Search

An atmospheric correction algorithm has been developed for the Airborne Imaging Spectrometer for Applications AISA imagery over optically shallow waters in Sugarloaf Key of the Florida Keys. The AISA data were collected repeatedly during several days in May 2012, October 2012, and May 2013. Non-zero near-infrared NIR remote-sensing reflectance Rrs was accounted for through iterations, based on the relationship of field-measured Rrs between the NIR and red wavelengths. Validation showed mean ratios of 0.94–1.002 between AISA-retrieved and in situ Rrs in the blue to red wavelengths, with uncertainties generally

(1) Dalhousie University, Halifax, NS, Canada, (9) LDEO, Columbia University, New York, NY, United States, (2) U.S. Geological Survey, St. Petersburg, FL, United States, (3) College of Marine Science, University of South Florida, St. Petersburg, FL, United States, (4) Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL, United States, (5) NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, United States, (6) Marine Sciences, The University of Trinidad and Tobago, Trinidad and Tobago, (7) National Commission for Knowledge and Use of Biodiversity (CONABIO), Mexico, (8) UAV Collaborative, Moffett Field, CA, United States

An Airborne Imaging Spectrometer for Applications (AISA) hyperspectral imager was deployed on a manned aircraft flown at 1305-m altitude to collect data over optically shallow waters in the Florida Keys with the ultimate goal of mapping water quality and benthic habitats. As a first step, we developed a practical atmospheric correction (AC) approach to derive surface remote-sensing reflectance ( ${{\bm{R}}_{{\bm{rs}}}}$ ) from AISA measurements using radiative transfer simulations and constraints obtained from field spectral ${{\bm{R}}_{{\bm{rs}}}}$ measurements. Unlike previously published method, the AC approach removes the surface Fresnel reflection and accounts for aircraft altitude and nonzero near-infrared (NIR) reflectance through iteration over the pre-established look-up tables (LUTs) based on MODTRAN calculations. Simulations and comparison with concurrent in situ ${{\bm{R}}_{{\bm{rs}}}}$ measurements show the feasibility of the approach in deriving surface ${{\bm{R}}_{{\bm{rs}}}}$ with acceptable uncertainties. The possibility of errors in the radiometric calibration of AISA is demonstrated, although a definitive assessment cannot be made due to lack of enough concurrent in situ measurements. The need for noise reduction and the difficulty in carrying out a vicarious calibration are also discussed to help advance the design of future AISA missions.

Light availability is an important factor driving primary productivity in benthic ecosystems, but in situ and remote sensing measurements of light quality are limited for coral reefs and seagrass beds. We evaluated the productivity responses of a patch reef and a seagrass site in the Lower Florida Keys to ambient light availability and spectral quality. In situ optical properties were characterized utilizing moored and water column bio-optical and hydrographic measurements. Net ecosystem productivity (NEP) was also estimated for these study sites using benthic productivity chambers. Our results show higher spectral light attenuation and absorption, and lower irradiance during low tide in the patch reef, tracking the influx of materials from shallower coastal areas. In contrast, the intrusion of clearer surface Atlantic Ocean water caused lower values of spectral attenuation and absorption, and higher irradiance in the patch reef during high tide. Storms during the studied period, with winds >10 m·s−1, caused higher spectral attenuation values. A spatial gradient of NEP was observed, from high productivity in the shallow seagrass area, to lower productivity in deeper patch reefs. The highest daytime NEP was observed in the seagrass, with values of almost 0.4 g·O2·m−2·h−1. Productivity at the patch reef area was lower in May than during October 2012 (mean = 0.137 and 0.177 g·O2·m−2·h−1, respectively). Higher photosynthetic active radiation (PAR) levels measured above water and lower light attenuation in the red region of the visible spectrum (~666 to ~699 nm) had a positive correlation with NEP. Our results indicate that changes in light availability and quality by suspended or resuspended particles limit benthic productivity in the Florida Keys.

