bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional association between apogeotropic aerial roots, mycorrhizas and paper-barked stems in a lowland tropical rainforest in North Queensland
Authors: Reddell Paul , Hopkins Michael S. , Graham Andrew W. 
Published: July 2009

ABSTRACTThe root and trunk characteristics of species in a complex, lowland, evergreen, tropical rainforest at a seasonally inundated, coastal site on siliceous sands were examined. Roots in the soil were predominantly colonized by arbuscular mycorrhizal fungi although ectomycorrhizas were found on four species which contributed almost 25% of total basal area. Surface root mats were not a characteristic of the study site. In contrast, the ability to produce apogeotropic (upwardly growing) aerial roots which grew on and within the bark on trunks and branches was a consistent feature of the dominant species of trees in this forest. Eleven species representing eight families and constituting more than 85% of the basal area at the site produced these roots. Most trunks with DBH greater than 20 cm supported apogeotropic aerial roots produced by a range of species including themselves. Apogeotropic roots were most frequently found on the basal 0.5 m of trunks; however, they did occur up to 5 m above the forest floor. Apogeotropic aerial roots originated both from epicormic buds under the bark and from soil, and they were frequently colonized by arbuscular mycorrhizal and ectomycorrhizal fungi. There was a strong association between the ability to support these upwardly growing roots and the occurrence of laminated papery and flaky bark. We postulate that production of apogeotropic roots may provide a mechanism for nutrient uptake and root respiration during periods of inundation, for intercepting nutrients in stemflow and/or for extracting nutrients from bark.
Specialization for canopy position by hemiepiphytic Ficus species in a Bornean rain forest
Authors: Laman Timothy G. 
Published: July 2009

ABSTRACTThe growth habits of five species of hemiepiphytic fig trees (Ficus subgenus Urostigma) were compared to see if any species occupied distinct canopy positions or showed unique host preferences in lowland rain forest in Gunung Palung National Park, Indonesian Borneo. Highly significant differences among species were found in the height of establishment on hosts, the level at which fig crowns were deployed, and the size and taxa of host trees. Ficus stupenda, F. dubia, and F. subtecta all had mean establishment heights between 29 and 31m above the ground, had their crowns in the upper canopy, and predominantly occupied large trees in the Dipterocarpaceae. F. consociata and F. xylophylla established at significantly lower mean heights of 24 and 18 m respectively, had their crowns predominantly in lower canopy layers, and disproportionately occupied smaller non-dipterocarp trees. These patterns were consistent both within lowland forest on alluvial terraces, which was most intensively sampled, and when data were combined from three other contiguous lowland forest habitats. Ficus species appear to be specialized to some extent for distinct microhabitats within the canopy.
Aspects of the morphology and ecology of two Panamanian ant-plants,Hoffmannia vesciculifera(Rubiaceae) andBesleria formicaria(Gesneriaceae)
Authors: Windsor Donald M. , Jolivet Pierre 
Published: July 2009

ABSTRACTTwo formicarial ant-plants endemic to Panama and adjacent areas of Costa Rica co-occur in mid-elevation cloud forest yet have distinctive modifications to house and feed small, retiring ants.Besleria formicaria(Gesneriaceae) hosts onlyPheidolesp. which harvest the oil-rich seeds of its host and other plants and insect parts.Hoffmannia vesciculifera(Rubiaceae) hosts onlySolenopsissp. ants which obtain lipid and possibly other nutrients from vescicular tissues. Judging by their abundance in refuse deposits, fern sporangia appear to be a plentiful and evenly distributed resource exploited by both ant species.
Leaf nutrient dynamics of two tree species and litter nutrient content in Southern Bakundu Forest Reserve, Cameroon
Authors: Songwe Nicholas C. , Fasehun F. E. , Okali D. U. U. 
Published: July 2009

