Dieter Mueller-Dombois

Biological Invasion by Myrica faya Alters Ecosystem Development in Hawaii

The exotic nitrogen-fixing tree Myrica faya invades young volcanic sites where the growth of native plants is limited by a lack of nitrogen. Myrica quadruples the amount of nitrogen entering certain sites and increases the overall biological availability of nitrogen, thereby altering the nature of ecosystem development after volcanic eruptions.

Changes in Soil Phosphorus Fractions and Ecosystem Dynamics across a Long Chronosequence in Hawaii

We tested the Walker and Syers (1976) conceptual model of soil development and its ecological implications by analyzing changes in soil P, vegetation, and other ecosystem properties on a soil chronosequence with six sites ranging in age from 300 yr to 4.1 x 10 6 yr. Climate, dominant vegetation, slope, and parent material of all of the sites were similar. As fractions of total P, the various pools of soil phosphorus behaved very much as predicted by Walker and Syers. HCl-extractable P (presumably primary mineral phosphates) comprised 82% of total P at the 300-yr-old site, and then decreased to 1% at the 20,000-yr-old site. Organic phosphorus increased from the youngest site to a maximum at the 150000 yr site, and then declined to the 4.1 x 10 6 yr site. Occluded (residual) P increased steadily with soil age. In contrast to the Walker and Syers model, we found the highest total P at the 150000-yr-old site, rather than at the onset of soil development, and we found that the non-occluded, inorganic P fraction persisted through to the oldest chronosequence site. Total soil N and C increased substantially from early to middle soil development in parallel with organic P, and then declined through to the oldest site. Readily available soil P, NH 4 + , and NO 3 - were measured using anion and cation exchange resin bags. P availability increased and decreased unimodally across the chronosequence. NH 4 + and NO 3 - pools increased through early soil development, but did not systematically decline late in soil development. In situ decomposition rates of Metrosideros polymorpha litter were highest at two intermediate-aged sites with high soil fertility (20000 yr and 150000 yr), and lowest at the less-fertile beginning (300 yr) and endpoint (4.1 x 10 6 yr) of the chronosequence. M. polymorpha leaves collected from these same four sites, and decomposed in a common site, suggested that leaves from intermediate-aged sites were inherently more decomposable than those from the youngest and oldest sites. Both litter tissue quality and the soil environment appeared to influence rates of decomposition directly. The highest mean soil N 2 O emissions (809 μg.m -2 .d -1 ) were measured at the 20 000-yr-old site, which also had the highest soil nitrogen fertility status. Plant communities at all six chronosequence sites were dominated primarily by M. polymorpha, and to a lesser extent by several other genera of trees and shrubs. There were, however, differences in overall vegetation community composition among the sites. Using a detrended correspondence analysis (DECORANA), we found that a high proportion of species variance among the sites (eigenvalue = 0.71) can be explained by site age and thus soil developmental stage. Overall, long-term soil development across the chronosequence largely coincides with the conceptual model of Walker and Syers (1976). How P is distributed among different organic and inorganic fractions at a given stage of soil development provides a useful context for evaluating contemporary cycling of P and other nutrients, and for determining how changes in P availability might affect diverse ecosystem processes.

Physiological and morphological variation in Metrosideros polymorpha, a dominant Hawaiian tree species, along an altitudinal gradient: the role of phenotypic plasticity

Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO2 m−2 s−1) and higher average stomatal conductance (0.18 mol H2O m−2 s−1) than their field counterparts (3.0 μmol CO2 m−2 s−1, and 0.13 mol H2O m−2 s−1 respectively). Foliar δ13C of most common-garden plants was similar among sites of origin with an average value of −26.9‰. In contrast, mean values of foliar δ13C in field plants increased substantially from −29.5‰ at low elevation to −24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211–308 g m−2 for common garden versus 107–407 g m−2 for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m−2 to 2.4 g m−2 and from 0.8 g m−2 to 2.5 g m−2 in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO2 assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species.

