Tag Archives: woolly adelgid

A Sampling of Forest Ecology Research

15 Jul

This summer I have spent most of my days working as an intern for the Botanic Garden of Smith College under the guidance of Gaby Immerman, assisting the staff there with the maintenance of the various gardens and trees around campus. On Fridays, however, each intern engages in a personal research project in order to create a final product that benefits the Botanic Garden in some way. I am being supported by CEEDS to work with Michelle Jackson, a 2015 graduate of Smith College and a researcher in Professor Jesse Bellemare’s laboratory, on research about the effects of Eastern hemlock tree (Tsuga canadensis) decline on the liverwort species Bazzania trilobata.

Eastern hemlock trees have been in decline as populations of two invasive Asian insects, the hemlock woolly adelgid and the elongate hemlock scale, get established and feed on the trees. In forests in Chesterfield and at Smith College’s MacLeish Field Station in Whately these hemlocks are gradually being replaced by black birch (Betula lenta), changing the composition of the understory, the interactions of various animals, and the forests as whole systems. B. trilobata is associated with Eastern hemlocks, but Michelle is interested in finding evidence as to whether these liverworts are actually dependent on Eastern hemlocks.

thumb_IMG_1273_1024Liverwort Bazzania trilobata

Michelle is testing the effects of different predictor variables on the survival of B. trilobata. Primarily, she is testing the difference between liverworts in areas with hemlock versus patches of forest with birch growth. She is also comparing these results to liverworts growing in areas that have been clear-cut, or those where hemlock trees have been salvage logged. Since hemlocks are coniferous and black birch are deciduous, Michelle is also looking at how being covered by the differing leaf litter affects B. trilobata. Her research takes into account variables such as aspect, slope, radiation, and soil moisture. I have been helping Michelle by flagging plots and making observations about the survival states of samples of B. trilobata.

I have also had the opportunity to help the other researchers in the Bellemare lab with their individual projects. I have helped collect data for Elizabeth Besozzi ’16, who is working to determine the effects of the shift of forests from hemlock to birch on salamanders and the food webs in which they are involved. I have helped collect soil samples for Aliza Fassler ’17, who is looking to see how this same shift in forest composition affects the soil and carbon-nitrogen cycling. I have also gotten the opportunity to help Anna George ’17 prepare tree core samples for her project involving the appearance of an increased spread of magnolia trees (Magnolia tripetala) into locations further north than their typical range.

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Eastern hemlock trees (coniferous), Tsuga canadensis, and black birch trees (deciduous), Betula lenta

I am hoping to write a more comprehensive article about the research going on at MacLeish Field Station, focusing especially on the research surrounding the hemlocks done by those I’ve worked with in Professor Jesse Bellemare’s laboratory. I think that this important research needs to be shared with the public to spread awareness about the impact of the actions of humans on the environment, including climate change and the resulting movement of species to new locations. Furthermore, I believe that this research is an important example of why places like the MacLeish Field Station, are conducive to research and preservation.

Isabella Fielding ‘17 is a rising Junior from Warwick, RI. She is majoring in Biology and English, and she aspires to be a scientific writer

Filling in the Gaps: Understanding the Effects of Hemlock Decline at MacLeish

3 Jul

With climate change altering species’ distributions as suitable habitats move, and with our increasing rates of global travel, biological invasions are becoming more widespread.  The hemlock woolly adelgid (Adelges tsugae), for example, an exotic insect accidentally introduced to eastern North America that feeds on eastern hemlock trees (Tsuga canadensis), has been steadily moving northward as a result of a warming climate and relatively easy transport via the wind, deer and human activity.  The woolly adelgid has now just reached the Ada and Archibald MacLeish Field Station, where the hemlocks that dominate the forest there are starting to show signs of infestation.  Hemlocks can’t defend themselves against these insects and can die within as few as four years of becoming infested, leaving skeletal forests behind.

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Woolly adelgid on an eastern hemlock tree at MacLeish.