The purpose of the study was to: (1) test if normative bark water storage capacities differed significantly among three co-occurring deciduous tree species; and (2) examine the extent to which stemflow production and resulting solute inputs in temperate deciduous forests are affected by bark water storage capacity. Normative bark water storage capacities were determined for: Betula lenta L. (sweet birch), Carya glabra Mill. (pignut hickory), and Quercus rubra L. (northern red oak). Using the computed normative bark water storage capacities, previously published allometric equations relating tree diameter to aboveground woody surface area, and stemflow yield and chemistry data from ten precipitation events, the influence of bark water storage capacity on stemflow production and solute inputs was examined. Results demonstrated normative bark water storage capacities differed significantly among the tree species examined. Quercus rubra was found to hold the most water and B. lenta the least. For a 30 cm diameter tree, normative bark water storage capacities ranged from approximately 100 l for B. lenta to 250 l for Q. rubra. Despite a higher normative bark water storage capacity, Q. rubra was computed to have the largest stemflow solute inputs. Differences in stemflow quantities as well as solute inputs were attributable to interspecific variation in bark morphology and branching architecture, characteristics that affect amount of storage and detention times. Bark water storage capacity is linked with the geoecology of temperate deciduous forests because stemflow volume and solute inputs are partly determined by bark water storage capacity.

Summary Leaf transpiration rates of Impatiens capensis were measured beneath a broadleaved deciduous forest canopy over successive growing seasons using a steady-state porometer. The transpiration measurements, which continued into early autumn, provided a framework for assessing whether I. capensis exhibits stomatal opening in response to the autumnal increase in available direct-beam radiation reaching the forest floor. The deciduous canopy LAI (leaf area index) decreased from a growing season maximum of 3.94 m 2 m −2 , while the understory I. capensis population located along a stream channel maintained LAI values ranging from 0.58 to 1.05 m 2 m −2 late into the growing season. Late morning and early afternoon leaf transpiration rates during the months of June and July averaged about 8 μg cm −2 s −1 , with a mean stomatal conductance of 0.5 cm s −1 . In August, leaf transpiration averaged almost 12 μg cm −2 s −1 , with stomatal conductance exceeding 1.5 cm s −1 . However, beginning in early to mid-September, before canopy leaf-fall, the persistent green leaves of I. capensis exhibited a sharp decline in transpiration, possibly a result of decreasing vapor pressure deficits or non-lethal physiological damage induced by cold stress. This physiological decline offsets any advantage that could have been gained by the increased exposure to direct-beam radiation after canopy leaf-fall in mid-October. Although green leaf area and seed-bearing capsules may persist until the first frost in October or early November, there is no evidence of stomatal opening suggestive of carbon assimilation for enhanced seed development during this early autumn period. We conclude that the persistent green leaf area of I. capensis fails to exploit the increase in available direct-beam radiation in the final stage of its life cycle.

Multispectral images were collected by an unmanned aerial vehicle over a commercial coffee plantation during the 2002 harvest season. Selected scenes were georegistered to a base map and a mosaic of the study area was created. Image segmentation was performed to identify and mask soil, shadow, and cloud pixels. The remaining pixels, representing sunlit canopy, were assumed to be a mixture of four components: green leaf, underripe fruit, ripe fruit, and overripe fruit. Field and laboratory instruments were used to measure the reflectance spectrum of each component. Based on these spectra, a ripeness index was developed for the airborne imagery that involved computing the per-pixel ratio of digital counts in spectral channels centered at 580 and 660 nm. Results were aggregated on a per-field basis. Mean ripeness index per field was significantly correlated with ground-based counts recorded by the grower, and to eventual harvest date. The results suggest that remote sensing methods may provide an alternative, more spatially comprehensive method for monitoring ripeness status and evaluating harvest readiness of this high-value agricultural commodity.

Stemflow leachate chemistry from a deciduous canopy tree species monitored during late winter and early spring precipitation events demonstrated significant chemical enrichment. By considering stemflow volume and chemical concentration in relation to the quantity that would be expected in a rain gage occupying an area equivalent to the trunk basal area, manganese was found to be enriched by a mean factor of 1450 and potassium by a mean factor of 580. The most pronounced enrichment was documented during a late winter rain-on-snow event characterized by temperature oscillations near the freezing point. During this event, manganese was enriched by a factor of 4400 and potassium by 1715. We conclude that mixed precipitation events with multiple freeze-melt cycles can generate significantly more leachate than spring rainfall events because of lower air temperatures and increased kinematic viscosity and surface tension of stemflow drainage. These physical properties lengthen the residence time of intercepted precipitation on the woody frame of the tree and promote its funneling from inclined branches. Stemflow represents a spatially localized and enriched point input that may affect tree vigor in early spring. The influence of localized aqueous chemical fluxes to the forest floor on forest biogeochemistry and ecophysiological functioning are discussed.

