Harvard Forest >

Summer Research Project 2024

• Title: Hemlock, Oak, and the Insects of Doom
• Group Project Leader: Audrey Barker Plotkin
• Mentors: Audrey Barker Plotkin; Taylor Lucey; Marcos Rodriguez; Diana Sharpe; Ahmed Siddig; Greta VanScoy
• Collaborators: Betsy Colburn; Meghan MacLean ; David Orwig; Sydne Record
• Project Description:

  Non-native insects are a major driver of forest change, especially in invasion hotspots such as the Northeastern United States. These insects can cause abrupt transformations in overstory and tree seedling composition and structure, with cascading effects on aquatic and terrestrial fauna. This summer we will investigate the consequences of invasive forest insects in two dominant forest types: hemlock and oak. Eastern hemlock is a foundation species that strongly shapes its environment and provides habitat for many species, but it is currently facing extirpation from the hemlock woolly adelgid (HWA). Oaks are a globally important genus, are a major driver of the Northeastern carbon sink, and provide critical wildlife food and habitat. Oak is the preferred host for spongy moth; a major spongy moth outbreak in southern New England from 2016-2018 caused extensive oak dieback and mortality.
  
  Students should indicate which sub-project is of most interest: (1) forest composition and structure after hemlock and oak loss; (2) tree seedling demography; (3) stream macroinvertebrate and salamander responses to hemlock loss; (4) wood quality responses to invasive insects. Mentors and students will gather together weekly for team meetings. In general, students will primarily work on one sub-project with some opportunity to help one another.
  
  Project 1: Forest composition and structure after hemlock and oak loss (2-3 students)
  Primary mentors: Audrey Barker Plotkin & Greta VanScoy
  Eastern hemlock (Tsuga canadensis) forests are declining in abundance as they are colonized by the invasive insect hemlock woolly adelgid (HWA, Adelges tsugae). Hemlock is replaced by hardwoods, causing an abrupt shift in ecosystem characteristics that is often exacerbated by salvage logging. Using data from a long-term experiment, we will explore shifts in canopy and understory vegetation species composition and structure. The Harvard Forest Hemlock Removal Experiment, initiated in 2003, includes girdling (hemlocks killed and left standing) and timber harvest treatments, along with unmanipulated reference plots. The hemlock reference plots were colonized by HWA in 2010 and their trajectory of decline and regeneration will be compared to the girdling treatment. This summer, we will conduct the Year 20 tree census.
  From 2016-2018 southern New England experienced a severe outbreak of spongy moth (Lymantria dispar) for the first time in more than 30 years. We seek to understand the long-term consequences of this outbreak on oak forest composition, structure, and carbon sequestration. In 2019, we established plots in 10 sites that experienced varying severity of defoliation, and can now assess how forest structure, composition, and growth have changed over the past 5 years.
  For both study areas, we will explore the trajectories of change in the forest vegetation by re-measuring all trees in the plots and mapping the trees that have grown into the forest since the last tree census in 2019. We will also assess changes in tree seedling regeneration and understory plant abundance and biodiversity.
  This is a field-based study, and the students should expect to spend ~75% of their time in the woods, with the joys and challenges associated with it, including biting insects, ticks, and the typical extremes of New England summer weather. Forest measurements skills and the ability to work with large, long-term datasets will be developed. Data from past years will be available to examine trajectories of vegetation change over time.
  
  Project 2: Seedling demography in a changing forest (2 students)
  Primary mentor: J. Marcos Rodriguez
  Seedlings comprise a dynamic and important life stage for plants, and are a key to understanding forests and how they change. However, long-term monitoring of individual seedlings in nature is rare, so seedlings are an often-overlooked component of forests and ecological theory more broadly. The continued observation of seedling demographics is important for ecologists to address questions ranging from how current regeneration is impacted by invasive species, to larger ecological theories about how metabolism scales across trees in forests across the globe.
  This summer, two students will continue measurements of seedlings within the ForestGEO site at Harvard Forest, in which hemlock and oak are the dominant overstory trees. Starting in 2017, all seedlings within 133 one-m2 plots are assessed each year for growth, mortality, and recruitment. If there is time, other fieldwork including taking canopy photos and measurements of adult trees and saplings in other plots may be conducted to link the dynamics of different size classes.
  It is expected that approximately 75% of time will be spent in the field while the remaining 25% will be spent on data entry and analysis, although this balance will likely vary throughout the season. Fieldwork will consist of ~8 hour field days carrying up to 25 lb (~11kg) worth of field equipment. This project will also require participants to spend a significant amount of time crouching and kneeling on the forest floor under the conditions of New England summers which include heat, humidity, and biting insects. Skills with R or identification of New England woody plants is useful, but students willing and eager to learn these skills are encouraged to apply.
  
