Monday, May 7, 2018

Wildflowers sometimes need to sleep for a few years

Posted by Richard Primack

“We must learn to reawaken and keep ourselves awake, not by mechanical aids, but by an infinite expectation of the dawn, which does not forsake us in our soundest sleep.”  
- Thoreau in Walden.   

In a famous short story, Rip Van Winkle falls asleep in colonial New York and wakes up 20 years later to discover that the American Revolution has changed everything.  In a recent article published in Ecology Letters, we report that a surprisingly large number of wildflower species display a similar phenomenon called prolonged dormancy, in which individual plants remain alive in the soil for one or more years, before reappearing above ground just like Rip Van Winkle.  Some plants have even been recorded to remain dormant for ten years or more. 

A large proportion of the examples of dormancy are found in orchids. Orchids apparently survive underground for one or more years by obtaining nutrients from soil fungi.

Pink lady’s slipper orchids in Massachusetts sometimes remain dormant in the ground for one or more years before re-emerging.  

These observations of dormancy are made during long-term studies of plant populations in which researchers monitor tagged and mapped individual plants. The results can inform conservation managers, who typically aim to protect rare plants and their habitats. Dormant plants represent special challenges to land managers if they are not seen for many years. 

The ability of some plants to successfully enter and emerge from dormancy may give them an advantage in surviving periods when there are harmful conditions, such as drought or large numbers of herbivores.  This seems to be a bet-hedging strategy in which the disadvantage of missing a growing season by remaining dormant is less than the disadvantage of emerging from the ground in an unfavorably year.  Our study demonstrates that wildflowers, just like Rip Van Winkle, sometimes need a good long sleep. 

This article has also been widely reported on in the popular press.  For example, here is an article in NexusMedia.

Friday, April 27, 2018

Giant Snow Mounds

Posted by Richard Primack

“For many years I was the self-appointed inspector of snow-storms and rain-storms.”  
- Thoreau in Walden. 

Giant snow mounds still towering in our parking lots in late April remind us of the three powerful northeaster snowstorms that made this past March one of the snowiest on record. Government departments and large landowners are no longer allowed to dump excess snow into rivers, the ocean, or other bodies of water because of salt, trash, and possible toxic materials that might be intermixed with the snow. So they create mountains of snow that melt in the spring.

The parkway snow mound was dirty white in late March

This year’s snow mound on the Hammond Pond Parkway in Newton was enormous; a 300 foot long, 48 foot wide, and 21 foot high wall of snow. Making some simple assumptions, this mound was about 5000 cubic yards in volume, or 400 dump truck loads of snow.

In late March the parkway mound was dirty white, but it has now become blackish, as the snow melted, leaving behind sand, soil, and other debris on the convoluted and eroded surface. Much of the surface dirt is jagged, rice grain-sized fragments of black rubber; this is probably “crumb rubber” used to provide cushioning on athletic fields. The surface of the mound also has scattered grass clumps, large rocks, logs, sticks, chunks of concrete, and metal and plastic junk.

As the snow melted, the surface became convoluted and increasingly black

Three weeks ago, the air temperature was a pleasant 55 degrees, and the nearby forest floor was 62 degrees where it was warmed by the sun. In contrast, the snow mound surface was a chilly 36 degrees and a frigid 28 degrees 6 inches below the surface. Water dripped from the sides and small springs of icy cold water emerged from the base of the mound. Most of the water leaving the mounds was probably evaporating and sublimating directly from snow to airborne water vapor.

Much of the debris on the surface was black crumb rubber from athletic fields

It is a fun game to guess when the giant snow mounds might finally melt in the spring. We will probably have many more opportunities to observe the melting of such snow mounds—because of climate change, winter storms are predicted to become more frequent for our region.

This posting is a summary of longer article published in the Newton Tab.

Friday, April 13, 2018

Walden Pond is not as pure as in Thoreau’s time

Posted by Curt Stager and Richard B. Primack

“Nothing so fair, so pure, and at the same time so large, as a lake, perchance, lies on the surface of the earth."
 -  Thoreau in Walden.

Walden Pond, like the rest of the world, is now quite different from what Thoreau knew 160 years ago. We have become a force of nature in our own right, and the story is written into Walden's muddy layers, as we describe in a recent article in PLOS One.
In Thoreau’s time, Walden Pond was a low nutrient pond of crystal clear purity. By studying six sediment cores extracted from the bottom of the lake, we showed that soil running off from disturbed shorelines, along with human wastes associated with swimmers, appear to have increased nutrient levels in the lake during the past 70 years. This has allowed algae to thrive, reducing the clarity of the water.

Efforts by the park department to protect the lake's purity have thus far kept it from turning green and murky.  But hotter summers and more swimmers will favor even more algal growth.   

Walden Pond is not as pure as in Thoreau's time

Recommendations to maintain and improve water quality include (1) reducing the swimmer-impacts through education programs, (2) stabilizing eroding banks, and (3) monitoring water quality and lake vegetation to see if there is any improvement or deterioration. 

Monday, March 26, 2018

Using eBird checklists to estimate bird population trends

Posted by Amanda Gallinat and Richard B. Primack (adapted from an editorial in Biological Conservation by Richard B. Primack and Vincent Devictor)

"He who cuts down woods beyond a certain limit exterminates birds.” 
-Thoreau in his Journal, 1853 

In a recent issue of Biological Conservation, researchers Joshua J. Horns, Frederick R. Adler, and Çağan H. Şekercioğlu describe a novel approach for using eBird data in bird conservation, in an article entitled Using opportunistic citizen science data to estimate avian population trends.

