Gordon Natural Area

Research Activities in the GNA

Since 2006 my grad students and I have been testing and evaluating field methods for tracking populations of salamanders in the GNA. Our studies have focused on novel designs for "coverboards," which are flat objects placed on the forest floor that tend to attract salamanders. Our most promising designs utilize a new material, Elephant Bark, which is made from recycled tires and is extremely durable. The photo shows an experimental array of 6 different coverboard designs. All are 16" squares of Elephant Bark, but they vary in thickness and in weight. The microclimate under the coverboards is being monitored by digital sensors wired to a data logger.

Beech Leaf Disease was first noted in 2012 in eastern Ohio.  Since then, the disease has been found in western Pennsylvania, southeastern New York, Ontario, and most recently, Connecticut.

The Spotted Lanternfly (Lycorma delicatula) is an invasive insect that has recently been introduced into the United States.  This species, which is native to China and Southeast Asia, was first detected in the US in Berks County (Pennsylvania) during Fall 2014.  The Spotted Lanternfly has quickly spread throughout southeastern Pennsylvania and adjacent states: by January of 2018, the species had been found in 13 counties in southeastern PA.

This species utilizes numerous agricultural and native plant species and potentially threatens billions of dollars of agricultural production.  Stone fruits (e.g., plums, cherries, peaches, etc.), apples, grapes and hops are particularly vulnerable.  The USDA has been very proactive in dealing with this threat, having allocated 17.5 million dollars in funding to fight against the Spotted Lanternfly.  The State has also been aggressive in addressing this threat, with the Pennsylvania General Assembly allocating an additional 3 million dollars towards control efforts.

The Gordon Natural Area could potentially be heavily impacted by the Spotted Lanternfly.  The species is a very adept 'hitchhiker' and the close proximity of Route 202 to the GNA provides an easy pathway for that species to become established in this area.  Three species of native grapes are known for the GNA, and an infestation of Spotted Lanternfly would undoubtedly threaten these species. Additionally, Spotted Lanternfly is known to utilize pines, so the native White Pines (Pinus strobus) at the GNA are also vulnerable.  The lanternfly is obligately associated with the invasive tree Ailanthus altissimus (Tree of Heaven).  There are two fairly large  stands of this species at the Gordon, and numerous additional individuals of Tree of Heaven are scattered throughout the GNA.

To determine the status of the Spotted Lanternfly and Tree of Heaven at the Gordon, undergraduate Christopher (Kit) Catranis initiated a surveillance and prevention project in the late Spring of 2018.   Initially, the work focused on mapping out (exhaustively) accurate locations of Tree of Heaven throughout the GNA.  The first Spotted Lanternflies were noted in the Gordon in the Summer of 2018, and the map has been continually updated by Kit and by the GNA staff as additional Spotted Lanternflies were encountered.  Kit has also made this map available for any relevant research efforts in the GNA.

In the Fall of 2018, Kit organized a group 'extermination' effort, in which volunteers visited the greater portion of the known individuals of Tree of Heaven and killed any Spotted Lanternflies that were observed and which were reachable from the ground.  Kit also has been surveying for lanternfly egg masses.  To date, no egg masses have been found.

Black Walnut (Juglans nigra; Juglandaceae) is a riparian species native to Eastern North America, with a population spanning as far south as Texas and as far north as southern Ontario.  The species is early-successional, shade-intolerant, and prefers a well-drained deep soil.  Black Walnut is susceptible to a variety of pests and pathogens which is the basis of this study at the Gordon Natural Area (GNA).  For an undergraduate independent research study, I looked at the density, size and health status of black walnuts at the GNA. While the status of Black Walnut at the GNA is healthy and stable, the many diseases that affect this species leave the population susceptible to decline.

Due to a scarcity of riparian habitat, Black Walnut is not particularly abundant in the GNA. Nevertheless, the trees that are still present should be preserved and managed to the best of our ability. For this study I, studied the density, size and health status of Black Walnut in three forest habitats (riparian, floodplain and lowland) in proximity to Plum Run, the stream running through the GNA.  Riparian habitats were those closest to the stream.  Floodplain habitats were adjacent to riparian habitats, but occupied a slightly higher elevation. Lowland habitats were higher in elevation and farthest from the stream in our study area.   I was assisted in this work by Dr. Greg Turner and Dr. Nur Ritter.

 Measurements taken included:

1)  Density of Black Walnut trees was estimated on a per hectare basis in order to relativize the plot size. 

2)  Tree health was characterized using US forest service management protocols, in which tree health was assigned scores ranging from 1-5 based on percent of alive branches above the bole, with a 5 being 100-80% of canopy alive, a 4 as 60-80% alive and so on.

3) Tree size was recorded as diameter at breast height (1.3 meters) using a DBH tape.

