Source Trees Research Articles

Plant Taphonomy: Ruminations on the Past, the Present, and the Future

Although the term “taphonomy” was coined by Ivan Efremov (1907–1972) in 1940 for the study of the various processes leading to fossil assemblages, a number of taphonomic experiments already had been undertaken in the early 19th century. Thus, while still in his thirties, John Lindley (1799–1865) showed that biodegradation of plant leaves in water is selective. Of the 86 angiosperm species he investigated, only 8 (9.3%) survived two years when kept in an iron tank. On the other hand, 13 of the 16 conifers (81.25%) remained intact (Lindley and Hutton, 1831– 1837). Another plant taphonomist avant la lettre was Charles Darwin, who published his observations on the flotation of fruits and seeds (diaspores; Darwin, 1856). Christ's College, Cambridge, was not only Darwin's alma mater, but that of Professor Tom M. Harris. Many years ago, he told me about a little project he conducted while at Cambridge (1922–1935). The oak leaves he found in a riverbed were smaller than those that could be observed at eye level on the source trees. As we now know, this phenomenon is caused by the predominance of sun leaves in plant assemblages. At roughly the same time, Ralph Chaney (1890–1971), working at Berkeley, formulated a set of rules regarding the factors affecting the composition of leaf assemblages. He believed that the following aspects were of prime importance (Chaney, 1924; Chaney and Sanborn, 1933): (1) distance of the species from the depocenter; (2) the heights of possible source plants; (3) the plant's leaf-shedding ability; (4) leaf size and shape, because these influence dissemination by wind and water; and (5) the original thickness of the lamina, as a measure of resistance to leaf destruction. Plant taphonomy became important to me in the late 1960s during my doctoral thesis (Ferguson, 1971) because it was necessary to …

Build-level components

Reuse between software systems is often not optimal. An important reason is that while at the functional level well-known modularization principles are applied for structuring functionality in modules, this is not the case at the build level for structuring files in directories. This leads to a situation where files are entangled in directory hierarchies and build processes, making it hard to extract functionality and to make functionality suitable for reuse. Consequently, software may not come available for reuse at all, or only in rather large chunks of functionality, which may lead to extra software dependencies. In this paper, we propose to improve this situation by applying component-based software engineering (CBSE) principles to the build level. We discuss how existing software systems break CBSE principles, we introduce the notion of build-level components, and we define rules for developing such components. To make our techniques feasible, we define a reengineering process for semiautomatically transforming existing software systems into build-level components. Our techniques are demonstrated in two case studies where we decouple the source tree of Graphviz into 46 build-level components and analyze the source tree of Mozilla.

Early fate of Myristica hypargyraea seeds dispersed by Ducula pacifica in Tonga, Western Polynesia

Abstract Although pigeons from the genus Ducula are considered among the best avian dispersers of large seeds in Asia and the Pacific, little has been documented on their role. The early fate of dispersed and undispersed seeds of the large‐seeded tree Myristica hypargyraea A. Gray was studied in order to understand the advantage of seed dispersal by the Pacific Pigeon, Ducula pacifica Gmelin in Tonga. Frequency of visits by frugivores to fruiting trees and dispersal distance of seeds were measured. Pre‐dispersal vertebrate seed predation was assessed, then post‐dispersal predation was measured over 160 days. Overall, pre‐dispersal seed predation by parrots was low but variable among trees sampled. Most seeds (54.7%) in the study area were estimated to be dispersed by D. pacifica; 79.7% of those ingested were expelled directly beneath conspecific fruiting crowns, 20% were dispersed locally and < 0.3% were dispersed more than 300 m into a different forest type. Flying foxes (Pteropus tonganus Quoy and Gaimard) dispersed very few seeds (0.7%) and all were dropped below fruiting crowns. Between 4% and 39% of dispersed and undispersed seeds were still viable, or had established seedlings after 160 days. Most seeds had been removed or killed by rats, and seed survival was highest for locally dispersed seeds (approx. 20 m from source trees and within the M. hypargyraea forest). Although D. pacifica was the only frugivore observed to disperse seeds into this higher zone of survival, overall they did not confer a great advantage to seed survival since significant numbers of seeds/seedlings also persisted under fruiting crowns (27% under crowns compared with 39% locally dispersed). Nevertheless, D. pacifica was the only vector by which seeds were regularly moved within the M. hypargyraea forest and over longer distances, and hence, D. pacifica still plays a significant role in the regeneration of M. hypargyraea.