ABSTRACTThe variations in macronutrient concentrations of the leaves of Terminalia superba and Pycanthus angolensis were studied and the concentrations of nutrients in leaves before abscission were compared with those after abscission. The amounts of nutrients returned to the forest floor were also computed from litter fall data at the start of maximum annual fall in the Reserve. With the exception of potassium in Pycanthus angolensis, there were significant variations in the nutrient concentrations of the two species with the time of year. With increasing leaf age the concentration of nitrogen, phosphorus, potassium and magnesium declined in Terminalia superba while magnesium concentration decreased in Pycanthus angolensis leaves. Furthermore, calcium showed an increasing concentration in Terminalia superba with increase in leaf age. The concentrations of nitrogen, phosphorus and potassium decreased before leaf fall. Estimated losses in nitrogen phosphorus and potassium before abscission were 44, 53 and 50%, respectively, whereas generally there was an increase (40%) in the concentration of calcium at leaf fall. Magnesium did not follow a definite pattern. The return of calcium through litter fall to the forest floor was the greatest of all the major elements. The distribution and variation of foliar nutrient concentrations in the leaves of Terminalia superba and Pycanthus angolensis and the importance of the amount of litter and the concentration of the various nutrients in the influencing soil fertility are discussed.
Removal of black palm (Astrocaryum standleyanum) seeds by spiny rats (Proechimys semispinosus)
Authors: Hoch Gregory A. , Adler Gregory H. 
Published: July 2009

ABSTRACTA seed-removal experiment was conducted to assess the role ofProechimys semispinosus(Central American spiny rat) as potential predator and disperser ofAstrocaryum standleyanum(black palm) seeds. One hundred fresh ripeA. standleyanumfruits were placed in semipermeable cages on each of 14 small islands in Panama, and seed disappearance rates were calculated for each island. Spiny rat density and biomass were determined by live-trapping on each island for 5 consecutive days and 4 nights. Censuses of fruiting trees were conducted on each island to control for effects of food availability on removal of palm fruits. Disappearance rates were related positively to total spiny rat density, density of adult and subadult spiny rats, and spiny rat biomass, but the density of fruiting trees accounted for very little variation. Spiny rats evidently prey heavily onA. standleyanumseeds, based on the high removal rates and on feeding observations of captive individuals. Since spiny rats may scatterhoardA. standleyanumseeds, they may also function as effective seed dispersers if seeds are removed to favourable germination sites unavailable to other seed predators. Results indicate that spiny rats, because of their abundance and wide distribution, may be important but overlooked predators and dispersers ofA. standleyanumseeds and of other large-seeded tree species.
Leaf-cutting ants and early forest regeneration in central Amazonia: effects of herbivory on tree seedling establishment
Authors: Vasconcelos Heraldo L. , Cherrett J. Malcolm 
Published: July 2009

ABSTRACTThe effects of herbivory by the leaf-cutting antAtta laevigataFr. Smith on the re-establishment of forest trees in an abandoned farm near Manaus, central Amazonia, were investigated. Experimental seedling transplants and observations on seedlings which emerged naturally in the study area showed that damage by leaf-cutting ants negatively affected tree seedling survival and growth. However, excluding leaf-cutting ants from experimental plots for 20 mo did not significantly increase tree seedling densities. The number of seedlings emerging varied considerably between plots and this obscured any effect the ants may have had on seedling survivorship. Taller seedlings, and seedlings attacked only once, suffered less mortality than smaller seedlings and seedlings attacked twice or more. In general, mortality was greater for those species preferred by the ants, indicating that selective herbivory by leaf-cutting ants affects tree species composition. The number of seedlings attacked byA. laevigataremained approximately constant throughout the period of this study in spite of the fact that the number available for attack increased. Thus, the chance of any individual seedling being attacked declined with time, suggesting that the effect ofAttaherbivory on tree establishment is stronger during the first few years of forest regeneration.
Seed damage tolerance and seedling resprouting ability of Prioria copaifera in Panamá
Authors: Dalling J. W. , Harms Kyle E. , Aizprúa Rafael 
Published: July 2009

