Steep Cliffs Research Articles

Pictorial 1 : Photograph Showing a Transition between Mantle Peridotite and Overlying Layered Gabbro Exposed at a Steep Cliff of the South-western Atlantis Bank (Dive 649, Shinkai 6500)

Pictorial 1 : Photograph Showing a Transition between Mantle Peridotite and Overlying Layered Gabbro Exposed at a Steep Cliff of the South-western Atlantis Bank (Dive 649, Shinkai 6500)

Triadic Positions of Tibetan Macaques Huddling at a Sleeping Site

We studied huddling of Tibetan macaques (Macaca thibetana) at a sleeping site in Huangshan, China, during the mating and birth seasons. Tibetan macaques in a free-ranging group made physical contact with each other and formed huddling groups on the ledge of a steep cliff at night. We analyzed the size and composition of huddling groups and the frequencies of dyadic huddles—two individuals in physical contact—in the huddling group to determine the social influences on huddling behavior. Affiliated dyads that frequently groomed in the daytime frequently formed dyadic huddles in night-time huddling groups. Female–male dyads formed dyadic huddles less frequently than expected. In addition, Tibetan macaques chose 2 partners with which they initiated contact when they approached a huddling group. The frequencies with which some combinations of 3 individuals contacted each other and formed triangular huddles are not consistent with the expected frequencies. For example, female–male–male triads frequently formed triangular huddles in the birth season but did so infrequently in the mating season because of male competition for estrous females. When all 3 dyads within a certain triad formed dyadic huddles frequently, the triad was more likely to form a triangular huddle. The choices of approaching individuals might make a systematic, rather than random, positioning of individuals in huddling groups at their sleeping site.

Genetic Planning Method and its Application to Planetary Exploration

This paper describes a genetic algorithm planning method for autonomous robots in unstructured environments. It presents the approach and demonstrates its application to a laboratory planetary exploration problem. The method represents activities of the robot with discrete actions, or action modules. The action modules are assembled into an action plan with a Genetic Algorithm (GA). A successful plan allows the robot to complete the task without violating any physical constraints. Plans are developed that explicitly consider constraints such as power, actuator saturation, wheel slip, and vehicle stability. These are verified using analytical models of the robot and environment. The methodology is described in the context of planetary exploration similar to the NASA Mars Pathfinder mission. More aggressive missions are planned where rovers will explore scientifically important areas that are difficult to reach (e.g., ravines, craters, dry riverbeds, and steep cliffs). The proposed approach is designed for such areas.

Echolocation signals of foraging killer whales (Orcinus orca)

Fish eating resident killer whales that frequent the coastal waters of Vancouver Island, Canada have a strong preference for chinook salmon. The whales in Johnston Strait often forage along the steep cliffs that extend into the water, echolocating their prey. Echolocation signals were measured with a four hydrophone symmetrical star array and the signals were simultaneous digitized at a sample rate of 500 kHz using a lunch-box PC. A portable VCR recorded the images from an underwater camera located close to the array center. Only signals emanated from close to the beam axis (1185 total) were chosen for a detailed analysis. Killer whales project very broad band echolocation signals (Q 1.3 to 1.5) that tend to have a bimodal frequency structure. Ninety seven percent of the signals had center frequencies between 45 and 80 kHz with a band-width between 35 and 50 kHz. The peak-to-peak source level of the echolocation signal decreased as a function of the one way transmission loss to the array. Source levels varied between 200 and 225 dB re 1 μPa. Using a model of target strength for chinook salmons, the echo levels from the echolocation signals are estimated for different ranges between whale and salmon.

