Why are genetically modified plants thought to pose a greater risk to the environment that GM animals?
Because plants can more easily ‘escape’ the confines of a testing site. A GM cow on a ranch is unlikely to get out and, even if she does, is unlikely to mate and produce enough offspring to alter the wild populations. A GM plant in a field could get out if even one seed gets out and that seed could be the parent of numerous generations that could act as an invasive species, decimating the populations of other plants. I find this scenario somewhat unlikely, (it assumes that features that humans prefer are also superior when competing with plants that have evolved to be best at surviving) but that is why people are worried.
