Ecosystem and Vegetation Management
Pollinator-Friendly Practices Case Studies
FEDERAL HIGHWAY ADMINISTRATION
Office of Project Development and Environmental Review
Vegetation Management "Toolbox" Benefits Indiana Bees and Budgets
Roadside managers have several tools to control invasive and noxious weeds and to promote native plant propagation in roadside rights-of-way (ROWs). Indiana has been studying methods that work best for better roadside habitat and cost efficiency. Some of the tools Indiana has recently added to its toolkit include a method to inventory invasive plant species using a smart phone application to enter data into the online database managed by the Early Detection and Distribution Mapping System (EDDMaPS) at http://www.eddmaps.org/. The Indiana Department of Transportation (INDOT) partnered with EDDMaPS through its membership in the Indiana Invasive Species Council, which was established by the State Legislature in 2009 to enhance the ability of government agencies to detect, prevent, monitor, and manage new and long-established invasions, as well as increase public awareness about these growing threats.
Other methods INDOT recently adopted include reduced mowing and selective herbicide use to control invasive and noxious weeds that suppress native plants, which are essential to ecosystem health and habitat for wildlife, including many species of pollinators. For example, Black Swallowwort is a threat to milkweed species, which is a very important plant to monarch butterflies, because they cannot reproduce without milkweed. Invasive species also out-compete a whole host of native plants that support pollinators, including monarch butterflies and honeybees.
Over the past three decades, INDOT, recognizing the need to promote native habitat and control invasive species, has studied ways to control weeds and increase native species in roadsides. In addition to its decades-long studies, INDOT recently conducted more intensive studies, leading to new vegetation management practices that have demonstrated habitat improvement benefits and cost savings.
Methods for Success
In the 1990s, INDOT established the Hoosier Roadside Heritage Program to promote and incorporate native plants and wildflowers into Indiana’s roadside landscape. Goals of the program are to: Enhance the beauty of the environment; reduce erosion; minimize costs associated with mowing; lessen storm runoff; control invasive plant species, enhance plant pollination; and improve soil quality. In achieving these goals, the program has planted more native grasses and wildflowers, which has resulted in reduced roadside mowing and decreased herbicide applications.
While the Hoosier Roadside Heritage Program successfully increased native plants and wildflowers along Indiana roadways over the past decade, INDOT decided to explore additional research to identify new methods to expand its roadside management program for positive fiscal and ecological outcomes. To that end, INDOT solicited Purdue University in 2010 to study alternative vegetation management practices. In its study, Purdue selected six vegetation management sites where it would apply different treatments. The objective of the research was to develop best management practices for INDOT that showed a cost savings of 10 percent or more from the pre-study baseline practices, which included 2-3 mowing cycles annually.
Following positive outcomes from the Purdue research, INDOT in July 2014 released an operations memorandum that outlined the agency’s plans for increasing the health of desirable vegetation to better manage roadsides, decrease long-range cost, and reduce invasive species on INDOT ROWs. This research led to several substantial changes to INDOT’s vegetation management practices. For example, INDOT now has four designated vegetation management zones: Zone 1, which is essentially the paved road or road prism; Zone 2, a safety or clear zone; Zone 3, a selective zone; and Zone 4 where it uses minimal vegetation management. The clear zone, measuring 30 feet out from pavement, is now the only area INDOT mows. INDOT also raised its mowing height from 4 inches high to 6 inches high to allow native plant roots to establish better and to reduce stress on native plants from mowing.
In the selective zone, measuring 80 feet out from pavement, INDOT manages for invasive weeds and woody vegetation. Management practices in zone 4 are similar to the selective management zone except that the only woody plants INDOT manages are hazard trees. For selective herbicide use in the clear zone, Purdue and INDOT examined the effects of converting anti-icing trucks to spray herbicide and found that one truck can cover 10 times the area of a mower.
Outside the clear zone, INDOT uses herbicides cautiously, targeting non-native species and monitoring the effects on nearby native species. INDOT minimizes herbicide use to control biennial species by managing them only every two years, when the timing is right for controlling them based on their two-year lifecycles.
Controlling invasive weeds so that native species can thrive requires long-term dedication and ongoing effort. INDOT recognizes that the ideal time for planting native species is when an area is clear of invasive species. Often this requires years of treatment before a roadway area is ready to receive native plantings. When it is time to plant, it can be difficult to find affordable good quality desirable native propagules, such as plugs and seeds. Once planted, native species take time to establish. By managing areas for invasive species and planting when the timing is right, however, INDOT can restore a compromised area of roadside habitat in as little as three years.
As a result of INDOT’s dedication to researching and testing different vegetation management practices, it discovered that reduced mowing resulted in measurable cost savings and efficiencies from previous practices. For example, from 2012 to 2013, mowing dropped from the third most labor-intensive agency maintenance activity to the ninth most labor-intensive activity. As a result, INDOT was able to divert labor resources to other priorities, saving more than $1 million in a one-year period.
Limiting mowing widths across INDOT’s designated vegetation zones has provided more space for native vegetation and the habitat it supports, including pollinator habitat. This practice has helped establish new wildlife corridors in INDOT ROWs. These corridors attract ground nesting birds, song birds, small mammals, and pollinators. Milkweed along roadsides provides monarch butterflies with more places across Indiana to lay eggs. In addition to milkweed, pollinator attractors like the monarda plant have helped increase bumblebee and honeybee populations along Indiana roadways.
By supporting research by outside experts and actively testing different vegetation management approaches, INDOT has provided pollinators and other wildlife with improved habitats and better ecosystem health. Improved pollinator health will provide long-term benefits to Indiana’s ecological processes. New vegetation management strategies also have generated immediate time savings and will produce long-term cost savings while creating more aesthetically pleasing rights-of-way.
In the future, INDOT plans to encourage more native plantings along ROWs and also intends to continue working with outside experts to determine which native plants will best weather Indiana’s changing seasons. Overall, INDOT plans to continue expanding its vegetation management “toolbox” in ways that produce cost-savings while preserving and enhancing Indiana’s natural environment.