ABSTRACTGermination and seedling resprouting capacity of the very large-seeded tree species Prioria copaifera Griseb. (Fabaceae) was studied in the seasonally moist forest of Barro Colorado Island, Panamá. Seeds with 60% of their cotyledonary mass removed did not suffer a reduced probability of germination compared to unmanipulated seeds and seeds infested with up to eight insect larvae germinated as well as uninfested seeds. Unmanipulated seeds were able to consecutively produce up to four functional resprout shoots after excision of the initial, and subsequent, fully expanded shoots. Even seeds with up to 60% of their reserves removed showed some capacity to resprout. Less than 10% of seeds we encountered in the field 2 mo after the end of the fruiting season were in a viable state, with the majority (55%) of mortality attributable to insect or pathogen damage. Of the 46 seeds that were viable, 30% had suffered partial removal of seed reserves similar to our manipulation treatments. These results indicate that P. copaifera seeds are capable of tolerating severe seed and shoot damage. The selective advantage conferred by damage tolerance may in part have contributed to the evolution of large seed size in this species.
Seed dispersal, spatial distribution and population structure of Brazilnut trees (Bertholletia excelsa) in southeastern Amazonia
Authors: Peres Carlos A. , Baider Claudia 
Published: July 2009

ABSTRACTSeeds of the Brazilnut tree (Bertholletia excelsaHumb. & Bonpl., Lecythidaceae) sustain one of the most important extractive industries in neotropical forests. Yet little is known about the demography and seed dispersal ecology ofBertholletia, particularly in natural stands which have not been previously harvested. This study presents data on the population density, spatial distribution, and seed dispersal ecology of Brazilnut trees at a pristine stand located within the Kayapó Indian Area of southeastern Amazonia, Pará, Brazil. Brazilnut trees were primarily found within groves (castanhais) of 75 to 149 trees, with a few isolated trees in between. Although the density of trees ≥ 10 cm in diameter at breast height (hereafter, dbh) at two groves was 4.8 to 5.1 trees ha–1, the overall density for the entire study area ofc.950 ha was estimated at 1.3 tree ha–1. Within-grove nearest neighbour distances averaged 21 m and were markedly skewed towards even shorter distances. Seed dispersal experiments using 709 marked seeds indicated that this pattern can be largely explained by the highly restricted seed shadows imparted by the main seed dispersal agents ofBertholletiaat this site, the red-rumped agouti (Dasyprocta leporina). Agoutis on average scatterhoardBertholletiaseeds to an average distance of 5 m, and rarely beyond 20 m, from seed stations. We suggest that, once edaphic and climatic conditions are suitable, the highly contagious spatial distribution ofBertholletiatrees at the landscape level can be largely accounted for by the quantitatively dominant effect of short-distance dispersal by caviomorph rodents, and rare events of long-distance dispersal provided by other vectors. This mechanism of grove formation need not resort to untested conjectures of human dispersal and intentional planting in prehistoric and historic times as it has often been suggested in the literature.
Phenological patterns of Ficus in relation to other forest trees in southern India
Authors: Patel Aviva 
Published: July 2009

ABSTRACTThe importance of figs as keystone resources depends partly on their year-round fruiting pattern. However, most non-equatorial fig species show seasonality in reproductive phenology. If fig and other species' fruiting peaks coincide, the importance of figs as key resources during lean fruiting periods may be reduced. Fig and other forest tree phenology was studied in a deciduous and an evergreen site in the Western Ghats, southern India, from January 1991 to May 1992. In the deciduous site, most non-fig flowering and leaf flushing occurred during the two dry seasons, while most fruiting occurred during the dry and early wet seasons. In the evergreen site, all non-fig tree phenological stages – flowering, fruiting and leaf flushing – were concentrated during the two dry seasons annually (dry and post-monsoon). Individual fig trees produced crops one to three times annually, at different times of the year for different trees. Fig community fruiting peaks in the evergreen site coincided with fruiting peaks of the other forest trees, but in the deciduous site occurred slightly offset from non-fig fruiting peaks. The role of figs as key resources is likely to differ among forests, and to depend on factors such as diversity of fruiting pattern among fig species, fig tree density and territoriality of frugivores.
Leaf litter effects on seed and seedling predation of the palm Astrocaryum murumuru and the legume tree Dipteryx micrantha in Amazonian forest
Authors: Cintra Renato 
Published: July 2009