Lateral shading of direct-beam irradiation among neighboring canopy tree crowns in a nonequatorial tropical rain forest canopy was modeled as a function of solar position using a photogrammetric database derived from large-scale color aerial stereopairs (1:1500–1:3000 scale) acquired in 1976. The interception of direct-beam irradiation by the orthogonally projected crown area of each tree was computed at hourly intervals over a full calendar year using a Parameterization model of cloud-attenuated direct-beam availability. The annual totals of intercepted direct-beam irradiation (Ib) ranged from 1.81 to 4.13 GJ·m−2·yr−1. Expressed as a percentage of the available incident direct-beam irradiation, these values ranged from 44% to 100%. Approximately 20% of the sample population intercepted

Past controlled growth experiments indicate that the seedling and sapling responses of the tropical rainforest canopy tree species Toona ciliata are most consistent with a light-demanding, early successional pioneer. This ecological niche assignment was tested in the mature stage of its life cycle after it achieves a position in the upper canopy. Mortality, survivorship and crown growth rates over the 18-y period 1976–1994 were measured using co-registered repeat airborne stereophotographic coverage of a representative forest stand in northeast Queensland, Australia, where T. ciliata had the fourth highest relative importance in a population of 46 co-occurring canopy tree species. The airborne re-inventory was conducted in a 3.6-ha sample area and limited to only canopy trees. The results were compared with a ground-based inventory of both canopy and subcanopy trees ≥10 cm dbh in a 0.5-ha permanent plot. Over the period 1976–1994, there was no mortality and no evidence of decline among T. ciliata conspecifics having crown areas >60 m2 and trunk diameters >30 cm. In the 3.6-ha airborne sample area, more than 85% of T. ciliata survivors experienced positive crown growth, in contrast to only 57% of the other co-occurring canopy trees. Toona ciliata's crown growth rates were highest in the 60–80-m2 crown size class. Upon reaching an upper canopy position, T. ciliata not only persisted as a dominant canopy tree species, but it also achieved some of the largest crown areas (>100 m2). Toona ciliata mortality in the ground-based plot involved mainly subcanopy trees of 10 – 30 cm dbh that had not yet assumed a canopy position and were not detectable in the aerial stereopairs. Both the crown and dbh growth rates of T. ciliata indicate enhanced vigour in the later stage of its life cycle. Its long-term survivorship and growth patterns are indicative of a persistent canopy tree species that fits the niche of a long-lived, shade-intolerant pioneer. These results demonstrate the usefulness of a long-term airborne database on the life-histories of canopy tree crowns for more clearly defining their ecological niches.

Under winter conditions, stemflow drainage in forested ecosystems is often assumed to be a negligible component of the hydrological cycle. This paper reports on mid-winter stemflow drainage from the broadleaved deciduous tree species Populus grandidentata. Stemflow volumes from this species at air temperatures of

Red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the Quaternary carbonate formations of the Bermuda oceanic island system. These paleosols provide a basis for reconstructing Quaternary atmospheric circulation patterns in the northwestern Atlantic. Geochemical analyses were performed on representative paleosol samples to identify their parent dust source. Fine-grained fractions were analyzed by energy-dispersive X ray fluorescence to determine trace element (Zr, Y, La, Ti, and Nb) concentrations and to derive geochemical signatures based on immobile element ratios. These ratios were compared with geochemical signatures determined for three possible sources of airborne dust: (1) Great Plains loess, (2) Mississippi River Valley loess, and (3) Saharan dust. The Zr/Y and Zr/La ratios provided the clearest distinction between the hypothesized dust sources. The low ratios in the paleosol B horizons most closely resemble Saharan dust in the

