Before the Europeans arrived, wildflowers in the Presidio had grown here for tens of thousands of years.
By introducing non-native flowers and other plant species, settlers drastically altered the landscape.
While some of these new flowers ... or "outsiders" ... don't seem to threaten our native species or ecosystems, many are invasive.
Invasive means "outsiders" can spread quickly to disrupt or push-out native plant species. There are a lot of reasons: "Outsiders" aren't bothered by local diseases or local animals don't like eating the new flowers or the "outsiders" produce a lot of seeds or they have accelerated reproductive cycles.
To bring balance back into our environment, these "outsiders" have to be removed ... by hand. It's incredibly hard work and takes literally years to change the land back to its original state.