The goal of this study was to determine if there are any differences of Black Walnut density, size and health status between the three habitats. This can be useful to ascertain if one habitat has healthier trees than the others, which can then be used forest management practices to analyze susceptibility to disease or if one habitat needs to be more closely monitored. Another beneficial reason for the study as I have said before is to provide a touchstone study on the status of Black Walnut in the GNA as well as a rough approximation for the status of Black Walnut in similar forests throughout the region.

The multitude of pests and pathogens I referenced earlier include, but are not limited, to bootstrap fungus and honey fungus (Armillaria mellea - see image), tent caterpillars (Malacosoma americanum and Hyphantria cunea), and the most threatening: the mutualistic symbiotic relationship between the Walnut Twig Beetle (Pityophthorus juglandis) and Thousand Cankers Disease (Geosmithia morbida).  Some of these threats are present in the GNA, such as tent caterpillars and bootstrap fungus (in small populations). Although Thousand Cankers Disease occurs in Pennsylvania and is creeping closer to effect forests throughout the region similar to the GNA, it has not yet been noted at the Gordon.  The introduction of this disease into the GNA could have severe effects on Black Walnut and possibly at an ecosystem level.

As I have indicated, the status of Black Walnut at the GNA, and possibly in similar eastern deciduous forests, appears to be stable but could be considered threatened based on the pests and pathogens mentioned above.  Aside from threats from pests and pathogens, Black Walnut population is healthy at the GNA.  When we relativized density on a per hectare basis, we calculated that the lowland areas had the highest density at over 150 trees/ha. This was surprising because being a riparian species we assumed Black Walnut would have the highest density in riparian or floodplain habitats.  We realize that this could be due to a lack of physical distinction between the habitat characteristics. As for the size of Black Walnut between the three habitats, we determined through statistical analysis that there was no significant difference in tree size. There was no significant difference in size however we did find that floodplain had the largest mean size of ~27 cm, followed by riparian having the second largest at ~24 cm, and lowland with the smallest mean of ~21 cm.  As for tree health in the GNA, we found that the overall population is very healthy. Between 80-90% of the trees were given a level 4 or 5 rating, which signifies that at least 60% of the tree's canopy was alive.  In our study, there were very few trees present that scored below a 3, and only a few trees that we could identify as dead Black Walnut. 

A lack of saplings seen in the study sites may indicate a low recruitment rate, which is theorized to be due to overgrazing by the overpopulated white-tailed deer in the area. This has not been determined one way or another due to the lack of evidence of deer grazing on Black Walnut, possibly because of juglone : an allelopathic toxin present in Black Walnut tissue. Overall, what we gathered from this study is that we have a healthy, stable Black Walnut population in the GNA. This is a good indication for present and future health of Black Walnut populations in similar eastern deciduous forests, as well as a frame of reference when the threatening pests and pathogens species move closer to this land.

Based on areal photos, the Gordon Natural Area (GNA) has been continually forested since at least 1937. There is evidence that the GNA was used as a woodlot during colonial times, but it appears that it was never clear-cut nor used agriculturally.

We were interested in learning the maximum age of the older GNA trees, so we cored and counted the rings of some of the larger diameter trees (70 + cm dbh) using an increment borer. This is a great technique because it allows us to determine tree age without causing significant damage.  The species chosen for coring were, American Beech (Fagus grandifolia), Northern Red Oak (Quercus rubra), White Oak (Quercus alba), Tulip Poplar (Liriodendron tulipifera), Black Tupelo (Nyssa sylvatica), and Hickory (Carya sp.). Of the nine trees sampled to date, ages ranged from 80-200 years old. 

Knowing the range of the trees age will allow those studying the site to more confidently compare the GNA to other Eastern deciduous forests of known stand age.

Tree Seedling Exclosure Research

Overview

During the preceding 11 years, a good deal of effort has been directed toward reforestation in the GNA, in response to overgrazing by deer and other factors which have severely limited recruitment of new trees.  However, tree planting is both labor intensive and expensive: the cost of a ‘reasonably-sized’ tree and the materials needed to protect it from browsing (e.g., metal fencing and either a t-post or rebar for supporting the fencing) is on the order of $25-$30/tree.  Additionally, when undertaken in the Spring, tree planting can be very impactful on the herbaceous flora of the forest floor. 

In an attempt to find a lower-cost, less damaging alternative to tree planting, we’ve been investigating installing ‘cages’ around naturally-occurring tree seedlings.  An obvious advantage of this approach is that the ‘tree’ is obtained free of cost.  And, although there are costs associated with the exclosures, they are approximately a quarter of the cost of fencing a purchased tree (the cages require just a third of the fencing as for a tree and do not require a t-post or rebar for support).

Methodology

In the late Spring of 2018, we installed cages around 50 seedlings. During the following Spring, we installed cages around an additional 96 seedlings.  It appeared that 2018 was a good mast year for hickories (Carya spp.) and the greatest portion of the seedlings that we caged in 2019 were hickory.  We had initially hoped to be able to include a large proportion of oaks in this trial. Regrettably, we encountered just two oak seedlings.  Our plan is to continue this research for at least a few more year and with luck, one of those years will have good oak germination.