The commercial development that threatens the biodiversity of coastal habitats is particularly severe along the sandy shores of subtropical Florida. The objective of our study was to test the applicability of the equilibrium theory of island biogeography to Cayo-Costa Island, the largest protected barrier island remaining in peninsular Florida. Our null hypothesis was that there would be no change in the number and composition of native vascular plant species on Cayo-Costa 15 years after the first inventory of the island's flora. Our reinventory documents a total of 230 native species in 1990-92 compared to 255 native species in 1975-77. Immigrants were represented by twenty-eight new species, while extinctions totalled fifty-three species. These results indicate a turnover rate of approximately 2.7 species yr -1 with an extinction rate of 3.5 species yr -1 and an immigration rate of 1.9 species yr -1 . The net loss of 1.6 species yr -1 suggests a non-equilibrium condition that is not readily explained by changes in habitat diversity associated with the documented patterns of shoreline erosion and deposition. Cayo-Costa's net loss of twenty-five native species (including one tree species and four shrub species) was localized mainly in those habitats where there had been a significant increase in the relative abundance of the naturalized weedy exotic species Schinus terebinthifolius and Casuarina equisetifolia. We conclude that the spread of naturalized weedy species limits the applicability of the equilibrium theory of island biogeography to species-rich subtropical barrier islands, even in cases where the islands are protected from human disturbance.

Science is often viewed by elementary school teachers as a fixed body of information. Using recently acquired planetary imagery from the Voyager spacecraft mission to the outer planets of our solar system, a university—elementary school collaboration implemented an inquiry approach that promoted active student participation. Formulating research questions in an exploratory context provided all participants with a sense of scientific community. This article documents the power of child-constructed inquiry through discovery and dialogue, and highlights its influence on the participating teachers. The results of the collaboration may serve as a model for city-based universities seeking to have a constructive effect on science teaching and learning in neighboring public schools. © 1996 John Wiley & Sons, Inc.

Many of the natural forested ecosystems that still remain in mainland China are being cleared with potentially detrimental effects on woody plant species diversity on both local and regional scales. The most extensive stand of subtropical broad-leaved forest remaining in China is located in Yunnan Province. In an effort to document the influence of human-induced disturbance on Yunnan's woody flora, floristic inventories were conducted in a stand of primary forest and in regrowth stands located in its interior and along its outer margin in the Xujiaba Nature Sanctuary in the Ailao Mountain Range. Of particular interest was the location of the disturbance relative to the primary forest source area. A total of 134 woody plant species representing 74 genera and 43 families were recorded. The floristics of the two regrowth stands were significantly different from each other, with 40% were still non-co-occurring. The principal families represented in the primary forest and the interior regrowth stand were Aquifoliaceae, Berberidaceae, Fagaceae, Lauraceae, Rosaceae, Smilacaceae, Symplocaceae, Theaceae, and Vacciniaceae. The three dominant species with relative importance values ranging from > 5% to 18% in both the primary forest and the interior regrowth stand were Castanopsis wattii, Lithocarpus jingdongensis, and Symplocos sumuntia. The edge regrowth stands had the lowest species diversity and were dominated by the native pine Pinus yunnanensis, with a relative importance of 24%. The principal families represented in the edge regrowth stand were Betulaceae, Ericaceae, Fagaceae, Myricaceae, Pinaceae, and Theaceae. Only the Fagaceae and Theaceae were well-represented in all three stands. The results of the study document the low species diversity in post-cutting regrowth on the margins of the primary forest as compared with post-cutting regrowth in the forest interior.

Field measurement of interception loss from rainforest vegetation in the cyclone-prone tropics is complicated by high wind speeds that cause incident rainfall to be inclined from vertical fall paths. Given the characteristic roughness of tropical rainforest canopies, we hypothesized that the more prominent canopy tree crowns create lateral rainshadows and intercept greater volumes of rainwater per unit projected crown area than less prominent neighboring canopy trees under inclined rainfall conditions. This hypothesis was tested by: (1) modeling the three-dimensional (3-D) geometry of a tropical rainforest canopy surface in northeast Queensland, Australia, using photogrammetrically derived crown elevation data; (2) computing the inclination angles and azimuths of wind-driven rainfall for raindays on which net rainfall was measured from selected canopy trees; (3) creating and applying a ray-tracing program to the 3-D canopy model to quantify lateral rainshadows and the effective rainfall-intercepting crown areas of the selected canopy trees; (4) calculating the C e C index (effective rainfall-intercepting crown area/projected crown area ratio) of each tree; (5) analyzing the relationship between the C e C index values and the measured net rainfall totals after correcting for differences in the trees' interception storage capacities. A significant correlation (P

