Person in the Spotlight: David Robertson, Ph. D.


David J. Robertson, Ph.D., Executive Director of the Pennypack Ecological Restoration Trust


For the spring Watershed Alliance newsletter David J. Robertson, Ph. D., Executive Director of the Pennypack Ecological Restoration Trust (PERT), was kind enough to share his experience working at PERT, as well as explain some of PERT’s priorities and recent initiatives.

How did you get involved with the Pennypack Ecological Restoration Trust (PERT)?

In late 1987, I noticed an advertisement in the journal Science seeking a Land Manager at what was then the Pennypack Watershed Association.  At that time, I had been employed for six years at a Florida state agency conducting and sponsoring research on land reclamation following phosphate ore surface mining, but I had begun seeking a new position and wanted to move north; the job at Pennypack sounded tailor-made for my education and experience.  The Pennypack Trust hired me in May 1988 as manager of the 540-acre Pennypack Wilderness, the natural area that the Pennypack Watershed Association had been creating through land donations and purchases.  Eighteen months after I was hired, I was promoted to Executive Director, the position I have held since.

How does living on the Pennypack Preserve help guide your decisions with PERT?

Because I am office-bound most of the time, I don’t get out into the Pennypack Preserve as often as I would like during the normal workday.  Fortunately, because I live on the preserve grounds, I usually have an opportunity to take a walk in the evening and on weekends to review the status of the property.  In that way, I can keep up with ongoing projects.

My land stewardship staff typically is very task-oriented during their workdays, and they usually drive to the areas where they are working.  By walking, I have a chance to observe things that the stewardship staff might miss by driving to their tasks.

In addition, by walking after work hours—especially on weekday evenings—I often encounter many more visitors than I would if I were walking during the typical workday when there are fewer visitors.  As a result, I get to interact with visitors more frequently, and they realize that there is a representative of the Pennypack Trust in the preserve even after normal working hours.  Being present when there are more visitors also informs me about prohibited public use and gives me some insight about how the Trust might address human activities.  For example, on a recent Sunday afternoon when none of the stewardship staff was working, I came across a group of rock climbers who were scaling a quarry face for a climbing exercise.  This quarry is also used by Turkey Vultures for nesting and the Trust does not want the birds to be disturbed nor do we want to have to deal with accidents.  If I had not been walking, the climbers could have disturbed the birds, and “word” could have gotten out that the Pennypack Preserve is a great place to climb, which it is not.


Meadow in Pennypack Preserve.

What are some of the challenges facing the Pennypack Preserve?

The three greatest challenges facing the ecological integrity of the Pennypack Preserve are (1) stormwater and flooding generated in the suburbanized upper sections of the watershed, (2) white-tailed deer present in numbers that prevent forest regeneration, and (3) invasive plants.  Four species of invasive plants—all vines—pose the greatest threat: porcelain-berry, Oriental bittersweet, Japanese honeysuckle and the most recent invader, mile-a-minute weed.  These vines grow extremely fast in full sun, but less vigorously in deep shade.

Of course, there are a score of other non-native invasive plants in the preserve, but the vines are particularly pernicious.  They climb up into existing trees and pull down the trees with their weight and spread their leaves over the tops of the trees, which act as if the tree were covered with a blanket that deprives the supporting tree of sunlight and eventually kills it.

When the Trust began to tackle the invasive vines in earnest in 1990, the staff focused largely on old fields and meadows.  We mowed the fields, allowed them to begin to regrow, and then sprayed the tender new growth with herbicide.  Then, we reforested the sites to try to restore shade, which would suppress the rank growth of the vines.  Now that some of the original vine dominated fields have been reforested for 20 years, it is definitely obvious that our strategy of restoring shade to formerly open field shows promise for suppressing the growth of invasive vines.

The floodplain along Pennypack Creek presents a similar but even more challenging problem than the fields and meadows because the constant disturbance caused by repeated flooding makes reforestation difficult.  Trees planted on the floodplain frequently have been washed away by the floods that accompany hurricanes and tropical storms.  On the floodplains, the Trust has to treat large, established trees whose crowns are enveloped in vines every few years to prevent the vines from killing the trees.   Such repeated treatment is expensive, time consuming and labor intensive.


Abundant deer populations in the Pennypack Preserve pose a serious threat to reforestation.

Tell us about the deer management research at PERT.

During the early 1980s, problems related to the expanding population of white-tailed deer in the natural area and surrounding lands became too obvious to ignore.  Visitors commonly observed groups of 40 or more deer, staff members documented damage to vegetation and a lack of forest regeneration, and the number of deer killed on roads adjacent to the natural area increased every year.   Deer management began in 1984 when the Trust’s board of directors interviewed several nationally prominent deer biologists seeking guidance for establishing a management program.  Controlled hunting began during the 1984-85 season and the continued efforts have resulted in a significant reduction of deer from 600 to 150.  While this reduction has been significant and dramatic, the herd is still 10 times larger than recommended (i.e., 8/sq. mi.) for good forest regeneration. Unfortunately, deer numbers have stabilized and hunters have been unable to reduce the numbers further because the deer move to neighboring residential properties during hunting season, making them inaccessible to the hunters.

