What is this map?
This interactive map shows areas in California that may be more vulnerable to infestation by the Invasive shothole borers–Fusarium dieback (ISHB–FD) beetle-pathogen complex. It is designed as a decision-support tool to help prioritize monitoring and management activities.
Tutorial on how to use this map:
For help in understanding and using the ISHB Statewide Risk Map, view the video tutorial here.
Key factors in understanding and using the map:
The map is based on a model developed by Lynch et al. (2025), which predicts risk of infestation by combining two key factors:
- Tree community composition (Host Related Risk): Areas with many trees that are closely related to known susceptible host species are at higher risk of infestation.
- Red areas indicate where local tree communities are predicted to be most vulnerable based on host-related susceptibility.
- Climate conditions (ISHB Generations): Warmer areas where the beetle can complete more reproductive cycles in a year are more favorable for its establishment and spread.
- Shading from light blue to yellow shows where climate conditions allow the beetle to reproduce more quickly in those locations, thus supporting more generations so that infestations may become more severe.
By overlaying these two factors, users can get a fuller picture of where the beetle is most likely to establish and spread.
Zoom in to see the potential risk in a specific area, or click here for full screen view.
How the Map Was Created
The map is based on a model developed and validated using a robust dataset from 207 research plots in Southern California forests (Lynch et al. 2025). It was then applied statewide using street tree inventories from 170 California cities, covering over 5 million individual trees and more than 1,000 species. These inventories, compiled from municipal records and private arborist companies, represent the largest dataset of urban trees currently available in the U.S. (Love et al. 2022). To account for effects of climate on infestation severity, weather data from the past 20 years were used to calculate how many beetle generations could occur annually at a location, once established.
California was divided into 1 km² grid cells, and the likelihood of infestation was estimated for each one based on tree species composition and climate. For areas without tree inventory data, the model does not make predictions.
How to Use the Map
This map is a planning tool and a starting point for proactive management, based on the best available data. Predictions will be refined as new information emerges. The map is a living resource that will be updated as additional tree inventories and monitoring results become available. Local knowledge and user contributions will be critical for improving future versions.
If you see your area highlighted as high risk, it doesn’t mean an infestation is happening now, but it signals that conditions are favorable and proactive management may be warranted.
If your area is low risk, it’s still wise to stay alert because the beetle could arrive later.
This interactive map was developed in collaboration with GIS specialist Jon Detka, Ph.D. (CSUMB), who transformed the static map into a web-based interactive tool.
References
Love, N. L. R. et al. 2022. Diversity and structure in California’s urban forest: what over six million data points tell us about one of the world’s largest urban forests. Urban For. Urban Green. 74, 127679.
Lynch, S.C., Reyes-Gonzalez, E., Bossard, E.L. Alarcon, K.S., Love, N.L.R., Hollander, A.D., Nobua-Behrmann, B.E., Gilbert, G.S. 2025. A phylogenetic epidemiology approach to predicting the establishment of multi-host plant pests. Commun Biol 8, 117. https://doi.org/10.1038/s42003-025-07540-y