Skip to main content
U.S. Forest Service
Caring for the land and serving people

United States Department of Agriculture

Invasive Pest Risk Maps

Phytophthora disease of alders - Phytophthora alni ssp alni

Phytophthora alni is a recently hybridized soil and waterborne pathogen causing root and collar rot of species of the genus Alnus (alder). Once introduced, the pathogen spreads naturally with streams, floods, and other drainage water.

Sample Areas were developed using the Susceptibility Surface. A total of 1,200 sample areas were assigned to one of four risk categories. Relative certainties were assigned to each category in order to create increasing plot intensifications for increasing risk stratums.

Risk Maps (Contiguous US)
Map Type Map Methods Metadata GIS Grids
Introduction Potential Adobe Acrobat File3MB Adobe Acrobat File3MB Adobe Acrobat File58KB Zip file553KB
Establishment Potential Adobe Acrobat File2MB Adobe Acrobat File2.7MB Adobe Acrobat File294KB Zip file1MB
Susceptibility Potential Adobe Acrobat File3MB Adobe Acrobat File3MB Adobe Acrobat File307KB Zip file1MB
Survey Sample Area Adobe Acrobat File466KB Adobe Acrobat File4MB Zip file2MB
Risk Maps (Alaska)
Map Type Map GIS Grids
Introduction Potential Adobe Acrobat File1MB Zip file77KB
Establishment Potential Adobe Acrobat File2.5MB Zip file167KB
Susceptibility Potential Adobe Acrobat File2.5MB Zip file153KB
Forestry Images:

Phytophthora alni (Website)