ABSTRACTThe amount of leaf litter fall produced by different tree species in tropical forests varies in space and time. Falling litter may cover seeds and thereby enhance their survival by making their detection by seed predators more difficult. Tests were made to determine whether Astrocaryum murumuru and Dipteryx micrantha seeds survive better in microsites covered by leaf litter. Seed numbers and litter cover on the forest floor were experimentally manipulated. How natural variation in leaf litter cover and thickness affects seed and seedling survival of these two plant species was also examined. Seed survivorship was significantly higher for both plant species in microsites with leaf litter than in those with bare soil. Results from an experiment in which the litter was not disturbed showed that Astrocaryum seed survival was positively correlated with litter thickness (defined as the number of overlying dead leaves). Astrocaryum seedling survival was also significantly affected by leaf litter; more seedlings survived in shallow litter. Leaf litter had no effect on Dipteryx seedling survival. The results of the study suggest that early recruitment of both Astrocaryum and Dipteryx is influenced by the spatial distribution and amount of forest leaf litter.
Fire resistance and bark properties of trees in a seasonally dry forest in eastern Bolivia
Authors: Pinard Michelle A. , Huffman Jean 
Published: July 2009

ABSTRACTAs forest fragmentation and intentional burning of grasslands increase, the frequency of fires penetrating the dry and subhumid tropical forests of Bolivia is also likely to increase. To expand our understanding of the role of fire in tropical dry forest, the physical and thermal properties of barks of tree species were studied to determine their relative resistances to cambial damage by fire. For 16 tree species found in the dry forest of the Lomerío region of eastern Bolivia, bark thickness, moisture content, and specific gravity were measured. Insulating capabilities of bark were measured by obtaining cambial and surface temperatures during experimental wick fires. Bark thickness on trees 5-100 cm dbh (diameter at 1.4 m) ranged from 2–51 mm and both thick- and thin-barked species were represented. For all species, bark thickness increased as stem diameter increased. Bark thickness explained more (63%) of the variation in peak cambial temperatures during fires than did bark moisture content (4%) or specific gravity (1%). A threshold bark thickness of 18 mm was associated with the ability to withstand lethal cambial temperatures during the experimental, low intensity fires. For 13 of the 16 species included in this study, trees ≤20 cm dbh have bark thickness below the threshold 18 mm and, therefore, are likely to experience cambial injury from low intensity fires. Our results suggest that the forest presently characteristic of the Lomerío region did not develop with frequent fires and that species composition is likely to be substantially affected by an increase in fire frequency.
Plant establishment on flooded and unflooded patches of a freshwater swamp forest in southeastern Brazil
Authors: Scarano Fábio R. , Ribeiro Kátia T. , de Moraes Luiz F. D. , de Lima Haroldo C. 
Published: July 2009

ABSTRACTPlant establishment was studied in a swamp forest in the lowland Atlantic rainforest in southeastern Brazil. A topographic gradient allowed a clear distinction between a periodically flooded and a permanently flooded site in the study area. Both sites were mosaics of patches: the former showed soil patches of varying sizes subject to distinct flooding durations (from 0 to 300 d per year) and in the latter, the tank bromeliads which densely occupied the understorey, trap litter and provided ‘suspended soil’ patches. In the periodically flooded site, the occurrence of regenerants (< 1.0 m tall) of the actively regenerating tree populations of Calophyllum brasiliense, Symphonia globulifera and Tovomitopsis paniculata (all Clusiaceae), originating from seed or vegetative organs, was recorded for 1 m2 quadrats placed in flooded (n = 82) and unflooded (n = 103) patches. In the permanently flooded site, dominated by Tabebuia cassinoides (Bignoniaceae), the presence of germinated seedlings was counted for 400 rosettes of the terrestrial tank bromeliad Nidularium procerum. The results showed that unflooded patches, including tank bromeliads, favoured seedling establishment. However, T. paniculata and T. cassinoides colonize patches where flooding lasts longer or is permanent mostly by reproducing vegetatively, while the seeds of C. brasiliense, which showed no form of vegetative reproduction, and S. globulifera are successful in colonizing flooded patches. Germination tests and field observations indicated that, for C. brasiliense, pre- and post-dispersal seed dormancy, a two-phase seed dispersal (water and bats) and seedling tolerance to flooding accounted for this pattern.
Choosing a reasoning style for knowledge based system: lessons from supporting a help desk
Authors: Dearden Andrew M. , Bridge Derek G. 
Published: July 2009