This study examines if the extensive records gathered by hobby birdwatchers can be used to determine changing trends in bird abundance. To investigate this question, the researchers compared trends in changing abundance over time calculated from two types of data: formal bird census data, which has long been considered the gold standard for determining population trends, and checklists of birds that have been gathered and submitted to eBird by birdwatchers.

Citizen scientists creating a checklist for eBird in Alta, Utah; photo by Joshua Horns 

eBird, a large citizen science database organized and maintained by the Cornell Laboratory of Ornithology, currently contains over 26 million checklists of birds submitted by over 330,000 users. This study finds that trends produced by eBird data are almost identical to the trends produced by the bird census data, in terms of which bird species are increasing and decreasing, and the rates of population change.

An eBird participant gathering data in Barrow, Alaska; photo by Joshua Horns 

The researchers also conclude that estimating changes over time from eBird data is best suited for widespread species, and improves with greater numbers of checklists. This validated eBird approach could be particularly valuable in tropical countries that lack formal bird census programs, where checklist submissions are increasing rapidly.

This study is a dramatic example of how well-designed, well-funded, and creatively analyzed citizen science programs can contribute to the science of conservation biology!

Wednesday, March 14, 2018

Borneo as a Carbon Sink

Posted by Richard B. Primack

“The woods I walked in in my youth are cut off. Is it not time that I ceased to sing?” 
-Thoreau in his Journal, 1852 

During the 1980s and 1990s I used long-term forest plots in Malaysian Borneo to determine how so many tree species could co-exist in one place, and how many years forests took to recover from logging. Forest plots from across Borneo are now being combined to examine how the island’s forests are responding to climate change. The results have recently been published as an article in Nature Communications titled Long-term carbon sink in Borneo’s forests halted by drought and vulnerable to edge effects.

Figure 1. Changes in forest biomass in Borneo were studied using 71 long-term plots. 

The main result is that these forests are gaining biomass, meaning they are out of equilibrium and are a net sink for atmospheric carbon dioxide.

Figure 2. Forests in Borneo are showing a net increase in biomass over time in the forest interior; this has also been observed in the Amazon and in Africa. Forests on the edges of fragments are declining in biomass.

Forest fragmentation from human activity has had negative effects as shown by the declining biomass of forests on the edges of fragments. Borneo’s forests are also vulnerable to the effects of climatic variation as a drought in 1997-1998 temporarily halted the increase in biomass and caused an increase in tree mortality. These forest plots will become more valuable in coming decades as a way of documenting the continued impacts of climate change.

Thursday, February 22, 2018

Herbarium specimens show patterns in wild fruiting phenology

Posted by Amanda Gallinat

The timing of fruiting in New England is important for wildlife that eat wild fruits and disperse seeds. However, surprisingly little is known about when different plant species fruit and what environmental variables determine fruiting times.

An American Robin consuming whole fruits in late-autumn (photo by Sam Roberts)

In a paper published last week in the American Journal of Botany, my co-authors and I describe patterns and predictors of fruiting times for 55 woody plant species across New England. Our team recorded fruiting dates and locations for over 3,000 herbarium specimens with ripe fruit, collected in the wild from 1849-2013, and housed at 6 major herbaria. We analyzed variation in fruiting times among 37 native and 18 invasive species, as well as within-species variation.

A Buckthorn (Rhamnus cathartica) specimen with ripe fruits, available through the George Safford Torrey Herbarium digital collections

We found a moderate phylogenetic signal to fruiting dates; in other words, related species tended to fruit at similar times. With phylogeny considered we found that, on average, invasive species fruited 26 days later than native species, and had more variation in their fruiting times. Since some birds are migrating through New England later with warming temperatures, this may increase the likelihood that migratory birds will encounter and consume invasive fruits, and disperse invasive seeds.

Spring temperature and year were significant predictors of fruiting times within species, but explained a very small amount of the variation. We conclude that herbarium specimens are an excellent resource for investigating differences in fruiting times among species, but present unique challenges for analyzing variation within species. Read more about those challenges, potential solutions, and more in the full text.

Friday, February 16, 2018

Chlorophyll content of conifer needles

Post written by Linnea Smith

“Knowledge is to be acquired only by a corresponding experience.”
-Thoreau, A Week on the Concord and Merrimack Rivers

Part of my undergraduate thesis on leaf longevity involves studying how leaf age affects the chlorophyll content of evergreen leaves. We have measured chlorophyll content for broadleaved evergreen species, such as Rhododendrons and hollies, using an AtLeaf+ chlorophyll meter.

Unfortunately, this instrument typically does not work for most conifers, such as firs, spruces, and yews, because the needles are too narrow to cover the width of the measuring window and the results are variable and unreliable. However, with just the tools shown below, we have been able modify the usual procedure for use with narrow conifer needles.

We cut an insert (middle left) out of a sheet of thin plastic; this allows the needles to be precisely placed over the measuring window. We arrange a few needles next to each other to cover the hole in the insert, with no gaps and minimal overlap between leaves, and then tape the leaves down with clear tape.

We then carefully place the insert in the chlorophyll meter so that leaves are over the measuring window, and we’re set to measure chlorophyll content! In effect, this simple procedure is a way to increase the width of the leaf surface area being measured.