  Project 3: Cascading impacts of hemlock loss on stream macroinvertebrate assemblages & salamanders (2 students)
  Primary mentors: Diana Sharpe & Ahmed Siddig
  The loss of Eastern hemlock (Tsuga canadensis) due to the invasive insect hemlock woolly adelgid (HWA, Adelges tsugae) is anticipated to have cascading impacts on the microenvironment of forest floor and headwater stream habitats and the fauna these habitats support. Hemlocks create a cool, shady understory, and the loss of hemlock leads to increased light penetration and higher and more variable temperatures in streams and soils. In addition, the replacement of hemlock by deciduous species along stream borders alters the quantity of quality of allochthonous inputs (leaf litter and woody debris) that are made available to stream primary consumers.
  For stream macroinvertebrate communities, these changes in the abiotic environment and nutritional inputs to streams are expected to alter their distribution, richness and composition. We will compare the macroinvertebrate communities of Harvard Forest streams that are bordered by hemlock-dominated vs. deciduous-dominated forests. This work will build directly on prior surveys conducted on Harvard Forest streams in 2005, allowing us to explore longer-term trajectories of stream community dynamics in these changing forests. We will sample macroinvertebrate communities biweekly and monitor water quality (e.g., temperature, pH, conductivity and dissolved oxygen) weekly at replicate sites within each stream.
  In the forest understory, salamanders are important creatures due to their abundance and ecological roles. Within the Hemlock Removal Experiment, we have studied the long-term impacts of hemlock decline on salamander populations. We compared baseline surveys from 2004 (before the experimental treatments) to population monitoring in 2013 & 2014. So far, the results of this study indicated that salamanders’ populations declined by about 20% after hemlock loss. We hypothesize that we will observe further declines in salamander populations as hemlock habitat declines and is replaced by hardwoods. We will test this hypothesis by repeating the population surveys this summer, focusing on the two most abundant salamander species: red backed salamanders and red spotted newts (efts). We may also conduct baseline surveys of salamander abundance & diversity in the Harvard Forest ForestGEO plot. We will use three assessment methods to estimate salamander populations, including coverboards, leaf litter searches, and visual encounter surveys.
  A typical week for these students will involve approximately 50% field work, and 50% laboratory and data entry/analysis/literature review work. Applicants should be excited to spend significant amounts of time wading through streams, working in wet and muddy conditions, and handling live salamanders and invertebrates. The student will have the opportunity to develop a variety of new skills, including field-based stream survey methods, water quality monitoring, taxonomic identification of aquatic invertebrates, microscopy, and data manipulation and analysis in R.
  
  Project 4: Assessment of wood quality and internal decay rates of eastern hemlock trees infested with hemlock woolly adelgid (1 student)
  Primary mentor: Taylor Lucey
  Note: we will know if this sub-project will run by early February 2024; interested applicants should indicate other sub-projects of interest in case this one is not available.
  Hemlock woolly adelgid (Adelges tsugae, HWA) is threatening eastern hemlock trees (Tsuga canadensis) across the eastern US and Canada. The influence of HWA on hemlock stands threatens forest resilience over time, especially under changing climate conditions. One suggestion for mitigating some of the climate impacts of hemlock mortality is to use infested trees for engineered wood products such as Mass Timber, to store more carbon in long-term wood products. However, little research has been done to understand a) how wood quality is impacted by HWA, and b) the decay rate of decaying hemlock trees in the forest.
  This project will investigate and quantify wood quality and internal decay rates of standing eastern hemlock trees infested by HWA with varying levels of defoliation, along with non-infested hemlock trees as a baseline reference. We plan to use three non-destructive evaluation testing approaches: 1) acoustic wave technology, Fakopp 1D Microsecond Timer (Fakopp Enterprise, Agfalva, Hungary) to measure stress wave velocity for tree sorting based on stiffness (dynamic MOE), 2) IML Resistograph® F500-S (IML North America,
  Moultonborough, New Hampshire, USA) to measure the drilling resistance and 3) Tree Core Reader to estimate moisture content. Field sampling of infested trees will take place at Harvard Forest, and then core samples will be taken back to the University of Massachusetts Building, Construction, and Technology laboratory oven for drying and additional measurement.
  From these non-destructive sampling methods, we will gain a better understanding of how hemlock wood quality changes during decline, as well as the rate of decay for dead wood left in the forest. This is primarily a field-based study with about 75% of the student’s role taking place in the woods using the non-destructive field equipment mentioned above. The remainder of the student’s role would be data-entry and analysis.

• Readings:

  Ellison A.M.; Orwig D.A.; Fitzpatrick M.C.; Preisser E.L. 2018. The Past, Present, and Future of the Hemlock Woolly Adelgid (Adelges tsugae) and Its Ecological Interactions with Eastern Hemlock (Tsuga canadensis) Forests. Insects, 9(4):172.
  
  Farrior, C.; Bohlman, S.; Hubbell, S.; Pacala, S. 2016. Dominance of the suppressed: Power-law size structure in tropical forests. Science. 351:155-157.
  
  Jevon, F. V.; Record, S.; Grady, J.; Lang, A. K.; Orwig, D. A.; Ayres, M. P.; Matthes, J. H. 2020. Seedling survival declines with increasing conspecific density in a common temperate tree. Ecosphere. 11(11)
  
  Lovett, G. M., Weiss, M., Liebhold, A. M., Holmes, T. P., Leung, B., Lambert, K. F., Orwig, D. A., Campbell, F. T., Rosenthal, J., McCullough, D. G., Wildova, R., Ayres, M. P., Canham, C. D., Foster, D. R., LaDeau, S. L., Weldy, T. 2016. Nonnative forest insects and pathogens in the United States: Impacts and policy options. Ecological Applications 26: 1437-1455.
  
  Siddig, A. A., Ellison, A. M., Mathewson, B. G. 2016. Assessing the impacts of the decline of Tsuga canadensis stands on two amphibian species in a New England forest. Ecosphere 7: e01574.
  
  Wang, Xiping; Ross, Robert J.; McClellan, Michael; Barbour, R. James; Erickson, John R.; Forsman, John W.; McGinnis, Gary D. 2000. Strength and stiffness assessment of standing trees using a nondestructive stress wave technique. Res. Pap. FPL–RP–585. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 9 p.
  
  Willacker, J.J., Sobczak, W.V. and Colburn, E.A., 2009. Stream macroinvertebrate communities in paired hemlock and deciduous watersheds. Northeastern Naturalist, 16(1), pp.101-112.

• Research Category: Large Experiments and Permanent Plot Studies, Invasive Plants, Pests & Pathogens, Group Projects, Biodiversity Studies