Spatial ecology of a threatened python (Morelia spilota imbricata) and the effects of anthropogenic habitat change

Abstract Large predators play important ecological roles, but often are sensitive to habitat changes and thus are early casualties of habitat perturbation. Pythons are among the largest predators in many Australian environments, and hence warrant conservation‐orientated research. Carpet pythons (Morelia spilota imbricata) have declined across much of south‐western Australia presumably because of habitat clearance and degradation. Information on habitat use, home range sizes and movements is needed to plan for the conservation of this important predator. We studied pythons at two study sites (Garden Island and Dryandra Woodland) with markedly different climates, habitat types and disturbance histories. We surgically implanted radio‐transmitters in 91 pythons and tracked them for periods of 1 month to 4 years. Dryandra pythons remained inactive inside tree hollows during cooler months (May–September), whereas some (especially small) pythons on Garden Island continued to move and feed. Overall weekly displacements (mean = 100–150 m) were similar at the two study sites and among sex/age classes, except that reproductive females were sedentary during summer while they were incubating eggs. Home ranges averaged 15–20 ha. Adult male pythons had larger home ranges than adult females at Dryandra, but not at Garden Island. Radio‐tracked snakes at Dryandra exhibited high site fidelity, returning to previously occupied logs after long absences and reusing tree hollows for winter shelter. Many of the logs used by snakes had been felled during plantation establishment >70 years ago, with little subsequent regeneration of source trees. In contrast, Garden Island snakes usually sheltered under dense shrubs. Habitat usage was similar among different sex/age classes of snakes at each site, except that juvenile pythons were more arboreal than adults. Although carpet pythons demonstrate great flexibility in habitat use, certain habitat elements appear critical for the persistence of viable populations. Fire plays a central role in this process, albeit in complex ways. For example, low‐intensity fires reduce the availability of hollow logs on the ground at Dryandra and fail to regenerate shrub thickets required by prey species. Paradoxically, high‐intensity fires stimulate shrub thickets and fell trees creating new logs – but might also threaten overwinter trees. Thus, the impact of disturbances (such as wildfires) on the viability of python populations will be mediated in complex ways by alteration to important microhabitats such as vegetation cover or log availability. At Dryandra, landscape management should include occasional fire events to generate new logs as well as shrub thickets used by prey. Strategic burning may also be required at Garden Island to regenerate some vegetation communities.

Seedling recruitment in a hurricane‐driven tropical forest: light limitation, density‐dependence and the spatial distribution of parent trees

Summary We used inverse modelling to parameterize spatially‐explicit seedling recruitment functions for nine canopy tree species in the Luquillo Forest Dynamics Plot (LFDP), Puerto Rico. We modelled the observed spatial variation in seedling recruitment following Hurricane Georges as a function of the potential number of seedlings at a given location (based on local source trees and the potential contribution of parents from outside of the mapped area) and of light levels and density‐dependent mortality during establishment. We adopted the model comparison paradigm and compared the performance of increasingly complex models against a null model that assumes uniform seedling distribution across the plot. Our data supported a model in which parents must reach a threshold size before any seedling production will occur. Once parents attain that size, the relationship between tree diameter and the number of seedlings produced is fairly flat for the majority of species. These results contradict previous analyses that simply assumed a linear relationship between biomass and seedling production and a uniform size threshold for seedling production across species. The majority of species tested supported models that included at least one of a bath term (contribution from non‐local trees), conspecific density dependence and light availability after the hurricane. Density dependence shifted the mode of the effective dispersal kernel away from potential parent trees and significantly reduced the number of seedlings established near parent trees. Recruitment from non‐local sources accounted for 6–81% of observed seedling recruitment depending upon the tree species. Light availability appeared to divide species into three groups that showed more successful seedling establishment at low (< 5% of full sun), intermediate or high light levels (> 30% full sun). Differences between individual species in the importance of local vs. bath recruitment and the intensity of density dependence suggest the existence of distinct recruitment syndromes that go beyond the traditional focus of tropical tree life histories. Understanding these syndromes will provide valuable insights into the spatial distribution of tropical tree species and the maintenance of tropical forest diversity.

