EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Biogeosciences, 10, 5171–5182, 2013 Open Access www.biogeosciences.net/10/5171/2013/ Biogeosciences doi:10.5194/bg-10-5171-2013 Biogeosciences Discussions © Author(s) 2013. CC Attribution 3.0 License. Open Access Open Access Climate Climate of the Past of the Past Discussions Origin of the Hawaiian rainforest and its transition states in Open Access Open Access long-term primary succession Earth System Earth System Dynamics 1 2 Dynamics D. Mueller-Dombois and H. J. Boehmer Discussions 1University of Hawaii at Manoa, Department of Botany, 3190 Maile Way, Honolulu, HI 96822, USA 2Technical University of Munich, Department of Ecology and Ecosystem Management, Chair for Strategic Landscape Open Access Open Access Planning and Management, Emil-Ramann-Strasse 6, 85350 Freising-Weihenstephan, GermanyGeoscientific Geoscientific Instrumentation Instrumentation Correspondence to: D. Mueller-Dombois ([email protected]) Methods and Methods and Received: 31 December 2012 – Published in Biogeosciences Discuss.: 11 February 2013 Data Systems Data Systems Revised: 3 June 2013 – Accepted: 21 June 2013 – Published: 30 July 2013 Discussions Open Access Open Access Geoscientific Geoscientific Abstract. This paper addresses the question of transition redeveloping in the more dissected landscapes of the older is- Model Development states in the Hawaiian rainforest ecosystem with emphasis lands loses stature,Model often Development forming large gaps that are invaded on their initial developments. Born among volcanoes in the by the aluminum tolerant uluhe fern. The ’ohi’a¯ trees still Discussions north central Pacific about 4 million years ago, the Hawai- thrive on soils rejuvenated from landslides and from Asian Open Access ian rainforest became assembled from spores of algae, fungi, dust on the oldest (5 million years old) island Kaua’iOpen Access but their lichens, bryophytes, ferns and from seeds of about 275 flow- stature and living biomassHydrology is greatly diminished. and Hydrology and ering plants that over the millennia evolved into ca. 1000 en- Earth System Earth System demic species. Outstanding among the forest builders were the tree ferns (Cibotium spp.) and the ’ohi’a¯ lehua trees (Met- Sciences Sciences rosideros spp.), which still dominate the Hawaiian rainfor- 1 Introduction: origin and evolution of Hawaii’s Discussions Open Access est ecosystem today. The structure of this forest is simple. rainforest Open Access The canopy in closed mature rainforests is dominated by co- Ocean Science horts of Metrosideros polymorpha and the undergrowth by The Hawaiian rainforestOcean was born Science among volcanoes in the tree fern species of Cibotium. When a new lava flow cuts north central Pacific in complete isolation. Its origin is an- Discussions through this forest, kipuka are formed, i.e., islands of rem- cient, probably pre-Pleistocene. The latest information gives nant vegetation. On the new volcanic substrate, the assem- the date of colonization of its dominant tree taxon Met- Open Access blage of plant life forms is similar to the assemblage dur- rosideros (’ohi’a¯ lehua) as 3.9 (to 6.3) Myr (PercyOpen Access et al., ing the evolution of this system. In open juvenile forests, 2008). This date range, obtained from phylogenetic meth- Solid Earth a mat-forming fern, the uluhe fern (Dicranopteris linearis), ods, puts its island origin intoSolid the Pliocene, Earth coinciding with Discussions becomes established. It inhibits further regeneration of the the emergence of the oldest high island Kaua’i. The arrival dominant ’ohi’a¯ tree, thereby reinforcing the cohort struc- date of the second main structural component of the Hawai- ture of the canopy guild. In the later part of its life cycle, the ian rainforest, the tree fern Cibotium (hapu’u), has not yet Open Access Open Access canopy guild breaks down often in synchrony. The trigger is been established, but is believed to be of equally ancient ori- hypothesized to be a climatic perturbation. After the distur- gin (Ranker, personal communciation, 2012). Even today, The Cryosphere the early communityThe assemblage Cryosphere on new volcanic surfaces bance, the forest becomes reestablished in about 30–40 yr. As Discussions the volcanic surfaces age, they go from a mesotrophic to a eu- follows the evolution of plant life from algae and fungi via trophic phase, reaching a biophilic nutrient climax by about lichens, mosses, and ferns (Smathers and Mueller-Dombois, 1–25 K yr. Thereafter, a regressive oligotrophic phase fol- 