Natural Dieback in Forests

urrently, much public concern and research effort focuses on forest dieback in industrial countries. Factors associated with air pollution, such as acid rain, nitrous oxide, changes in the ozone level, and heavy metal deposition are often considered responsible for tree mortality on both sides of the Atlantic. While it is absolutely clear that air pollution from nearby smelters can cause stand-level tree mortality by toxification (Smith 1981), the acid-rain relationship with forest dieback (Ulrich 1981, 1982) is as yet highly conjectural (Cramer 1984, Johnson 1983, Kandler 1983, Nihlgard 1985, Rehfuess 1983, Schiitt and Cowling 1985). This article is not intended to diminish concern about air pollutions relationship to forest dieback. The objective instead is to point out that stand-level dieback in forests is by no means a new phenomenon and further that, in many cases, it is due to natural causes. While it is sometimes possible to distinguish between manmade and natural causes of standlevel dieback, it is usually difficult to determine the exact causes. Dieback is the death of groups of neighboring trees rather than isolated trees dying in an otherwise green forest matrix. Dieback stands are forest segments having significant loss of canopy. In these stands the majority of trees are either dead or display reduced vigor. The term dieback is

Response of Metrosideros polymorpha seedlings to experimental canopy opening

Twenty 100-m2 plots in a forest dominated by tree fern (Cibotium spp.) and ohia (Metrosideros polymorpha) on the island of Hawaii were subjected to different degrees of canopy removal. Seedlings growing in the control plots received an average of 10% full irradiance, whereas those growing in completely cleared plots received an average of 43% full irradiance. Invasion of Metrosideros tree seedlings into the completely cleared plots averaged more than three times that in the undisturbed forest. These open-born seedlings grew in height by an average of 3.5 cm/yr, 80% more than comparably sized seedlings that had started life in the shade and were then subjected to higher irradiances. The average height increment of all shade-born seedlings was 2.5 cm/yr in the control plots and 6.6 cm/yr in open plots; in terms of relative growth rates, this represents an increase from 0.19 to 0.47 cm -cm- yr-1. Height growth was optimal (10.5 cm/yr) at microsites receiving 55- 60% relative irradiance. During the course of monitoring the growth and irradiance of 1130 seedlings that were tagged before canopy disturbance, it was found that these shade-born seedlings suffered mortality at a rate of 57%/yr when growing at 5 50% indicate that many of these Metrosideros seedlings cannot be readily conditioned to open habitats. It therefore appears that shade-born seedlings of this variety of Metrosideros are intermediate in shade tolerance. Although seedlings may survive in the shade for a year or two, dense canopies of tree ferns or older Metrosideros trees are able to suppress their growth effectively, so that the Metrosideros population may have to depend on canopy gaps or canopy diebacks to maintain itself in mature rain forests. Some individuals were nevertheless able to acclimate successfully to very high light intensities, and this same species is a successful colonizer of barren volcanic deposits, suggesting that Metrosideros polymorpha exhibits broad acclimation ability and/or a wide range of genetic variability.

Primary succession of Hawaiian montane rain forest on a chronosequence of eight lava flows

Abstract. The primary-successional sere of a Hawaiian montane rain forest was inferred from an age sequence of eight closely located ‘a’ ā flows (clinker type lava); 8, 50, 140, ca. 300, ca. 400, ca. 1400, ca. 3000 and ca. 9000 yr, on a windward slope of Mauna Loa, Hawaii. All study sites (0.2 ha each) were at 1120 — 1250 m a.s.l. with 4000 mm mean annual rainfall. The 400-yr, 1400-yr, and 9000-yr flows had younger volcanic ash deposits, while the others were pure lava. Comparisons of tree size and foliar nutrients suggested that ash increased the availability of nitrogen, and subsequently standing biomass. An Unweighted Pair Group Cluster Analysis on the samples (flows) using quantitative vascular species composition revealed that clusters were correlated with age regardless of the substrate types (pure lava vs. ash), and an indirect ordination on the samples suggested that the sequence of sample scores along axis 1 was perfectly correlated with the age sequence. Although ash deposits increased biomass, they did not affect the sequence of the successional sere. Both pubescent and glabrous varieties of Metrosideros polymorpha (Myrtaceae) dominated upper canopy layers on all flows ≥ 50 yr and ≤ 1400 yr, but the pubescent variety was replaced by the glabrous on the flows ≥ 3000 yr. Lower layers were dominated initially by a matted fern, Dicranopteris linearis, up to 300 yr, and subsequently by tree ferns, Cibotium spp., to 9000 yr. The cover of Cibotium declined slightly after 3000 yr, while other native herb and shrub species increased. A ‘climax’ stage in the conventional sense was apparently not reached on the observed age gradient, because the sere changed continuously in biomass and species; this divergent successional phenomenon may be unique to Hawaii where the flora is naturally impoverished and disharmonic due to its geographic isolation in contrast to more diverse and harmonic floras in continents.