Multi-shared-trees based multicast routing control protocol using anycast selection

A novel internet multicast routing protocol is presented to possess efficiency and effectiveness for multicast packet routing with short delay, high throughput, resource utilization and scalability for a single multicast group g. The protocol has two features: (1) Multiple Shared-Trees (MST) are configured to provide efficient, dynamic and quality multicast routing; (2) Anycasting approach is applied by forming the tree roots into an anycast group so that the multicast packets can be anycast to the nearest node at one of the shared trees to achieve the best routing service for the packets. The performance of the MST protocol is analyzed through extensive simulations and compared with well-known source tree and shared-tree routing.

Refactoring-aware versioning in Eclipse

To fully support refactorings in a team development environment we have implemented a refactoring-aware repository provider as an extension plug-in to the Java Development Tools in Eclipse. The versioning system treats refactorings as first-class changes described as semantic ac- tions rather than the set of resulting changes scattered over the source tree. We also introduce refactoring-aware merge, which merges refactorings as well as traditional changes utilizing the se- mantics of the refactorings to detect and resolve merge conflicts. It also ensures that the semantic meaning of a refactoring is preserved after the merge.

Gene Flow in European Beech (Fagus sylvatica L.)

Three relatively isolated stands were used to study gene flow in European beech (Fagus sylvatica L.) in Northern Germany. Nine allozyme loci (Got-B, Idh-A, Lap-A, Mdh-B, Mdh-C, Mnr-A, 6-pgdh-A, Pgi-B and Pgm-A) were utilized for multilocus-genotyping adult trees and seeds. Expected heterozygosity (He) ranged from 0.325 to 0.351 for the three stands. F(ST) revealed that there was small differentiation among stands (mean F(ST) = 0.013). The indirect estimates of gene flow (Nm) based on the mean F(ST) were high and the average Nm was 19.14. External gene flow by pollen ranged from 0.7 to 1.2% inferred from new alleles in seed samples. Moreover, paternity analysis was used to assess effective pollen dispersal by inferring paternity of offspring. The weighted mean distances of pollen dispersal for these three stands were 36.8 and 37.1 m based on simple exclusion procedure and most-likely method, respectively. Two of the trees in one stand had rare allozyme alleles (Lap-A1 and Idh-A4, respectively), which were used to directly measure pollen movement away from those trees. The frequency of the rare Lap and Idh alleles in seeds declines as the distance from the source tree increases. The weighted mean distance of pollen dispersal with rare allele Lap-A1 or Idh-A4 was 26.3 m.

Molecular evidence for limited dispersal of vegetative propagules in the epiphytic lichenLobaria pulmonaria

Propagation, whether sexual or asexual, is a fundamental step in the life cycle of every organism. In lichenized fungi, a great variety of vegetative propagules have evolved in order for the symbiotic partners to disperse simultaneously. For lichens with the ability of sexual and asexual reproduction, the relative contribution of vegetative dispersal is unknown but could, nonetheless, be inferred by studying genotype distribution. The genetic structure of three Lobaria pulmonaria (Lobariaceae) populations from Switzerland was investigated based on the observed variation at six microsatellite loci. All three populations had a clustered distribution of identical genotypes at small spatial scales. The maximum distance between identical genotypes was 230 m. At a distance of 350 m from a source tree, seemingly suitable habitat patches were too far apart to be colonized. Some multilocus genotypes were frequent within local populations but no genotypes were shared among populations. The restricted occurrences of common genotypes as well as the clustered distributions are evidence for a limited dispersal of vegetative propagules in L. pulmonaria. Gene flow among isolated populations will ultimately depend on the capacity of long-distance dispersal and thus probably depend on sexual reproduction.

