

If you are in the Boston area or your region also experienced a late spring frost, we encourage you to look for signs of frost damage to flowers and leaves!

Frost damage is clearly visible on the flowers of this Magnolia stellata 

Mapping leaf-out times using satellites and ground observations

Posted by Richard B. Primack

"Rather than love, than money, than fame, give me truth."

Henry David Thoreau, Walden

Data gathered by satellites are increasingly being used in studies of plant ecology, landscape ecology, and climate change biology. Researchers from the BU Biogeosciences Program are now using data from the Landsat satellite to determine the places where trees leaf out early and leaf out late at the scale of 30 m pixels. This unprecedented level of detail allows researchers to measure and predict how present and future climate change will affect the onset of leaf-out in our forests. Our research group is working with Eli Melaas to provide field observations of plants, in order to help verify the maps made using remote sensing data.

In this map of the Allandale Woods in the Jamaica Plain area of Boston, the average leaf-out times are shown, with the red indicating early leaf-out and the light tan indicating later leaf-out. Areas shown in green are lawns, fields, and other areas not occupied by trees (these areas were excluded from the phenology maps). We will be monitoring leaf-out times once a week along a transect through the Allandale Woods that ranges from early leaf-out to late leaf-out, during the spring season. We will also monitor several other transects that span the range of early to late leaf-out, around the Boston area.

Above, Richard Primack and Lucy Zipf observe the phenology of an urban tree at Bellevue Hill, while Eli Melaas marks the GPS point to later map the tree with its phenology 

Will leaf-out times on the ground correspond to leaf-out times using remote sensing data? Are different leaf-out times due to microsite differences in temperature, different species of trees in each location, or different shrub understory? Stay tuned to find out!

Humid spring days

Posted by Lucy Zipf

March was an important month for me in the Primack lab! With help from lab members, I conducted my first experiment as a graduate student: an investigation of the effect of air humidity on leaf-out times in native and invasive shrubs and trees.

Collecting twigs in Newton, MA

This study was motivated by a recent paper, Laube et al. 2014 (doi: 10.1111/nph.12680), showing that dormant twigs in a high humidity growth chamber leafed out about seven days earlier than dormant twigs in a lower humidity chamber. Could leaf-out in the spring be affected by humidity as well as temperature? We decided to test Laube’s hypothesis.

For our experiment, Richard Primack, Amanda Gallinat and I collected twigs from 15 species, including native and invasive shrubs and native trees from the Boston area. We brought the twigs back to BU, cut the stems, and placed them in cups of water, with help from BU undergraduates Luca Russo, Dillon Travis, Melissa Ruano, and Lucas Stegman! 

Processing twigs in the lab, with Luca Russo and Dillon Travis

Twigs of every species were exposed to each of four humidity treatments: high, medium-high, medium-low, and low. In the course of this experiment we realized that our building is extremely dry – it has the humidity of the Sahara Desert!

A clipping of multiflora rose leafing out in the low humidity treatment

We monitored the twigs daily for leaf-out over the following four weeks. Do twigs leaf out earlier in humid environments? Stay tuned for the results.