Doesn’t the addition of a non-native species increase biodiversity?
Yes – if you are only concerned with the number of species in the short term. Invasive exotic plants will become a “new” species in an area but may also decrease the number of native species found there as well. Purple loosestrife, now common in many Vermont wetlands will, out-compete rare, native wetland plants that are only found in Vermont or northern New England. Local biodiversity may increase at the first arrival of these plants but then plummet once the invasive exotics replace the native plants. When this happens, global biodiversity will decrease at the loss of the rare plant.