Seed Transmission of Citrus leaf botch virus: Implications in Quarantine and Certification Programs.

Citrus leaf blotch virus (CLBV) was purified and characterized from a Nagami kumquat (Fortunella margarita (Lour.) Swingle), showing bud union crease when propagated on Troyer citrange (Citrus sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.) (2). The complete nucleotide sequence of its genomic RNA was determined (4), and biological and molecular diagnosis methods were developed (1,3). CLBV, detected in several citrus cultivars from Australia, the United States (Florida and California), Japan, and Spain is usually associated with bud union crease on citrange or citumelo (C. paradisi (Macfad.) × P. trifoliata). The economic importance of CLBV for the citrus industry is presently unknown since its incidence in different citrus areas has not been evaluated, and its actual involvement in causing bud union crease on trifoliate rootstocks has not yet been proved. To assess seed transmissibility of this virus, 120 to 210 seeds from CLBV-infected Troyer citrange, Nagami kumquat, or sour orange (Citrus aurantium L.) plants were grown in a greenhouse. Individual 4-month-old seedlings were analyzed for CLBV by reverse transcriptase polymerase chain reaction, and infection was confirmed by biological indexing on Dweet tangor (C. tangerina Hort. ex Tanaka × C. sinensis (L.) Osbeck) when seedlings were approximately 18 months old. Seed transmission was found in 2.50, 2.52, and 2.46% of the citrange, kumquat, and sour orange seedlings, respectively. This finding indicates that control of CLBV spread during citrus propagation will require, not only virus-free buds, but also rootstock seedlings that originate from CLBV-free seed source trees. Because CLBV is seed transmissible, regulations of citrus certification programs may need to be changed to include increased control of seed source trees. Also, international regulations for citrus seed movement likely will have to be augmented to include a phytosanitary certification indicating that seeds have been collected from CLBV-free trees.

Variable order revised binary treecode

Three essential improvements are described to the treecode in terms of the expansion formula, the choice of the expansion order as well as the tree structure. Firstly, the multipole expansion is based on the real spherical harmonic functions to reduce the CPU time. Secondly, the expansion order is given in terms of the ratio of the distance of a field point to a source box to the box size, which reflects the relative error of the expansion. With that, a large portion of the sources has been evaluated by the multipole expansion at low levels of the source tree, which is around two-thirds of sources at the first two levels of the tree averagely. The algorithm reduces the CPU time dependency on expansion order p from O( p 2) of the classical treecode to be lower than a linear dependency in p max, where p max is the maximum expansion order used in the variable order expansion. Thirdly, a revised binary tree is built by performing the bisections thrice at each tree level, discarding the boxes generated in the first two bisections and remaining only the boxes generated in the last one. This tree avoids the disadvantage of a binary treecode demanding significantly more CPU time than an oct-treecode. It has high adaptiveness to the source distribution and perfect load balancing for performing the parallelization. Simulations are carried out for N vortex elements and N field points distributed randomly in a cube, a 5:1:1 parallelepiped, and a 10:1:1 parallelepiped, using the oct-tree and revised binary tree, respectively. The algorithm is an order of magnitude faster than those of Strickland et al. [ESAIM: Proceedings 7 (1999) 408], Warren and Salmon [Comput. Phys. Commun. 87 (1995) 266], and Lindsay and Krasny [J. Comput. Phys. 172 (2001) 879]. Simulations also demonstrate the efficiency of the revised binary treecode for an inhomogeneous source distribution.

