Blog Archives

Save the Tangled Bank!

Nice article Michelle. Too bad the paper didn’t publish it. The site has historical significance and is a great outdoor laboratory for students.

In the Forgotten Forest

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  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…

View original post 463 more words


Experiential learning on the Tangled Bank: plant traits and ecological succession

An opportunity for experiential learning

Student reads a handout describing the objectives of a botanical survey of the "Tangled Bank" on the campus of Lehigh University.

Student reads a handout describing the objectives of a botanical survey of the “Tangled Bank” on the campus of Lehigh University. Photo: Christa Neu

In 1967 Lehigh University Professor Francis Trembley convinced the university to stop mowing a small area of the campus.  Professor Trembley named the area the “Tangled Bank,” and it became a place where students could observe nature right outside the classroom.  At one point in time there was even a “Tangled Bank” sign on the slope. One year after the mowing stopped, Professor Trembley had the foresight to encourage an undergraduate student to collect and identify all plant species growing on the Tangled Bank, and these collections were archived in the Lehigh Herbarium.  Read the full story of the Tangled Bank here (including some great recollections of Lehigh alumni in the comments).

A student identifies trees growing on the Tangled Bank.

Students identifying trees growing on the Tangled Bank. Photo: Christa Neu

In the fall of 2013, the Lehigh University ecology class (EES-152) completed a botanical survey of the “Tangled Bank” to document what species occupy the site today. The primary objective of this project was for the students to use their data in conjunction with the 1968 plant collections to assess how plant characteristics, such as functional and life history traits, change from early to mid succession. In addition to learning about plant traits and succession, the project allowed students to learn how to apply some commonly used statistical tests to assess differences between groups. They also compared their tree data to a similar dataset collected earlier in the semester from the Lehigh University Experimental forest, a forest that has undergone secondary succession for approximately twice as long as the Tangled Bank. The goal of this comparison was to assess how tree density and biomass change with succession.

Students conducting a botanical inventory of the Tangled Bank.

Students conducting a botanical inventory of the Tangled Bank. Photo: Christa Neu

Student conducting a botanical inventory of the Tangled Bank.

Student identifying a tree on the Tangled Bank. Photo: Christa Neu

Functional traits and succession

What are functional traits?  Functional traits are characteristics of species that strongly influence performance, and are therefore fundamental to survival and reproduction. They can be physiological, morphological, or represent reproductive strategies (the latter are oftentimes referred to as life history traits).  Plant functional traits include things like photosynthetic pathway (C3, C4, CAM), growth rate, shade tolerance, number of seeds, size of seeds, growth form, life span, seed-dispersal method, and seed viability. Functional diversity (i.e., the total diversity of these traits represented by an ecological community) is increasingly used as an important measure of biodiversity.

What functional traits might be expected to change with ecological succession?  Shade tolerance, growth form (herb versus tree), and lifespan might be a few of the more obvious traits that would be expected to change, as plants of later succession include many long-lived trees that compete for light. However, changes in other traits with succession may be less obvious.  For example, how might you expect seed viability (i.e., the length of time a seed can survive in the soil before germination) to change with succession?

Students pressing a collection of Tulip polar (Liriodendron tulipifera) from the Tangled Bank.

Students pressing a sample of tulip poplar (Liriodendron tulipifera) from the Tangled Bank. Photo: Christa Neu.

Field work

The Tangled Bank was divided into nine plots, with 3 or 4 students responsible for a complete botanical inventory of each plot.  The students identified and estimated the abundance of all plant species, and collected voucher specimens for archival in the Lehigh Herbarium. For trees, diameter at breast height (dbh) was measured and used to calculate total basal area of the forest and the average basal area per tree. The total density of trees (per 1000 m2) was also calculated.  Each group submitted an excel spreadsheet with their inventory results and dbh measurements as the first deliverable for the project.

Table 1. Common plant species of Lehigh University's Tangled Bank in 1968 and in 2013 after 45 years of ecological succession.

Table 1. Common plant species of Lehigh University’s Tangled Bank in 1968 and in 2013 after 45 years of ecological succession.

Pressing and identifying plants from the Tangled Bank.

Pressing and identifying plants from the Tangled Bank. Photo: Christa Neu

Data compilation and research on plant traits

The data from each group were combined into a class dataset. Students developed lists of the dominant species that grew on the bank in 1968 and 2013 (Table 1, above). Each student was then assigned two plant species (one from 1968 and one from 2013), and required to gather information about the attributes of these species, particularly with respect to life history and functional traits. The objective was to compile as much quantitative and semi-quantiative information on the traits of these species as possible.

Collecting Japanese Barberry on the Tangled Bank.

