Land Trust stewardship staff have begun early stage work developing a project centered on a large Heartleaf Milkweed (Asclepius cordifolia) population on our Sutro Ranch Preserve. The goal of the project is to assist with conservation and recovery of the western monarch butterfly population.  

The monarch butterfly population is estimated to have decreased in size by over 95% since the 1980s. Declines have been attributed to habitat loss and degradation, including the loss of milkweed, along with pesticide use and climate change. Milkweed is critical to monarch reproduction, and Heartleaf Milkweed could be of particular importance with regard to mitigating climate change-related shifts in monarch migration and breeding because it emerges early in the growing season. 

Stewardship staff have already documented over 600 individual Heartleaf Milkweed plants on the Preserve, and confirmed that this milkweed population is being actively utilized by monarchs. 

Working in coordination with the Napa County Monarch Work Group, the project will include mapping and tracking individual milkweed plants, propagating milkweed to restore and enhance western monarch breeding habitat on Land Trust Preserves and around the Region, restoring habitat to improve nectar resources for monarchs, and tracking use of the project area by monarchs during different stages of the life cycle. 

As work progresses, we look forward to providing more information on this project. 

Heartleaf Milkweed (Asclepius cordifolia) with monarch caterpillars on Land Trust protected land.

During a recent visit to Sutro Ranch Preserve, Stewardship Program Assistant Jennifer Colin captured footage of a monarch butterfly.