Aim: To test the extent to which the vertical structure of tropical forests is determined by environment, forest structure or biogeographical history. Location: Pan-tropical. Methods: Using height ...and diameter data from 20,497 trees in 112 non-contiguous plots, asymptotic maximum height (H AM ) and height—diameter relationships were computed with nonlinear mixed effects (NLME) models to: (1) test for environmental and structural causes of differences among plots, and (2) test if there were continental differences once environment and structure were accounted for; persistence of differences may imply the importance of biogeography for vertical forest structure. NLME analyses for floristic subsets of data (only/excluding Fabaceae and only/excluding Dipterocarpaceae individuals) were used to examine whether family-level patterns revealed biogeographical explanations of cross-continental differences. Results: H AM and allometry were significantly different amongst continents. H AM was greatest in Asian forests (58.3 ± 7.5 m, 95% CI), followed by forests in Africa (45.1 ± 2.6 m), America (35.8 ± 6.0 m) and Australia (35.0 ± 7.4 m), and height—diameter relationships varied similarly; for a given diameter, stems were tallest in Asia, followed by Africa, America and Australia. Precipitation seasonality, basal area, stem density, solar radiation and wood density each explained some variation in allometry and H AM yet continental differences persisted even after these were accounted for. Analyses using floristic subsets showed that significant continental differences in H AM and allometry persisted in all cases. Main conclusions: Tree allometry and maximum height are altered by environmental conditions, forest structure and wood density. Yet, even after accounting for these, tropical forest architecture varies significantly from continent to continent. The greater stature of tropical forests in Asia is not directly determined by the dominance of the family Dipterocarpaceae, as on average non-dipterocarps are equally tall. We hypothesise that dominant large-statured families create conditions in which only tall species can compete, thus perpetuating a forest dominated by tall individuals from diverse families.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
The deposition of polycyclic aromatic hydrocarbons on substrate surfaces is a key step for using such disklike molecules in nanoelectronic devices. An alternative to the (frequently problematic) ...preparation by evaporation or deposition from solution is to use the substrate surface as a template for the planarization that accompanies the cyclodehydrogenation (see picture).
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Tree architecture determines a tree's light capture, stability, and efficiency of crown growth. The hypothesis that light demand and adult stature of tree species within a community, independently of ...each other, determine species' architectural traits was tested by comparing 53 Liberian rain forest tree species. We evaluated whether species differed in their tree height, crown depth, and crown diameter, when compared at a standardized size of 15-cm diameter at breast height, and how their architecture changed early during ontogeny. Tree height was positively correlated with adult stature and light demand. By producing a relatively slender stem, large-stature species are able to rapidly reach their reproductive size, at a low cost for construction and support. Light-demanding species need a slender stem to be able to attain or maintain a position in the canopy. Both crown depth and crown diameter were negatively correlated with adult stature, but not with light demand. This is in contrast with the hypothesis that shade-tolerant species should have a shallow crown to reduce self-shading in a light-limited environment. Investing energy in height growth rather than lateral crown growth allows a rapid vertical stem extension, but crown diameter has to be sufficiently small to reduce the risk of mechanical failure. All architectural patterns were maintained during ontogeny. The key factors driving interspecific differences in tree architecture are the costs of height extension and mechanical stability. In general, light demand and adult stature represent independent axes of architectural differentiation, affecting tree architecture in different ways.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem ...allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: 1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap). 2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A). 3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level H across all plots to within amedian −2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account.
1 A height-light trajectory (HLT, a fitted curve relating canopy exposure to tree height) was determined for populations of individuals of each of 47 tree species in a Liberian lowland rainforest. ...The HLTs were compared and related to tree allometry and adult stature. Crown exposure was measured for 7460 trees and related to tree height using a multinomial regression analysis. Individual trees were followed for 2.8-9.8 years. 2 The trajectories of the 47 species were compared with the average vertical light profile in the forest canopy. Evidence was found for the existence of all nine trajectories hypothesized on the basis of three possible light environments (high, intermediate and low) for juveniles and adults. The classical paradigm of pioneer vs. shade tolerant, based on seed and seedling responses, does not therefore apply to post-seedling stages. 3 The majority of the species followed the vertical light profile in the forest canopy, starting in low light environments in the juvenile stage and ending up in high light environments in the adult stage. Only two species complied with the classic notion of whole-life shade tolerants and whole-life shade intolerants (one each). 4 The predictable vertical light gradient in the forest canopy has led to a close association between adult height, light trajectories and allometric traits. Large-stature species tend to have relatively slender stems and narrow crowns, and therefore realize a faster temporal and height-related increase in crown exposure. 5 Tree species have different height-light trajectories when they grow from seedling to adulthood. This may have profound repercussions for our current views on plasticity and adaptation, light partitioning and species coexistence, and on silviculture and management.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
6.
