Acacia Koa Research Articles

Reforestation and Topography Affect Montane Soil Properties, Nitrogen Pools, and Nitrogen Transformations in Hawaii

Land use changes, such as deforestation and reforestation, modify not only the organisms inhabiting affected areas, but also above‐ and belowground environments. Topography further influences local vegetation and environment. Effects of topography and re‐establishment of N‐fixing koa (Acacia koaA. Gray) trees in +100‐yr‐old montane grassland on surface soil properties, N pools, and N transformations were assessed using standard and15N‐isotope pool dilution methods. Data were collected for soils on slopes and in drainage bottoms located in grassland, under 9‐ to 11‐yr‐old planted koa, and in nearby old‐growth koa‐ohia (Metrosideros polymorphaGaud.) forest. Soil under planted koa had significantly lower fine soil bulk density and pH than soil in grassland, and had concentrations of total C, total N, and extractable Mg and C/N ratio intermediate between grassland and forest. Topographic position affected pH and concentrations of total C, total N, and extractable P. Ten years after koa trees were re‐introduced to grassland, the concentration of soil NH4+–N had increased above levels found even in intact forest, and the concentration of NO3−–N was intermediate between forest and grassland. Ammonium dominated the inorganic N pools in grassland soil and NO3−dominated in forest soil. Under planted koa, NH4+domination was beginning to give way to NO3−domination. Soil microorganisms were potentially strong competitors for inorganic N on grassland slopes where they immobilized nearly all the inorganic N that was produced during short‐ and medium‐term field incubations, thus leaving little for plant growth. Re‐establishment of koa trees increased soil N availability.

Art and medicine 2: Pethidine by Dr Matthew Clark

This curvaceous carving in English lime on Pacific koa wood (16 × 6 cm) won second prize last July in the Brooke Epidemiology Art Prize, arranged jointly by the Section of Epidemiology & Public Health and the Medical Art Society. But why the title Pethidine and how did it fit with the theme of inequalities chosen for the 2003 prize? Dr Clark's commentary on the work explains: 'Earlier this year I became a father. My knowledge of childbirth before this had been rather limited. Other than a couple of mandatory deliveries during an obstetrics attachment as a student, my main experiences had come from a medical elective in Papua New Guinea. In that country, the limited medical resources are complemented by traditional 'alternative' medical beliefs. While working in Wewak General Hospital on the North coast, my wife and I were continually amazed by the tenacity and toughness of the local women giving birth. Often they had walked for days to reach the hospital, and the maternity ward was a simple wooden building kitted out with little more than unmattressed metal beds lined against one wall. Running above these, so that it was within reach, was a long metal pole. Its function became clear. It was the pain relief. The hospital had such a limited supply of drugs that pain relief for women in labour was considered frivolous. Instead, the pole was gripped tightly by way of distraction and childbirth progressed with the slightest fuss or noise. Our recent experience here in the UK showed us how different the process can be. There was a bombardment of choice—various analgesics, alternative therapies, TENS machines, aromatherapy and calming music, to name but a few. In memory of our PNG experiences, I carved Pethidine. Its shape is designed to fit comfortably into the grip of the hand, with the thumb in the curve of the back. Thus, it could perform the function of the pole from the PNG maternity ward. And when my wife, at the height of labour, screamed for the pethidine, I could turn to the midwife with a knowing smile and say that what she really wanted was my sculpture to grip'. In the event, Dr Clark did not pursue this 'tongue in cheek' pain-relieving option for his wife's labour. His real aim was to show, in this sculpture, the contrast in care between the two cultures, neatly symbolized by the use of both English and Pacific woods. The design also draws on Venus figurines and prehistoric palaeolithic carvings thought to be symbols of fertility.

Revegetation in Dead Dicranopteris (Gleicheniaceae) Fern Patches Associated with Hawaiian Rain Forests

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. linearis 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. Morton 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.

Rediscovery of Blackburnia anomala (Coleoptera: Carabidae), in East Maui, Hawai'i, after a 107-Year Hiatus

The highly distinctive and diverse native Hawaiian carabid beetle fauna includes a suite of species not recently observed in nature. These are predominantly historical residents of the mesic Acacia koa forest formation. We report rediscovery of one of these species, Blackburnia anomala (Blackburn), in the shrubland formation near Paliku Cabin, and in koa forest of Kaupo Gap. Prior records of B. anomala are limited to the leeward edges of historical koa forest near Olinda, on the northwestern slope of Haleakala. Rediscovery on the far southeastern side of Haleakala Crater in similar, though conserved, habitats suggests that other long-missing koa associates may persist in similar situations on Haleakala.