Two types of fencing were used for the cages: 1) 2" x 3" coated welded wire fencing; and, 2) ½" x ½" galvanized wire mesh.  The 2" x 3" fencing was expected to prevent browsing from larger animals (principally deer), while the ½" x ½" material was intended to also prevent browsing by small mammals.  Cages were ca. 24" tall and 24" in diameter and were staked to the ground in 3-4 locations.  Each cage was topped with ½" x ½" plastic mesh to prevent deer from reaching into the cages to browse.  For the galvanized wire mesh cages, we attempted to affix the plastic mesh in such a way that it would serve as a barrier to small mammals.  However, in practice, the installation of these tops was quite variable, and in a number of instances mice, or similar size animals would have had no problem in finding ways into the cage from the top.

Throughout the growing season, we monitored each individual's status (alive, dead, or 'removed') of each seedling.  Removed seedlings are those that had been 'removed', either by falling wood or by vandalism.  To date, although there have been a few instances of branches falling on the cages, the seedlings were not killed.  Subsequently, we removed the branches and repaired the cages.  Any, during that time no seedling cages (or seedlings) were vandalized.

The two types of seedling cages: a) 2" x 3" fencing; b) ½" x ½" wire mesh.

Results

To date, survivorship of the seedlings from both years has been quite high, with 92.0% of the 2018 seedlings and 97.9 % of the 2019 seedlings still alive (Tables 1 and 2).  Some species did particularly well (e.g., Hickory and White Ash in 2018 and again in 2019).  However, many of the White Ash seedlings have declined in quality during the period of monitoring.

Table 1.   Results from monitoring of the seedlings that were caged in 2018.

Table 2. Results from monitoring of the seedlings that were caged in 2019.

Summary

Although early in the research, it appears that caging tree seedlings may be a less expensive and more effective approach to enhancing tree establishment in a heavily-browsed setting.  As noted, we're planning to continue this research for at least the next few years.  And, we'll continue to update this page.

Close-up of a White Ash (Fraxinus americana) seedling in a ½" x ½" wire mesh cage.

Box Turtle Census

by Paige Vermeulen, GNA Intern

The Eastern Box Turtle (Terrapene carolina) is a terrestrial turtle, living mostly near wooded areas. They hibernate in the winter and are most active during cooler days of spring and fall. These turtles are omnivores - they like to munch on insects, berries, snails, fungi, and much more. The lifespan of the turtle is not well-established. Some sources say 25-35 years, others say up to 80-120 years! A slow-moving and humble animal, the state of North Carolina is happy to call the Eastern Box Turtle its State Reptile.

Sadly, Eastern Box Turtle populations are threatened by habitat destruction, pollution and pesticide effects, vehicle strikes, and direct removal for the pet trade. The IUCN cites “extensive research on status and conservation biology, and monitoring of population trends” as an important resource for the conservation of this species. 

Although here at the Gordon Natural Area we are by no means doing a full-blown research project on these turtles, it is still helpful to keep track of them - more or less, to see what we can see. For the past year or so we have been photographing every EBT we see in the Gordon Natural Area, and entering these photos into our database. From there, we can identify the turtle based on its shell patterns. This will help us to keep track of how many EBT’s we have in the Gordon (41 at the moment!).

Our hope for future work is that as we learn more about the Eastern Box Turtle, we can make conservation efforts to protect this lovely species, and hopefully see the population trend start increasing again. Currently, we do place an emphasis on planting tree species that are utilized by EBTs. Some of these species are Black Cherry (Prunus serotina), Elderberry (Sambucus canadensis), Flowering Dogwood (Cornus florida), and Hackberry (Celtis occidentalis). Additionally, we have been inoculating logs with spawn of edible fungi and have placed a portion of the inoculated logs so that they are accessible to turtles.

All box turtles that are found in the Gordon Natural Area, after being photographed and identified to gender (hopefully), are named. The names are based on the pattern on the scutes of the turtle’s back. The naming is done in this way so that the turtle can be identified if it is seen again, and it is an easy way to get a (very) rough estimate how many turtles inhabit the GNA. The GNA staff take great pleasure in naming the turtles - and they often get quite creative! 

*The IUCN Red List of Threatened Species: Terrapene carolina – published in 2011. 

Eowyn is a personal favorite of mine. She is named after the heroine in the Lord of the Rings, because the pattern on the central plates going down her back resembles swords. It is probably thanks to Eowyn that we have no Witch-king lurking in these woods. 

Honest Abe is an excellent example of the GNA staff’s naming skills. She was found near the road that goes through the GNA, and judging from the crack in her shell, she had sadly been hit by a vehicle. Named for the pattern of the plate just forward of the crack in the shell, many think there is a resemblance to the profile of our 16th president.   

Cee-Cee is a more straightforward example of how we name the turtles based on their shell patterns. You can probably figure this one out without an explanation - the two lateral plates distinctly show the letter ‘C’.