Abstract
Metropolitan areas play an undetermined role in supporting migratory monarch butterfly (Danaus plexippus) populations by providing habitat areas rich with milkweed (Asclepias spp.), the obligate host plants for monarch larvae. Researchers from the US Geological Survey and collaborating institutions have called for an “all hands on deck” approach to establishing monarch butterfly habitat by focusing on potential contributions from all land use sectors at levels necessary to sustain the eastern migratory monarch butterfly population. Our research teams surveyed milkweed densities across four major metropolitan areas (Chicago, Minneapolis-St. Paul, Kansas City, and Austin) using a new “metro-transect” protocol. We developed Geographic Information System (GIS) tools that use these data to model the baseline, or existing, milkweed stems present in metropolitan areas, and to estimate the potential to add additional milkweed stems with the adoption of milkweed-friendly planting practices across different land use classes (e.g., residential, institutional, commercial). By extrapolating metropolitan Chicago milkweed densities across US Census urbanized areas in the entire eastern range of monarch butterflies, we estimate that approximately 36 million stems of milkweed can be added under modest “enhanced” milkweed densities, and up to 795 million stems may be added under “exemplary” milkweed densities. Both estimates are derived from a two percent “adoption rate,” or landowner conversion of green spaces, based on field observations. These findings show that metropolitan areas provide important habitat opportunities and should be included prominently in Midwestern monarch conservation strategies when working toward national goals to increase the amount of milkweed stems and monarch habitat across the Midwest. Municipal decision-makers and planners can estimate their capacity to add stems across the metropolitan landscape by identifying where the biggest opportunities exist with help from our Urban Monarch Conservation Planning Tools.
Highlights
Monarch butterflies (Danaus plexippus) east of the Rocky Mountains migrate annually between central Mexico and Canada (Flockhart et al, 2013)
This research is the first in-depth examination into understanding the role that metropolitan areas play in supporting monarch butterflies, and what their capacity may be for supporting breeding populations
Our three main goals of this study were to (1) estimate the current and potential contribution that metropolitan areas provide for monarch butterfly habitat, (2) provide geospatial planning tools to support the development of conservation strategies, and (3) estimate the potential for adding milkweed within urbanized areas across the monarch butterfly’s eastern range
Summary
Monarch butterflies (Danaus plexippus) east of the Rocky Mountains migrate annually between central Mexico and Canada (Flockhart et al, 2013). Research at the national scale suggests that a fivefold increase in milkweed stems is needed to address extinction risks associated with the eastern monarch population (Pleasants, 2017; Thogmartin et al, 2017a). To accomplish this increase, Thogmartin et al (2017b) recommend an “all hands on deck” approach, with participation in milkweed restoration efforts by five land-cover sectors including “perennial herbaceous vegetation on protected lands, land enrolled in Conservation Reserve Program (CRP), lands in rights-of-way status, land associated with agricultural practices, and the urban/suburban sector.”. To accomplish this increase, Thogmartin et al (2017b) recommend an “all hands on deck” approach, with participation in milkweed restoration efforts by five land-cover sectors including “perennial herbaceous vegetation on protected lands, land enrolled in Conservation Reserve Program (CRP), lands in rights-of-way status, land associated with agricultural practices, and the urban/suburban sector.” The USFWS and Monarch Joint Venture have expanded the “all hands on deck” initiative to recommend a collaborative partnership effort by organizations and individuals to increase pollinator habitat
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