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Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies (2020)

Chapter: Chapter 7 - Conclusions and Suggested Research

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Suggested Citation:"Chapter 7 - Conclusions and Suggested Research." National Academies of Sciences, Engineering, and Medicine. 2020. Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies. Washington, DC: The National Academies Press. doi: 10.17226/25693.
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Page 96
Page 97
Suggested Citation:"Chapter 7 - Conclusions and Suggested Research." National Academies of Sciences, Engineering, and Medicine. 2020. Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies. Washington, DC: The National Academies Press. doi: 10.17226/25693.
×
Page 97
Page 98
Suggested Citation:"Chapter 7 - Conclusions and Suggested Research." National Academies of Sciences, Engineering, and Medicine. 2020. Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies. Washington, DC: The National Academies Press. doi: 10.17226/25693.
×
Page 98

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96 The products developed through this project serve as an important foundation for ROWs conservation activities that have multiple benefits. Not only do well-informed conservation projects benefit monarchs and other pollinators, they provide a suite of environmental benefits (e.g., water filtration, carbon storage) and can improve cost savings (in some but not all cases) for ROWs long-term management activities. The charismatic and familiar monarch butterfly serves as a flagship species for pollinator conservation and gives ROWs entities opportunities to engage a diverse array of stakeholders who are invested in not only restoring monarch numbers to sustainable levels, but also mitigating many other environmental and economic issues. Roadsides provide promising monarch habitat as they frequently contain nectar and host plants but present a range of risks, including pesticide spillover, vehicle collisions, contami- nant runoff, and non-native vegetation. This project sought to maximize the potential of roadside restorations for monarchs by developing four tools targeted to roadside managers across the United States, including a) a GIS-based Landscape Prioritization Model, customiz- able to each state, that identifies roadsides with the greatest potential for monarch conserva- tion, b) methods for assessing the quality of a given roadside for monarchs through rapid assessment (RA), c) putting the assessment data through a “habitat calculator,” and d) a series of best management recommendations. The Landscape Prioritization Model developed in this project is the first of its kind at this scale. It provides a transportation manager the ability to evaluate the landscape in their state with regard to areas where diverse roadside habitat could complement already existing natural habitats or where high-quality roadside plantings might create a corridor of suitable habitat where there is otherwise very little. In addition, this model depicts roads and their associated hazards in a way that helps managers to think about the importance of traffic volume, traffic speed, and ROW width—all factors that can potentially affect the roadside environment for monarchs. Together, this landscape information and road metrics inform managers’ under- standing of their road systems in a novel way. The RA is a way for transportation managers to readily assess the habitat currently in their ROWs, and to track it through time. While many land management entities often lack time and capacity to conduct habitat assessment work, this tool was designed to be quick and easy to implement with different skill levels and also feeds into broader-scale monarch and habitat- monitoring initiatives and tracking efforts. Tracking and evaluating monarch habitat projects using the RA creates a feedback loop of information that will tell ROWs managers the base- line quality of their site as well as provide continued tracking of how the project is doing. In turn, this will provide a valuable data set that will improve the seed mix design and habitat management practices implemented by the land management authorities as they learn what is performing well and what may not be. Not only will this reduce costs over time, but, if applied C H A P T E R 7 Conclusions and Suggested Research

Conclusions and Suggested Research 97 in an adaptive management framework, the quality of the habitats for monarchs and pollinators should also improve (or minimally be sustained) over time. The Habitat Calculator provides managers an easy to interpret breakdown of the functional components of the habitat. Using data collected through the RA, it provides users with scores about how a particular project or site area is performing in the areas of monarch breeding habitat, foraging, landscape context and threats, and management. The scores for each of these com- ponents are combined into an overall score but also presented independently such that a land manager can pinpoint specific problem areas that could be improved on that site. For example, if the breeding habitat score for a site is low, this means that it is lacking sufficient milkweed host plants for monarchs. Actions to increase the milkweed density at that site could improve the habitat score over time. The Habitat Calculator also provides a reportable metric that can be used in internal or external reporting. The research team provided several types of decision-support tools in response to the needs of the roadside management community. The team recognized that there were several infor- mation needs, including guidance on mowing, herbicide applications, milkweed identification, and native seed guides (including milkweed). The team identified some resources that were currently available, linked to them in our online manager toolbox, and developed several other materials that were not yet in existence. The team developed regionally appropriate milkweed guides, single-sheet handouts that may be given to road management crews to help them identify milkweed growing in their roadside corridors and choose appropriate management actions, such as avoiding the application of herbicide to milkweed and planning mowing activity to avoid when monarchs are breeding in their locality. The team also developed the resource sheet, Monarch Butterflies, Weeds, and Herbicides. Recognizing that road managers operate within single states, the team facilitated information sharing across states, including case studies. A set of frequently asked questions and answers to optimize information sharing about best practices has also been developed. This work has highlighted several opportunities and needs for future research. There are several gaps in knowledge where expert opinion was used to develop the project tools. The research team identified the following research priorities: • Exploration of how field-level habitat quality values (such as derived from the Habitat Calcu- lator) and use of roadside areas by monarchs relate to the landscape factors depicted in the Landscape Prioritization Model. • Milkweed and nectar plant abundance in various land-use types and regions of the United State and how these values relate to the habitat quality within road ROWs in various regions. • Response of milkweeds, nectar plants, and monarch eggs and larvae to management practices, including mowing and haying at various times of year. • Differences in utilization of various species of milkweed by monarchs in roadside areas. • Quantification of traffic collisions (adult mortality) in relation to production of monarchs in roadside habitat (and in relation to traffic volume, speed, and surrounding habitat type). • Chemical exposure risks to monarchs in highly agricultural or heavy traffic areas, e.g., >30,000 cars a day typical of highly urbanized areas (pesticides and vehicle/road chemical runoff/drift). • Effective treatments of invasive species to enhance future restoration activities. • Economic studies on the short-, mid-, and long-range costs of implementing monarch/ pollinator programs within a roadside management entity, which may be influenced by the upcoming proposed listing decision by USFWS for species listing under the Endangered Species Act. • Assessing the value of roadsides as important habitat corridors in “habitat deserts,” such as areas in the Midwest that are dominated by agriculture.

98 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies The research also needs more detailed information about the recruitment of monarchs from roadside sites (e.g., from egg to adult) and the mortality associated with traffic collisions for adult monarchs. Additional research into the effects of pesticide drift into roadway corridors near agricultural fields is an ongoing (yet difficult) research need. Another area of future research includes longitudinal studies that document various management steps for revegetation. Many managers have reported that sometimes high-diversity pollinator plantings are very successful, while other times invasive plants take over, and the project is less successful. Published docu- mentation of well-designed studies will help roadside managers determine which practices over what time scales are most successful. As deliverables emerged from the project, it became apparent that a website is needed to house the toolbox and provide support to roadside managers interested in providing habitat for monarchs. The team plans to seek implementation funds to further develop such a website, along with additional communication about the tools developed here, perhaps at regional meetings. To fully implement the tools, states may require additional training (online or in-person) for DOT personnel and ongoing technical support to revise and maintain the tools.

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Roadsides provide promising monarch habitat as they frequently contain nectar and host plants; however, they also present a range of risks, including pesticide spillover, vehicle collisions, contaminant runoff, and non-native vegetation.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 942: Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies provides guidance for roadside managers to determine the potential of their roadway corridors as habitat for monarch butterflies.

The report also includes several tools and decision-support mechanisms to optimize habitat potential in a manner that is compatible with the continued operation and maintenance of the roadside.

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