Habitat preferences of waders (Charadrii) on the coast of the Orkney Islands

Capsule Twelve species of wader were surveyed on 494 coastal sections, revealing features in addition to substratum type that are important in habitat selection. Aims To determine which habitat characteristics affect the probability of waders occurring on coastal sections of Orkney in winter, and to measure the strength of these habitat preferences. Methods A total of 494 sections of shoreline in the Orkney Islands were surveyed for 12 species of wader in winters 1982/3 and 1983/4. A series of environmental variables (exposure, substratum type within the inter-tidal zone, shore width and steepness) were noted in the field and taken from maps. Logistic regression models were used to examine the probability of a given species occurring on a section, with given physical characteristics. Results Ringed Plover Charadrius hiaticula, Sanderling Calidris alba and Bar-tailed Godwit Limosa lap-ponica preferred sand shores; Lapwing Vanellus vanellus, Snipe Gallinago gallinago, Redshank Tringa totanus, Curlew Numenius arquata and Dunlin Calidris alpina preferred mud; Oystercatcher Haematopus ostralegus, Golden Plover Pluvialis apricaria and Purple Sandpiper Calidris maritima preferred rock; and Turnstone Arenaria interpres preferred gravel and rock shores. The strength of a preference for substratum type was greatest in Sanderling, Bar-tailed Godwit, Lapwing and Purple Sandpiper, and least in Oystercatcher, Curlew, Golden Plover and Turnstone. Some species displayed additional preferences for exposed shores (Purple Sandpiper, Ringed Plover and Bar-tailed Godwit), sheltered shores (Curlew and Redshank) and wide shores (Sanderling, Purple Sandpiper, Dunlin, Bar-tailed Godwit and Turnstone). No species preferred steep shores or cliffs. Conclusions Simple habitat descriptions coupled with map-derived variables, can provide an initial insight into the habitat preferences of waders. Further work relating wader distribution to invertebrate food supplies is required.

Potential Profile Surveyed Directly by Nanomanipulator with Probing Tip in Al/Poly(3-alkylthiophene)/Au Diodes

ABSTRACTThe potential profiles along the channel of Al/Poly(3-hexylthiophene), PHT film/Au diode from Al to Au electrodes have been measured directly using nanomanipulator with potential probing tips. The steep potential cliff is observed at the interface of Al/PHT, indicating the existence of depletion layer with higher resistance than that of bulk region. For the forward bias, the resistance at the depletion layer decreased significantly and the potential gradient in the PHT bulk region is observed above the onset bias of 1 V. It is found that the contact resistance of PHT/Au is unexpectedly large in spite of the ohmic behavior and also for Al/PHT at forward bias. The effect of light on the depletion layer will be also mentioned. It is stressed that the contact resistances of PHT and metals are significantly important to improve the performance of organic electronics devices.

Vertical jets from standing waves

When a shallow‐water wave meets a steep cliff or harbour wall, a jet is sometimes thrown upwards with very high initial acceleration. In the present work it is shown that a similar phenomenon can occur in a standing wave in deep water, provided that the initial shape of the trough is narrow and an almost circular arc. During collapse of the trough, vertical accelerations exceeding 10 g are found, with subsequent vertical velocities exceeding 1.7 c , where c is the phase‐speed of a small‐amplitude progressive wave. The vertical acceleration, plotted as a function of the time, is shown to be very sensitive to the initial shape of the wave trough. The presence of a much shorter wave superposed on the initial wave profile can further increase the maximum acceleration and velocity.

Atlas of Hawai’i (Third Edition) ed. by Sonia P. Juvik, James O. Juvik (review)