Collecting Japanese barberry (Berberis thunbergii) on the Tangled Bank. Photo: Christa Neu

The students could use any source of information for this research, as long as they documented their sources; but, we anticipated that they would rely heavily on some of the publicly available databases that have been developed to describe plant characteristics. Unfortunately the shutdown of the US government prevented access to several of these resources, and limited the number of traits that we could examine. However, the students made the best of the situation and found as much information as possible using a variety of sources. They submitted their research in the form of an excel spreadsheet (a template was provided to help standardize the data collection), and this was the second deliverable for the project. Information on sixteen characteristics were found for most species, so we focused our analyses on these (Table 2).

Table 2. Comparison of sixteen plant characteristics of early and mid successional plant communities on the Tangled Bank. Significant differences are denoted with asterisks (*p<0.05, p<0.01**)

Table 2. Comparison of sixteen plant characteristics of early and mid successional plant communities on the Tangled Bank. Significant differences are denoted with asterisks (*p<0.05, p<0.01**)

Data analysis and results

Student measuring dbh of tree on the Tangled Bank.

Student measuring dbh of a tree on the Tangled Bank. Photo: Christa Neu

Students then performed chi-squared and t-tests using excel, for categorical and continuous data respectively, to assess differences in functional traits of the plant communities in 1968 and 2013 (Table 2). The results of these statistical tests were submitted by each student as the third deliverable of the project.

The students found that plants of early succession generally had smaller seeds, longer seed viability in seedbanks, lower age of first flowering, shorter lifespans, smaller maximum height, and smaller average leaf area (Table 2, Figures 1 & 2).  The mid-successional plant community had a greater percentage of species with seed dispersal via mammals and birds (Table 2, Figure 1). Early successional species also tended to be less tolerant of shade and were likely more readily eaten by vertebrate herbivores than those of mid succession (Table 2, Figure 1). Plants of early succession also tended to produce more seeds per plant and have faster growth rates, although differences in these two traits did not meet our threshold for statistical significance (p<0.05). Also, no significant differences were found between N-fixation capacity, frost tolerance, fire tolerance, and drought tolerance of plants in the two communities.

Comparison of the frequency of selected plant traits in 1968 and 2013 on the Tangled Bank.

Figure 1. Comparison of the frequency of selected plant traits in 1968 and 2013 on the Tangled Bank. Results of Chi-squared tests are shown in Table 2.

Box plots showing the distribution of selected quantitative traits for plants occupying the Tangled Bank in 1968 and 2013. These plots show the distribution of values for each plant community, with the median indicated with a horizontal line, the boundaries of the box indicating the 25th and 75th percentiles the whiskers indicating the 10th and 90th percentiles, and outlier points shown with dots.

Figure 2. Box plots showing the distribution of selected quantitative traits for plants occupying the Tangled Bank in 1968 and 2013. These plots show the distribution of values for each plant community, with the median indicated with a horizontal line, the boundaries of the box indicating the 25th and 75th percentiles, the whiskers indicating the 10th and 90th percentiles, and outlier points shown with dots. Results of T-tests are shown in Table 2.

Connecting functional traits to Grime’s life history classification

Figure 3. Species of the Tangled Bank plotted according to  Grimes life history classification. Species positions estimated based on functional traits.

Figure 3. Species of the Tangled Bank plotted according to Grime’s life history classification. Species positions estimated based on functional traits.

Various life-history classification methods have been developed by ecologists to facilitate thinking about how species are adapted to environmental conditions. J.P. Grime proposed one such classification scheme for plants, which focused on adaptations to the amount of disturbance (i.e., processes that destroy biomass) and stress (i.e., external constraints that limit the rate of production) in the environment.  Under conditions of frequent disturbance, ruderal (i.e., “weedy”) species tend to be favored. Under conditions of high stress, plants tolerant of environmental extremes (e.g., cacti, carnivorous plants) tend be favored. Under conditions of low stress and infrequent disturbance, competitive species tend to be favored.

As an example of how species during succession may fit into Grime’s classification scheme, the functional trait data from the Tangled Bank was used to develop indices related to competition, stress, and disturbance.  Traits that would likely be selected for in these different environments were grouped and each species was given a composite score for each of the axes shown in Figure 3 based on the total standardized score of the grouped traits. The figure highlights the shift from ruderal species to better competitor species that has taken place between 1968 and 2013 on the Tangled Bank (Figure 3).

