Pacific Science (1992), vol. 46, no. 3: 308-314 © 1992 by University of Press. All rights reserved

Population Size and Frequency of Branching in the Eke Silversword, caliginis (), on Eke Crater, West , Hawaii!

2 ELIZABETH ANN POWELL

ABSTRACT: The Eke silversword, , is a rosette endemic to the summit bogs ofEke Crater and Puu Kukui, West Maui, Hawaii . On 2 November 1985, a belt transect across Eke Crater was used to estimate the population of silverswords on the summit bog. Total population of the Eke silversword on Eke Crater was estimated to be about 76,000 . Although the plant has been described as a branching that reproduces vegetatively, the majority of the individuals in the sampled population of the Eke silversword on Eke Crater were unbranched, monocarpic plants that appeared to reproduce by .

THE EKE SILVERSWORD (Argyroxiphium calig­ different species from that found on either the . inis Forbes) is a rosette plant endemic to the uplands of the island of Hawaii or of East summit bogs and ridges of Eke Crater (1360 Maui. It differs from the other described m elevation) and Puu Kukui (1600 m) of West species in its much smaller size." Maui , Hawaii (Figure 1). The Eke silversword Monocarpic silverswords live for many is one of five extant species in the Hawaiian years as a vegetative single-stemmed rosette genus Argyroxiphium (family Asteraceae, sub­ and die after a single episode offlowering and tribe Madiinae). All members ofthe genus are subsequent seed set. Branching is extremely endemic to Hawaii . rare in the Haleakala silversword (A . mac­ The Eke silversword has been frequently rocephalum Gray) (pers . obs.), occurs in less described as a branching, dwarf shrub (Keck than 8% of the plants in a population of 1936, Degener 1937, Neal 1965, Carlquist the Ka'u silversword (A. kauense (Rock and 1974, Carr 1985, 1990). Degener (1930) de­ Neal) Degener and Degener) in the Upper scribed the growth habit of the Eke silver­ Waiakea Forest Reserve on the island of sword as "creeping profusely over the ground Hawaii (unpublished data), and is present in and progressively dying back at the base, about 26% of the remnant naturally occur­ thus isolating the branches into independent ring population of the silversword plants." Carlquist (1974, 1980)suggested that (A. sandwicense De Candolle) (Powell 1992). the Eke silversword on Puu Kukui rarely Therefore, the habit described by Degener flowered and depended on branching for re­ (1930) for the Eke silversword is unusual for production. However, Forbes (1920), in his silverswords. No other silversword species description ofthe species, did not describe the has been reported as capable of vegetative Eke silversword as a branching plant, but reproduction. However, the greensword stated simply, "The plant proves to be a (A . grayanum (Hillebrand) Degener) may be capable of vegetative reproduction in nature

I This study was partially funded by a fellowship from (G. Carr, pers. comm.). the National Wildlife Federation. Manuscript accepted The purpose of this paper is to present an 30 September 1991. estimate of the population size, frequency of 2 Department of Botany, University of Hawaii at Manoa, Honolulu, Hawaii 96822. Corresponding ad­ branching, and mode of reproduction of the dress: P. O. Box 61872, Boulder City, Nevada 89006­ Eke silversword on the summit bog of Eke 1872. Crater. 308 The Eke Silversword-PowELL 309

FIGURE I. A flowering Eke silversword on the summit bog of Eke Crater, West Maui , Hawaii . 310 PACIFIC SCIENCE, Volume 46, July 1992