The phylogeny of acorn weevils (genus Curculio) from mitochondrial and nuclear DNA sequences: the problem of incomplete data

We considered the contribution of two mitochondrial and two nuclear data sets for the phylogenetic reconstruction of 22 species of seed beetles in the genus Curculio (Coleoptera: Cuculionidae). A phylogenetic tree from representatives found on various hosts was inferred from a combined data set of mitochondrial DNA cytochrome oxidase subunit I, mitochondrial cytochrome b, nuclear elongation factor 1α, and nuclear phosphoglycerate mutase, used for the first time as a molecular marker. Separate parsimony analyses of each data set showed that individual gene trees were mainly congruent and often complementary in the support of clades but the analysis was complicated by failure of PCR amplification of nuclear genes for many taxa and hence missing data entries. When the four gene partitions were combined in a simultaneous analysis despite the missing data, this increased the resolution and taxonomic coverage compared to the individual source trees. Alternative approaches of combining the information via supertree methodology produced a comparatively less resolved tree, and hence seem inferior to combining data matrices even in cases where numerous taxa are missing. The molecular data suggest a classification of the European species into two species groups that are in accordance with morphological characteristics but the data do no support any of the previously recognised American species groups.

New tricks: how open source changed the way my team works

A commercial software team contributed to an open source implementation of the Windows API on X-Windows and Unix. Wine is an open source implementation of the Windows API, a compatibility layer that lets native windows programs run on X-Windows and Unix. With our contribution filling in some gaps, our client planned to include Wine with a slightly modified product. Expecting chaos in the organization and code, the team instead found a structured community with procedures all its own. The version control tool on the Wine team is CVS (concurrent version system), an open source, network-transparent version control system. Patches on Wine are relatively small, which makes them easier to review and less risky to add to the source tree.

A supertree of early tetrapods

A genus-level supertree for early tetrapods is built using a matrix representation of 50 source trees. The analysis of all combined trees delivers a long-stemmed topology in which most taxonomic groups are assigned to the tetrapod stem. A second analysis, which excludes source trees superseded by more comprehensive studies, supports a deep phylogenetic split between lissamphibian and amniote total groups. Instances of spurious groups are rare in both analyses. The results of the pruned second analysis are mostly comparable with those of a recent, character-based and large-scale phylogeny of Palaeozoic tetrapods. Outstanding areas of disagreement include the branching sequence of lepospondyls and the content of the amniote crown group, in particular the placement of diadectomorphs as stem diapsids. Supertrees are unsurpassed in their ability to summarize relationship patterns from multiple independent topologies. Therefore, they might be used as a simple test of the degree of corroboration of nodes in the contributory analyses. However, we urge caution in using them as a replacement for character-based cladograms and for inferring macroevolutionary patterns.

Novel Versus Unsupported Clades: Assessing the Qualitative Support for Clades in MRP Supertrees

Matrix representation with parsimony (MRP) supertree construction has been criticized because the supertree may specify clades that are contradicted by every source tree contributing to it. Such unsupported clades may also occur using other supertree methods; however, their incidence is largely unknown. In this study, I investigated the frequency of unsupported clades in both simulated and empirical MRP supertrees. Here, I propose a new index, QS, to quantify the qualitative support for a supertree and its clades among the set of source trees. Results show that unsupported clades are very rare in MRP supertrees, occurring most often when there are few source trees that all possess the same set of taxa. However, even under these conditions the frequency of unsupported clades was <0.2%. Unsupported clades were absent from both the Carnivora and Lagomorpha supertrees, reflecting the use of large numbers of source trees for both. The proposed QS indices are correlated broadly with another measure of quantitative clade support (bootstrap frequencies, as derived from resampling of the MRP matrix) but appear to be more sensitive. More importantly, they sample at the level of the source trees and thus, unlike the bootstrap, are suitable for summarizing the support of MRP supertree clades.