So many plants.  So many more plant traits. Photo: Christa Neu

So many plants. So many more plant traits. Photo: Christa Neu

Changes in tree density and biomass with succession

Tree data from the Tangled Bank was compared with data that the students collected earlier in the semester from the Lehigh Experimental Forest. Tree density (trees/1000m2) was higher on the Tangled Bank than the Lehigh Experimental Forest, and the average size (basal area) of trees was larger in the Lehigh Experimental Forest  (Figure 4A, 4B). Total basal area of trees, which takes into account both density and size, was greater on the Tangled Bank (Figure 4C).

Figure 3. Comparison of A) average basal area per tree, B) Tree density, and C) Total basal area of all trees for the modern Tangled Bank and the Lehigh Experimental Forest.

Figure 4. Comparison of A) Average basal area per tree, B) Tree density, and C) Total basal area of all trees for the modern Tangled Bank and the Lehigh Experimental Forest.

For the students, deliverable #4. Due 8 November. Complete the following tasks/questions:

1) In less than one page (single-spaced), summarize the differences in functional traits of plant communities in early and mid succession on the Tangled Bank. Your summary should include descriptions of why the observed differences likely occur (i.e., processes).

2) What other functional traits, not included in our analyses, might be expected to differ between 1968 and 2013?

3) For many of the traits we were only able to obtain categorical values, and the number of categories we defined varied among traits. For example, dispersal mode had six defined categories whereas nitrogen fixation capacity only had two. Do you think that the number of categories and how we defined them affected our statistical results and interpretation? Using the original excel spreadsheet, create new, broader categories for a trait of your choice by merging data into a smaller number of categories. Does reducing the number of categories impact the chi-squared test result? Does it change the interpretation?

4) What are the assumptions of a t-test? Did our data violate any of these assumptions?

5) Describe the position of the 1968 and 2013 species in the Grime’s life history diagram (Figure 3). What traits do you think were used to develop the species scores along each axis? In other words, which particular traits would likely be most related to each axis?  Some traits could be favored under more than one environmental condition (i.e., high stress, high competition, high disturbance). Justify your answers.

6) Where would the species of the Lehigh Experimental Forest likely be place on Figure 3?

7) Assuming that the differences in successional age are solely responsible for the differences in the density, size of trees, and total tree basal area of the Tangled Bank and the Lehigh Experimental Forest, what specific processes likely resulted in these differences?

8) Your answer to #7 assumed that the only difference between the two sites was age, a common approach often referred to as space-for-time substitution. However, what other factors might contribute to the differences between the two sites?

9) Using the data in Table 3 (below), calculate the rate of change of tree density and average tree basal area in a) early succession (first 45 years) and in b) mid-succession (45 to 98 years). Explain what processes likely contribute to these different rates of change.

Table 3. Tree density, average tree size, and total basal area of the Tangled Bank and Lehigh Experimental Forest (data for Figure 4).

Table 3. Tree density, average tree size, and total basal area of the Tangled Bank and Lehigh Experimental Forest (data for Figure 4).

We may have the new STEPS building, but nothing beats a classroom like this one.

We may have the new STEPS building, but nothing beats a classroom like this one. Photo: Christa Neu

The Herbarium…and virtual herbarium…at Lehigh University

Herbarium specimen collected by Francis Trembley in 1935 from the Lehigh University Arboretum.

Herbarium specimen collected by Francis Trembley in 1935 from the Lehigh University Arboretum.

Stacks and stacks of flattened, dried plants. Each meticulously labeled with a scientific name, collection date, location, habitat details, and other relevant information.  Collectively, the over 300 million specimens housed in herbaria throughout the world provide a wealth of information on the world’s botanical diversity and are a rich resource for ecological, taxonomic, and genetic studies. Because location and date are recorded on the specimens, they are an important source of information in studies of past and present plant distribution patterns.  DNA can also be extracted from herbarium specimens, and has been used to answer evolutionary and genetic questions. Herbarium specimens have also been used to provide information on changes in plant phenology, i.e., the timing of flowering, fruiting, and other life events, that have occurred over the past couple centuries in response to global change. And they have been used to investigate things that are not directly botanical as well. For examine, leaf damage and other evidence has been used to study changes in herbivory and pathogens. Chemical analyses of herbarium plants have even been used to reconstruct trends in atmospheric pollution. The scientific and educational values of herbaria are varied (for some more examples see here and here), and they will likely be useful for other sorts of investigations in the future.

Portion of the Lehigh University Herbarium.

Portion of the Lehigh University Herbarium.