[1] The origin of terra rossa, red or reddish-brown, clay-rich soils overlying high-purity carbonate substrates, has intrigued geologists and pedologists for decades. Terra rossa soils can form from accumulation of insoluble residues during dissolution of the host limestones, addition of volcanic ash, or addition of externally derived, long-range-transported (LRT) aeolian particles. We studied soils and paleosols on high-purity, carbonate aeolianites of Quaternary age on Bermuda, where terra rossa origins have been debated for more than a century. Potential soil parent materials on this island include sand-sized fragments of local volcanic bedrock, the LRT, fine-grained (

The long-term studies of water and chemical budgets in the Hubbard Brook watershed, White Mountains, New Hampshire, have assumed that the underlying bedrock is watertight and that all of the liquid water discharged from the experimental subcatchment areas was measured using stream gauging instrumentation. This paper reviews the evidence used by past workers to support this assumption. In a reanalysis of the reported relationship between precipitation inputs and stream outputs of chloride, the mean annual groundwater discharge beneath the stream gauging stations was computed to be at least 5–10% of the mean annual precipitation. Groundwater discharge of this quantity would change both the evapotranspiration and the rock-weathering rates reported for the Hubbard Brook watershed. On-site hydrogeological field tests are recommended in all watersheds that are assumed to be underlain by watertight bedrock. [Key words: forested ecosystems, groundwater hydrology, bedrock fractures, water budgets, evapotranspirati...

Soil-filled pipes consisting of calcite casings were found in all of the eolianite formations of Bermuda except the Rocky Bay Formation. The pipes are cylindrical in shape, taper vertically downwards, and occur in aggregated clusters. They are most commonly exposed in areas of shoreline erosion in the form of soil-filled cylindrical rims of calcite projecting up from the surrounding host eolianite. In the early literature on the geology of Bermuda, it was suggested that these features were fossilized stumps of the Bermuda palmetto tree Sabal bermudiana. In the study presented here, this hypothesis is rejected on the basis of the morphology and stratigraphic position of these geomorphic features and their basal area and areal density compared with existing natural stands of S. bermudiana. The soil-filled pipes of Bermuda, however, cannot be simply explained as random solutional features that correspond to points where percolating soil water happened to converge and cause localized subsurface dissolution. In situ measurements of stemflow from indigenous tree species suggest that the soil-filled solution pipes of Bermuda may be the product of stemflow drainage from particular tree species. Stemflow from S. bermudiana was the most acidic, with pH values as low as 4.29 compared to the gross rainfall in the open, which had a pH of 5.58. The crowns of the Bermuda cedar (Juniperus bermudiana) and the subtropical tree species Eugenia axillaris had the most significant funnelling effect. Stemflow volumes from individual trees representing these two species were 20 times greater than the volume of water that would have been collected in rain gauges with orifice areas equivalent to the trees' trunk basal areas. Tree species capable of acidifying intercepted rainwater and funnelling large quantities down their trunks as stemflow may be the cause of subsurface dissolution loci extending vertically downward through Bermuda's soluble eolianite formations. Stemflow from long-lived trees representing these species could account for the diameters, the cyclindrical shape, the vertical orientation, and the soil-filled interiors of the pipes. Successive generations of these trees in preferred habitats could explain their clustered distribution and high areal densities (>103 pipes/ha).

The above-ground productivity and summer water-use patterns of five species of Western- and central-Australian eucalypts were examined in irrigated plantations in the northern Negev Desert of Israel. Biomass production was evaluated by whole-tree harvesting. Leaf transpiration rates were measured using a steady-state porometer. Eucalyptus salubris was considered the most efficient in its water use because it had the highest productivity (1169 kg ha−1 year−1) and the lowest transpiration rates. Eucalyptus torquata was only slightly less efficient than E. salubris. Eucalyptus woodwardii was comparable in terms of productivity but it transpired at much higher rates. Eucalyptus socialis and E. grossa were the least efficient in their water use because of their significantly lower productivity (