AbstractIn this paper, we present two broad styles of KBS reasoner: those based primarily on some general, explicit model of the knowledge of the domain (whether that model be expressed by heuristic rules or by a deep model of structure and function), which we term domain model-based reasoners; and those based primarily on a set of examples of events in the domain, which we term example-based reasoners (EBR), of which case-based reasoners are a subset. The aim of this paper is to guide developers in considering the trade-offs between these different styles of reasoning. We believe that this cannot be done in general, but may be possible for specific domains. Thus, the paper provides an example analysis of the usefulness of these reasoning styles. We assess the suitability of these styles against a series of requirements which we have identified that KBSs must fulfil if they are to support help desk operations. We conclude that EBR systems are more likely to meet those requirements (the analysis draws on our earlier work in Bridge & Dearden, 1992).
An AI view of the treatment of uncertainty
Authors: Saffiotti Alessandro 
Published: July 2009

AbstractThis paper reviews many of the very varied concepts of uncertainty used in AI. Because of their great popularity and generality “parallel certainty inference” techniques, so-called, are prominently in the foreground. We illustrate and comment in detail on three of these techniques; Bayes' theory (section 2); Dempster-Shafer theory (section 3); Cohen's model of endorsements (section 4), and give an account of the debate that has arisen around each of them. Techniques of a different kind (such as Zadeh's fuzzy-sets, fuzzy-logic theory, and the use of non-standard logics and methods that manage uncertainty without explicitly dealing with it) may be seen in the background (section 5).The discussion of technicalities is accompanied by a historical and philosophical excursion on the nature and the use of uncertainty (section 1), and by a brief discussion of the problem of choosing an adequate AI approach to the treatment of uncertainty (section 6). The aim of the paper is to highlight the complex nature of uncertainty and to argue for an open-minded attitude towards its representation and use. In this spirit the pros and cons of uncertainty treatment techniques are presented in order to reflect the various uncertainty types. A guide to the literature in the field, and an extensive bibliography are appended.
Dialogue management for co-operative knowledge based systems
Authors: Stenton S. P. 
Published: July 2009

AbstractThis review presents a brief survey of approaches to describing dialogues with computers which are relevant to improving communication between users and knowledge based systems. One approach to achieving improvements is to exploit the conventions of human communication. The review draws together some of the work on co-operative behavour which reflects these conventions. An analysis is presented which goes some way towards identifying the knowledge required and the issues to be tackled.
The Linköping approach to technology transfer in knowledge engineering
Authors: Hägglund Sture 
Published: July 2009

AbstractA technology transfer programme, where people from industry have been educated and trained in knowledge engineering on a project basis, has been in operation since 1984 in the Computer and Information Science Department at Linköping University. This review presents the background for the programme, its organization, examples of training projects, educational activities and plans for the future development.
On distributed artificial intelligence
Authors: Eduardo Luis , Hern Castillo 
Published: July 2009

AbstractDistributed Artificial Intelligence has been loosely defined in terms of computation by distributed, intelligent agents. Although a variety of projects employing widely ranging methodologies have been reported, work in the field has matured enough to reveal some consensus about its main characteristics and principles. A number of prominent projects are described in detail, and two general frameworks, theSystem conceptual modeland theagent conceptual model, are used to compare the different approaches. The paper concludes by reviewing approaches to formalizing some of the more critical capabilities required by multi-agent interaction.