Exotic plants that to pose no significant threat or nuisance in surrounding natural areas are exempt from control efforts within the boundaries of developments and cultural landscapes. Exotic plants that pose a threat or are a nuisance will be managed as appropriate, taking cultural and historic resource needs into account, to prevent further natural resources management problems. Introductions must be carefully controlled so as not to harm other native plants or species of economic importance, and are introduced only after several years of scientific evaluation. Succession can be encouraged. For example, a hot surface fire tends to kill native mycorrhizae and to release much plant-available nitrogen.
Abundant nitrogen favors weedy pioneers, such as thistles, foxglove, and fireweed.
A dense stand of competing weeds, combined with a lack of native seed and mycorrhizae slows re-establishment of native plant species. An herbicide may be considered as a means to control an invasive plant species if it is determined that alternative mechanical, physical, cultural, or biological means are either not acceptable or not feasible. Herbicides will not be considered for control in natural vegetation unless other control techniques prove ineffective. If herbicides are used, they are applied in strict accordance with IPM guidelines under the supervision of the park IPM coordinator by a trained, certified pesticide applicator. To the extent possible, herbicides are used only as a last resort.