Atlas of Hawai'i (Third Edition) Sonia P. Juvik and James O. Juvik (Eds.) Honolulu: University of Hawai'i Press Reviewed by A n t o n ia H u ssey California State University, Northridge T h is th ird ed itio n of the Atlas ofHawai'i is substantially revised from the 1994 edition. This edition differs in the topic array, size, and format, but the most significant difference is the quantity and qual­ ity of the maps, graphics, and photographs. Thomas R. Paradise, the chief cartographer of the atlas, put to excellent use new produc­ tion technology. The application of new computer technology allowed the cartographers to enhance the atlas's graphic presenta­ tion with the use of digital reconstruction, better resolution, and color enhancements. The size change to a 10" x 12" format allows for regu­ lar shelving as opposed to oversized volume shelving. There are a number of new offerings in this edition, including informative, boxed sidebars; suggestions for further reading in a reference section; a list of graphic sources; sets of statistical tables; and a gazetteer. The Atlas ofHawai'i is divided into five sections. The first section presents reference maps of each of the islands. The new size signifi­ cantly benefits the presentation of the reference maps, as enhanced resolutions allow for clarity of place names and terrain features. The quality of the reference maps is excellent; in fact, they remind one of National Geographic Society fold-out maps. The next four sections display and discuss the complex physical, biotic, cultural, and so­ cial environments of the Hawaiian Islands. Hawai'i is a state of contrasts and extremes, from wet tropical forests to towering steep sea cliffs, and a seemingly endless variety of coastal environments. Mountain masses descend into isolated valleys that contain species unique to the islands. Few states have an erupting volcano and newly formed volcanic terrain on and off shore. Hawai'i has a number of well-defined and densely populated urban areas, yet many areas on the islands appear undeveloped and 152 H u ssey : Review of Atlas ofHawaii (Third Edition) 153 rural. A hallmark of the Hawaiian Islands is ethnic diversity, which has resulted in a lively cultural heritage. The Atlas of Hawai'i has managed thorough liberal use of photographs and pertinent dis­ cussions to capture much of the drama and excitement of the state's physical and cultural setting. Given the north Pacific setting of the Hawaiian Islands chain, along with its recent geologic origins and relative isolation, the two sections on the physical and biotic environments make for a fasci­ nating read and provide a visual stimulus. Even a casual peruser of this atlas is bound to be fascinated with the chapter on the geology of the islands. Graphics and photographs are used effectively to il­ lustrate volcanic island growth cycles, volcanic cones, faulting blocks, caldera, and the geology of each island. Hawaiian lavas are discussed in a box format aside from the primary discussion, and several clas­ sic photographs depict pahoehoe, ‘a'a, and pillow lavas. The 11-page climatology chapter is a well articulated, informative, and presents excellent diagrams and maps throughout the discussion. Atmo­ spheric change is discussed in a separate chapter, while paleoclimate and geography are combined into one chapter. Natural hazards such as earthquakes, tsunamis, hurricanes, and volcanic and coastal haz­ ards are discussed in the atlas. A mix of figures, photographs, satellite imagery, and computer simulations are used to illustrate causes and effects of the various hazards. The biotic environment of the Hawaiian Islands is presented in a separate section wherein categories of ecosystems found through­ out the islands are discussed. The addition of large color photographs has greatly enhanced the chapters on Hawaiian native plants and insects and their kin. The problems associated with the introduction to the islands of alien species and problems of extinction are dis­ cussed in two separate chapters. The distribution map of endangered species habitat is particularly informative. Another map shows pro­ tected areas. Both the endangered species and the protected area maps are the same scale, which allows the reader to observe, for example, that endangered species habitats and protected areas are not...

THE PEOPLING OF THE ARICA COAST DURING THE PRECERAMIC: A PRELIMINARY VIEW

In this paper Chinchorro mobility and ecology will be presented. The research was accomplished as a multidisciplinary effort using surveys of the upper and lower coasts of Arica, excavations of two shell middens, and radiocarbon dating of 21 samples from mummies and middens. The following observations can be drawn from our ongoing study: 1) the peopling of the coast moved along the smooth paths from the upper coastal cordillera rather than the lower rocky coast; 2) there was intense preceramic occupation of the coast illustrated by Macarena, Hipodromo, Chinchorro, Citroen, Maderas Enco, Colon, Morro, Playa Miller 8, and Quiani cemeteries in Arica. Also the harvesting grounds of Punta Palomo, Punta Baquedano and El Muertito toward the south could have a preceramic component. The latter three sites are located at the bottom of steep cliffs and are accessible by zigzagging paths which are still visible along the slopes of the mountains; and 3) the ancient environment was milder than it is today. Water and plants were abundant based on the geomorphology of the chimbas and the fossilized pollen of graminaes and compositae found in the shell middens.

Koeleria macrantha (Ledeb.) Schultes (K. alpigena Domin, K. cristata (L.) Pers. pro parte, K. gracilis Pers., K. albescens auct. non DC.)

<i>Koeleria macrantha</i> (Ledeb.) Schultes (<i>K. alpigena</i> Domin, <i>K. cristata</i> (L.) Pers. pro parte, <i>K. gracilis</i> Pers., <i>K. albescens</i> auct. non DC.)

Checklist of plant species of the coastal fynbos and rocky head­lands, south of George, South Africa

A checklist of vascular plants and cryptograms was compiled for the fynbos and rocky headland communities of the coastal region south of George The area studied is a 12 km stretch of steep sandstone cliffs forming alternating bays and headlands situated between Glentana and Wilderness. The plant communities of the natural vegetation inhabiting the coastline are a mixture of coastal thicket, riparian thicket, fynbos and rocky headland types. The extent of natural vegetation has been reduced by the spread of agricultural land and urban development and is under further threat from the spread of naturalised alien invader species, particularly Acacia cyclops. The checklist records the occurrence of 271 taxa including 16 alien species (6% of taxa). Of the flowering plant species recorded, 6% were regional or local endemics.

