Image: Mortensen Lab/Penn State
A team of researchers in Penn State's College of Agricultural Sciences has found that invasive, non-native plants are making significant inroads with unconventional natural gas development. The team has been tracking invasive plant surveys on and around 127 Marcellus shale gas well pads and adjacent roads in the Allegheny National Forest.
"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. "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."
Sixty-one percent of pads had at least one invasive, non-native plant species, and 19 percent of those had three or more species. Reed canary grass, spotted knapweed, creeping thistle, Japanese stiltgrass and crown vetch were the most common invasives found.
The study provides striking evidence that invasive plant presence on well pads is correlated with the length of time since pad construction; the number of wells drilled per pad; invasive plant abundance on adjacent well pad access roads; and the density of roads in the area of the pad prior to construction. Using field data from the 127 well pads, researchers created a model to evaluate direct and indirect relationships among mechanisms and conditions that could account for invasive plant presence.
Lead researcher, Kathryn Barlow, found evidence that invasive plants were introduced in gravel delivered to build pads and roads, and in mud on the tires and undercarriages of trucks traveling those roads. "Given the fact that, on average, 1,235 one-way truck trips delivering fracturing fluid and proppant are required to complete an unconventional well, the potential to transport invasive plant propagules is significant," she said. Propagules are parts of a plant that can generate a new plant, such as seeds, spores and roots.
Non-native plant invasion into forests can lead to the demise of native plants in surprising ways, Mortensen pointed out, referring to a study his lab conducted at the Penn State Deer Research Center that was published in April 2016. That research demonstrated that white-tailed deer prefer native plants and seem to avoid eating invasives.
"So if we have Microstegium filling the forest understory and deer are looking for something to eat — since they don't feed much on Microstegium at all — the deer clip off any native plant growth that manages to get through the invasives," he said. "That allows the invasives to further dominate the plant community.
"As a result, the recruitment of economically important tree species will be curtailed. This process can be really damaging to the health of the forest in the long run, and even in the short term."
Highlights of the study are:
- Shale gas development is implicated in spreading invasive non-native plants.
- 61% of well pad sites surveyed had 1 species and 19% had 3 species.
- Invasion drivers were propagule pressure, dense road networks, and heavy traffic.
- Monitoring should focus on areas with multi-well pads and dense road networks.
The complete article published in Penn State Today. The article was published July 20, 2017 in the Journal of Environmental Management