The timber industry says, "Wild fires would increase in both size and intensity. Brush, which provides fuel to forest fires, could not be cleared with pesticides."
Herbicides are used to kill broadleaf trees and plants (yes, trees). They try to catch them in seedling stage right after a cut/replant to give the conifers a foothold. Subsequent sprays are to try to keep down the understory of the same type of trees. Yes, all this can provide fuel for forest fires, but the only reason a large fuel load starts in the first place is that they have clearcut the land. You know what happens when you over prune a plant - it grows back like gangbusters so dense as to almost choke itself, often destroying the natural symmetry of the tree. The forest is the same. If you logged sensibly, over time, you would be leaving the forest intact. A natural old growth or succession growth forest sustains itself in two ways - 1) most of the understory trees and brush is shaded out by the canopy 2) low temperature brush and grass fires clear out the rest every 20 years or so, usually never reaching the canopy trees.
Also, the trees that are replanted by the industry are usually monoculture - single species - trees (sometimes even clones per the pro web site - I did not know this). The trees usually planted are Doug Fir in unusually dense relationship with each other. Doug Fir is notoriously fire sensitive, especially in trees younger than 80 years or so (old growth, big and tall). Not only is this bad for pest resistance, but devastating once a fire does start.
Another contributing factor is the virulence of the Smoky the Bear "Stop Forest Fires" campaign over the past 50 years. Nature and even the Indians used to start controlled small scale fires that burned off some of fuel, but unlike a clear cut and herbicide use, the forest had adapted to even devastating fires in ways that continued forest ecosystems (in the case of Pondorosa Pines (which are themselves very fire resistant), leading to new seedlings as the cones don't open until after exposed to high heat). The fire hazard that exists is in essence a direct result of the forest practices of the last 50 years, most especially clear cuts and herbicide use (whose real purpose again is to cut out competition from broadleaf trees, not to reduce fire hazard as they claim).
The timber industry web site states, "The
herbicides used in forests are the same as those used in home gardens
and they pose no health risk to workers or animals." It's
important to note the specifics about the environmental impacts:
consider that home garden use doesn't get into the water table to the
same extent as it does in a rural setting, whose watersheds usually
supply the water for said homes. Also, there is some scientific
controversy about the safety of these items even for home use.
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