Soil nutrients and beta diversity in the Bornean Dipterocarpaceae: evidence for niche partitioning by tropical rain forest trees

1   The relative importance of niche- and dispersal-mediated processes in structuring diverse tropical plant communities remains poorly understood. Here, we link mesoscale beta diversity to soil variation throughout a lowland Bornean watershed underlain by alluvium, sedimentary and granite parent materials ( c . 340 ha, 8–200 m a.s.l.). We test the hypothesis that species turnover across the habitat gradient reflects interspecific partitioning of soil resources. 2   Floristic inventories (≥ 1 cm d.b.h.) of the Dipterocarpaceae, the dominant Bornean canopy tree family, were combined with extensive soil analyses in 30 (0.16 ha) plots. Six samples per plot were analysed for total C, N, P, K, Ca and Mg, exchangeable K, Ca and Mg, extractable P, texture, and pH. 3   Extractable P, exchangeable K, and total C, N and P varied significantly among substrates and were highest on alluvium. Thirty-one dipterocarp species ( n  = 2634 individuals, five genera) were recorded. Dipterocarp density was similar across substrates, but richness and diversity were highest on nutrient-poor granite and lowest on nutrient-rich alluvium. 4   Eighteen of 22 species were positively or negatively associated with parent material. In 8 of 16 abundant species, tree distribution (≥ 10 cm d.b.h.) was more strongly non-random than juveniles (1–10 cm d.b.h.), suggesting higher juvenile mortality in unsuitable habitats. The dominant species Dipterocarpus sublamellatus (> 50% of stems) was indifferent to substrate, but nine of 11 ‘subdominant’ species (> 8 individuals ha −1 ) were substrate specialists. 5   Eighteen of 22 species were significantly associated with soil nutrients, especially P, Mg and Ca. Floristic variation was significantly correlated with edaphic and geographical distance for all stems ≥ 1 cm d.b.h. in Mantel analyses. However, juvenile variation (1–10 cm d.b.h.) was more strongly related to geographical distance than edaphic factors, while the converse held for established trees (≥ 10 cm d.b.h.), suggesting increased importance of niche processes with size class. 6   Pervasive dipterocarp associations with soil factors suggest that niche partitioning structures dipterocarp tree communities. Yet, much floristic variation unrelated to soil was correlated with geographical distance between plots, suggesting that dispersal and niche processes jointly determine mesoscale beta diversity in the Bornean Dipterocarpaceae. Journal of Ecology (2005) doi: 10.1111/j.1365-2745.2005.01077.xPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72822/1/j.1365-2745.2005.01077.x.pd

Horizontal Inequity and Vertical Redistribution with Indirect Taxes: the Greek Case

Non-uniform indirect taxes treat equals and those unequal differently (horizontal inequity and vertical redistribution). Horizontal inequity is caused by taste differences among similar households, but some excises are designed to reflect social, not revealed, preferences. We apply two methodologies for decomposing the overall redistributive effect of the present and three alternative indirect tax structures into vertical and horizontal effects for Greece, using the Household Expenditure Survey micro-database. In all cases the taste component is considerable, even when we allow for social preferences, while improvements in vertical redistribution can be achieved, albeit at the cost of increased horizontal inequity.distributional effect of taxes, horizontal inequality, vertical redistribution, indirect tax reform, Greece.

Tree architecture in a Bornean lowland rain forest: intraspecific and interspecific patterns

Intraspecific and interspecific architectural patterns were studied for eight tree species of a Bornean rain forest. Trees 5–19 m tall in two 4-ha permanent sample plots in primary forest were selected, and three light descriptors and seven architectural traits for each tree were measured. Two general predictions were made: (1) Slow growing individuals (or short ones) encounter lower light, and have flatter crowns, fewer leaf layers, and thinner stems, than do fast growing individuals (or tall ones). (2) Species with higher shade-tolerance receive less light and have flatter crowns, fewer leaf layers, and thinner stems, than do species with lower shade-tolerance. Shade-tolerance is assumed to decrease with maximum growth rate, mortality rate, and adult stature of a species. Two light descriptors (crown position index and available space, but not canopy height) indicated higher light conditions for trees with more rapid growth, and for trees of greater height. Light levels were higher for species with high maximum growth rates and with greater adult stature. Most intraspecific architectural patterns conformed to the predictions: total leaf area and the number of leaf layers increased with increasing height and higher growth rates, and crown length/tree height ratio and stem slenderness respectively increased and decreased with growth rate. Yet, crown width/tree height ratio and relative crown length did not change with tree height, nor did they with previous growth. Slow growing (and short) trees may not have the reserves to invest in further horizontal crown growth, and to avoid leaf self-shading sufficiently within their relatively narrow crowns. Predictions on interspecific architectural patterns were not supported by the data. Species that were expected to be more shade-tolerant (lower maximum growth, lower mortality, and shorter stature) had deeper crowns, greater leaf areas, and more leaf layers, than did less shade-tolerant species. These patterns may be explained by lower loss rates of branches and leaves of the more shade-tolerant species. These species avoid leaf self-shading by distributing their leaves at the crown periphery. The role of lateral light appears to be more important than hitherto realized. The crown width/height ratio and height/dbh ratio were negatively correlated, both intraspecifically and interspecifically. It is suggested that trees co-ordinate their crown and stem growth so that they maintain their stability at small safety margins in the forest understore

Comparing Investment on New Transport Infrastructure: Roads vs. Railways?

This paper contributes to the debate on investment in transport infrastructure and the allocation of public funds between road and railway projects. We use a consistent social cost-benefit methodology to appraise investment in typical new inter-urban road and rail project. Our results suggest that road improvements have substantially higher returns than railway schemes. These findings cast doubt on the rationale of the new transport policy for the UK which proposes to allocate more public funds to the (private) railways than total new investment in strategic roads.

The Environmental Benefits from Road Pricing

In this paper the environmental benefits of optimal tolls in eight English towns are estimated. Tolls are simulated using the SATURN model (Simulation and Assignment of Traffic to Urban Road Networks) with associated software to simulate the changes in traffic patterns resulting from cordon tolls. With these results the optimal tolls are computed together with the resulting levels and speeds of traffic in each of our study towns. Changes in vehicle emissions are estimated and reduction in health and global warming costs computed. One of the main results is that any toll designed to reduce traffic congestion would yield positive environmental benefits.

Using Probabilistic Analysis to Value Power Generation Investments Under Uncertainty

This paper reviews the limits of the traditional ‘levelised cost’ approach to properly take into account risks and uncertainties when valuing different power generation technologies. We introduce a probabilistic valuation model of investment in three base-load technologies (combined cycle gas turbine, coal plant, and nuclear power plant), and demonstrate using three case studies how such a probabilistic approach provides investors with a much richer analytical framework to assess power investments in liberalised markets. We successively analyse the combined impact of multiple uncertainties on the value of alternative technologies, the value of the operating flexibility of power plant managers to mothball and de-mothball plants, and the value of mixed portfolios of different production technologies that present complementary risk-return profiles.investment, uncertainty, Monte-Carlo simulation, operating flexibility

Fair payment from road-users A review of the evidence on social and environmental costs

SIGLEAvailable from British Library Document Supply Centre-DSC:98/08525 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Optimal rates of tax during systemic reform

SIGLEGBUnited Kingdo