General ecology (EES-152) students have finished resurveying a portion of the Lehigh Experimental Forest, with the goal of assessing changes in tree growth, mortality, and recruitment since 2013. A total of 690 trees were measured from across the forest, representing more than a 1/4 of all trees. In the three years since 2013, 70 of these 690 trees have died and only three new trees have established in the study area. Data for the dominant tree species are shown in the plot below.
We will use these data to discuss the processes controlling forest dynamics as the semester progresses. However, for now, students should answer the following questions:
- The dbh measurements were converted into estimates of area, assuming that each tree was a perfect circle in cross-section. Why do you think basal area was used to compare growth rates among the different species? Why was this expressed as the average change in basal area per tree? What factors might have caused the observed differences in radial growth among species?
- What does the pattern of mortality and recruitment suggest about the future of the Lehigh Experimental Forest? What factors might have caused the differences in mortality among species during these two years? What factors might be contributing to the lack of new tree recruitment in the forest?
- Assuming the rates of total tree recruitment and mortality are representative of future years, when will there be no trees left in this forest? In 2013, there were ~2000 trees in the forest. Show your work and describe how you arrived at your estimate. Do you think it is likely that the trees will really be gone by this time? Why or why not?
- Which species had both very high mortality and very low growth during this time period? Do some research on current threats to this particular species, and summarize your research in a short paragraph.
Students in general ecology (EES-152) resurveyed a portion of the Lehigh Experimental Forest, to assess changes in tree growth, mortality, and recruitment since 2013. No new trees greater than 1.4 m high were documented, and both growth and mortality varied considerably among species. Over 500 trees were measured, and the plot above shows data for the dominant trees (those with >15 individuals included in the survey).
We will use these data as a springboard for discussion of processes controlling forest dynamics, and will examine some of these issues in greater depth during our discussions and future lab activities.
For now, students should answer the following questions:
1. The dbh measurements were converted into estimates of area, assuming that each tree was a perfect circle in cross-section. Why do you think basal area was used to compare growth among the different species? Why was this expressed as the average change in basal area per tree, as opposed to the total change in basal area for all individuals of the species? What factors might have caused the observed differences in radial growth among species?
2. What does the pattern of mortality and recruitment suggest about the future of the Lehigh Experimental Forest? What factors might have caused the differences in mortality among species during these two years? What factors might be contributing to the lack of new tree recruitment in the forest?
3. Which species had both very high mortality and very low growth during this time period? Do some research on current threats to this particular species, and summarize your research in a short paragraph.
The Pymatuning Wetlanders visited Presque Isle today, where we observed coastal processes and successional change. After a stop at the Tom Ridge Environmental Center, explored the peninsula to observe coastal wetlands and processes. This included a hike out to Gull point, located at the tip of the peninsula, to observe the youngest landscape and wetlands. We did some wading in Lake Erie to cool off, had lunch on the beach, on our way home we stopped for the long-promised ice cream. A fun day before tomorrow’s final exam.
Today the Pymatuning wetlands spent the entire day in the lab. Our first day without any fieldwork since the course began. However, we made up for it by doing a bit of time travel…
We examined the core we collected from Titus Bog yesterday. We subsampled the sediment and peat, sieved the samples to isolate plant macrofossils (i.e., seeds, leaves, needles, etc.), and identified and tallied the microfossils to determine how the vegetation of the wetland has changed over the past 8000 or 9000 years. The students determined that the site was occupied by a shallow lake prior to the establishment of the modern peatland, with submerged and floating leaved aquatic plants like Najas (water nymph), Nuphar (spatterdock), and Nymphaea (water lily) growing in the deeper portions of the littoral zone. Emergents like Cladium (sawgrass), Rhynchospora (beaked sedge), and other sedges likely occupied the lake margin along with small amounts of Sphagnum moss. The area abruptly became a floating peatland about 350 years ago, when Sphagnum became dominant. The upland vegetation around the site contained Tsuga canadensis (hemlock), Pinus strobus (white pine), and Betula alleghaniensis (yellow birch) for much of the record. Most of the species in the paleoecological record have been observed at the wetlands we have visited during the past two weeks of the course; in fact, quite a few are the “must-know” list.