Vegetation changes along gradients of long-term soil development in the Hawaiian montane rainforest zone

The development of the Hawaiian montane rainforest was investigated along a 4.1-million-year soil age gradient at 1200 m elevation under two levels of precipitation, the mesic (c. 2500 mm annual rainfall) vs. wet (>4000 mm) age gradient. Earlier analyses suggested that soil fertility and foliar nutrient concentrations of common canopy species changed unimodally on the same gradients, with peak values at the 20,000–150,000 yr old sites, and that foliar concentrations were consistently lower under the wet than under the mesic conditions. Our objectives were to assay the influences of soil aging and moisture on forest development using the patterns and rates of species displacements. The canopies at all sites were dominated by Metrosideros polymorpha. Mean height and dbh of upper canopy Metrosideros trees increased from the youngest site to peak values at the 2100–9000 yr sites, and successively declined to older sites. A detrended correspondence analysis applied to mean species cover values revealed that significant variation among sites occurred only on one axis (axis 1), for both soil-age gradients. Sample scores along axis 1 were perfectly correlated with soil age on the mesic gradient, and significantly correlated on the wet gradient. Higher rainfall appeared to be responsible for the higher rates of species turnover on the wet gradient probably through faster rock weathering and greater leaching of soil elements. We concluded that the changes in species cover values and size of the canopy species was a reflection of the changing pattern of nutrient availability associated with soil aging.

Fate of a wet montane forest during soil ageing in Hawaii

KANEHIRO KITAYAMA*, EDWARD A.G. SCHUURt, DONALD R. DRAKE: and DIETER MUELLER-DOMBOIS? *The Japanese Forestry and Forest Products Research Institute, PO Box 16, Tsukuba Norin Kenkyu Danchi, Ibaraki 305, Japan, tEcosystem Sciences Division, University of California at Berkeley, Berkeley, California 94720, USA, tSchool of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand, and ?Department of Botany, University of Hawaii, 3190 Maile Way no. 101, Honolulu, Hawaii 96822, USA

Fire in Tropical Ecosystems and Global Environmental Change: An Introduction

Fire has always been an important ecological stress factor in the seasonal tropics. The dry deciduous forest and the savanna grasslands, in general, have evolved with fire. The plant life forms of these tropical biomes can cope with fire through various adaptive traits (Budowski 1966).

Crown Distortion and Elephant Distribution in the Woody Vegetations of Ruhuna National Park, Ceylon

A major wild elephant refuge occurs in the southeastern dry zone of Ceylon. The effect of the elephants on the woody vegetation is manifested in crown distortions mainly of the 2— to 5—m—tall woody plants. A survey of this phenomenon was made in 18 sample stands of four different structural woody vegetation types. A species crown—distorion index was established from summing the number of crown—distorted individuals in each species across the structural vegetation types. A list of species from high to low crown—distortion index is presented, which may serve as a guide to preferential elephant food plants for southeastern Ceylon. A stand crown—distortion index was established for each vegetation sample by summing the number of crown—distortion individuals per stand and relating these to the total number available. It was found that crown distortion is particularly high among earlier seral rather than late seral species, and stands, in spite of equal availability of both. This shows that the elephant is more...