Broom is a non-native shrub frequently targeted for eradication in native plant restorations. Its seedbed lives in the ground for up to 60 years. If broom is not eradicated before every bloom cycle, that 60 year seed-cycle continues ad infinitum. Foliar spraying of glyphosate (Roundup) is the preferred method of eradication because it is the cheapest. Although trees are the main focus of A Million Trees, we will talk about broom because it illustrates two important issues: (1) The futility of trying to eradicate a completely entrenched non-native species, and (2) the largely unknown risks of using herbicides.
We know that Roundup is harmful to amphibians. This fact was established by a suit brought by the Center for Biological Diversity on behalf of the Red-Legged frog (RLF), an endangered species. As a result of that suit, US Fish and Game has banned the use of Roundup in proximity of known populations of the RLF (and more recently extended to other herbicides in proximity of other endangered amphibians).
However, the Center for Biological Diversity is closely allied with the native plant movement. Therefore, when negotiating for a ban on the use of toxic herbicides in proximity of endangered amphibians, they also negotiated for an exception to the ban when the herbicides are used for the purpose of eradicating invasive plants, as defined by the California Invasive Plant Council. Broom is one of hundreds of plants deemed invasive by that council, which is dominated by native plant advocates.
Recent research has found evidence that Roundup may also be harmful to humans. Scientific American reports, “But now researchers have found that one of Roundup’s inert ingredients can kill human cells, particularly embryonic, placental and umbilical cord cells…scientists found that Roundup’s inert ingredients amplified the toxic effect on human cells—even at concentrations much more diluted than those used on farms and lawns.”
This research has implications for other pesticides and herbicides. Presently, the EPA does not require that the manufacturers of these chemicals list all the inert ingredients. If the inert ingredients in other herbicides were known to us, we would be in a better position to assess the potential danger.
Conservation Sense and Nonsense 
The more I read, the more upset I get. Imagine living near the factories where these poisons are made. Pity the person who applies them and wonder how soon they will die of cancer. The bureaucrats who decide to contaminate the environment never dirty their hands with the poison. They should have to drink it!
Broom is one of my most favorite of all shrubs and flowers. What an evocative scent! The Spanish broom is almost all flowers. All the brooms species are tough, gorgeous and perfect for arid wasteland. Instead of bare ground where humans have disturbed the earth and destroyed topsoil (roadsides and after the ground is impacted by heavy machinery), beautiful broom will still grow. These idiots should be grateful! But I console myself with knowing it will outlive humans.