Soil Phosphorus Fractions and Symbiotic Nitrogen Fixation across a Substrate-Age Gradient in Hawaii

We evaluated soil phosphorus (P) fractions, other soil characteristics, and rates of symbiotic N2 fixation across a substrate-age gradient in Hawaii that was dominated by the leguminous tree Acacia koa (koa). Patterns of soil P observed on this gradient were compared to those on a slightly wetter gradient dominated by the nonfixer Metrosideros polymorpha (ohia). Along both gradients, concentrations of primary-mineral P fell sharply between the young and intermediate-aged sites, while labile inorganic P declined most steeply between the intermediate-aged and old sites. The most marked difference between the two gradients was that total soil carbon (C), nitrogen (N), and P, as well as nonoccluded organic P, were more variable across the ohia gradient, increasing to the intermediate-aged sites, then declining sharply at the old site. On the koa gradient, specific nitrogenase activity, measured by the acetylene-reduction (AR) assay, decreased three- to eightfold between the young site and the intermediate-aged and old sites, respectively. Nodule biomass showed no clear pattern. N2 fixation rates, estimated by combining AR activity and nodule biomass measurements, were up to 8 kg N · ha−1 · y−1 at the young site and no more than 2 kg N · ha−1 · y−1 at the older sites, suggesting that koa may be a modest source of N in these Hawaiian forests.

Dieback of Acacia koa in Hawaii: ecological and pathological characteristics of affected stands

Koa ( Acacia koa) is an endemic Hawaiian tree that serves as a keystone species in the upper elevation forests of all the main islands. In the Mauna Loa Strip area of Hawaii Volcanoes National Park, mature koa stands are suffering from an unexplained dieback that has increased in severity since it was first noticed approximately 25 years ago. The dieback is often evident in patches, and generally spreads within stands in a radial fashion from a localized infection center. Entire crowns of affected trees become wilted, with foliage gradually progressing from an apparent healthy to a completely chlorotic condition. Although most trees die soon after the onset of symptoms, some trees are able to survive crown death by producing epicormic shoots on the lower portions of the trunk. Previously published studies reported that a vascular wilt fungus ( Fusarium oxysporum f. sp. koae) was associated with koa seeds and the rhizosphere of healthy and dieback-affected koa stands. The purpose of this study was to characterize the stand structure, soil conditions, and physiological condition of dieback-affected trees, and to assess the possible role of F. oxysporum f. sp. koae in the current dieback stands. This fungus was isolated from branches of symptomatic koa in dieback-affected stands and roots from healthy and dieback-affected stands. Possible differences in the pathogenicity and virulence of F. oxysporum f. sp. koae isolates obtained from the roots of healthy koa in unaffected stands and those from branches of dieback-affected koa were determined by greenhouse inoculations of koa seedlings. Healthy koa saplings in stands unaffected by dieback were also inoculated to determine if disease symptoms could be induced by inoculation of injured roots in the field. Both branch and root isolates were pathogenic; with the percent mortality of inoculated seedlings ranging from 30 to 60% for all isolates. Disease severity between branch and root isolates was not significantly different. Wilt symptoms were not observed in field inoculations of koa saplings after 8 months. Investigation of the dieback stand structure determined that the larger size classes (i.e., DBH>3 cm ) were all affected equally, with the smallest size class (i.e., 0–3 cm DBH) having the lowest percentage of dieback at each site. Soil from dieback stands had higher water content and was more acidic than that from neighboring unaffected stands. Phyllodes on epicormic shoots of dieback trees had a reduced area, mass, and mass to area ratio. Phyllodes on dieback trees also had reduced stomatal conductance and higher (less negative) leaf water potential. Results from the greenhouse inoculations demonstrated that F. oxysporum f. sp. koae is pathogenic to koa, but the pathogen’s activity in the field may be influenced by predisposing factors such as temperature fluctuations, water availability, soil type, and interactions with other soil organisms. F. oxysporum f. sp. koae appears to play an important role in regulating koa stand dynamics, growth, and physiology under environmental and edaphic conditions favorable for disease development.