Index Herbariorum, maintained by the The New York Botanical Garden, provides a global directory of herbaria. Increasingly, information about the specimens housed in these collections has been digitized and compiled into databases so that they can be available for research and education. The process is time consuming and labor intensive, but many herbaria have made all or a good portion of the information about their collections publicly available online. For example, in the northeastern US, the Consortium of Northeastern Herbaria (CNH) provides an integrated portal to search the collections of regional herbaria. Through the CNH portal you can search for records of any species contained in these collections, and if the samples have been georeferenced you can even display the collection locations within Google Maps or Google Earth. For example, here is link to all collections of the the American Chestnut (Castanea dentata) in the database.

The Francis J. Trembley Herbarium at Lehigh University

American chestnut (Castanea dentata) collected in 1970.

American chestnut (Castanea dentata) collected in 1970.

Recently the herbarium at Lehigh University has been added to the Consortium of Northeastern Herbaria (CNH), although additional specimens are still being entered into the database and many entries still need to be checked. Reorganizing and entering the information about the specimens into a database has been a labor of love, performed by myself and “volunteer” undergraduates (most of the undergraduates that helped had to do this because they missed a course field trip).  Data entry has slowly progressed since I first unearthed the herbarium from the basement of Williams Hall in 2010, and is now more than 90% completed. I have added my personal herbarium collection as well, and the Francis J. Trembley herbarium now serves primarily as a teaching resource, although plenty of research opportunities exist. The addition of the herbarium to the CNH makes it more accessible for research, as now this “virtual herbarium” is publicly available.

The collection is small in comparison with the large herbaria of the world (see here for a list of the largest herbaria), only containing about 2200 specimens. However, collectively small herbaria contain a large number of plants; furthermore, small herbaria oftentimes contain important regional collections and the collections of important scientists. The Lehigh University Herbarium includes the collection of Francis Trembley, a pioneering professor of ecology at Lehigh University. His plants were primarily collected from eastern Pennsylvania in the 1930s. The collection represents about 200 plant families and over 500 genera. Below are some figures showing some other characteristics of the collection.

Some summary statistics of the Francis J. Trembley Herbarium. States with at least 10 specimens shown at top, collectors attributed to at least 10 samples in the middle, and the distribution of sample years in the collection at bottom.

Some summary statistics of the Francis J. Trembley Herbarium. States and collectors were only included here if they were associated with a significant number of specimens.

Searching for specimens in the herbarium

To search for specimens in the herbarium, go here. You can search by collector last name, genus, species, location, or other fields. For example, here is a link to all the specimens collected by the herbarium’s namesake, Francis Trembley, and here is a link to all of the specimens he collected in the old Lehigh Arboretum (see here for more information on the arboretum). Or perhaps you want to know what specimens were collected in Pennsylvania, New Jersey….or even Alaska. Or maybe you are interested in plants of the Okefenokee Swamp in Georgia, or you are student in my wetland ecology field course 🙂 and want to see what species have been collected in Pymatuning Creek Marsh in western Pennsylvania. Of course, you can also search the entire CNH database, including Lehigh’s collection and other regional herbaria, by going here.

Future plans and new specimens

The remaining specimens in the herbarium will hopefully be made “virtual” in the coming months.  Samples from the Northeast will also be georeferenced so that they can be plotted geographically, and eventually images of the herbarium sheets will be uploaded. At this point, few attempts to update taxonomy have been made and the specimens are organized based on the original species identifications. However, it appears that synonyms can be searched through the portal, although I have not experimented with this yet.

Of course, new collections will also be added. Plant collecting is a great way to learn plant identification, and archiving the specimens in herbaria contributes to our knowledge of the world’s botanical diversity. And besides, there is just something fulfilling about standing on a full plant press, pulling the straps to tighten it, and feeling the crunch of cellulose compression beneath your feet.

Trembley’s “tangled bank” on the Lehigh campus

Francis Trembley, pioneer ecologist, environmentalist, and professor of ecology at Lehigh University. In 1967, he convinced the administration to stop mowing the slope behind Williams Hall. The site was meant to be a place where students could observe secondary succession, righout outside (Image from

Francis Trembley (1904-1978), pioneer ecologist, environmentalist, and professor of ecology at Lehigh University. In 1967, he convinced the administration to stop mowing the slope behind Williams Hall. The site was meant to be a place where students could observe secondary succession, right outside the classroom (Image from

“It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. . .” – Charles Darwin

Where is the tangled bank?

Snippets of what little I could recall of the above quote from Charles Darwin bounced around my head as I read labels on some herbarium specimens.

Label of a herbarium specimen that was collected from Lehigh's "Tangled Bank" in 1968.

Label of a herbarium specimen that was collected from Lehigh’s “Tangled Bank” in 1968.

My task was to reorganize this collection of carefully flattened and labeled dried plants, to make it more useful as a teaching resource.