Ionic adsorbates on metal surfaces Bagus, P. S.; Wieckowski, A.; Wöll, Ch
International journal of quantum chemistry,
December 2010, Volume:
110, Issue:
15
Journal Article
In higher education choral curricula, the opportunity to study the breathtakingly rich scope of music rooted in Africa and the African diaspora with rigor and depth is often marginalized, neglected, ...or missing. If studied, it may be framed in the context of “other music” in contrast to music of the Western European canon, creating an oppositional framework rather than an interdependent one. Moreover, opportunities to study the political economy of this music in relationship to race, class, gender, and religion are lacking. This has multiple ramifications for music students’ preparedness to engage in global habits of citizenship in support of racial justice.Through an experimental design and case study of a college course, this qualitative research project explores the questions, “How are higher education choral curricula connected to racialized political and economic realities?” and “How do they perpetuate or undermine these realities?” Using Manning Marable’s Living Black History: How Reimagining the African-American Past Can Remake America’s Racial Future (Marable 2006) as a touchstone, the research is grounded in a combination of theories about race, history, music, and pedagogy applied to the design of a college course, “Choral Music of the African Diaspora in the United States: Toward a 'Living Black History'”. The case study is an assessment of students’ reflective writing that analyzes shifts in perspective from views that are oppositional to ones that are interdependent and is located in an inquiry into habits of citizenship toward racial justice in a global context.
Membrane patches were excised from enzymatically dissociated frog toe muscle. High-conductance anion channels could be induced in previously quiet patches by 20-120 s depolarizations beyond +20 mV ...and then studied in the potential range from -80 to +60 mV for a long time. From reversal potentials the estimated permeability ratios PCl/PNa and PCl/Pglucuronate were near 3.5 and 4, respectively. There were probably 5 or more conductance levels (substates) for a single channel, the most common in symmetrical 110 mM NaCl being 260 and 70 pS at 10 degrees C. Gating was complex, with rapid and slow events and several gating modes, including periods of rapid flickering. Channels closed reversibly at potentials more negative than -50 mV. The channel was blocked by application to the cytoplasmic face of tannic acid, gallic acid, and zinc but not of DIDS or 9-anthracene-carboxylic acid, and it was blocked by extracellular zinc.
Single ATP-sensitive K channels were studied in membrane patches excised from enzymatically dissociated mouse toe muscle. The channel conductance is 74 pS in symmetrical 160 mM KCl solutions. ...Replacement of K+ by Na+ in the internal solution or 2 mM internal Ca2+ or Mg2+ induced a rectification of the current-voltage curve at positive potentials. No change of the current-voltage curve was observed by adding small amounts of the channel blockers ATP (20-100 microM) or tolbutamide (0.5 mM) to internal 160 mM KCl solutions. The openings of the channel occurred in bursts. Open (tau o), closed (tau c) times within bursts and pauses (tau p) between bursts were determined over a wide range of positive and negative membrane potentials. At increasing potentials tau o increases, tau c reaches a minimum near 0 mV and tau p decreases. According to the voltage dependence and the time scale of channel blockage three types of blocking agents could be distinguished: (i) small internal cations (Na+, Ca2+, Mg2+) are "fast" blockers at positive voltages; at negative voltages they decrease tau o and increase tau c. (ii) Internal ATP anions produce a voltage-dependent decline of the open-state probability and strongly decrease tau o. (iii) Tolbutamide causes a voltage-independent decrease of the open-probability and its main effect is an increase of tau p. The results suggest that the ATP-sensitive K channel has an internal gate like those of other voltage-gated cation channels and that different blockers interfere with different transitions in channel gating.
PDF
