Showing papers by "Peter S. White published in 1983"

Evidence that temperate east north american evergreen woody plants follow corner's rules

Abstract: Summary Coener's rules, first developed for tropical trees, predict a spectrum of woody plant forms, from ones with small leaves, thin twigs (first-year shoots) and many branches, to ones with larger Waves, thick twigs and few branches. These rules were confirmed for nine broad-leaved and 12 needle-leaved evergreen woody plants of temperate eastern North America: for each of these groups, leaf size was positively correlated with twig cross-sectional area and both of these were negatively correlated with the number of twigs needed to bear 104 cm2 total leaf area. When compared to deciduous trees, characterized in a previous study, broad-leaved evergreens had leaves that were 85% smaller at a given twig thickness and needed 750% more twigs to bear a given total leaf area (at least when leaves older than 1 year were ignored). Needle-leaved evergreens bore relatively small leaves but large numbers of leaves per first-year shoot; they bore fewer twigs per 104 cm2 total leaf area than broad-leaved evergreens, but more than broad-leaved deciduous species. Broad-leaved deciduous trees were characterized by relatively large leaf sizes as a function of twig cross-sectional area and low numbers of twigs per 104 cm2 total leaf area. Although Corner's rules are a significant index of plant form, a full resolution of the differences between deciduous and evergreen species awaits further study.

Eastern Asian-Eastern North American floristic relations: the plant community level

Abstract: Most comparisons of the temperate floras of eastern North America and eastern Asia have addressed the systematic or floristic level. Data on vegetation pattern and structure, when present, have been broadly descriptive, with little detail on gradient relations or intercommunity pattern. Great Smoky Mountains National Park, the largest eastern temperate preserve of floristic diversity in the United States, lies near the center of development of the North American deciduous forest. The flora of this park was used to model the gradient distributions and ecological characteristics of species with east Asian near-relatives. The disjunct taxa (162 species or 13 percent of the flora) were a highly nonrandom assortment of the native flora (total = 1,21 1 species) as a whole: they were more likely to be primitive in phylogenetic standing, perennial, and woody. They were also non-randomly distributed among habitats, being more likely to be found on exclusively terrestrial, forested, and mesic sites. Taxa belonging to genera absent from eastern Asia (232 species or 19 percent of the flora) were an equally interesting non-random sample of the native flora: they were more likely to be herbaceous and advanced in phylogenetic standing. Absent taxa, however, essentially represented a random sample of the flora as a whole in terms of degree of habitat openness and substrate type. When gradient distributions were corrected for overall species richness distributions, absent taxa showed their peak importance on xeric sites. Taxa in wide-ranging north temperate genera (817 species or 67 percent of the flora) generally constituted a random sample of the flora as a whole; they showed peak importance at higher elevations. These data are used to make inferences about the distribution of species richness in the Smokies landscape. Evidence that the eastern Asian temperate deciduous forests were the most diverse temperate forests on earth is also reviewed. Alternative hypotheses concerning the nature of this heightened diversity are discussed. Investigations of the floristic relationship between temperate eastern Asia and eastern North America generally have treated such relationships at the geographical, systematic, or evolutionary level. There are, however, important ecological correlates to this relationship that have gone, for the most part, untested. This investigation uses a well-known eastern North American landscape, the Great Smoky Mountains, to examine ecological correlates of the floristic relationship. Although others have qualitatively described many of these patterns (cf. Hu, 1936; Cain, 1943; Li, 1952; Wang, 1961), quantitative studies have been lacking. An objective of this research, then, was to develop explicit tests for the distribution of ecological properties in the flora as a function of phytogeography. The landscape distribution of the Great Smoky Mountains flora was used to develop and discuss community level hypotheses on the eastern AsianNorth American floristic relationship. NORTH TEMPERATE DISJUNCTION

The reaction of S2NAsF6 with halogens: preparation and X-ray crystal structure of bis(difluorothio)nitronium hexafluoroarsenate(V), (SF2)2NAsF6; preparation of (SBr)2NAsF6, and vibrational spectrum and normal-co-ordinate analysis of the (SX)2N+(X = Cl or Br) cations