In September 2002, NASA's solar-powered Pathfinder-Plus UAV conducted a proof-of-concept mission over the 1500 ha plantation of the Kauai Coffee Company (KCC), Hawaii. While in U.S. National Airspace, the transponder-equipped UAV was supervised by Honolulu air traffic as a conventionally piloted aircraft. Two digital camera systems were housed in exterior-mounted environmental pods, and were controlled from a ground station established at plantation headquarters. During four hours on-station, the UAV exhibited the ability to navigate pre-planned flightlines, as well as perform spontaneous maneuvers to collect imagery in cloud-free areas. A line-of-sight (local area network) telemetry system using unlicensed radio frequency enabled rapid image download at rates exceeding 5 Mbit sec -1 . All images were thus available for viewing, enhancing, and printing within a few minutes of collection. During the latter part of the mission, the payload was operated over an established wide area network by an operator located on the U.S. mainland at a distance of 4000 km. The mission demonstrated the ability of a solar-powered UAV, equipped with downsized imaging systems, to monitor a localized region for an extended time period and deliver high-resolution imagery on demand. I. INTRODUCTION

A Nighttime UAV Vineyard Mission will demonstrate the use of a UAV-based thermal infrared imaging system for improved direction of frost damage mitigation efforts in agricultural crops. The UAV selected for this April 2005 mission is the APV-3. A flight height of 8,000 ft is planned, enabling thermal mapping coverage of the largest vineyard in California on an hourly basis. To accomplish the Nighttime Mission, it is necessary to demonstrate that the ground-based autopilot has the capability to see-and-avoid potentially conflicting aircraft in the National Airspace System (NAS). This paper provides a review of a daytime UAV test flight conducted in-visual range over the vineyard in August 2003 and describes additional tests being conducted to satisfy FAA see-and-avoid requirements for the planned out-of-visual range nighttime mission.

An airborne test was conducted, demonstrating wireless remote operation of a high-resolution airborne digital imaging system and near real-time wireless transfer of acquired imagery to a ground station. Low cost, portability, ease of use, and the data transfer rates are major strengths of this telemetry system. This new technology represents a significant contribution to the further development of UAVs as image acquisition platforms.

In September 2002, NASA’s solar-powered Pathfinder-Plus (PF+) UAV was used to collect digital imagery within the National Airspace System (NAS) over the 1400 ha Kauai Coffee Plantation on southern Kauai, HI. The U.S. Navy Pacific Missile Range Facility (PMRF), on westernmost Kauai, served as the range provider. The aircraft control station was established at PMRF, and a payload control station 25 km to the east at KCP. The transponder-equipped PF+ climbed to 21k ft within restricted PMRF airspace before entering the NAS above Kauai, where it was monitored by Honolulu Air Traffic Control. Pre-planned flight tracks were combined with spontaneous, controlled maneuvers to guide the UAV to cloud-free areas. PF+ loitered for four hours over KCP, continuously acquiring imagery with two solar-powered imaging systems. Image data were transmitted to the payload station tracking antenna at rates of 3-6 Mbit sec over a line-of-sight wireless local area network, and were available for ground station viewing, enhancement, and photo quality printing within five minutes after collection. Mission planning included development of an airspace management plan, an Application for Certificate of Authorization (COA), a Memorandum of Agreement with the FAA Honolulu Control Facility (HCF), and Notice to Airmen (NOTAM) data for issuance by the FAA Honolulu Automated Flight Service Station (AFSS).

The economic potential of UAVs serving as long-duration platforms equipped with high resolution real-time imaging systems is being demonstrated. In September 2002, the UAV Pathfinder-Plus will be used to collect high-spatial resolution, multispectral imagery of the Kauai Coffee Plantation, the largest coffee plantation in the USA. Imagery from two digital camera systems will be analyzed for the mapping of coffee field ripeness, and for the identification of drip irrigation problems and weed proliferation. A payload test was conducted aboard a conventional piloted aircraft during the harvest season in 2001. Use of "off- the-shelf" wireless technology was implemented to remotely control camera operation and downlink imagery in near-real time. Image analysis and the acquisition of ground-based data revealed a positive relationship between brightness of the coffee tree canopy and the harvested yield of ripe coffee cherries.