2007). However, seed plants now arrive early, commonly lows; the soils become exhausted of nutrients. The shield vol- after 4 yr, with the endemic Metrosideros polymorpha tree canoes break down. Marginally, forest habitats change into among the first. bogs and stream ecosystems. The broader ’ohi’a¯ rainforest The Hawaiian flora of seed-bearing plants consists of about 275 successfully established indigenous populations Published by Copernicus Publications on behalf of the European Geosciences Union. Figures 5172 D. Mueller-Dombois and H. J. Boehmer: Origin of the Hawaiian rainforest and its transition states (Fosberg, 1948; Wagner et al., 1999). They arrived by long- distance transfer either by wind in the jet streams (small seeds only, such as those of Metrosideros, as did the fern spores and lower plant forms) or attached to the feet, feath- ers or in the guts of storm tossed birds (Carlquist, 1980). A minor number of plant propagules arrived within ocean cur- rents. Most of the latter form Hawaii’s native coastal vegeta- tion, which is rather impoverished compared to those of the islands in Micronesia and Melanesia (Mueller-Dombois and Fosberg, 1998). This process of natural invasion took many millennia. In that period new species evolved as endemics from only about 10 % of the original colonizers. Together they now form a native Hawaiian flora of about 1000 species (Wagner et al., 1999). 575 Fig. 1. 1. TheThe 1955 1955 Kamā`ili Kam `a`āa’ili¯ flow ’a’witha¯ kipuka flow in with background kipuka (photo in background by D. Mueller- 2 Early primary succession Dombois,(photo by 1971). D. Mueller-Dombois, 1971). Three distinct stages in early rainforest succession can be recognized. 2.1 Stereocaulon lichen stage When a lava flow cuts through a Hawaiian rainforest, patches of rainforest often survive as so-called kipuka, i.e., islands of remnant vegetation (Fig. 1). These vegetation islands and nearby intact vegetation provide most of the propagules for plant invasion on the new volcanic surfaces (e.g., Drake, 1992; Drake and Mueller-Dombois, 1993; Kitayama et al., 1995). Typically, such invasion starts with blue-green al- gae, such as Anacystis montana, Scytonema myochrous, Stigonema panniforme, among others. Early mosses include 26 species of Campylopus and Rhacomitrium lanuginosum. These settle in lava fissures together with low-growing fern species of Nephrolepis and Pityrogramma. A lichen, Stereo-580 Fig. 2. 2. TheThe same same Kam Kamā`ili `a`a’ili¯ ā flow ’a’ fourteena¯ flow fourteenyears later yearswith cohort later of with Metrosideros cohort caulon vulcani, becomes obvious in four years, often grow- ofsaplingsMetrosideros (photo by D.saplings Mueller-Dombois, (photo by1985). D. Mueller-Dombois, 1985). ing as continuous cover on lava rock surfaces. Together with the invasion of this white-grey dendroid lichen, invasion of seed plants are noted. They include typical native pioneer 2.2 Dicranopteris fern stage shrubs such as Dubautia scabra, Vaccinium reticulatum, and species of endemic Rumex. Simultaneously, tree seedlings of After about 50–100 yr, the new Metrosideros seedlings have Metrosideros polymorpha appear in the lava cracks, soon de- grown into a juvenile tree stand. Typically at this ad- veloping into saplings (Fig. 2). Early successional shrubs, vanced stage, the native uluhe fern (Dicranopteris linearis) such as the native Coprosma ernodeoides, Leptecophylla has moved onto the new volcanic substrate beneath the tameiameiae, and Dodonaea viscosa soon begin to supple- trees (Fig. 3). Juvenile Metrosideros trees have rather short ment the first group. branches along their entire stems, and the trees thus form In the lichen stage, rock fissures become filled with min- open stands, which allows for much direct sunlight to pen- eral dust and organic matter and the Stereocaulon itself is etrate to the ground. This light environment is ideal for known to work on the breakdown of the rock surfaces (Jack- the heliophytic fern Dicranopteris linearis, a stoloniferous son, 1969) by producing carbonic acid and thus releasing iron mat-former, which covers the open bedrock surface, thereby chelates, an essential plant nutrient. Potassium is another soil preventing further Metrosideros seedlings to develop into nutrient dissolved early from glass-coated basalt fragments. saplings. Metrosideros seedlings are relatively shade toler- Limited amounts of atmospheric nitrogen become available ant but they only grow into the sapling stage in well lighted 27 from fixation by blue-green algae. situations (Burton and