american samoa - University of Hawaii at Manoa Botany Department

Option 4: Restore Mangrove Forest Upstream of the Puna Stream and Tapua Stream MouthsRestoration of the mangrove forest immediately upstream of the Puna Stream and TapuaStream mouths (Figure 4-3) would initially require the clearing of sand, vegetation and solidwaste material that presently blocks tidal exchange via the Puna Stream mouth. This effort willrequire clearing within the existing 12-foot wide x 3.5-foot high culvert upstream of the Punastream mouth, as well as on the upstream and downstream sides of the culvert. A backhoe willalso be needed to facilitate the excavation of sand and heavier solid waste material.Machetes and weed-eaters can be used to mow vegetation upstream and downstream of theTapua Stream and Puna Stream culverts. Lighter, solid waste material should be burned.Excess material should be bagged in plastic garbage bags; arrangements should be made withASPA for a special collection of this material.In November 1999, the double culverts underneath the shoreline vehicular trail were clear ofany obstructions that might impede tidal exchange via the adjoining Tapua Stream mouth.Consequently, no clearing is anticipated at the Tapua Stream mouth or the upstream culvertunderneath the shoreline trail.The second task of the restoration effort would involve the planting of red and orientalmangrove trees within and along the margins of the estuary in the fresh-water swamp, as wellas the banks of Tapua Stream and Puna Stream between the culverts and the fresh-waterswamp.Roughly 50 red mangroves should be planted within the streambed because this plant readilycolonizes in estuaries and can sustain itself in waters with somewhat higher salt waterconcentrations (Stemmermann, 1981). Propagules or seedlings should be plantedapproximately three feet apart. Within three years, the mangroves should be thinned to about asix-foot spacing between each plant (Steele, 1999).In contrast, 25 oriental mangroves would more desirably be planted along the stream banksbecause it is less tolerant of salt water. Propagules or seedlings should again be spacedapproximately three feet apart. Plants should be thinned to a spacing of six feet within aboutthree years.Other smaller trees, shrubs and grasses that can survive successfully in a brackish, estuarineenvironment would supplement mangrove plantings. In-stream plantings of red mangrovewithin the estuary, for example, would be supplemented with approximately 25 fao trees (beachhibiscus). Along stream banks, the planting of oriental mangrove trees would be interspersedwith about 25 milo trees (Thesepesia populnea). Salt resistant grasses would be planted in theestuary to increase the amount of available habitat of fish upstream of the Tapua Stream andPuna Stream outlets.Comparative Benefits and ImpactsPPC’s evaluation of the four alternate restoration and enhancement strategies is summarized inTable 4-5. Option 4 would achieve significant benefits to wetland vegetation, reduce floodpotential in the vicinity of the Puna Stream mouth, expand a fish spawning area in the estuaryupstream of the Puna Stream mouth, and create new habitat for invertebrates. These potentialbenefits can be derived for considerably lower project costs.American Samoa Wetland/Stream Restoration and Enhancement PlanFebruary 2001, Aoa Wetland, Page 4-12