Our age estimates for the record are tentative and come from a broader study of peatland development at the site by Ireland and Booth (2011). We will discuss our paleoecological record in class tomorrow, along with the Ireland and Booth study, emphasizing the implications for understanding long-term wetland development and hydroseral succession.
One afternoon. Nine students. Approximately 8500 years of history.
The Pymatuning wetlanders spent the morning learning about wetland development and the roles that wetlands play in the broader earth system. In the afternoon, we examined the sediment core that we collected from Titus Bog yesterday – all 8.5 meters of it! The students sieved samples from along the core, and identified and tallied plant macrofossils (e.g., leaves, seeds). By applying age-depth information from previous work on the bog (Ireland et al., 2011), we estimated the age of the samples along the length of the core.
The diagram below shows our paleoecological results, and clearly shows that the site started as a deep kettle lake (the lower samples lacked macrofossils) some 8500-10,000 years ago, and was occupied by a shallow lake with abundant submerged aquatics like nodding waternymph (Najas flexilis) and pondweed (Potamogeton sp.) throughout much of the mid Holocene. In the later Holocene the area was shallower, supporting a mix of submerged aquatic plants like nodding waternymph, along with floating leaved plants like white water lilies (Nymphaea odorata). About 800-900 years ago a floating peatland established at the site, with various sedges, Sphagnum, cranberries (Vaccinium oxycoccos), and leatherleaf shrubs (Chamaedaphne calculata) characterizing the surface vegetation. We will discuss the record in the context of peatland developmental models tomorrow…
The Pymatuning wetlanders started their time-travel project today. We visited Titus Bog and observed the floating bog mat and discussed the developmental history of this unique ecosystem. The students had read previous paleoecological research on the site, part of the dissertation research of Alex Ireland (see here and here for summaries), and so they were well prepared to examine the wetland and think about its history.
We collected a peat core, recovering over 8 meters of peat and lake sediment (a class record!), and tomorrow we will collectively analyze the macro-botanical remains to reconstruct the vegetation and developmental history at our coring location. We added a few plant species to our must-know list (bringing our total for the course to 55), including sundews (Drosera sp.), leatherleaf (Chamaedaphne calyculata), cranberries (Vaccinium oxycoccos), and bog bean (Menyanthes trifoliata). We also saw two species of orchid in bloom.
After spending some time at the bog, we took another short hike at a nearby location to observe a small population of purple pitcher plants (Sarracenia purpurea), where we were fortunate enough to see a 4-toed salamander (Hemidactylium scutatum)!
The Pymatuning wetlanders began the day with an overview of salt marsh ecology and biogeochemistry, including examples of trophic cascades in these ecosystems. Although salt marsh food webs are typically detritus-based, numerous examples of trophic cascades have emerged in recent years, particularly in response to human-caused changes (e.g., overfishing, land-use changes). We then drove north to Presque Isle to observe and discuss coastal processes (e.g., longshore drift, erosion, deposition) and the implications of this dynamic environment for the development of wetlands.
We had lunch on beach #11, and then hiked the Gull Point Trail to the tip of the youngest portion of Presque Isle. The students were able to observe the pond and dune successional patterns along the way (a chronosequence!). It was an enjoyable and relatively low-key day….perfect for the day before a midterm. We ended a little early to give the students some additional time to
Some additional pictures….
Nice article Michelle. Too bad the paper didn’t publish it. The site has historical significance and is a great outdoor laboratory for students.
Although I submitted this article to Lehigh’s student newspaper a few months ago, The Brown and White, it never got published (in the paper or online) for unbeknownst reasons. It refers to the upcoming plans to renovate Williams Hall, and my concerns for the future fascinating and historical forest directly adjacent to the building.
The recently drafted Campus Master Plan lays out the administrative vision for future improvements to Lehigh’s Campus. (Check out the whole plan at https://www.lehigh.edu/~inspig/lu_cmp_book_10-4-12.pdf). I had the opportunity a few weeks ago to attend a graduate student senate meeting focused on aspects of this plan, and was very troubled by the idea to re-landscape the area behind Williams Hall (the building behind Linderman Library that housed Earth and Environmental Sciences before STEPS was built) to allow more pedestrian access. Although plans have not been implemented yet, I worry that the ecological, historical, and educational significance…
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