Preliminary observations on the distribution and status of dwarf blue sheep Pseudois schaeferi

Dwarf blue sheep Pseudois schaeferi are known to survive only in Batang County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China. According to the results of a survey between 19 November and 21 December 1997, the species has declined steeply in both range and numbers since the 1950s and 1960s because of excessive hunting. The survey found that dwarf blue sheep were concentrated on steep cliffs between 2700 and 3200 m. In the area near Batang, the species's range was estimated to cover 295 sq km and the population to number c. 200 individuals. The average group size was 6.2 individuals, with a male: female ratio of 67.7:100. The authors recommend that the species be included in Class I of the National List of Protected Animals in China.

Preliminary observations on the distribution and status of dwarf blue sheep Pseudois schaeferi

AbstractDwarf blue sheep Pseudois schaeferi are known to survive only in Batang County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China. According to the results of a survey between 19 November and 21 December 1997, the species has declined steeply in both range and numbers since the 1950s and 1960s because of excessive hunting. The survey found that dwarf blue sheep were concentrated on steep cliffs between 2700 and 3200 m. In the area near Batang, the species's range was estimated to cover 295 sq km and the population to number c. 200 individuals. The average group size was 6.2 individuals, with a male: female ratio of 67.7:100. The authors recommend that the species be included in Class I of the National List of Protected Animals in China.

Geomorphological aspects of road construction in a cold environment, Finland

Traditionally, road alignments followed easy landscapes and suitable landforms. When traffic and the size and weight of vehicles increased and higher speeds were used, straighter roads were required; the easygoing relief could not always be used, and problems arose. Road contractors could save money in building and maintenance costs by considering the geomorphic facts. The examples from Finland document why road construction is very expensive in the conditions generated by severe winters. In Finland, more paved roads cross the Arctic Circle than in the whole of North America. This paper gives examples of geomorphic elements affecting road construction in a cold environment: eskers, drumlins, plains of late and postglacial glaciolacustrine and marine sediments, mires, steep rock cliffs, river channels and ice-dams, fluvial erosion, and palsas. Solutions to these problems include removal of frost sensible materials and replacement by more favorable sediments. Road surfaces, kept snow-free in the wintertime, are subjected to deep freezing. The maintenance of roads can be supported with some solutions that affect snowdrift and icing problems, avoidance of geomorphic factors that cause problems, and by using natural processes to help people. Some examples of how road construction affects geomorphic processes and vice versa are provided. For example, bridges block moving river ice, and on special occasions, road banks cause icing.

Subtropical carbonates in a temperate realm; modern sediments on the Southwest Australian shelf

The southwestern continental margin of Australia (19 degrees S-22 degrees S) in the western Indian Ocean is transitional between cool-water and warm-water carbonate realms. It comprises the incipiently rimmed, flat-topped, steep-fronted Rottnest Shelf in the south, the uniform subtropical starved Carnarvon Ramp off Shark Bay, and the Ningaloo fringing reef in the north. The margin is strongly influenced by the poleward-flowing, warm, nutrient-poor Leeuwin Current, which promotes overall downwelling and strong summer equatorward-blowing winds, which generate local seasonal upwelling. The structurally quiescent northern part of the Rottnest Shelf, with minimum accommodation, is characterized by luxuriant stands of sea-grasses and macrophytes growing on coralline-encrusted hardgrounds and rooted in sediments rich in coralline algae and larger, symbiont-bearing foraminifers together with abundant cool-water elements such as bryozoans, molluscs, and small foraminifers. Halimeda is poorly calcified and does not contribute to the sediment. Azooxanthellate corals, although present, are not common. Such a sediment pattern has many analogs in the geologic record, especially the early Cenozoic. The incipient rim is a morphologically complex linear ridge system interpreted to be a buried mid-Pleistocene barrier reef or beach-dune complex. The northern part of the ridge complex is capped by the Houtman Abrolhos reef platforms. Subphotic sediments on the deep, outer shelf and upper slope, affected by seasonal upwelling, are typical cool-water, poorly sorted, bryozoan-dominated deposits rich in small foraminifers and sponge spicules. The inner part of the more structurally active Carnarvon Ramp ranges from steep eolianite cliffs to hypersaline environments of Shark Bay to the Ningaloo fringing reef. Mid-ramp sediment, especially off Shark Bay, is mostly relict or stranded and foraminifer-dominated sand with abundant Mg-calcite-cemented intraclasts. These sediments, accumulating on a relatively barren seafloor, likely represent attenuated carbonate production brought about by downwelling and episodic incursions of saline, Shark Bay-derived waters onto the ramp. The outer ramp is either planktic foraminiferal sand, sorted by strong bottom currents, or spiculitic mud. Such sedimentation patterns should typify the western margins of large ocean basins during those periods in geologic history when circumglobal equatorial circulation was active, and equatorial gateways narrow, in contrast to eras of supercontinents, when cool-water carbonate sedimentation and upwelling prevailed in similar settings. Furthermore, because low-latitude trade winds relax during glacial epochs and the cool-water, upwelling belt moves equatorward into otherwise tropical realms, temperate and subtropical sedimentation patterns in these regions should oscillate at the 100 ky scale in the stratigraphic record.