According to the labels on these particular specimens, they were collected from the “Tangled Bank.” No other location information was given.  Where was this place? What was its significance? The labels indicated that they were all collected by a person named David J. Mazsa. Maybe I could track this person down…

Finding David Mazsa

Google is amazing. Within a minute of searching, I found a person by the name of David Mazsa with a degree from Lehigh Unversity. Perhaps he was the collector? I sent him an email and received a prompt response….

“You are in luck-  I am the guy you are looking for.

“Tangled Bank” is the sloped area right behind Williams Hall.  Dr. Trembley had an idea to allow that mowed and manicured area to proceed through natural succession and become a “tangled bank” (I think the term is from Charles Darwin).  Dr. Trembley convinced Lehigh to stop mowing and allow the area to begin to revert to it’s more natural state.  In his view this would be so much more attractive and diverse than the mowed lawn.  I honestly do not remember the exact chronology but my best guess is that they stopped mowing some time in 1967 and my samples were from the following year but I am not sure.  Dr. Trembley found some money for me to work on the bank and take samples to record changes in the plant species distributions.  I am amazed to learn that I left a mark!  I graduated from Lehigh in 1969 and although I visited Dr. Trembley once or twice afterwards, I don’t know how long the project lasted or what additional data was collected.

Dr. Trembley was one of the people responsible for my career path.  I was born and raised in Bethlehem and he wrote a lot in the local newspapers.  He was one of the reasons I chose Lehigh.  He was a combination of an old time naturalist who loved the diversity of living things and was eternally curious about how they interacted.  Walking on a field trip with him was like having a window to the world of nature.  We hung on his every word and loved his stories.  But he was also politically astute and he was in the middle of Environmentalism of the 60s and 70s.

He taught Ecology with a set of note cards that were at least thirty years old.  When we asked him if it was boring teaching the same stuff over and over again, he noted that the Ecology material was much the same, but the students changed every year and his interaction with them made it different every year.  I have just finished my 40th year as a high school teacher and now I understand how right he was about the difference in students from year to year.

I also remember that our grade in Ecology was determined by a semester exam and that the question was “Describe life in, on, and around inland waters.”  Although that was the only science course at Lehigh that I didn’t ace (I got a B I think), That course and Dr. Trembley are certainly one of the big reasons I have spent much of my life teaching and working toward making the world a more sustainable place.

I hope I helped identify the location for you.  Thanks for bringing back some very fond memories.

David Mazsa”

So the “tangled bank” is the slope behind Williams Hall!

Of course! This is the only non-manicured place on the Asa Packer campus. And before the Department of Earth & Environmental Science moved from Williams Hall into the STEPS building, my office used to face it. For five years I looked directly out my window at the “tangled bank.” And I agree with Trembley, it is more beautiful and diverse than a mowed lawn. An aerial photograph from 1971 shows that much of the slope was still characterized by low-growing vegetation four-years after they stopped mowing.

The "tangled bank" on the slope behind Williams Hall in 1971 and today. In 1971, four years after the mowing stopped, low-growing vegetation on much of the slope is seen in the photographs. A few trees remained on the southern margin.

The “tangled bank” on the slope behind Williams Hall in 1971 and today. In 1971, four years after the mowing stopped, low-growing vegetation on much of the slope is seen in the photograph. A few trees remained on the southern margin, which is the top of the slope.

After David’s email, I also found mention of the “Tangled Bank” in a book on the history of education at Lehigh University (Yates 1992, page 238):

“The biologist Fran Trembley was speaking and writing on the dangers of technology long before the subject became popular with the general public. In 1951 he had his title changed to professor of ecology. Students flocked to his classes. In order that they might have a nearby spot in which to study ecosystems, he asked that the slope above Williams Hall be left in a wild state – a tangled bank, he called it, using a term coined by Darwin. The administration complied with the request and put up a sign, “Tangle Bank,” to identify the place.”

The “tangled bank” today
The "tangled bank" behind Williams Hall.  Trees are higher than the building today.

The “tangled bank” behind Williams Hall. Trees are higher than the building today.

Today, the “tangled bank” is a small, diverse woodlot, with an overstory that includes tulip poplar (Liriodendron tulipifera), American beech (Fagus grandifolia), black cherry (Prunus serotina), several species of maples (Acer spp.), as well as several other deciduous species. Various shrub species occur throughout, particularly along the margins, and poison ivy (Toxicodendron radicans) and Virginia creeper (Parthenocissus quinquefolia) are common. It is a very different place than it was in 1968. A few more photographs are below (click on one to view as slides).

What can students learn from the tangled bank?

