Report on weed monitoring program in areas which have been developed by True Geothermal Energy Co. in BLNR designated geothermal development subzone Middle East Rift Zone of Kilauea

Abstract

"During each visit to the site after road and drill site clearing occurred, observations were made of the distribution of species colonizing all areas cleared during the process of geothermal development. The preclearing survey was made on Nov. 14, 1987, and post-clearing surveys were made on: July 9, 1989, December 16, 1989, January 13,1990, May 18,1990, June 9,1990, August 12, 1990, December 1, 1990, and February 2, 1991. A summary of these observations is provided in the table which follows. A total of 67 species and varieties of higher plants have been found colonizing cleared sites. Of these 49 are alien species, 2 are probably Polynesian introductions, 1 is either indigenous or a Polynesian introduction, 6 are indigenous and 9 are endemic to the Hawaiian islands. Methods of control of the alien species are currently being applied on an experimental basis, with due care taken to protect the native species and to encourage the expansion of the area occupied by natives. There are several native species which have increased in abundance in these cleared areas. Most notable are mamaki (Pipturus albidus), "uki (Machaerina angustifolia and M. mariscoides ssp. meyeniit, and Pycreus polystachyos. These are species which often occur in disturbed areas early in succession. Mamaki is of special interest since it grows into a shrub, 10 feet or more tall, which casts dense shade that can inhibit the growth of alien species that might otherwise occupy the area. Efforts should be made to encourage this species, both by scattering seeds in areas where it is not growing thickly, and by controlling alien species which are growing near it and inhibiting its growth. The alien species which is competing most effectively is sourbush (Pluchea symphytifolia); this species should be controlled since it has increased in abundance in the cleared areas, and it is the only alien species which has increased in these areas that is likely to persist and inhibit the recovery of native species. Some of the alien species which were conspicuous immediately after clearing are annual species that are typical of the earliest stages of succession but are quickly shaded out and are now decreasing in numbers. These include fireweed (Erechtites valerianifolia) and Crossocepha/um crepidioides, These species do not persist in closed canopy for est except in small numbers in areas disturbed by pigs, and they should continue to decrease as succession proceeds in the cleared areas. The goal of the weed control program in these cleared areas should be to promote natural succession of native species as much as possible. To this end, general application of herbicides over large areas is not desirable, since widespread vegetation removal merely results in setting back the successional process to an earlier stage and providing further opportunity for invasion of alien species. Rather, herbicide use should be limited to spot applications on particular target species, or areas of particularly dense infestation of aliens."