Abyssal erosion and scarp retreat: Deep Tow observations of the Blake Escarpment and Blake Spur

Deep Tow surveys conducted at two sites at the base of the Blake Spur and Blake Escarpment serve to delineate the contact between Mesozoic platform carbonates of the Blake Plateau and adjacent abyssal strata. The continental margin in the surveyed areas consists of steep limestone cliffs and headlands with over 2 km of relief. This extreme topography distorts the hydrographic structure of the water column and intensifies abyssal current flow in the surveyed areas. Significant lateral scarp retreat is indicated by the presence of broad, nearly horizontal benches of Mesozoic limestone presently exposed at the base of the Blake Spur and Escarpment in 4.5–5 km water depth; and by angular, apparently truncated limestone ledges that crop out on the cliff face. At the Blake Spur, the contact between Mesozoic platformal limestones and basinal Tertiary strata does not occur directly at the foot of the cliff, but is exposed on the abyssal plain within a 50 m deep erosional moat. Here, strong (>2 knots) south-flowing bottom currents occur within 100 m of the sea floor. The coincidence of this vigorous current flowing within the moat near the base of the escarpment and the eroded character of the sea floor suggests that currents are an important mechanism in sculpting this abyssal headland and contributing to lateral scarp retreat. Similar erosional processes are indicated along the Blake Escarpment near 29°03′N, where the relatively straight cliff face is interrupted by occasional steep-walled box canyons. On the headland between the canyons, the Mesozoic outcrop projects into the Blake–Bahama Basin for several kilometers as a broad, arcuate, gently-sloping bench. These outcropping benches of Mesozoic strata at the base of the escarpment are analogous to larger-scale buried benches observed in the subsurface that were formed by pre-Miocene erosion. Neogene and Quaternary scarp retreat is suggested by the location of the contact between Mesozoic rocks and younger strata seaward of the steeper cliff face, and is probably the result of current-induced erosion. Focused erosion may be facilitated by the presence of a thin (∼50 m) filament of corrosive Antarctic Bottom Water (AABW) that flows vigorously along the base of the cliff at both sites. The recessed position of the canyons shelters them from the main flow of this abyssal current, but the steepness and morphology of the canyon walls suggest that additional unidentified erosional processes are focused at the canyon heads.

Brachyuran Crabs of Cocos Island (Isla Del Coco), Costa Rica: Leucosiidae, Calappidae, and Parthenopidae, With Descriptions of Two New Species

Recent additions from Cocos Island, Costa Rica, to the collections of the Natural History Museum of Los Angeles County have increased the number of species in the brachyuran crab families Leucosiidae, Calappidae, and Parthenopidae known from the island from 4 to 10. Two of these are described: Thyrolambrus verrucibrachium, new species, and Osachila kaiserae, new species. Review of all material in the LACM collections for these species has resulted in range extensions and increases in the known maximum size for several of the species. The increase in species richness suggested by these collections may make Cocos the most speciose single island in the eastern Pacific, after the remaining crab families are studied. The zoogeographic relatedness of the oceanic islands of the eastern Pacific is supported, and the link between Cocos and the Revillagigedo Islands is strengthened. Cocos Island, which is now one of the national parks of Costa Rica, sits on the Cocos Ridge at 5032'57N, 86059'17W, 494 km west of Cabo Blanco, Costa Rica, 673 km northeast of La Pinta (Abingdon) Island in the Galapagos, and 2,375 km southeast of Clipperton Island. Cocos is volcanic in origin, with lavas dated at around two million years old (Bellon et al., 1983; Castillo et al., 1988), and is covered by wet tropical forest. Much of the 23.3 km of coastline is bounded by steep cliffs, and only two areas afford protected anchorage: Chatham Bay and Wafer Bay. The island is situated in the path of the eastward flowing North Equatorial Countercurrent for much of the year, but from December-April westerly currents reach the island from the mainland when the counter current shifts to the south (Wyrtki, 1965). The brachyuran fauna of Cocos Island has been somewhat undercollected, when compared to the other oceanic islands of the tropical eastern Pacific (Revillagigedo, Clipperton, and the Galapagos Islands), although numerous collecting expeditions have visited Cocos Island in the past. Among those cruises reporting decapods were the Albatross in 1891 (Faxon, 1895), the Arcturus in 1925 (Boone, 1927), the Velero III in 1933 and 1938 (Fraser, 1943), and the Presidential Cruise of 1938 (U.S.S. Houston) (Schmitt, 1939). None of these expeditions stayed at the island for more than a few days, and only 31 species of Brachyura were listed by Hertlein (1963), who reported on what was known of the fauna of the island at the time. A review of the literature by the authors has increased