This fall, students in general ecology (EES-152) at Lehigh University, will revisit Trembley’s “tangled bank.” Forty-seven years of ecological succession have passed since the mowing was stopped, and because of David Mazsa’s collections we know many of the pioneer species that grew on slope after just one year.

Francis Trembley on the cover of the Lehigh Alumni Bulletin in 1970.

Students in the ecology class will complete a botanical inventory of the slope, and the data will be used to introduce and explore the topic of secondary succession. Furthermore, the students will use modern databases to research and compare information on the functional traits (e.g., seeds per plant, energy content per seed, growth habit, mode of dispersal) of plants in early succession versus mid-succession (i.e., today). We will report our results on this blog later in the fall semester!

Trembley’s last lesson.

Unfortunately, this will probably be the last lesson taught by Trembley’s “Tangled Bank.” A renovation of Williams Hall is planned to begin later this year, and as part of this effort the area will be relandscaped…removing the “tangle” from the bank.

Perhaps only this ecologist would be saddened by such a thing.

From prized arboretum to forgotten forest: a century of change.

A white pine (Pinus strobus) growing in the old Lehigh University Arboretum.  Once an open park with scattered native trees, after more than half a century of ecological succession the arboretum now blends in with surrounding South Mountain forest.  However, the legacy of arboretum can still be seen by the careful observer.  For example, the extensive lateral branches on this white pine were formed when the tree was growing in the open environment of the arboretum.  As the forest filled around the tree, the lower limbs no longer had access to abundant light and died.  The top of the tree is still quite healthy. Photo: Douglas Benedict.

On July 30th 1935, Francis Trembley walked along the north-facing slope of South Mountain above the campus of Lehigh University.  Dr. Trembley was a biology professor, and he stopped along the road to collect some goldenrod and several other herbaceous plants that were in flower at this time.  He then likely entered a semi-open area on the southern side of the road that was carefully planted with clusters of different tree species.  There, in a plot of land only about 11 acres in size, he probably observed over 90 of the tree species native to Pennsylvania, and as many as 200 types of North American trees (Emery 1915, Hall 1951). At least 20 species of oaks were represented alongside maples, pines, basswood, beech, yellow buckeye, tulip poplar, red spruce, and many others (Hall 1951).  This museum of trees resulted from the foresight and passion of another Lehigh biology professor, Robert Hall.  Dr. Hall was instrumental in acquiring the land for the university in 1908, and he designed and oversaw the plantings, which were apparently positioned on the property to broadly reflect botanical relationships (Hall 1951).  This “informal park,” as Hall envisioned it, was the Lehigh University Arboretum.  By all accounts, it was one of the finest university arboretums in the country.

On that day in July, Trembley probably also walked a bit further east past the arboretum, where he would have observed a young, wedge-shaped forest that was meticulously divided into a series of 42 experimental plots.  Initially established and planted in 1915, the plots included over 20 tree species native to North America and Europe.  Some plots were planted with a single species and others a mixture of two species.  This was the Lehigh University Forest Plantation. Set up as a forestry experiment to assess what economically valuable species would grow best on the rocky, thin soils of South Mountain and similar areas in Pennsylvania, the value of the experiment was highlighted by the President and Vice-President of the University, Henry Drinker and Nat Emery, at a speech to the Pennsylvania Forestry Association in 1915.   However, by the end of the 20th century both the arboretum and the forest plantation would be almost completely forgotten…engulfed by the surrounding forest.

How do we know that Trembley went up to the arboretum on that day in 1935?  The plants that he collected on the edge of the arboretum are archived in the Lehigh University Herbarium.  In fact, the discovery of the herbarium specimens is what first sparked our interest in relocating the arboretum.

One of the plant specimens collected by Francis Trembley in 1935, a species of goldenrod, is shown above in panel A. A closeup of the label indicating that it was collected in the arboretum is shown in panel B (Photographs by Douglas Benedict).  Panel C shows a picture of the faculty of the Department of Science at Lehigh University in 1935 (from the yearbook, The Epitome). Francis Trembley is in the top row, second from the right. Robert Hall, who established the arboretum in 1909, is second from the right in the bottom row. Panel D is a picture of a portion of the tract of land occupied by the arboretum in 1910, taken from the 1910 yearbook.

The History of the Arboretum

In 1951, Robert Hall finished a manuscript entitled “History of the Lehigh University Arboretum,” and although he clearly doubted that it would have much use to anyone, he filed it away in the University library.  The document contains much of what we know about the arboretum – how and why it was established, the role of the adjacent nursery and seedbeds, the adjacent forest plantation,  and the many challenges he had to overcome.  It might sound like dull reading, but it isn’t.  In fact, the second half is a bit of a political thriller.  Well, perhaps not a thriller, but it does provide a fascinating window into university politics of the early 1900s.  Other sources of information on the arboretum include a brief statement in the 1910 yearbook regarding the purchase of the land, various articles in the student newspaper (The Brown and White) which mention or describe the arboretum, and two publications in the journal “Forest Leaves,” which was published by the Pennsylvania Forestry Association.

