"Although only a limited amount of all transported firewood is likely to be infested by forest insects, this still represents a considerable increase in dispersal potential beyond the
insects natural spread capabilities."(emphasis added)
This quote is from the abstract of an excellent new scientific article, Dispersal of Invasive Forest Insects via Recreational Firewood: A Quantitative Analysis, in The Journal of Economic Entomology. I think the authors did an impressive job of showing how firewood movement by campers results in the very real spread of invasive forest pests. You can see the abstract at this link without being a subscriber http://dx.doi.org/10.1603/EC11270 , or if you are a member of BioOne Journal service, you can access a full PDF from that site.