Study Site RESULTS

Eke Crater is an extinct volcanic dome with The belt transect covered 720 m2 and rep­ eroded sides and gently concave summit. The resented 0.005% (1/189) of the area of the summit bog is underlain by a clay hardpan summit of Eke (13.6 ha), as determined by over a compressed lava core and is character­ planimeter. A total of 404 individual plants, ized by numerous pits and open water ponds. ofwhich three were in , occurred within The vegetation of the summit bog, which the belt transect. If one assumes that the consists primarily ofgrasses, sedges, and low­ density of silverswords within the transect growing , was in a pristine state at the (0.56 plants per m") is the same as the density time of this study: Alien plants were absent of silverswords on the summit of Eke Crater, and the vegetation appeared not to have been then the total population is estimated as the disturbed by humans or animals. The number of silverswords found in the transect summit of Eke Crater has been designated a (404) times the number of possible transect Natural Area Reserve by the State of Hawaii areas on the summit of Eke (189), or about Department of Land and Natural Resources. 76,000 silverswords. The distribution ofrosette diameters of the sampled silversword population showed a METHODS reverse J curve typical of expanding popula­ On 2 November 1985, a 2 m x 360 m belt tions (Figure 2). Forty-eight percent of the transect was extended in IO-m intervals from plants within the transect were < 10 cm in the north rim of Eke Crater across the center diam. There were, however, few seedlings < 3 of the summit to the edge of the south rim. em in diam. It is possible that the silverswords The number ofsilversword plants, the rosette in this bog grow more rapidly than 1 or 2 em diameter of each plant, and the number of per year. If so, seedlings that resulted from the rosette branches for each plant in the transect seed crop of 1984would have been larger than were recorded. The transect covered only flat 2 em by the time of this census in 1985. It is and gently sloping surfaces and did not in­ also possible that seedling recruitment occurs clude pits. Less than 25 m2 ofthe transect was irregularly and that few seedlings were re­ open water ponds. cruited in 1984. The number of flowering silverswords on Sixty-nine of the 404 silverswords (17%) the summit of Eke Crater was estimated by within the transect had multiple rosettes and counting the number of flowering plants en­ were considered branched; the remaining 335 countered and in view during a 5-hr walk had only one rosette and were unbranched around the perimeter of the summit bog. The (monocarpic). Of the branched individuals, rosette diameter and inflorescence height were 33% (n = 23) had two rosettes, 17% (n = 12) measured on 81 flowering individuals, and the had three rosettes, and 14% (n = 10)had> 10 number of flowering stalks from previous rosettes. The maximum number ofrosettes on flowering seasons that were encountered in any silversword plant in the transect was 36. the walk was recorded. The height of the Branched silverswords had several shoots inflorescence from the ground surface was that terminated in rosettes radiating from a measured for 39 flowering silverswords that central point on the aboveground shoot ofthe had fully elongated inflorescences. plant (Figure 3). The radiating shoots did not The area of Eke Crater was determined by extend farther than about 20 em from the planimeter from a I : 24,000, 7.5-min. series central shoot. In only one case was a radiating topographic map published by the U.S. Geo­ shoot found to be rooted in the soil and the logical Survey. However, because the surface connection between it and the parent shoot of the summit is not flat, but concave with broken. Although no silverswords were exca­ numerous pits, the planimeter reading for the vated to make these determinations, no con­ summit is an underestimate of the total sur­ nections between plants were obvious in the face area of the summit of Eke Crater. surface layers ofvegetation, nor were connec- The Eke Silversword- PoWELL 311

40

~ 30 z ~ D... l..L. o 20 D::: W CD 2 ~ z 10

PlIA ~ IA l/l J~~ ~~ o Jr Jr IAIAPlIA o 10 20 30 40 50 ROSETTE DIAMETER (em)

FIGURE 2. Distribution ofrosette diameters ofthesampled silversword population on Eke Crater. Graph does not include two plants: one had a rosettediameter of 61 em andtheother had a rosette diameter of 84 em.

tions between silverswords fou nd by gently DISCUSSION probing the vegetation to the soil surface in areas between plants. It is, however, possible The estimated population of about 76,000 that mo re connections existed than were en­ Eke silversword plants on Eke Crater was countered by these methods. large r than the total estimated population of About 200 silverswords were in flower or any other species of silversword. The esti­ beginning to come into flower on the summit mated population of the Haleakala silver­ bog on 2 November 1985. Of the 81 flowering sword was about 50,000 plants in 1986 (Loope plants measured for inflorescence height, 39 and Crive llone 1986). The Haleakala silver­ plants (48%) had fully elongated inflores­ sword has suffered disturbance from humans cences; the remainder (42 plants) had por­ and feral . The Mauna Kea silverswo rd, tions of the inflorescence in bud. The rosette a federally listed endangered species, has been diameter of the 81 flowering silverswords reduced to a naturally occurring population ranged from 15 to 44 em. The mean diameter size ofless than 40 individuals from a popula­ was 27.0 em (n = 81, SD = 5.5) (Figure 4). tion that probably ranged over the alpine and The height of inflorescences ranged from subalpine slopes of Mauna Kea before the 29 to 81 em. The mean inflorescence height introduction of goats and to Hawaii was 51.8 em. Only 22 flowering stalks Island (Powell 1992). The largest Ka'u silver­ from previous flowering seasons were found . sword population, which is located on Kahu­ These stalks were fragi le and partially decom­ ku Ranch, Hawaii Island, has declined rapidly posed. from a "magnificentcolony" of"several thou- 312 PACI FIC SCIENCE, Volume 46, Ju ly 1992

FI GURE 3. A branched Eke silversword on Eke Crate r. sand plants" in 1974 (Degener et al. 1976) to Carlquist (1974, 1980) suggested that the an estimated population size ofless than 2000 Eke silversword on Puu Kukui rarely flowered individuals in 1984 (unp ublished data). This and, therefore, depended on branching for species has suffered greatly from browsing by reproduction. Thi s did not appear to be the mo uflon sheep and has been pr oposed for case on Eke Crater. Becau se few branc hin g listing as an endangered species (U .S. Fish silverswords were encountered, numerous un­ and Wildlife Service 1990). attach ed seedlings were found, and numerous Although the Eke silversword has repeat­ plants were in flower, I conclude that the Eke edly been described as a branching or creeping silversword reproduces primarily by seed on shrub (Degener 1937, Neal 1965, Carr 1985), Eke Crater. only 17% of the sampled population on Eke It is unknow n whet her the level offlowering Crater was found to be branched. Th e major­ observed in 1985 (about 200 plants) was high ity of the sampled population consisted of or low compared to that of other flowering monocarpic, unbranched plants. This result seasons. No other flowering censuses have does not support the description of the Eke been reported for the Eke silversword during silversword as a creeping shrub that repro­ peak flowering periods. Becau se old floweri ng duces vegetatively. The freq uency of branch­ stalks decompose rapi dly, it was impossible to ing observed for the Eke silversword on Eke assess the level of flowering in previous years. Crater is less tha n the frequency of branchin g Th e vegeta tion of Eke Crater was in a obse rved for the naturally occurring popula­ pristine condition in 1985. The high density of tion of the , which is silverswords on Eke Crater (about 5600 silver­ considered primarily monocarpic. swords per ha) suggests that other silversword The Eke Silversword -s-Powm.i, 313