Abstract: Solutions of S2NAsF6 in liquid SO2 react with elemental chlorine and bromine yielding (SX)2NAsF6(X = Cl or Br), essentially quantitatively. No reaction was detected with iodine. The vibrational spectrum of (SBr)2N+ was similar to that of (SCl)2N+ of known structure, implying a similar structure for the bromine derivative. This conclusion was supported by a normal-co-ordinate analysis of (SX)2N+. The analysis was consistent with some positive interaction between the halogen atoms in (SX)2N+, possibly accounting for the cis planar geometry of these cations. Attempts to prepare (SF)2NAsF6 were unsuccessful. However, (SF2)2NAsF6 was synthesised by the reaction of S2NAsF6 and XeF2 in liquid SO2F2, essentially quantitatively. The structure of (SF2)2NAsF6 was determined by X-ray diffraction. The crystals are orthorhombic with a= 14.909(1), b= 9.843(4), c= 12.113(1)A, and Z= 8. The structure was refined in space group Pbca to a conventional R factor of 0.076 for 902 independent reflections with I 2σ(I). It consists of discrete (SF2)2N+ and AsF6– with some cation–anion interactions. The (SF2)2N+ cation has approximate C2v. symmetry with essentially eclipsed fluorine–sulphur bonds as viewed along the sulphur–sulphur axis. The average S–N and S–F distances are 1.551(10) and 1.523(8)A, and the average FSF and FSN bond angles are 94.0(5) and 100.2(6)°. The SNS bond angle is 121.1(6)°. The vibrational spectrum of (SF2)2NAsF6 is reported.

The preparation and X-ray crystal structure of [Se6I+]n·n[AsF6–] containing the catena-poly[cyclohexaselenium(I)-4 : 1-µ-iodo] cation

Abstract: [Se6I+]n·n[AsF6–] has been prepared quantitatively and its crystal structure determined by single crystal X-ray diffracticn; the cation consists of strands of [Se6I+]n, and the hexaselenium rings, of a chair conformation, are joined to two neighbouring hexaselenium rings by two weak [2.736(3)A] exocyclic 1,4 axial selenium–iodine bonds.

The preparation and crystal structure of the 3:1 adduct of antimony trifluoride and antimony pentafluoride containing the (Sb3F8+)∞ cation

Abstract: Antimony pentafluoride and SbF3·SbF5 are reduced by an excess of phosphorus trifluoride, in liquid arsenic trifluoride to form (SbF3)3SbF5 together with possibly small amounts of antimony trifluoride. Antimony pentafluoride is similarly reduced by an excess of elemental iodine to (SbF3)3SbF5 but with larger amounts of antimony trifluoride. A single crystal X-ray diffraction study of (SbF3)3SbF5 shows that it is monoclinic, space group P21/m, with cell dimensions a= 10.895(3), b= 10.941(3), c= 4.772(1)A, β= 96.66(3)°, and Z= 2. The structure was refined to a final R of 0.039 for 1 694 reflections. The structure consists of discrete SbF6– anions and parallel strands of (Sb3F8+)∞ which lie along the b axis. The polymeric strand can be considered to be composed of SbF3 and Sb2F5+ units joined by antimony–fluorine bridges [2.270(5), 2.414(5)A]. The vibrational spectrum of (SbF3)3SbF5 is reported.

Electrophilic behaviour of nitrosyls: the Boedeker reaction, the reactions of sulphite with nitrosyls, and the crystal and molecular structure of cis-bis(2,2′-bipyridine)chloro(nitrosylsulphito)ruthenium

Abstract: Similar adducts to that, [Fe(CN)5{(NO)(SO3)}]4–, formed in the Boedeker reaction have been obtained by the reaction of SO32– with trans-[RuCl(py)4(NO)]2+(py = pyridine) or cis-[RuX(bipy)2(NO)]2+(X = Cl or Br, bipy = 2,2′-bipyridine). These adducts, [RuCl(py)4{N(O)SO3}] and cis-[RuX(bipy)2{N(O)SO3}], are shown, principally by i.r. spectroscopy, to contain identical [N(O)SO3]– ligands to [Fe(CN)5{N(O)SO3}]4–. The structure of cis-[RuCl(bipy)2{N(O)SO3}] has been determined by X-ray diffraction. It is best regarded as a ruthenium(II) complex containing the hitherto unknown ligand [ONSO3]– which is N-co-ordinated to RuII. The ligand has a long (1.82 A) and weak (force constant 137 N m–1) N–S bond. The reversibility of the adduct formation is demonstrated. Crystal data for cis-[RuCl(bipy)2{N(O)SO3}]: orthorhombic, space group Pbca, a= 14.48(2), b= 19.49(2), c= 14.49(1)A, final R= 0.063 for 290 variables and 1 370 observed reflections. The ruthenium is in a distorted octahedral environment.

The preparation and X-ray crystal structures of 4-methyl-1,3,2-dithiazolium hexafluoroarsenate(V) and 5-methyl-1,3,2,4-dithiadiazolium hexafluoroarsenate(V) and their reduction to stable free radicals

Abstract: Acetonitrile, propyne, and acetylene react essentially quantitatively with S2NAsF6 to give the hexafluoroarsenate salts of 5-methyl-1,3,2,4-dithiadiazolium, 4-methyl-1,3,2-dithiazolium, and 1,3,2-dithiazolium respectively, the structures of the former two salts being determined by X-ray crystallography; the cations have been reduced chemically and electrolytically to form long-lived free redicals identified by their e.s.r. spectra.