Revegetation in Dead Dicranopteris (Gleicheniaceae) Fern Patches Associated with Hawaiian Rain Forests 1
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Revegetation in Dead Dicranopteris (Gleicheniaceae) Fern Patches Associated with Hawaiian Rain Forests 1 Peter' A. Follett,1,2,3,4 Puanani Anderson-Wong,3,5 M. n'acy ]ohnson,3,6 and Vincent P. ]ones3,7 Abstract: Dieback of Dicranopteris linearis (Burm. f.) Underwood on wet, open valley slopes and ridgelines of Maui, O'ahu, and Kaua'i has been attributed to feeding by the introduced leafhopper Sophonia rufofascia Kuoh & Kuoh. We studied early plant succession at a variety of low-elevation D. lineans dieback sites to assess the vulnerability of these disturbances to invasion by nonnative weeds. Dead patches of D. linearis were colonized by both native and alien plant species; the number and assemblage of colonizing plant species was site specific. Clidemia hirta (L.) D. Don and Nephrolepis multiflora (Roxb.) Jarrett ex C. Mor ton were the most common invasive species colonizing and spreading in dieback patches. Recolonization of dead patches by live D. linearis spreading from the margins was also common. In a simulated fern decomposition study, seedling germination increased as the depth of the thicket decreased. Fern dieback may enhance regeneration of the native tree Acacia koa A. Gray. THE ULUHE OR false staghorn fern, Dicra eans are often the early colonists of severely nopte1'is linearis (Burm. f.) Underwood, is an disturbed sites, such as landslides (Wardlaw important gap species in the wetter Hawai 1931, Scott 1969, Guariguata 1990), lava ian forests and watersheds (Merlin 1995). flows (Atkinson 1970), and abandoned farm Mueller-Dombois and Fosberg (1998) rec land (Kochummen and Ng 1976). Thicket ognized D. linearis as forming a distinct forming, vinelike ferns such as D. linearis indigenous vegetation type, designated as play an important role in stabilizing soils, Dicranopteris fernlands, in the Hawaiian rain particularly in areas of steep slope and high forest. As such, it plays an important role rainfall (Scott 1969). They also have a dy in structuring the plant community in many namic function in early and late successional habitats. In the Tropics, ferns such as D. lin- development in the Hawaiian rain forest be fore Metrosideros ('ohi'a lehua) canopies close and when canopies open up due to tree die I Manuscript accepted 9 March 2003. 2 Corresponding author. back (Mueller-Dombois 2000). These ferns 3 Department of Entomology, University of Hawai'i spread laterally by extensive rhizomes that at Manoa, Honolulu, Hawai'i 96822. grow at or just beneath the soil surface and 4 Current address: USDA-ARS, u.s. Pacific Basin periodically send up fronds; a single rachis Agricultural Research Center, P.O. Box 4459, Hilo, Hawai'i 96720 (E-mail: pfollett®pbarc.ars.usda.gov). grows one stage at a time, climbing on the 5 Current address: Department of Botany, University dead and decaying fern stems in monotypic of Hawai'i at Manoa, Honolulu, Hawai'i 96822. stands, or using the support of other plants in 6 Current address: Hawai'i Volcanoes National Park mixed stands (Holttum 1957). Quarantine Facility, USDA Forest Service, P.O. Box In the late 1980s, many monotypic stands 236, Volcano, Hawai'i 96785. 7 Current address: Department of Entomology, Tree of D. linearis in open areas along valley slopes Fruit Research and Extension Center, Washington State and ridgelines on the islands of Maui, O'ahu, University, 1100 North Western Avenue, Wenatchee, and Kaua'i began to die, leaving behind Washington 98801. thickets of dead stems (Palmer 1993). Die back of D. linea1'is coincided with the acci Pacific Science (2003), vol. 57, no. 4:347-357 dental introduction and proliferation of the © 2003 by University of Hawai'i Press two-spotted leafhopper, Sophonia rufofascia All rights reserved Kuoh & Kuoh. Sopbonia rufofascia was first 347 348 PACIFIC SCIENCE· October 2003 detected in 1988 on G'ahu on fiddleleaf fig, along the Manoa Cliff Trail, Pu'u Pia in Ficus lyrata Warb., and quickly spread to all Manoa Valley, and 'Aihualama along the the major Hawaiian islands (Heu and Kuma 'Aihualama Trail on the leeward side (Fig shiro 1989). It now has a host list of over 300 ure 1). At each site, plots were selected that plant species in 80 families (Fukada 1996), were primarily dead D. linearis stems, with including ferns, grasses, shrubs, and trees. minimal recolonization. Plots were 20 by Laboratory and field studies implicate S. ru 10 m, which was approximately one-half fofascia as the cause of dieback of D. linearis the total area of the smallest patch sampled (Jones et al. 2000). However, on the island of and one-tenth the area of the largest patch. Hawai'i, where S. rufofascia also occurs