Structural and petrologic evolution of the Lihue basin and eastern Kauai, Hawaii

The topography of the eastern part of the Hawaiian island of Kauai is dominated by the Lihue basin, a large (∼110 km 2 ) semicircular depression bounded by steep cliffs and partly filled by late rejuvenated-stage (or posterosional stage) volcanic material. As with other large, semicircular basins on ocean-island volcanoes, the subsurface geology and origin (e.g., structural collapse vs. fluvial erosion) of the Lihue basin are poorly understood. New analyses of samples collected from eastern Kauai and drill holes within the basin document several important features of the late-stage geologic evolution of Kauai. First, thick (>300 m) sequences of rejuvenated-stage Koloa Volcanics in the Lihue basin show systematic, basin-wide geochemical trends of increasingly incompatible elements with time, indicating a gradual decrease in the extent of partial melting of mantle sources with time. Second, beneath the rejuvenated-stage volcanics in the basin, a thin layer of postshield alkalic stage lavas (e.g., hawaiites and mugearites) overlies older shield-stage tholeiitic lavas of the Napali Member, indicating that the Lihue basin formed by structural collapse, not fluvial erosion. Third, a large (∼2–5 km 3 ) matrix-supported breccia, interpreted as deposits of one or more debris flows, is within the rejuvenated-stage volcanics throughout the basin, and correlates with surficial exposures of the Palikea Breccia west of the basin. Isotopic compositions of the bulk breccia are similar to those of tholeiites from the east side of Kauai, and distinct from those of west Kauai tholeiites. Clasts within the breccia are dominantly hawaiite and alkali gabbro. The source region of the breccia in the steep cliffs and highlands of the central massif to the west of the basin must contain magmatic products of an extensive postshield alkalic stage, including hawaiite flows and one or more large intrusive bodies or ponded sequences of alkali gabbro.

Rain forest composition and patterns of secondary succession in the Vava'u Island Group, Tonga

Abstract. The Vava'u island group, Tonga, comprises ca. 60 limestone islands on a single submarine platform overlain with rich soils derived from tephra deposits from nearby volcanic islands. The island group has moderate topographic relief (215 m) and is characterized by plateaus and steep cliffs. Humans settled in Tonga ca. 3000 yr ago and have exploited the flatter terrain for agriculture since that time. We conducted the first survey of forest composition in Vava'u, sampling remnant patches of late‐successional forest as well as stands in various stages of secondary succession following agricultural abandonment. Plant species composition did not vary greatly with elevation over this short gradient, in contrast with patterns found on‘Eua, a higher island in Tonga. The most significant environmental gradient affecting species composition was coastal or maritime influence. However, the greatest variation in species composition and structure appeared to be related to species turnover during secondary succession, and we hypothesize a sequence of species replacements. Secondary forest begins to resemble late‐successional forest in 30–50 yr in terms of structure and native species richness and therefore is of significant conservation value.

Two New Chromosome Numbers in an Unusual Albuca (Hyacinthaceae) from Saudi Arabia

The 50 taxa of the bulbous genus Albuca L. (Hyacinthaceae) grow throughout most of Africa, extending eastwards into the south western part of the Arabian peninsula. Albuca pendula B. Mathew in the subgenus Pallastema (Baker 1873) is an interesting new Saudi Arabian species which has recently been described by Mathew & Collenette (1994, 1997). This rare and unusual species is unlike any other Albuca, and indeed almost all other bulbous monocotyledons, in its long strap-like leaves up to 2 metres in length and 4 6 cm wide which hang down steep rocky cliff faces. Albuca pendula is related to A. abyssinica Dryand. which is common throughout East Africa and extends into the Arabian peninsula. The characteristic chromosomes of Albuca have been extensively studied by many workers. Most recently, Jong (1991) added 10 new counts, three of which were for new species which had been described by Hilliard & Burtt (1985). A study was undertaken of this new species to contribute further data to the cytology of the genus.