When most people think of preserving natural areas, they envision saving green growing things from encroachment by parking lots and housing development. Nativists focus on a different agenda – removing non-native plants and substituting natives.
What’s wrong with that?
1. Toxic herbicides. Since non-native plants are well-established, and the air in our city is full of dispersing seeds from hundreds if not thousands of species, the only way to carve out native plant gardens is by using toxic herbicides – Roundup, Garlon, Imazapyr. And it’s not a one-off effort; the pesticide use has to be repeated several times each year, as we see at Twin Peaks or Stern Grove.
2. Destruction of trees. The Native plant movement in San Francisco works actively to reduce the number of trees and the extent of tree cover. This directly conflicts with the importance of trees in sequestering carbon.
3. Quixotic conversion to native trees. Even where they are willing to accept trees, they would remove the eucalyptus and black acacia and Monterey cypress and Monterey pine, and plant oak, douglas fir, and a few other species. Unfortunately, most of these have problems. Oak is slow-growing, and vulnerable to Sudden Oak Death, a fungal infection that has spread widely through California. (Oak is also quite allergenic.) Douglas fir requires more rain than San Francisco gets.
4. Habitat destruction. San Francisco’s wildlife is adapted to non-native plants, and for good reason. Eucalyptus, blackberry, ivy and holly provide excellent cover, and are a rich food source. They all flower and provide bee-pasture. Generally, native plants offer lower nutrient density than the non-natives – they do not grow as thickly, they have fewer flowers for a shorter season, and most have less fruit (the toyon is an exception). Many die back for much of the year, unlike the eucalyptus and blackberry, the holly and the ivy. Returning these areas to native plants would kill off birds and animals who no longer had territories in which to live and breed, and their populations would fall.
In fact, our lives depend on non-native plants. Almost everything we eat is non-native; very few people would want to revert to a diet of acorn-flour, fish, and game. Most of what we plant in our gardens is non-native.
We support the preservation of current native plant areas. Like old-growth chaparral, for instance.
We just oppose destruction of other habitats for conversion to native plants.