and is Quadrat and line intercept sampling were trapped in high numbers in D. linea17s (Jones done at 0, 6, 14, and 27-32 months to esti et al. 2000, Yang et al. 2000) no dieback has mate changes in plant species composition been observed, suggesting that other factors and percentage cover (Mueller-Dombois and must have contributed to the process. Ellenberg 1974). Ten 1-m2 quadrats were Stands of D. linearis in Hawai'i can range randomly selected and permanently estab in height from a few centimeters to a few lished within each plot at the beginning of meters (Kepler 1984). Dense thickets can the experiment, and on subsequent sampling prevent the growth of other plants (Walker dates the number of stems and percentage 1994, Mueller-Dombois 2000). In addition cover of each plant species within each quad to exposing slopes to soil erosion, the decline rat were determined. In addition, on each and death of stands of D. linearis (typically sampling date four transects were established 0.1-0.5 ha) can radically alter the composi across the lO-m width of the plots and plants tion of the plant community through species were scored at O.S-m intervals along each replacement. In Hawai'i, opportunistic alien transect (84 point intercepts per plot) as weeds, such as Clidemia hirta (L.) D. Don an alternate estimate of percentage cover for (Koster's curse), Citharexylum caudatum L. various plant species. (fiddlewood), Nephrolepis spp. (swordfern), Lantana camera L., Psidium cattleianum Sa Wayside Vegetation Analysis bine (strawberry guava), Rubus rosifolius Sm. (thimbleberry) and others, can invade dis TRAIL TRANSECTS. Hiking trails can be turbed sites and form large monotypic stands, thought of as transects across the landscape preventing native species replacement (Cud and are useful for vegetation analysis in areas dihyand Stone 1993). We studied early plant that are otherwise inaccessible due to steep succession in a variety of low-elevation D. terrain or thick vegetation. The 'Aiea Loop linearis dieback areas to assess the vulnerabil and Maunawili Trails (Ball 2000) were used ity ofthese disturbed sites to invasion by non as transects across two steep valleys on G'ahu native weeds. known to have areas of D. linearis dieback to estimate percentage cover of D. linearis in those valleys. Sampling was conducted MATERIALS AND METHODS in June 1996 at 100-m intervals along both Permanent Plots trails. At each interval, both sides of the trail were sampled using the quadrat-on-a-stick The fern dieback sites sampled all occurred method (a 1-m2 PVC pipe quadrat at the within 100 m ofwell-maintained hiking trails. end of a 2-m-Iong PVC pole). This extended Six patches of dead D. linearis in the southern quadrat device enabled us to sample vegeta Ko'olau Range of G'ahu were selected to tion beyond the disturbed area bordering the monitor revegetation patterns through time, trail. At each sampling interval the quadrat and plots were established between May was positioned at points above and below the and July 1996. Sites were Ironwood and St. trail and estimates were made of percentage Stephen along the Maunawili Trail on the cover within the quadrat on the ground and windward side, and MC-steep and MC-flat in the overstory above. The survey included Oahu a Kauai b FIGURE 1. Dicrnnoptl!'ris dieback sites sampled on the islands of O'ahu (II) and Kaua'i (b): 1, Ironwood; 2, St. Stephen; 3, MC-steep; 4, MC-flat; 5, Pu'u Pia; 6, 'Aihualama; 7, 15 min; 8, MW-site A; 9, MW-site C; 10, 3-mile; 11, Guavakai 1; 12, Guavakai 2; 13, Powerline; 14, Manoa Falls 1; 15, Manoa Falls 2; 16, Mau'umae 1; 17, Mau'umae 2; 18, Mau'umae 3. 350 PACIFIC SCIENCE· October 2003 6.9 krn of the Maunawili Trail and 8 krn of ling germination data from the mulch plots the 'Aiea Loop Trail. were taken at 3 and 9-11 months after the DIEBACK PATCHES. Hiking trails also are plots were established. Data on plant counts the best access to many of the D. linearis die were subjected to analysis of variance after back areas. In addition to the 10 by 20 m log(x + 1) transformation. Tukey-Kramer's permanent plots, 12 wayside patches of dead HSD (IX = 0.05) was used to make paired D. linearis were sampled in June 1997 along comparisons between treatment means (SAS four ridges on the islands of G'ahu and Kaua'i Institute 2002). using point-intercept sampling. Sites were 15 min, MW-sites A and C, and 3-mile along the Maunawili Trail on the windward side of the RESULTS southern Ko'olau Range on G'ahu; Guavakai The plant species occurring in patches of 1 and 2 and Powerline near the Powerline dead D. linearis sampled from 1995 to 1999 Trail on Kaua'i; Manoa Falls 1 and 2 along are shown in Table 1. The most frequently the Manoa Falls Trail; and Mau'umae 1, encountered species in addition to D.