As campers and picnickers head outdoors in greater numbers for the summer season, many government agencies are urging them to not bring their own firewood. The discovery in the past few years of several diseases deadly to a variety of plants has sparked concern about this practice. Research in a few states has found that tens of thousands of loads of firewood have typically been imported from home each year, sometimes from thousands of miles away.
So far, the identified problems have been limited to a modest number of plant species and only to certain parts of the US and Canada. But since not much is known yet, and the problem of invasive species of many types is becoming a high priority for many agencies, the US Forest Service's Robert Mangold,  703-605-5340, strongly recommends that no one should transport firewood any substantial distance.
That distance remains a matter of debate, as some officials recommend keeping firewood within the state, while others have mandated not even crossing county lines with firewood. An example of a county-level quarantine was provided by Maryland's Invasive Species Council for Prince George's County, sparked by concerns about the emerald ash borer (media coverage ). See the Nov. 3, 2006, article  in The Capital(Annapolis), by Ellen Scarano. In addition, there have been federal quarantines for specific areas, such as parts of several counties and boroughs in New York (including Manhattan, Brooklyn, Queens, Nassau, and Suffolk), and New Jersey (including Middlesex and Union) due to concerns about the Asian longhorned beetle. Some additional information is available here. 
Other bugs and diseases for which the firewood vector is already a known or suspected concern include European and Asian gypsy moths, bronze birch borers, hemlock wooly adelgids, pine shoot beetles, Sirex woodwasps, Dutch elm disease, sudden oak death, chestnut blight, and oak wilt.
There is no central repository of information for all diseases, pests, and affected vegetation (although the US Forest Service says it is beginning to contemplate such a resource), but many federal, regional, state, and provincial resources are available. A few of these are provided below as starting points, so you can get a feel for the issues, and begin to localize conditions for your audience.
In addition to these resources, it will be very helpful to contact the federal, state, provincial, county, and city agencies that have jurisdiction over local camping, picnicking, and hunting areas to pin down their policies.
- Emerald ash borer program  (addresses IL, IN, MD, MI, OH, WI, and Ontario, but other states are concerned) and related USFS information. 
- Minnesota Department of Agriculture. 
- Missouri Department of Conservation. 
- New York Dept. of Environmental Conservation. 
- Oregon Dept. of Agriculture, Plant Division. 
- USDA Animal and Plant Health Inspection Service.