STAND DYNAMICS, NITROGEN ACCUMULATION, AND SYMBIOTIC NITROGEN FIXATION IN REGENERATING STANDS OFACACIA KOA

Recently, abandonment of montane cattle pastures in Hawaii has stimulated interest in forest restoration both for expansion of habitat for native species and for plan- tation forestry. Acacia koa is one of the most common forest trees in Hawaii, the most abundant native legume, and the most economically valuable native tree; it could be im- portant to restoration efforts in many areas. Using an age sequence of even-aged, 6- to 20-yr-old stands of A. koa, we evaluated stand characteristics, N accumulation, and rates of N fixation. Average diameter at breast height (dbh) and height increased linearly during the first 20 yr of tree growth, while stem density, dbh increment, and leaf area index declined. An experimental thinning in the 9- yr-old stand more than doubled dbh increment, suggesting that high tree densities could constrain tree growth. In contrast, N fertilization did not affect dbh increment. Nodule biomass was more than an order of magnitude less in the 20-yr-old stand than in the 6-yr- old stand, which corresponded to a similar decline in estimated input of N via fixation. Neither thinning nor N fertilization affected nodule biomass, but measurements of foliar and root phosphorus (P) suggest that a decline in P availability over time may have con- tributed to the decline in N fixation. In these stands, large amounts of decomposing litter remaining from stand establishment may have provided much of the N that accumulated in koa biomass. In more degraded sites, N fixation by A. koa may play a relatively more important role in restoration and in soil and ecosystem development.

Productivity, resource use, and competitive interactions of Fraxinus uhdei in Hawaii uplands

We examined stand growth, canopy development, and resource use of Fraxinus uhdei (Wenzig) Lingelsh, a nonindigenous tree grown in Hawaii, and its interactions with the native, N-fixing tree Acacia koa Gray. Along a gradient of decreasing rainfall with elevation, on Histosols, F. uhdei had decreased stand basal area, productivity, and canopy development. At high-elevation sites, productivity of F. uhdei was limited by N, and F. uhdei benefitted from association with A. koa, as (i) foliar N content of F. uhdei was positively related to aboveground net primary productivity (ANPP), (ii) leaf area index, biomass increment, and ANPP of F. uhdei increased in a single-species stand after N additions, but there was no response by either F. uhdei or A. koa in a mixed stand, and (iii) productivity of F. uhdei in mixed stands with A. koa at high-elevation sites was greater than in single-species stands, and F. uhdei foliage was enriched with N in proportion to the fraction of stand basal area in A. koa. Seemingly, growth of F. uhdei on Histosols was also limited by water availability, as an index of carbon isotope composition of leaves (δ13C), and, therefore, intrinsic water-use efficiency (WUE) increased with elevation. Biomass production of F. uhdei stands per unit leaf area and per unit intercepted radiation (ε) decreased with increasing elevation on Histosols. Decreased nitrogen-use efficiency and ε of F. uhdei on Histosols were both traded off against increased WUE.

Genetic Differentiation of Intrinsic Water‐Use Efficiency in the Hawaiian Native Acacia koa

We examined genetic differentiation of intrinsic water‐use efficiency (WUE) and the relationship between WUE and phyllode morphological and nutritional traits in the native Hawaiian tree koa (Acacia koa Gray, Fabaceae). We obtained both integrated (stable isotope 13C composition of phyllode tissues; δ13C) and instantaneous (assimilation/stomatal conductance to water vapor; A/g) estimates of WUE on koa accessions grown in a progeny trial at Maunawili on the island of O`ahu. The accessions were from sites along an elevation (900–1300 m) and rainfall (ca. 2200–1300 mm) gradient on the southwestern slopes of Mauna Loa on the island of Hawai`i. The δ13C values of koa phyllodes at Maunawili ranged between −28‰ and −31‰ and were positively related to elevation of the seed source. Among seed sources grown at the common site, phyllode δ13C varied with similar magnitude and direction to that associated with the field populations, indicating genetic differentiation of WUE in koa. Instantaneous measurements of WUE showed similar trends of increasing WUE with elevation of the seed source. Phyllode δ13C was not correlated with foliar concentrations of nitrogen (N), indicating that differences in δ13C were not caused by nutrient‐related changes in photosynthetic capacity but rather by stomatal limitation. Phyllode morphological traits such as specific leaf mass (SLM), length, and area were unrelated to δ13C. The similarity between the slopes of SLM and phyllode N content at Maunawili and Honaunau supported the contention that there is global interdependence between these two traits. The finding of genetic differentiation of WUE in koa is important for native forest restoration and seed selection.

