Electronic Field Guide » Invasive Plant Management

Prepared by Emily Rauschert (Plant Science)
Pictures from Art Gover and Patrick Drohan

Marcellus shale exploration has the potential to create invasive plant problems, and we currently do not know the extent of the problems that will result. Invasive species can create economic problems, such as interfering with forest regeneration, but this does not happen in all cases and can be prevented with careful precautions.
The term “invasive species” refers to species that keep expanding their territory if left unchecked, and crowd out native species. A native species is one whose presence results only from natural processes, rather than human-influenced processes. A nonnative species is present due to human intervention. Not all nonnative species are invasive.
In general, invasive plants are associated with both disturbance and roads, both of which are prevalent with Marcellus shale exploration and development. Disturbance of the soil can kill or weaken native plants, allowing invasives to take over a site. Disturbance of the soil also provides a ripe seed bed for the growth of invasive plants. Road creation and road maintenance can both spread invasive plants by carrying seeds on truck wheels or tracks.
Presurveying for Invasive Species
Before construction begins, a qualified botanist should survey all areas to be disturbed during the growing season (May to September), plus an appropriate buffer area. This presurvey should determine which invasive species are already present and how their spread can be limited or controlled. See the Department of Conservation and Natural Resources (DCNR) list of which plants are considered invasive in Pennsylvania.
A simple way to do this presurvey is to divide the area into a grid of cells, no greater than 150 feet square. In each cell, record the presence and abundance of each species (trace = less than 1% cover, low = 2-5% cover, moderate = 5-25% cover, high = 26-100% cover). Also record the dominant tree, herbaceous, and shrub plants. It is also important during the presurvey to establish who is responsible for managing invasive species.

Prevention of Invasive Plant Germination and Spread
Prevention of problems is the best tactic with invasive species. Certified seed- and weed-free soil, dirt, gravel, and mulch should be used.  Equipment and vehicles must be cleaned regularly to prevent contamination between sites. Pre-existing invasive species infestations should be treated, particularly when they are small.
It is especially important to prevent seed production in annual plants, such as Japanese stiltgrass (Microstegium vimineum), and it is important to treat rhizomes or other means of vegetative spread in perennial plants. 

If possible, plan work so that vehicles are not moving from heavily infested sites to uninfested sites. If this is not possible, vehicles need to be thoroughly cleaned between sites.

Control of Invasive Plants
Invasive plants are generally approached through mechanical and/or chemical control. The species present will most directly determine the best method and timing of control. See the DCNR tutorial for specific recommendations for species. The extent of the area affected will determine whether minimally invasive methods, such as hand-pulling, are possible. For large infestations, chemical control may be the most effective. Species-specific treatment is recommended whenever possible to avoid damaging desirable plants.  Landscapes features can also affect the choice of treatment option. For a severe invasion along a waterway, extra care must be taken with herbicides, and for an especially pristine waterway, the operator may wish to avoid use of herbicide altogether.
Postdisturbance Monitoring
Any area that has been disturbed should be carefully revegetated. For more information, see Revegetation in this field guide. The site must also be monitored annually for at least 5 years after construction ends or after the last invasive plant is seen, whichever happens last. Many species have a persistent seed bank, so the potential for invasives to return lasts several years after the last individual was seen. If more plants are found, they should be treated as soon as possible, depending on timing recommendations for that particular species.