In an effort to better understand the behavior of the deer herd and develop strategies to improve hunting efficiency and effectiveness, in 2007 the Trust entered into a cooperative relationship with investigators at Bryn Athyn College who had secured funding to conduct research that would benefit both organizations mutually.   The goal of the program is to correlate deer movement and habitat use with land management and restoration in the preserve.  In order to accomplish their goal, the Bryn Athyn College scientists captured deer and fitted them with collars that transmitted GPS coordinates every five minutes.  Since the study began, the scientists have fitted 38 deer with collars and tracked their movements for periods of up to four months each.   Their work, producing information about deer movement and human activity, weather, invasive plants, and even moonlight, has generated reports presented as oral and poster presentations at scientific conferences and several papers in peer-reviewed journals.

What is the impact of the Delaware River Watershed Initiative (DRWI) and StreamKeepers program on PERT’s mission?

DRWI is a new initiative that has not yet had much of an effect on the Trust’s mission.  The Trust was founded as the Pennypack Watershed Association, which had as its primary goal improving water quality in Pennypack Creek.  The Association worked to achieve this goal through environmental education, land development review, and working collaboratively with municipalities—the same goal and much the same strategy advocated by DRWI for the larger Delaware watershed.  However, in the early 1990s, water quality in Pennypack Creek began to improve, impairment increasingly came from diffuse non-point sources that were very difficult to control, and the Trust’s natural area preserve continue to grow.  As a result, the Trust turned its attention to the Pennypack Preserve and focused on land protection and stewardship.  In a sense, the DRWI is a return to the organization’s original mission, although the Trust also has made a very significant commitment to maintaining and restoring the ecological integrity of the Pennypack Preserve natural area now.  As a result, the DRWI is an added program that the Trust is still evaluating how best to incorporate into our operations.

The citizen science StreamWatch volunteers who are monitoring water quality and serving as our “eyes and ears” on the creek are a growing group.  We have had a few StreamWatch volunteers working since 2014, but it is only recently that we have recruited large numbers of volunteers to help.  I’m hoping that the program will expand Pennypack’s visibility in the community, and that the Trust will be able to report on water quality trends to the municipalities in the watershed to encourage them to pass and enforce ordinances that will yield better water quality.  Because we have only recently begun to gear-up, it’s too early to determine how effective the StreamWatch program will be in the long run.

What is PERT’s relationship with the surrounding municipalities?

The Pennypack Preserve natural area includes land in four Montgomery County municipalities:  Abington Township, Bryn Athyn Borough, Lower Moreland Township, and Upper Moreland Township.  The preserve and its 11-mile trail system are open to the public without charge during daylight hours every day, so most municipalities look upon our protected lands as passive recreational complements to their active recreational facilities and amenities.  In general, the relationship between the municipalities and the Trust is one of cooperation; in fact, two of the municipalities provide financial support and appoint an elected municipal official to serve on the Trust’s board of directors.

Relations with the communities have not always been so cooperative or cordial, though.  One of the first projects that the organization undertook shortly after its founding in 1970 was an effort to establish a cluster of localized wastewater treatment systems that would treat small volumes of wastewater and then apply the effluent to upland areas.  The project’s goal was to avoid building an interceptor sewer running alongside Pennypack Creek and that would collect and then export all of the area’s wastewater directly to Philadelphia for treatment.  At the same time, the effluent from the small plants would recharge the depleted groundwater aquifer and would maintain undeveloped land where the effluent was to be applied.  The municipalities did not embrace this revolutionary concept and actively challenged the Trust for years, creating enmity that took decades to reverse.

Autumn Creek 1

Pennypack Creek in Autumn

Tell us about your efforts to create a continuous greenway along Pennypack Creek.

When Montgomery County’s Green Fields/Green Towns open space program was providing support to the municipalities for open space protection, several of the communities worked cooperatively with the Trust to provide financial support to help the Trust purchase undeveloped natural land and add it to the preserve, thereby helping to expand the greenway at its northern end.

Beginning around 2005, the Pennypack Trust began to participate actively with Montgomery County, the Fairmount Park Commission in Philadelphia, and other non-profit organizations in the Pennypack Creek valley in a coalition called the Pennypack Greenway organized and funded by the GreenSpace Alliance, a project of the Pennsylvania Environmental Council.  One of the goals of the coalition was to create a continuous greenway along the creek from its mouth at the Delaware River to the Pennypack Preserve natural area.  North, or upstream, of the Pennypack Preserve, suburban development has encroached to the banks of the creek almost all the way to the creek’s source in Horsham Township.  As a result, extending the physical greenway north of the Pennypack Preserve is impossible, although trail linkages as part of the Circuit will eventually allow users to travel from the mouth of the creek to its headwaters and beyond.

A protected continuous greenway now exists along the entire creek corridor between PERT and the Delaware River except for a short segment in Lower Moreland Township consisting of two parcels that remain in private ownership—the “missing link!”  The lands in these parcels are largely undeveloped because they lie almost completely in the Pennypack Creek floodplain.  Montgomery County is actively pursuing the acquisition and protection of these parcels as important natural areas and as buffers to its recently completed Pennypack Trail, which forms a common border to both parcels.

Article and photos by David Robertson.

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