10 ,..------, (f) I­ Z :5 0.... 8 l') Z 0::: W 6 5 o ...J u, u, 4 o 0::: W rn 2 2 ~ z

O +----J~...1..>o...I.:~Lf'_"_':u.....>..t~~~~~~~..:LT_l---n~----CI...J.....-.I::>...'l..j 10 15 20 25 30 35 40 45 ROSEnEDIAMETER (em)

F IGUR E 4. Distribution of rosette diam eters of 8I flowering plants on Eke Crater on 2 November 1985.

species may have been very numerous, and LITERATURE CITED had high population densities, before distur­ bance by humans and feral animals. CARLQUIST, SHERWIN. 1974. Island biology. Although the Eke silversword population Columbia Uni versit y Press, New York. appeared to be large and to be reproducing in ---. 1980. Hawaii: A natural history, 2d 1985, the silversword is threatened by fera l ed. SB Printers, Inc ., Honolu lu. (Gagne 1987). Where fera l pigs have CARR, GERALD D . 1985. Monograph of the gained access to pristine bog hab itats in Ha­ Hawaiian Madiinae (Astera ceae): Argyroxi­ waii, the native vegetation has declined rap­ phium, , and . Allertonia idly and alien weeds have replaced the native 4: 1-123. vegetation (Medeiros et aI., in press) . Unless ---. 1990. Argyroxiphium DC Silversword. Eke Crater is completely protected from feral Pages 258-262 in Warren L. Wagner, Der­ pigs, the Eke silversword will probabl y suffer ral R. Herbst, and S. H .Sohmer. Manual a rapid and drastic reduction of population of the flowering plants of Hawai'i. Vol. I. size. Bishop Mus. Spec. Publ. 83. Uni versit y of Hawaii Press, Honolulu. DEGENER, OTTO. 1930. Plants of Hawaii Na­ tional Pa rk illustrative of plants and cus­ ACKNOWLEDGMENTS toms of the south seas.Braun-Brumfield, I thank Lani Stemmermann, Betsy Gagne, Inc., Ann Arbor. Tom Hauptman , James Jacobi, and Lawrence ---. 1937. Argyroxiphium caligini. In Flo ­ Walker for their help and suppor t with differ­ ra Hawaiiensis. Family 344: Arg yroxi­ ent phases of this study. phium. Honolulu. 314 PACIFIC SCIENCE, Volume 46, July 1992

DEGENER, OTTO, I. D EGENER, K. SUNADA, and MEDEIROS, ARTHUR c., LLOYD L. LOOPE, and A. SUNADA. 1976. , BETSY H. GAGNE. In press.D egradation of the Kau silversword. Phytologia 33: 173­ vegetation in two montane bogs of Hale­ 177. akala National Park. Cooperative N ational FORBES, C. N. 1920. New Hawaiian plants. Park Re sources Studies Unit Technical Occas. Pap. Bernice Pauahi Bishop Mus. Report. University of Hawaii at Manoa, 7:38-40. Honolulu. GAGNE, WAYNE C. 1987.Conservation corner. N EAL, M ARIE C. 1965. In gardens of Hawaii. Newsl. Hawaii.Bot. Soc. 26 : 10-11. Bernice P. Bishop Mus. Spec. Pub!. 50. KECK, D AVID D . 1936. The Hawaiian silver­ POWELL, ELIZABETH A. 1992. Life history, swords : Systematics, affinities, and phyto­ reproductive biology, and conservation of geographic problems of the genus Argy­ the Mauna Kea silversword, Argyroxiphium roxiphium. Occas. Pap. Bernice Pauahi sandwicense D C (Asteraceae), an endan­ Bishop Mus. II (19): 3-38. gered plant of Hawaii. Ph .D. diss. Univer­ LOOPE, LLOYD L., and CARMELLE F . CRIVEL­ sity of Hawaii. LONE. 1986. Status of the silversword in U.S. FISH AND WILDLIFE SERVICE. 1990. Haleakala National Park: Past and pres­ Endangered and threatened wildlife and ent. Cooperative National Park Resources plants; proposed endangered status for Studies Unit Technica l Report 58. Univer­ Argyrox iphium kauense (Ka'u silversword). sity of H awaii at Manoa, Honolulu. Fed . Regi st. 55(151): 31860-31 864 (6 August 1990).