Moderating Night Radiative Cooling Reduces Frost Damage to Metrosideros polymorpha Seedlings Used for Forest Restoration in Hawaii

AbstractWinter frosts caused by radiative cooling were hypothesized to limit successful reintroduction of Hawaiian plants other than Acacia koa to alien‐dominated grasslands above 1700 m elevation. We determined, in the laboratory, the temperature at which irreversible tissue damage occurred to Metrosideros polymorpha leaves. We also conducted a field study of this species to determine if (1) leaf damage was correlated with sub‐zero leaf temperatures, (2) radiative cooling could be moderated by canopies of A. koa, and (3) low soil temperatures contributed to seedling damage. The last was evaluated by thermally buffering seedlings with water‐filled bladders placed at their base to keep roots warm, or by installing a radiation shield to reduce early morning transpiration when water uptake from cold soils would be least. Leaf temperatures were monitored between midnight and 7:00 a.m. using fine‐wire thermocouples, and leaf damage was recorded monthly. In the laboratory, supercooling protected leaves from mild sub‐zero temperatures; irreversible tissue damage occurred at about −8°C. In the field, leaf damage was strongly correlated with degree‐hours below freezing. Unprotected seedlings suffered the greatest leaf damage. Those sheltered under A. koa trees rarely experienced temperatures below −3°C, and damage was minimal. Shaded and thermally buffered seedlings suffered less damage than unprotected plants, probably due to elevated leaf temperatures rather than improved water relations. Using A. koa or artificial devices to reduce radiative cooling during winter nights should enhance establishment of M. polymorpha in high‐elevation rangeland.

Water supply regulates structure, productivity, and water use efficiency of Acacia koa forest in Hawaii.

We studied changes in stand structure, productivity, canopy development, growth efficiency, and intrinsic water use efficiency (WUE=photosynthesis/stomatal conductance) of the native tree koa (Acacia koa) across a gradient of decreasing rainfall (2600-700 mm) with increasing elevation (700-2000 m) on the island of Hawaii. The stands were located on organic soils on either smooth (pahoehoe) or rough (aa) lava flows. In the greenhouse, we also examined growth and WUE responses to different water regimes of koa seedlings grown from seeds collected in the study area. We tested the hypotheses that (1) stand basal area, aboveground net primary productivity (ANPP), leaf area index (LAI), and growth per unit leaf area decreased with decreasing rainfall, (2) WUE increased with decreasing rainfall or water supply, and (3) WUE responses were caused by stomatal limitation rather than by nutrient limitations to photosynthesis. The carbon isotope composition of phyllode tissues (δ13C) was examined as an integrated measure of WUE. Basal area and LAI of koa stands on both pahoehoe and aa lava flows, and ANPP on aa lava flows decreased with elevation. Basal area, LAI, and ANPP of koa in mixed stands with the exotic tropical ash (Fraxinus udhei) were lower compared to single-species koa stands at similar elevations. Along the gradient, phyllode δ13C (and therefore WUE) increased with elevation from -30.2 to -26.8‰. Koa in mixed stands exhibited higher (less negative) δ13C than in single-species stands suggesting that koa and tropical ash competed for water. In the greenhouse, we observed the same trend observed in the field, as phyllode δ13C increased from -27.7 to -24‰ as water supply decreased. Instantaneous gas exchange measurements in the greenhouse showed an inverse correlation of both maximum (morning) photosynthesis (A) and conductance (g) with δ13C values and, also, a good agreement between instantaneous (A/g) and integrated measures of WUE. Phyllode δ13C was not correlated with foliar concentrations of N or other nutrients in either the field or the greenhouse, indicating that differences in δ13C were caused by stomatal limitation rather than by nutrient-related changes in photosynthetic capacity. This study provided evidence that long-term structural and growth adjustments as well as changes in WUE are important mechanisms of koa response to water limitation.

Genetic Variation in Morphology and Growth Characters of Acacia koa in the Hawaiian Islands

Substantial phenotypic variation in Acacia koa has been reported in the Hawaiian Islands. We grew 72 A. koa families from the islands of O`ahu, Kaua`i, and Hawai`i in two common gardens to determine whether phenotypic differences in phyllode morphology, extrafloral nectary morphology, and other characters have a genetic basis. Significant differences among islands and families were observed for phyllode width, curvature, and pubescence, as well as extrafloral nectary size and pigmentation, retention of juvenile leaves, and branch bark color. Seed shape also differed significantly among islands. Discriminant analysis revealed that families from the island of Hawai`i are distinct from O`ahu and Kaua`i families. The O`ahu and Kaua`i families, however, could not be reliably distinguished based on sapling morphology or growth characters.

