Following the concept of “rewilding,” Marris brings forth another controversial conservation idea: assisted migration. While rewilding attempts to recreate environments without human impact, assisted migration tries to help species shift to from rapidly warming places, mainly as a result of global warming, to more suitable climates. An argument for assisted migration is that global warming is changing the climate faster than species can migrate and adapt, thus causing them to die out quickly. Although assisted migration involves human inference, it seems like a plausible way to help prevent species from going extinct. In New York City and other cities, where there seems to be a loss of species diversity, assisted migration may be helpful in slowing or reversing this process.
The most appealing factor that distinguished assisted migration from rewilding is that in most cases, assisted migration is more like a guiding hand that is speeding up what is already occurring naturally. A prime example of this type of assisted migration is in British Columbia, where they are “systematically moving its trees” (Marris 91). A large population of pine beetles is decimating trees in an area the size of Greece in British Columbia. The large population is attributed to the milder winters that allow more of the beetle population to survive. Whereas rewilding might have simply began planting seeds far away from where the trees were originally, the assisted migration team here plants seeds within a certain range of its origin to help shift the population. As of right now, no tree species are planted “outside of that species’ historical range” (Marris 92). In this case, scientists are not transplanting species to unknown places, just encouraging species to grow in places where it might not have grown in for a while. Scientists are not changing how a species would behave, they are simply encouraging some behaviors over others.
Assisted migration would be quite useful in increasing species diversity in urban areas since species richness seems to be decreasing in cities. According to the article by Puth and Burns, only six studies with historical data showed species richness over time while seventeen showed a decrease in species richness out of a total of twenty-six studies with historical data. The decrease may be caused by native species in urban areas migrating away from the city and a lack of new species migrating into the city. Urban areas may not be an ideal place for a species to migrate to since it may be vastly different from its origin. Since “a single road will be an effective barrier to a little species,” it is possible that the high concentration of roads and buildings can act as a barrier to species (Marris 75). Cities may almost act like roadblocks to species in their migration. Assisted migration may be helpful in encouraging migrating species to stay in urban areas and increase species richness. Though assisted migration can be difficult in predicting the outcome of changing an ecosystem, it is positive since it is not trying to completely change nature.