The decline of hemlocks is of particular concern because eastern hemlock is a foundation species.  This means that the species (e.g., eastern hemlock) influences the conditions of the ecosystem they inhabit in such a way that their presence helps determine which other organisms can live there.  Because hemlocks create a unique “microclimate” in the forests they dominate – one that is cool, dark, and damp – and tend to acidify the soils beneath them, the removal of this species and replacement by deciduous tree species is bound to produce large changes in the forest.  These changes will be both in environmental conditions and ecosystem processes as well as in the animal and plant communities that inhabit these forests.

I started working on the question, “What are long-term effects of hemlock removal on New England forests?” early in my Smith career and, after completing a senior thesis on this topic, I am now spending the summer before grad school as a SURF intern continuing to collect long-term data.

The Field Station offers a unique opportunity for us to look at what forests devastated by adelgid infestations might look like in twenty years, a result of logging that occurred before MacLeish became a research site.  In the late 1980s, patches of hemlock trees were logged as part of a larger cut to help promote the growth of maple and other economically valuable trees.  Young black birch trees (Betula lenta) have since grown in these logged patches.  This logging activity produced an “accidental experiment” for us to use, in that we can compare environmental conditions in the young black birch patches to those in the hemlock-dominated forest next to them.  This data will help us predict what the forests in New England may look like decades after the wooly adelgid infestation causes hemlock populations to decline and disappear. 

Several labs at Smith have been using these plots and exploring this question.  I’ve been working since my junior year with both Jesse Bellemare in Biological Sciences and Amy Rhodes in Geosciences, and with several other students in the professors’ labs, to predict how nutrient cycling and other ecosystem processes change with the loss of eastern hemlock.  I examined several facets of this question for my thesis, exploring precipitation chemistry, leaf litter decomposition, and soil nutrient cycling.  This summer, I am primarily continuing our work on soil nutrient cycling, comparing nitrogen cycling between a hemlock forest, a young black birch forest, and a mature deciduous forest.

To do this we measure the production of nitrate (NO3) and ammonium (NH4+), nitrogen-containing compounds that plants can use and that are produced when microbes digest leaf litter on the forest floor, by performing regular soil incubations.  For each incubation, we take soil cores from each plot and measure “initial” concentrations of nitrate and ammonium in our lab at Smith.  For each soil core we take back to lab, we leave a second soil core, obtained next to the first, in the ground in a PVC sleeve.  We come back to the forest after at least three weeks, bring those incubated cores back to lab, and measure the “final” concentrations of nitrate and ammonium in those samples.  We then use the difference between the initial and final nitrogen concentrations to calculate the rate at which these compounds are being produced in the soil, and use these rates as a quantitative way to compare nutrient cycling between the three forest types.

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Soil cores ready to go back to the lab for processing (left), and a soil core incubating in a PVC sleeve in the field (right).

Our research hasn’t always gone as planned.  In 2010, professor Rhodes’s lab established their hemlock plot as one representing a “healthy, mature hemlock forest.”  Last year, however, we started to notice the adelgid near this plot, and began to see an increase in the amount of nitrogen produced in the soil as well, a typical sign of adelgid invasion.  This summer we want to see if this trend is still evident, and though we can’t really think of this hemlock plot as our “healthy hemlock forest control” any more, now we can track how the soil changes at the beginning of an infestation, using the data collected before the infestation as our baseline.

Our work and the work of other Smith students and professors will contribute to the growing body of literature on the effects of the hemlock woolly adelgid infestation on our New England forests.  This will help scientists, foresters, and policymakers confronted with the daunting task of dealing with the adelgid infestation to make more informed management decisions.  And though I’m not actively working to eradicate the adelgid, I’m proud to be doing my own small part, gathering information that might be useful for managing this invasion and other similar biological invasions as well.

–       Jenna Zukswert ‘13

Jenna graduated in May with a double major in Biological Sciences and Environmental Science and Policy.  She will be attending the University of British Columbia in Vancouver this fall to pursue a Master of Science degree in Forestry. She hopes to pursue a career in science education.