Identifying priority survey sites for early-season milkweed conservation

Monarch butterfly (Danaus plexippus) populations are experiencing decline
due to habitat degradation and climate threats. In 2024, this iconic
species became protected under the Endangered Species Act. Critical to the
persistence of this species of cultural and ecological importance is
milkweed (Asclepias spp.), which monarchs rely on as an essential resource
for food and reproduction. Motivated by concerns over the loss of monarch
habitat, the Santa Barbara Botanic Garden (SBBG) and local collaborators
are working to identify potential restoration areas in the Los Padres
National Forest (LPNF). However, the vast size and complex terrain of the
LPNF pose a logistical challenge to surveying. Therefore, there is a need
for a tool to aid in selecting sites to prioritize. Our team created a
priority index for surveying milkweed within the LPNF by predicting the
habitat suitability for four early-season milkweed species using Maximum
Entropy (MaxEnt) species distribution modeling and creating a novel survey
site accessibility index. We identified high priority sites for the team
to survey based on high predicted suitability for each species of
early-season milkweed and high physical accessibility. To communicate
these results, we created an interactive web dashboard, which the SBBG
team will use for field planning to support the ongoing monitoring of
milkweed populations for monarch habitat restoration efforts within the
LPNF.