Table of contents:  Methods, Partners, Citations, Funding, Civil Rights

CalWeedMapper enables natural resource managers, scientists and others to create maps and reports of invasive plant distribution, to identify management opportunities in a county, WMA or region, and to maintain up-to-date species distribution data statewide. CalWeedMapper is integrated with Calflora and Consortium of California Herbaria (CCH) databases, so that new occurrence data submitted to either informs quad data in CalWeedMapper.


The California Invasive Plant Council (Cal-IPC) interviewed hundreds of natural resource managers around the state to collect a baseline of “expert knowledge” on abundance, spread and management status by USGS 7.5-minute quadrangle (“quad”). Dates and names from these interviews are noted for each quad. This expert knowledge data forms the foundation of the quad mapping tool.

Quads measure approximately 8.5 miles north to south, and in California range from approximately 7.2 miles east to west on the southern border of the state to 6.5 miles east to west on the northern border of the state. There is a complete grid of quads over the United States.

Occurrence data from Calflora and CCH is also included, in particular for quads where expert knowledge indicates that a species is not known to occur but where occurrence data documents observations. Verifying quad data for such discrepancies is a key opportunity.

CalWeedMapper identifies management opportunities based on the current distribution of a given plant in an area. If a plant is not known to exist in the region, but is found within a given distance (50 miles) of the region, it is identified as a surveillance target. If a plant exists only in single, isolated quads in the region, it is identified as an eradication opportunity. Finally, if a plant is present in the region at levels higher than this, it is identified as a containment opportunity.

CalWeedMapper also maps suitable range based on climate. This modeling uses Maxent modeling software; occurrence data documenting where the plant currently grows in California; and climate data for California. Projections of future suitable range use an ensemble of 17 Global Circulation Models (GCMs) for the mid-21st century with climate change scenarios from the International Panel on Climate Change (IPCC 2007) and climate projections from PRISM. Models were based on temperature and precipitation variables from Bioclim.

CalWeedMapper displays projected suitable range in 2010, projected suitable range in 2050, and the change (expansion or reduction) in range between those dates. Suitable range for 2050 shows areas where at least four of the 17 GCMs agreed. Our projections are based on climate only and do not consider factors such as soil, vegetation communities, and methods of spread. For more detailed information on our methods, click here.

Data shown on CalWeedMapper, while very useful, should not be considered to be 100% accurate. Quad data, while having the great benefit of drawing on the extensive experience of individual local resource managers, is inexact. Occurrence data, though of higher precision, may not always be correct, either, since species may be misidentified or locations not captured correctly. Data of either type can become outdated if not maintained. Range modeling is predictive, providing an estimate of the probability that a plant will find conditions in a given are suitable for growth.

For more detailed information on methods contact mapping@cal-ipc.org.


CalWeedMapper was developed by the California Invasive Plant Council. Cal-IPC works to protect the state’s wildlands by building strategic tools for natural resource managers. TerraGIS and GreenInfo Network helped build CalWeedMapper.

The Calfora database is the home for data on plant locations in California. Calflora provides numerous mapping tools for using that data. Calflora hosts CalWeedMapper.

The Consortium of California Herbaria compiles data on plant voucher specimens from herbaria around the state. This data is provided by the participants of the Consortium of California Herbaria, University of California, Berkeley.

The California Department of Fish & Game’s Biogeographic Data Branch  compiles a variety of ecological data, and advises CalWeedMapper on conservation analysis.

EDDMapS is a national invasive species mapping system. CalWeedMapper and Calflora are sharing data with this system.

A generous ESRI Conservation Grant enables our statewide data collection and suitable range modeling effort.

Agency partners include the California Department of Fish and WildlifeCalifornia State ParksUS Forest Service, and National Park Service. US Forest Service and Calfornia State Parks share datasets annually, helping to keep distribution maps of invasive plants in California up-to-date for the land management community. We continue to work with other agencies towards annual data sharing.





Cal-IPC. 2006. California Invasive Plant Inventory. Cal-IPC Publication 2006-02. California Invasive Plant Council. Berkeley, CA. Available: www.cal-ipc.org

IPCC. 2007. Climate Change 2007: The Physical Science Basis.Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK

Phillips, S.J., R.P. Anderson, and R.E. Schapire. 2006. Maximum entropy modeling of species geographic distributions.  Ecological Modelling. 190:231–259. doi:10.1016/j.ecolmodel.2005.03.026

Data Sharing Agreements/Licensing:

Calflora.  2011.  Data provided by The Calflora Database, a not-for-profit organization. Available: calflora.org.

Consortium of California Herbaria. 2010. Data provided by the participants of the Consortium of California Herbaria,  University of California, Berkeley. Available: ucjeps.berkeley.edu/consortium.

California Protected Areas Database (CPAD) Version 1.6.  Available: calands.org/download/CPAD_Manual_1.6.pdf.

Cal-Atlas.  Cal-Atlas is a free service and many different departments, division, federal and local government submit data to the site. Several of the base layers for this site were obtained online and comply with the metadata that specifies allowable public use. Available: atlas.ca.gov.


American Recovery and Reinvestment Act funding provided by the USDA Forest Service, State and Private Forestry Program through the California Department of Food & Agriculture. Additional funding from the USDA Forest Service Special Technology Development Program, National Fish and Wildlife Foundation, Resources Legacy Fund, California Landscape Conservation Cooperative and Richard and Rhoda Goldman Fund.

Civil Rights

In accordance with Federal law and US Department of Agriculture policy, Cal-IPC is prohibited from discriminating on the basis of race, color, national origin, sex, age, or disability.  (Not all prohibited bases apply to all programs.)

To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW, Washington, DC 20250-9419 or call (202) 720-5964 (voice and TDD).  USDA is an equal opportunity provider and employer.