Controlled environment treatments were applied to assess the effects of temperature on the seedling mortality and growth rates of Toona australis and Flindersia brayleyana, two tropical rainforest tree species from northeast Queensland, Australia. Past workers have assigned these two species to the same ecological niche in terms of their response to canopy disturbance and gap-phase regeneration; however, their geographic ranges are very different. The hypothesis was that the species confined to the warm tropics (F. brayleyana) would have higher seedling mortality and a slower growth rate at lower temperatures than the species that occurs over a wide latitudinal range from the warm tropics to cooler temperate environments (T. australis). Significant differences were found in the growth rates of these two species in the warm (29/22° C) and cool (22/10°C), but not the intermediate (24/16° C), day/night temperature regimes. Their growth rates both decreased with decreasing temperature, but the decrease was significantly less for F. brayleyana which had the faster growth rate and lower seedling mortality in the cool regime. These results led to the rejection of the hypothesis and a test of the assignment of these two species to the same ecological niche. The test involved monitoring their growth to sapling-size in the intermediate temperature regime together with four other co-occurring tropical rainforest tree species belonging to different ecological niches. The growth rates and proportions of above-ground biomass allocated to woody tissue distinguished T. australis and a fast-growing pioneer species from F. brayleyana and three primary forest species. The stem heights and aboveground biomass of T. australis and the pioneer species exceeded the other four species by factors ranging from two to five. It is concluded that T. australis does not belong to the same ecological niche as F. brayleyana, and it is recommended that more research be conducted on the ecotypic temperature responses of the taxon T. australis.

The Bermuda oceanic islands are comprised mainly of lithified dunes (i.e. calcareous eolianites) which formed during Quaternary sea-level regressions. This short communication considers the vegetation history of Bermuda in relation to these dune-building episodes. At 32?N, Bermuda is the northernmost limit of most frost-intolerant stibtropical vascular plant species in the northern hemisphere. The global cooling that caused the Quaternary glacial periods and also the lowering of sea level, may have led to the local extinction of Bermuda's subtropical interglacial floras. Located >900 km from the nearest continental source area, the filling of the vacated niches on Bermuda by long-distance dispersal may have involved low frequency events requiring more than 6000 years. The result would have been a very sparse vegetative cover during the dune-building episodes which would explain why the Bermuda eolianites reach elevations greater than 60 m above the present-day sea level. This hypothesis is supported by: (1) the absence of reliable fossil evidence for vegetation interfering with, or interbedded within, the eolian deposits; and (2) preliminary palynological analyses of.the clay-rich fossil soils intercalated between the eolianite formations which have revealed pollen that does not appear to correspond to the existing native flora of Bermuda.

Aboveground adventitious roots emerging from the stems and branches of the montane tropical rain forest canopy tree species, Ceratopetalum virchowii, do not require epiphyte mats to stimulate their growth. The adventitious roots grow in dense clumps on fully exposed aboveground woody surfaces of this species on Mount Bellenden Ker in northeast Queensland, Australia, where mean annual rainfall exceeds 6000 mm. While the soil at the study site is nutrient-poor, the nutrient content of the rainwater draining from the stems of C. virchowii is unusually high compared to the stemflow of other neighboring canopy tree species. Ceratopetalum virchowii is particularly prone to the leaching of Ca2+, Mg2+, K+, and Na+. The aboveground adventitious roots of C. virchowii, therefore, may serve the adaptive function of nutrient recovery before its nutrient-rich stemflow reaches the ground and becomes available to other plants. I hypothesize that the growth of the aboveground adventitious roots of C. virchowii is influenced by the high nutrient content of its stemflow and branchflow drainage, and by the moist condition of its woody surfaces which remain wetted for relatively long periods after rainfalls.

A tree introduction experiment that seeks to promote plant productivity on rocky desert hillslopes using only the available surface runoff is currently underway in the Negev Desert. The system of harvesting runoff consists only of small runoff-collecting furrows located on the upslope side of the trees. This water harvesting system was evaluated by considering the water use patterns of introduced carob trees in relation to the quantities of runoff collected in the hillslope furrows. The transpiration losses were found to represent only a limited proportion of the harvested water. We estimate that this water surplus will lead to a localised increase in available soil water stored at depth that could support carob trees having leaf surface areas >13 m2. The leaf area of such trees would be substantial for evergreen woody plants growing on hillslopes in the Negev.