A Late-Quaternary Pollen Record from Ka‘au Crater, O‘ahu, Hawai‘i

A pollen record from Ka‘au Crater, O‘ahu, Hawai‘i contains evidence for changes in vegetation and climate since about 28,000 14C yr B.P. Zone 1 (ca. 28,100–ca. 22,800 14C yr B.P.) has pollen of dry to mesic forest species, including Pipturus-type, Dodonaea viscosa, Acacia koa, Chenopodium oahuense, Claoxylon sandwicense, Myrsine, and Metrosideros-type. In zone 2 (ca. 22,800–ca. 16,200 14C yr B.P.) Myrsine and Coprosma increase, with herbs, fern allies, and Grammitidaceae suggesting open canopies. Zone 3 (ca. 16,200–ca. 9700 14C yr B.P.) has pollen of wet forest species, including Freycinetia arborea, abundant Pritchardia, and Metrosideros-type. Zone 4 (ca. 9700–ca. 7000 14C yr B.P.) is similar, with less Pritchardia and more Metrosideros-type. Climate reconstruction was based on modern climatic ranges of flowering plants and an index derived from abundance of pollen in surface samples. Both methods agree on a qualitative reconstruction, although the ages are poorly constrained: 28,000–25,000 14C yr B.P. cool and dry; 25,000–23,000 14C yr B.P. dry and warmer; 23,000–20,000 14C yr B.P. moderately dry with declining temperature; 20,000–16,000 14C yr B.P. moderately dry and cool; 16,000–9000 14C yr B.P. warm and wet; 9000–7000 14C yr B.P. warm and possibly drier. Lower precipitation at Ka‘au Crater during the late glacial period and last glacial maximum is consistent with the interpretation that the North Pacific subtropical anticyclone was south of its present position. The pollen-derived temperature index yields an estimate of 3°–5°C temperature depression during the last glacial maximum.

673 Resistance and Resilience of Native Forests to Disturbance by Hurricane Iniki

Two studies were established in upland native forest of northwestern Kauai before Hurricane Iniki (Sept. 1992). One study was a gradient study in Acacia koa forest in the leeward rain shadow and the second study was a replicated fertilization experiment in mesic Metrosideros polymorpha forest. Both studies escaped devastation by high-intensity microbursts. Removal of LAI (from 3% to 80%) was proportional to pre-hurricane LAI, suggesting that resistance to damage was higher in low LAI, low-productivity sites. LAI recovered to prehurricane levels within 2 years, except in plots with major limb and stem loss. In the Acacia forest, damage to overstory trees was less than to understory trees, whereas in Metrosideros forest, larger trees were more damaged than smaller trees. During 2 years of recovery, both forests lost LAI in winter storms nearly equivalent to the hurricane damage. Disturbance is more frequent than previously known, which suggests that chronic disturbance needs to be better understood as a force regulating ecosystem structure and function. In both studies, the relative rate of recovery was faster in the more productive but more disturbed plots, suggesting that ecosystem resistance and resilience were traded off. These results have application to land use planning, agroforestry systems management, and other perennial crop management decisions following damage by a tropical cyclone.

Potential significance of frost, topographic relief, and Acacia koa stands to restoration of mesic Hawaiian forests on abandoned rangeland

Beginning in the 1850 s, logging, land clearing, and burning were used to convert high elevation Hawaiian forests to cattle pasture. Recently, declining profits from ranching, the need to expand habitat for endangered species, and diminishing supplies of native saw-timber have prompted interest in restoring native forests. The Forest Service, in cooperation with the Fish and Wildlife Service, is studying climatic, edaphic, and biotic limitations in the reforestation of grassland and savanna in the Hakalau Forest National Wildlife Refuge, island of Hawaii. Frost damage has been implicated in poor survival of Acacia koa, a dominant native nitrogen fixing tree, and other endemic plants. Data showed that for some years freezing temperatures were common above 1800 m elevation, and that A. koa seedling survival was poorest on micro-topographic sites where freezing temperatures were lowest and most prolonged. Artificial frost protection devices enhanced A. koa seedling survival, presumably by reducing radiative cooling. A similar reduction in radiative cooling was observed under a stand of 4 m tall A. koa. Such stands also changed soil chemical properties, making them intermediate between those of grassland and forest. Light levels near the ground under A. koa were similar to those found in forests, but not as low as those found under pasture grasses. Biomass and nutrient pools of the litter-herbaceous layer were affected by micro-topographic position in the landscape and by the presence of stands of A. koa. Using A. koa as a nurse crop may create understory conditions favorable for the establishment of other plant components of a mixed-species forest.

