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article imageInvasive plants follow fracking into Marcellus shale forests

By Karen Graham     Jul 24, 2017 in Environment
Invasive, non-native plant species have been making significant inroads into Pennsylvania's forests along with unconventional natural gas fracking, a long-term study by researchers has found.
For a number of years, researchers in Penn State's College of Agricultural Sciences have been tracking the ecological impact of hundreds of well pads, access roads, and pipelines built to extract gas from the Marcellus Shale.
In its most recent study, published in the Journal of Environmental Management on July 20, Penn State researchers documents that nonnative plants are rapidly invading Pennsylvania's northern forests and establishes a link between new invasions and shale gas development activity.
Team member David Mortensen, a professor of weed and applied plant ecology at Penn State warns that the spread of non-native plants in the forest ecosystem could have long-term negative impacts, affecting timber revenue, wildlife habitat, and ecotourism, reports
"Studies have shown that when invasive plants such as Microstegium vimineum (Japanese stiltgrass) move into an area, it changes the plant community, and native plants tend to decline," Mortensen said.
Japanese stiltgrass  or Microstegium  is one of the most common invasive plants in Pennsylvania  and...
Japanese stiltgrass, or Microstegium, is one of the most common invasive plants in Pennsylvania, and is often seen around shale gas well pads and access roads. It establishes dense stands in forest understory and chokes out native vegetation.
David Mortensen, professor of weed and applied plant ecology at Penn State.
"Soon we will see a ripple effect in the forest ecosystem that will affect organisms that depend on the native plants. Ultimately, economic factors such as timber harvests may be affected, and wildlife and bird communities likely will change."
In the investigation, researchers conducted invasive plant surveys on and around 127 Marcellus Shale gas drill pads, including the access roads in seven state forest districts in the Allegheny National Forest. The study sites were distributed across Pennsylvania forests that overlay the Marcellus and Utica shale formations.
The investigation
The areas included the Allegheny Highlands, the Pittsburgh Plateau; and the Ridge and Valley regions of central Pennsylvania, dominated by mixed-oak and Northern hardwood forests. A piecewise structural equation model was used to determine the direct and indirect factors associated with the establishment of invasive plants at the different well pads.
The researchers also factored in measured or calculated variables that included "current propagule pressure on local access roads, the spatial extent of the pre-development road network ( a potential source of invasive propagules), the number of wells per pad ( an indicator of traffic density), and pad age," according to the study.
Of the total number of well pads surveyed, 61 percent had at least one non-native invasive plant species, while 19 percent had three or more non-native species. Reed canary grass, spotted knapweed, creeping thistle, Japanese stiltgrass, and crown vetch were the most common invasives found.
The invasive grass Phragmites  or common reed  can be seen growing on the edges of many gas well pad...
The invasive grass Phragmites, or common reed, can be seen growing on the edges of many gas well pads in Pennsylvania.
David Mortensen, professor of weed and applied plant ecology at Penn State.
Needless to say, the study provides good evidence that invasive plant species at well pads correlates with the age of the well pad, and the number of wells drilled at each pad. The study also gives evidence of invasive plant growth, based on the number of access roads to the well sites compared to the numbers of invasive [plants before the roads were constructed.
The evidence points to the gravel delivered to build pads and roads, and in mud on the tires and undercarriages of trucks traveling those roads, notes lead researcher Kathryn Barlow, a doctoral degree candidate in ecology. She also cites previous Penn State research that demonstrated Japanese stiltgrass seeds were moved by road-grading equipment on gravel roads in forests.
"Material and equipment used for road construction and maintenance can play an important dispersal role. Road development can create pathways for invasive plant establishment and spread," Barlow added.
The study concludes that "continued development of this underground resource must be paired with careful monitoring and management of surface ecological impacts, including the spread of invasive plants."
More about Hydraulic fracturing, Invasive plants, marcellus shale, Pennsylvania, Environment
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