Spatial patterns in long‐distance dispersal ofQuercus ilexacorns by jays in a heterogeneous landscape

In this paper, I analyse the interaction between the holm‐oakQuercus ilex, and one of its main dispersers, the European jayGarrulus glandarius, in an heterogeneous Mediterranean landscape. I quantify the spatial dispersal pattern of the seed shadow at two spatial scales, landscape (among patches) and microhabitat (within patches), by directly tracking the movement of seeds. Two main traits of the jay‐mediated dispersal of holm‐oak acorns across the landscape, the spatial pattern of dissemination and the distance from the source tree, are significantly and directly influenced by jay activity. Jays moved acorns nonrandomly, avoiding one main patch type of the study area to cache acorns, the shrubland‐grasslands, and moving most of the acorns to pine stands, whether afforestation or open pinewoods. Within each patch type, jays had also a strong preference for caching acorns in some microhabitats, since&gt;95% of the acorns dispersed by jays were cached beneath pines. The distance of holm‐oak acorn dispersal was long in the study site, over 250 m, with some dispersals occurring up to 1 km from the source oaks. The shape of the dispersal kernel function fitted to the dispersal pattern produced by jays differed from those quantified for many other plant species. Jay‐mediated dispersal had two components, one local and another produced by long‐distance dispersal. Due to the heterogeneity of these Mediterranean environments, this difference in scale overlaps with a difference in habitat composition, short distances events resulting in dispersals within the same oak stands and long distance events resulting in dispersal outside of oak stands, usually to other vegetation units. Jay activity and movement pattern can have thus dramatic effects on both the local regeneration as well as the potential for regional spread of the holm‐oak populations.

THE INFLUENCE OF SOURCE TREE ON SOMATIC EMBRYOGENESIS FROM EASTERN BLACK WALNUT (JUGLANS NIGRA) IMMATURE COTYLEDONS

The influences of stage of fruit development, media treatments and source tree (genotype) on somatic embryogenesis in Juglans nigra L. were studied over two years. Beginning at 12 weeks and continuing until 15 weeks postanthesis, 1 cm 2 explants from cotyledons of immature seeds were excised from eastern black walnut fruit during 1999 and 2000. Fruits from different trees were tested each year because of the alternate bearing habit of this species. Explants were placed on WPM, DKW, or LP medium with 1 g L -1 casein hydrolysate, 30 g L -1 sucrose, 5.0 μM thidiazuron (TDZ), 0.1 μM 2,4-D, and 7 g L -1 Sigma agar. The explants were under 16-hour photoperiod and 25 °C for four weeks. Explants were then transferred to basal media with 1 g L -1 casein hydrolysate and no plant growth regulators and incubated in darkness. Each year, the experimental design was a completely randomized design with 20 replications per treatment with factorial combinations of media salts, source tree and number of weeks post anthesis. During 1999, there was a significant interaction between genotype and media with LP being a consistently good medium for all three genotypes, with a range of 1.0 to 1.9 somatic embryos per explant and 24 to 30 percent of the explants producing somatic embryos depending on genotype. During 2000, there was a significant interaction between genotype and medium, and between genotype and number of weeks postanthesis. Explants from the best source tree produced 2.8 somatic embryos per explant plus 34 to 38% of the explants were embryogenic when DKW or LP salts were used. Medium had little effect on explants from one of the other two genotypes; the third genotype produced the most embryos when LP medium was used. Explants tended to be the most embryogenic 12 weeks postanthesis with 0.8 to 4.2 embryos per explant depending on source tree.

Does Early-Season Defoliation of Crabapple (Malus sp.) by Eastern Tent Caterpillar (Lepidoptera: Lasiocampidae) Induce Resistance to Japanese Beetles (Coleoptera: Scarabaeidae)?