Leaf area allometry and evaluation of non-destructive estimates of total leaf area and loss by browsing in a silvopastoral system

Tree growth and competition with other vegetation are strongly affected by leaf area, which can be modified by livestock browsing in silvopastoral systems. We studied the relationship of leaf area to stem diameter and sapwood area of koa (Acacia koa), a valuable hardwood tree species native to Hawaii. Because browsing alters allometric relationships, we compared harvest data with two non-destructive optical techniques (LAI-2000 canopy analyzer and photographic estimation of projected crown area). Destructive harvests of 30 trees showed that leaf area was equally well correlated with the diameter at breast height (dbh) or sapwood area of trees ranging from 2 to 16 cm in diameter, 1.3 m above ground level. Both optical techniques correlated with the leaf areas obtained by destructive analysis, but the photographic estimation of projected crown area provided more reliable estimates than the canopy analyzer. The photographic method based on projected crown area provided reliable estimates of leaf area removal within the browse zone (less than 2 m height). this method provides a simple, low-cost means of obtaining non-destructive estimates of changes in leaf area in isolated trees.

Impact of Hurricane Iniki on native Hawaiian Acacia koa forests: damage and two-year recovery

ABSTRACTDamage to Hawaiian Acacia koa forest by Hurricane Iniki was assessed by comparison with our previous measures of stand structure and leaf area index (LAI) at sites along a precipitation/elevation gradient on western Kauai. Reductions in LAI ranged from 29 to 80% and were correlated with pre-hurricane LAI and canopy height. The canopy damage resulted in a large pulse of litter, ranging from 4 to 19 t ha-1 across our study sites. In the first year post-hurricane, LAI recovery and relative increase in stand basal area were negatively correlated with the fraction of canopy LAI lost. The two major overstorey species, A. koa and Metrosiderous polymorpha, were damaged less than the sub-canopy species, Dodonaea viscosa and Psidium guajava. Although D. viscosa and P. guajava were both severely damaged in the hurricane, the alien species P. guajava had much higher survival than the native D. viscosa, both as adults and as seedlings. However, seedling density of P. guajava was limited by low recruitment. At these sites, there was no drastic change in species composition following hurricane disturbance, and forest structure and productivity had recovered to a great degree within 2 y.

Coexistence and Community Structure of Tropical Trees in a Hawaiian Montane Rain Forest

We measured the diameter at breast height of all trees and shrubs 25 meters in height, including standing dead trees, on 68 0.04-hectare study plots in a montane, subtropical rain forest on Mauna Loa, Hawai'i. The canopy species consisted of 88 percent Metrosideros polymorpha (ohia) and 12 percent Acacia koa (koa). Negative associations were found between the densities of koa and ohia, the density of koa and the total basal area of ohia, and the total basal areas of koa and ohia. The two-species lottery competition model, a stochastic model in which the coexistence of two species in a space-limited community results from temporal variation in recruitment and death rates, predicts a quadratic-beta distribution for the proportion of space occupied by each species. A discrete version of the quadraticbeta distribution, the quadratic-beta binomial distribution, was fit to the live koa and ohia densities and assessed with goodness-of-fit tests. Likelihood ratio tests provided evidence that the mean adult death rates of the two species were equal but that the relative competitive abilities of the two species favored ohia. These tests were corroborated by a contingency table analysis of death rates based on standing dead trees and growth rate studies which report that koa grows much faster than ohia. The lottery model predicts a positive covariance between death rates and ohia recruitment when mean death rates are equal and koa has a higher growth rate than ohia. We argue that the competitive advantage of ohia is due to its superior dispersal ability into large gaps, which would yield the positive covariance described above, and it is this positive covariance term that skews the occupation of space in favor of ohia.

Distribution of Bradyrhizobium spp. and Endemic Leguminous Tree Acacia Koa Along an Altitudinal Transect on the Windward Slope of Haleakala, Maui, Hawaii

Distribution of Bradyrhizobium spp. and Endemic Leguminous Tree Acacia Koa Along an Altitudinal Transect on the Windward Slope of Haleakala, Maui, Hawaii

A New Hawaiian Hanging Firmoss (Lycopodiaceae: Phlegmariurus) from the Eastern Hawaiian Islands

A New Hawaiian Hanging Firmoss (Lycopodiaceae: Phlegmariurus) from the Eastern Hawaiian Islands