Tropical rainforest canopy trees that have large projected areas of upwardly inclined branches are capable of funnelling large volumes of rainwater down their trunks. During periods of prolonged heavy rainfall on Mount Bellenden Ker in northeast Queensland, Australia, stemflow volumes were found to be as much as two orders of magnitude greater than the volume of incident rainfall expected in a rain gauge occupying an area equal to the trunk basal area. Stemflow totals ranging from 6000 to 70000 litres were generated by individual trees from 7800 mm of rainfall over two successive wet seasons. The combination of high intensity rainfall and the funnelling effect results in significant quantities of infiltration-excess at the ground surface. Stemflow fluxes as high as 31.4 cm3 min−1 per cm2 of basal area (i.e. the equivalent of 314 mm min−1) were recorded when rainfall intensity was only 2 mm min−1. The mean infiltration capacity of the topsoil was determined to be 6.2 mm min−1. The areas over which the stemflow would have had to spread in order to infiltrate were computed to be as much as 3 m2 around the bases of individual canopy trees. Approximations of the distances that the infiltration-excess would have travelled away from the tree bases were calculated by assuming that the infiltration area either expands radially outward in the form of an annulus or extends straight downslope from the tree base.

During heavy rainfall events, the buttresses of tropical rainforest trees limit the occurrence of stemflow-generated overland flow and soil erosion on hillslopes. Buttresses promote infiltration by causing stemflow to diverge into separate flow paths on the trunk and by increasing the stemflow contact area at the ground surface. Buttresses oriented normal to hillslopes function as barriers that further promote infiltration and limit the downslope transport of sediments and chemically-enriched stemflow water. These relationships between buttressing, stemflow, and hillslope processes have not been previously noted in the literature. Buttresses are generally regarded as mechanically efficient support structures that increase the resistance of trees to windthrow and uprooting; however, this also has an inhibiting effect on hillslope processes because the mounds of bare soil uprooted by tree falls are particularly vulnerable to rainsplash erosion.

Summary Rainfall was measured over a 3-year period along an altitudinal transect on Mount Bellenden Ker which is the wettest known locality in Australia. The mean annual rainfall totals recorded at 10 stations along the transect ranged from 4433 mm yr−1 to 8577 mm yr−1. Mean annual cation inputs were calculated for each site along the transect using rainfall chemistry data collected by BRASELL & GILMOUR (1980) and the measured rainfall totals. The weighted mean annual inputs to the entire windward slope of the mountain were calculated to be 11.8 kg ha−1 for Ca2+, 14.9 kg ha−1 for Mg2+, 122 kg ha−1 for Na+, and 8 kg ha−1 for K+. Despite the considerable variation in mean annual rainfall totals along the transect, these values were not significantly different from the estimates obtained by only using the rainfall data recorded at the base and summit of the mountain.

A useful index of nutrient use efficiency (NUE) is the relationship between litterfall mass and the quantity of a nutrient returned to the ground by litterfall and by aqueous leaching from aboveground vegetative surfaces. Using previously published data, Ca, Mg and K use by tropical rainforests in widely separated geographic localities were considered in relation to the availability of these nutrient elements in the soil. Significant inverse relationships were found between Ca use efficiency and soil Ca availability (P 0.1). The predicted inverse relationship between tropical rainforest NUE and soil fertility is evidently not consistent for all nutrient elements.

The relationship between above-ground net primary productivity (ANPP) and actual evapotranspiration (AE) has been previously shown by Rosenzweig (1968) to be significant for a variety of mainly temperate terrestrial ecosystems. Our study of ANPP and AE data from the humid tropics showed that AE remains a useful predictor of ANPP in tropical rainforest environments. However, we also noted that 80% of the tropical rainforest data points were depressed below Rosenzweig's original regression line. We attribute these lower-than-predicted ANPP values to transpiration losses and rainfall interception losses that do not result in a corresponding production of biomass.

The objective of our study was to determine whether Z. dumosum exhibits a significant difference between the upslope and downslope distribution of its roots on these hillslopes