We tested the hypothesis that early-season defoliation of flowering crabapple, Malus sp., by eastern tent caterpillars, Malacosoma americanum F., induces localized or systemic resistance to Japanese beetles, Popillia japonica Newman, feeding on the same trees in late June. ‘Candymint Sargent’ crabapple trees were inoculated with M. americanum egg masses, resulting in extensive defoliation during March and April. Second flush leaves of defoliated trees were smaller and thinner than those of control trees. In laboratory feeding assays with non-damaged foliage, beetles generally preferred fully expanded leaves over partially expanded ones, regardless of whether or not the source tree had been defoliated. Detached first flush leaves with caterpillar damage were fed upon less than comparable non-damaged leaves, suggesting that early-season wounding causes some within-leaf reduction in palatability to P. japonica. Other assays with detached first- and second-flush leaves, however, indicated absence of induced, systemic resistance. Previously-defoliated and control trees sustained comparable damage from natural beetle populations in the field. Our results suggest that defoliation of Malus sp. by tent caterpillars in early spring is unlikely to reduce feeding damage by Japanese beetles later in the same growing season.

Evidence for an in situ early Paleocene rainforest from Castle Rock, Colorado

A very diverse, early Paleocene (63.8 ± 0.3 Ma) fossil leaf site located in Castle Rock, Colorado represents nearly autochthonous burial of a rainforest floor. This is an unusual fossil flora preserved in an unusual manner. The site, on the western margin of the Denver Basin in synorogenic sediments associated with the rise of the Laramide Front Range, is dated using multiple methods. Leaves are preserved in three distinct units overlying a poorly developed paleosol that contains in situ tree trunks. Fossil-bearing units are continuous along 150 m of outcrop. The leaves were apparently preserved as a result of rapid deposition of sand and mud onto the floor of a mature rainforest via overbank flooding. Five quarries were excavated and the leaves from these quarries were segregated by morphotype and scored for leaf area and margin type. From 1030 specimens, we document 93 unique dicotyledonous angiosperm leaf types, three cycads, three ferns, two conifers, and seven seed types. There is little taxonomic variation among leaf-bearing units of a single quarry, but the taxonomic composition varies significantly among laterally spaced quarries, suggesting that the fossil leaf litter reflets the original growth positions of the source trees. We compare the fossil leaf litter to leaf litter of modern forests and show that the Castle Rock flora has numerous features in common with extant equatorial rainforests, including dominance by angiosperms, high species richness, large leaves that often have smooth margins and drip tips, and high spatial heterogeneity from quarry to quarry.

Suppression of Decline-inducing Isolates of Citrus Tristeza Virus by Nondecline-inducing Isolates

Bark chips from six container-grown citrus trees, infected with nondecline-inducing citrus tristeza virus (CTV) isolates and maintained in a vector-free greenhouse for 10 years, 15 commercial grapefruit (Citrus paradisi Macf.) trees, and 16 commercial sweet orange [C. sinensis (L.) Osbeck] trees were used to inoculate three indicator plants each of `Madam Vinous' sweet orange [C. sinensis (L.) Osbeck], sour orange (C. aurantium L.), `Duncan' grapefruit (C. paradisi Macf.), `Mexican' lime [C. aurantifolia (Christm.)], Swingle citrumelo [C. paradisi Macf. × Poncirus trifoliota (L.) Raf.], and sour orange grafted with `Hamlin' sweet orange [C. sinensis (L.) Osbeck]. All plants providing bark chips had repeatedly tested positive by enzyme-linked immunosorbent assay (ELISA) for CTV [reacted with monoclonal antibody (MAb) 17G11], but tested negative for Florida decline-inducing isolates of CTV (did not react with MAb MCA13). After 6 months in vector-free greenhouses, all in oculated trees (except Swingle citrumelo, which is considered CTV resistant) were positive for CTV by 17G11 ELISA. In addition, some indicator plants inoculated from nine (two container, two commercial grapefruit, and five commercial orange trees) of the 37 bark chip source trees also were positive for decline-inducing CTV by MCA13 ELISA. Some of these positive indicators also showed vein-clearing symptoms characteristic of infection with a severe isolate of CTV. No control, noninoculated indicators in the same greenhouse, became infected with either decline-inducing or nondecline-inducing CTV. These results indicate that decline-inducing isolates of CTV can be present as a minor component of a mixture at levels undetectable by ELISA, and that these decline-inducing isolates can become detectable by ELISA and sometimes by symptoms when inoculated into indicator plants.