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| Kaua‘i Watershed Alliance Management Programs |
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| Weed Management Program: The goal is to maintain or improve the structure and composition of the watershed’s forest by containing, eradicating, and excluding priority habitat-modifying weeds. |
| Controlling invasive plants across the large and rugged terrain of the primary watershed of the island of Kaua‘i requires a well conceived process informed by current information from the field. From May 2003 – June 2006, numerous ground and aerial weed surveys were conducted by The Nature Conservancy and partners from the Kaua‘i Invasive Species Committee (KISC), Koke‘e Resource Conservation Program (KRCP), and the Department of Forestry and Wildlife (DOFAW). The information gathered in these surveys, as well as from interviews with knowledgeable partners, has formed the basis of the weed management plan. |
| Weed management
priorities:
Kahili ginger (Hedychium gardnerianum) Australian tree fern (Sphaeropteris cooperi) Strawberry guava (Psidium cattleianum) Miconia (Miconia calvescens) Koster’s curse (Clidemia hirta) |
| Other weed species are also problematic in specific areas even though they do not possess all the aforementioned characteristics. These species were ranked as second priority species. They may be identified as priorities only in certain management areas, and ongoing surveys and assessments may add additional species to the list. |
| Weed Management Areas Core areas of the watershed were prioritized for weed management actions according to the intactness of the native forest, diversity of the native biological resources, hydrological value, and urgency of the threat. Weed management should be applied to areas with a high feasibility of success and reasonable cost. High-priority weed management areas in the watershed were identified. |
| Adaptive Management Actions
Because of great differences among management areas, specific objectives and methods should be set for each area. Suppression is the primary objective where the target weed is widely distributed in large patches with surrounding outliers. This involves eliminating reproductive, larger patches. In contrast, containment is the primary objective where the target weed is distributed in many small patches with very few large patches. This involves treating reproductive, small, outlying patches and mapping larger patches. If the target weed is sparsely distributed and is found only in very small patches, elimination is the primary objective. This involves surveying and removing all individuals. Finally, exclusion is the main focus if the target weed has not yet been detected in the area. This combines suppression and containment of buffer infestations, and conducting surveys in 3-year intervals to detect incipient patches. Most weed management actions in high priority areas will concentrate on containment, elimination, and exclusion. This combined approach, called “quick sweep,” is more appropriate for large landscapes because field personnel move rapidly, only removing weed patches with a high potential to spread, and keeping overall costs relatively low. |
| Priority Weed Species
Although numerous weed species exist throughout the core watershed, some have a proven detrimental effect on watershed forest structure and function. These are called Habitat Modifying Weeds and can: • Establish and survive in undisturbed native forest; • Disperse long distances via wind or birds; • Affect large portions of core areas; • Grow and reproduce rapidly and prolifically; • Displace native vegetation; and • Convert diverse assemblages of native vegetation to monocultures of alien vegetation. Priority weeds for management possess all of these characteristics, and unless we engage in urgent and sustained management actions, they will irreversibly convert core native forests within the next few decades. The feasibility of successfully controlling these weeds diminishes exponentially as weeds spread beyond controllable levels. Immediate, aggressive, and strategically implemented management actions are essential to minimize long-term costs and, more importantly, maintain the integrity of the current forest. Based on the above criteria, surveys, and interviews, five weeds were determined to pose the greatest threats. |
| Secondary weed
management priorities: Prickly Florida blackberry (Rubus argutus) Vaseygrass (Paspalum urvillei) Bushy beardgrass (Andropogon condensatum) Downy rose myrtle (Rhodomyrtus tomentosa) Banks melastoma (Melastoma candidum) Faya tree (Morella faya) Lantana (Lantana camara) Molasses grass (Melinis minutiflora) |
| Weed Management Approach Effective management of weeds in the Kaua‘i watershed demands a strategic, systematic, and comprehensive approach, and includes mapping weed distributions, updating and storing spatial data, and using this information to adaptively manage priority areas. |
| Mapping and Data
Currently, the most effective approach to mapping weeds in the Kaua‘i watershed combines helicopter-based surveys with ground-based follow-up surveys. Aerial surveys entail flying at low speeds just above the tree canopy along transects spaced at 100-meter intervals. All first and second priority weeds and other threats (e.g., pig disturbance) are mapped with a hand-held GPS unit and entered into a GIS database. |
| Weed Management Objectives
Objective 1: Develop accurate and complete distribution maps and a GIS database for all priority weed species. Objective 2: Implement adaptive management actions to suppress, contain, eradicate, and exclude high priority weeds in the highest priority management areas. |
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| Koster's Curse |
| Strawberry Guava |
| Kahili Ginger |
| Australian Tree Fern |
| Miconia |
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| Blackberry is a problem in the Koke‘e and Alaka‘i areas. Thorns injure hikers and impede management efforts. |
| Banks melastoma and Downy rosemyrtle were both introduced as an ornamentals, but are now growing out of control in the lowland watershed of Kaua‘i. |
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| Ground-based surveys then focus in specific problem areas identified by the aerial surveys and can be conducted concurrently with weed removal operations. During ground-based surveys and all other field operations, managers collect spatial data in remote areas using GPS. The information is then compiled into a GIS and disseminated to the KWA partners and appropriate field staff at periodic intervals to inform ongoing management efforts. |
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Aerial surveys provided managers with weed distribution data, enabling formation of weed control objectives for the top three priority species: Kahili ginger (above left), Strawberry guava (above right), and Australian tree fern (left). Click on maps to enlarge. |
| Kahili Ginger Objectives |
| Australian Tree Fern Objectives |
| Strawberry Guava Objectives |