With MBF’s support, Ambiomas, a Mexican non-profit established by Salvador Huitrón (a 2022 Lincoln Brower Award recipient!) is leading a drone flight project at the monarch overwintering sites. The purpose of this project is to develop a forest health monitoring and alert system using remote-sensing technology.
In 2023 during months monarchs are not present, drones flew over sites where monarchs typically roost, using historical areas of overwintering sites. Images of the forest were obtained from these flights and a Digital Surface Model (DSM) was developed to estimate the total number of trees present and tree density per hectare in each site.
The Ambiomas team, along with FOCEN (Neovolcanic Axis Conservation Fund), who also supported this project, analyzed the information collected in each flight area to determine a Normalized Difference Vegetation Index (NDVI) range for these oyamel trees, using NDVI as a measure of tree vigor. The monitored sites revealed different degrees of tree vigor, ranging from "Healthy" (NDVI=0.74-0.90) to "Extremely Devitalized" (NDVI=0.46-0.56). Two monitored areas showed apparent favorable conditions with high densities of trees and a high proportion of trees in the Healthy Tree Category. Other sites, however, showed signs of stress and decay and a higher proportion of trees in the "Severely devitalized" category.
Because NDVI values can change after the rainy season, possibly related to the greening of the understory, it is important to assess how much of this difference may be an actual change in tree health over time. A comparison of NDVI values in dry seasons of consecutive years is highly recommended and can help identify processes of recovery or decline in the vigor of the trees.
While tree vigor categories allow comparisons to be made, there is a need for fine tuning to determine more precise indicators of devitalization processes in Oyamels.
This project represents a first effort in the construction of a Baseline Tree Vigor database at Monarch Butterfly Overwintering Sites in Mexico, and ultimately will contribute to the development of the forest health monitoring and alerting system. This project is expected to continue for another year to strengthen the current database.
This is an excellent example of how using the latest technology can help conservation efforts!