Some headlines and excerpts from the Lehigh student newspaper in the 1920s and 1930s.

Archives of the student newspaper reveal that the arboretum played practical, educational, and cultural roles for the university and students until sometime in the 1950s.  For example, the arboretum and associated nursery provided replacement trees after the American chestnut blight eliminated the chestnut trees on the main area of campus (Brown & White, March 10, 1916) and it was a continual source of trees for the rest of campus in the 1920s and 1930s.  Students and faculty also went to the arboretum and forest plantation to learn, observe, admire, and even have a little fun.  Francis Trembley used the arboretum for his classes.  An open-air theater within the arboretum, referred to as Top ‘o The Mountain theater, was used for plays during the summer session in the 1930s (Brown and White, Sept 26, 1936).  And for fun, mischievous Lehigh students occasionally swapped the labels on the trees (Brown & White, Oct 6, 1943).  Lehigh students were apparently just as wild and crazy then as they are today!

Number of news articles in The Brown and White (the student newspaper) about or mentioning the Lehigh University Arboretum during the past century. The arboretum vanishes from campus culture in the 1950s.

The last mention of the arboretum in the student paper was an anecdotal mention in 1954, and Robert Hall seems to have recognized the declining interest in the arboretum in his 1951 manuscript:

 “The last time I saw it, the arboretum looked like a monument to neglect – grass uncut, limbs stretching out over the road. It had seemingly been years since any car had tried the road.”

“What is the condition of the arboretum today? I do not know. If I were not seventy-nine years old I would climb up there and see.” – R.W. Hall

When Hall wrote those words in 1951, a new forest was likely already sprouting within the spaces between the carefully planted trees.  Priorities change. Human memories fade.  There were no more plays at Top ‘o The Mountain Theater.  The students stopped moving the tree labels.  The arboretum disappeared from campus maps.

Participants in Gordon Bearn’s freshman seminar entitled “Emerson/Thoreau: Kindling Life” pose for a photograph in the old arboretum in September 2012. The large oak in the background was one of the original arboretum trees, and fell last fall after an unusual October snowstorm.

Rediscovering the trees

The arboretum and forest plantation were relocated in the fall of 2011, and the story of this rediscovery was recently told in the Lehigh Alumni Bulletin (see here).   Luckily for us, both the arboretum and the plantation land are still forested and have not been extensively disturbed by development.  These areas of campus, and the trees that are on them, provide a potentially rewarding scientific opportunity to better understanding the legacy of a planting and reforestation experiment.  Furthermore, they represent an opportunity for the Lehigh community to reconnect with the history of the university and explore our changing values and priorities.

The Lehigh Experimental Forest Plantation

The forest plantation was less commonly mentioned in the student newspaper, although the archives reveal that it was occasionally  mistaken to be just another name for the arboretum.  Given that its mission was scientific, it is not surprising that it received less attention.  Although two articles on the experimental forest plantation were published, it appears that it was forgotten about quickly.

Plots of the Lehigh Experimental Forest Plantation, established in 1915.  Forty plots were established, with trails generally between each set of two plots.  Although indicated on this map, no seedlings of bald cypress, cucumber magnolia, or scarlet oak were planted in 1915 (Rothrock 1920).  However, scarlet oak was likely added to its plot a bit later because it grows there today.  Cucumber magnolia may have been added a bit later as well.

Henry Drinker elicited the help of others in the establishment of the forest plantation.  Joseph Rothrock, the first president of the Pennsylvania Forestry Association, and Simon Elliott of the Forestry Reservation Commission, were called on to assist in its design (Emery 1915).  Seedlings, all the same age and less than about six inches tall, were densely planted in the plots in 1915.  It was meant to be a natural experiment with little to no intervention after the the initial planting, and it appears that no additional management was performed. In fact, Rothrock assessed the experiment after 5 years and noted that several tree species had already established naturally (i.e. without planting) within the plots, including black birch (Betula lenta), black oak (Quercus velutina), and black cherry (Prunus serotina).  The latter two species were also planted in several plots.  The total number of each species that were planted was as follows:

Simon Elliott (left) and Joseph Rothrock (right) pictured together. Both men assisted in the design of the Lehigh Experimental Forest Plantation in 1915.  Photo source:

  • 600 Basswood (Tilia americana)
  • 300 Black cherry (Prunus serotina)
  • 300 Black oak (Quercus velutina)
  • 400 Bur oak (Quercus macrocarpa)
  • 100 Elm (Ulmus americana)
  • 400 European larch (Larix europa)
  • 100 Grey birch (Betula populifolia)*
  • 100 Hemlock (Tsuga canadensis)
  • 300 Honey locust (Gleditsia triacanthos)
  • 500 Jack pine (Pinus banksiana)
  • 500 Norway spruce (Picea abies)
  • 100 Pin oak (Quercus palustris)
  • 500 Pitch pine (Pinus rigida)
  • 100 Red spruce (Picea rubens)
  • 400 Scotch pine (Pinus sylvestris)
  • 400 Sugar maple (Acer saccharum)
  • 600 Tulip poplar (Liriodendron tulipifera)
  • 400 Western yellow pine (Pinus ponderosa)
  • 700 White ash (Fraxinus americana)
  • 300 White oak (Quercus alba)
  • 500 White pine (Pinus strobus)

Like most science of the time, Rothrock’s assessment of the forest plantation after five years of growth was very qualitative. He attempted to summarize both the relative height and general health of the planted species.  He noted that 1919 was a locust year (he was likely referring to cicadas), and that the hardwoods, particularly the oaks, suffered extensive damage.  Although cicadas are not usually a problem for adult trees, their egg laying can damage small trees.  He also noted that several species were damaged by fire, which apparently was common at the time on South Mountain  (Rothrock 1920).  In fact, the arboretum had a fire break around its perimeter (Hall 1951).

Summary of qualitative observations on the general health and height of tree species in the Lehigh Forest Plantation after 5 years of growth (summarized from Rothrock 1920). *The initial plant list indicated that yellow birch was planted, but present-day observations suggest that it was probably grey birch. **Black birch was not planted, but was establishing naturally along with black cherry and black oak (both also planted) within the first five years.

Although Rothrock’s assessment was qualitative it still provides a nice picture of the changes that occurred in those first few years.  Some clear winners and losers were emerging by this time.  In general, conifers initially did better than the hardwoods. Hemlock, elm, and honey locust all perished quickly.  Tulip poplar, basswood, white oak, and ponderosa pine were all alive but not faring well, as several of these species were hit hard by cicadas and/or fire.  A number of species were moderately successful, including sugar maple, white ash, and white pine; however, the tallest growing and healthiest trees were the european larches, scotch pines, and jack pines.  Black birch, which wasn’t planted but colonized the site naturally, and black cherry were also doing quite well after five years.  Although much slower growing, the spruces were thriving.  Of course, Rothrock recognized that his report only captured a small piece of a long-term experiment – an experiment that would continue to play out for decades to come:

This experimental tree plantation was the beginning of a practical scientific experiment, so far unique in this country, which is bound in ten, twenty and fifty years to be productive of information of great value to the forestry interests of Pennsylvania and of the country at large. – J.T. Rothrock

Students in general ecology (EES-152) measuring and identifying trees in the Lehigh University Experimental Forest.

A student in general ecology (EES-152) working to reestablish and resurvey the plots of the Lehigh Experimental Forest.

A century of change

Fast forward nearly 100 years.  What happened?  Did Rothrock’s initial observations forecast what the forest would look like today?  How many of the planted species survived?  How did natural ecological succession play out against this backdrop of plantings?  How did plant and animal invasions of the past century impact this unusual forest?  Were some plots more susceptible to invasion than others?  If Rothrock, Elliott, Drinker, or Hall had had the ecological knowledge of today, could they have predicted what the area would look like in 2012?  How do other ecosystem characteristics and processes (e.g., soil characteristics) vary in the different plots today?  What other legacies of the plantings exist?  Given knowledge of the past, present-day patterns, and forecasts of the future, what might this forest look like in another 100 years?  Students at Lehigh University are now investigating these and other questions, using this unique experiment as a natural laboratory.  Stay tuned for the results.


Michelle Spicer, Lehigh graduate student, coring trees in the Experimental Forest Plantation.


The Epitome, Lehigh University Yearbook, 1935.  Download here.

The Epitome, Lehigh University Yearbook, 1910.  Download here.

All Brown and White articles mentioning the arboretum can be downloaded here.

Hall, R.W. 1951 (1945-51). History of the Lehigh Arboretum.  Download here.

Emery, N.M. 1915. A demonstration tree plantation at Lehigh University. Forest Leaves 15: 56-58. Download here.

Rothrock, J.T. 1920. The demonstration tree plantation at Lehigh University. Forest Leaves 18: 9-13. Download here.

%d bloggers like this: