The Influences of Conventional and Low Density Thinning on Leaf Area, Growth, and Growing Space Relationships of Eastern White Pine (Pinus Strobus L.)

Despite the commercial importance and widespread management of eastern white pine {Pinus strobus L.) in the Northeast, surprisingly little is known about the effects of thinning on even-aged stand development. To address this, patterns of leaf area, bole form, volume growth, and growth efficiency - defined as volume increment per unit leaf area - were examined over a 17-year period within a thinning study in central Maine designed to compare the conventional B-line and low density thinning regimes. At the tree-level, many of the effects of thinning were as expected. Heavier, low density thinning resulted in significantly larger and deeper crowns with greater leaf area than equivalent trees in both the B-line and unthinned control treatments. These changes explained higher rates of diameter and volume growth. Thinning did not alter growth efficiency per se. but larger trees had slightly (but significantly) lower growth efficiency than smaller trees. Reconstruction of bole taper - quantified as Girard form class -showed that, surprisingly, B-line thinning produced more tapered butt-logs (first 5-meter) than low density thinning, resulting from a thinning-induced growth response at breast height but not at the top of the butt-log. At the stand-level, an annual record of leaf area index (LAI) attained by litterfall collection showed that leaf area in the control treatment was relatively constant or slightly declined over the study period. Thinning significantly reduced stand leaf area and thus gross volume growth, but the thinned treatments had nearly equal LAIs for the ten years following the initial thinning. This explained the similar gross volume growth rates and growth efficiencies of the thinning treatments. Following the re-entry harvest, B-line leaf area increased until the stands reached crown closure, while the low density treatment continued rates of crown expansion and LAI increase without reaching a peak. Due to greater LAI, B-line gross stand volume growth and growth efficiency were significantly higher during the latter growth period: low density stand growth efficiency was still no different from the control. Growth efficiency of the unthinned stands was found to be positively related to stand density. Results of this study have important implications to managers of eastern white pine. The contention that thinning below B-line stocking has deleterious effects on stand yield was in general not supported. On the contrary, only a minor loss of gross stand volume growth was found by thinning to a low density. In addition, low density trees were larger, faster growing, and had better stem form than comparable B-line trees. Therefore, low density thinning was found to be a viable alternative to conventional management

Size structure and inequality in a commercial stand of the seaweed gelidium-sesquipedale

The temporal dynamics of the frequency distributions of 2 measures of Gelidium sesquipedale frond size, length and weight, was investigated in a subtidal stand under commercial exploitation. Frond weight/length allometry was highly variable, both seasonally and between years, showing that in this species weight and length cannot be used interchangeably as a measure of frond size. Physical disturbances played a fundamental role in allometric variability. The loss of branches due to commercial harvest and storms reduced the slope of the log weight/log length relationship. During spring the slope increased, indicating the production and growth of lateral branches. Size differences among individuals in the population (inequality) were quantified by 3 statistics: the skewness coefficient (g(1)), the coefficient of variation (CV), and the Gini coefficient (G). Highly significant changes in frond length inequality, but not weight, were shown. These correspond to periods when G. sesquipedale length structure varied due to the combined effects of the demographic parameters that regulate the population (frond recruitment, survival, breakage and growth). Graphical analysis of significantly different length structures revealed that a recruitment peak of vegetatively developed fronds occurred during winter, following periods of high frond mortality and breakage caused by both human (summer harvesting) and natural (late fall storms) disturbances. During late spring and summer, the density of smaller fronds decreased due to mortality and growth into higher size classes. To assess density-dependent regulation processes, such as suppressed growth of smaller fronds and self-thinning, the time variation of both relationships, inequality/mean frond weight and biomass/density, was analysed. Inequality/mean frond weight and biomass/density values decreased from summer to winter and increased to the following summer. The increase of inequality while mean frond weight is increasing is consistent with the asymmetric competition theory on the development of crowded plant stands, and supports the hypothesis that the slower growth of smaller fronds during this period (Santos 1994; Mar. Ecol. Prog. Ser. 107: 295-305) is due to intraspecific competition. The time trajectory of the biomass/density relationship is perpendicular to and lies above the theoretical self-thinning line. Evidence for self-thinning was thus not detected. A conceptual model for the functioning of this population is proposed. Thinning and frond breakage caused by disturbances might be keeping intraspecific competition in these G. sesquipedale crowded stands (up to 18 000 fronds m(-2)) at low levels.info:eu-repo/semantics/publishedVersio

Drainage of a nanoconfined simple fluid: rate effects on squeeze-out dynamics

We investigate the effect of loading rate on drainage in molecularly thin films of a simple fluid made of quasi-spherical molecules (octamethylcyclotetrasiloxane, OMCTS). We find that (i) rapidly confined OMCTS retains its tendency to organize into layers parallel to the confining surfaces, and (ii) flow resistance in such layered films can be described by bulklike viscous forces if one accounts for the existence of one monolayer immobilized on each surfaces. The latter result is fully consistent with the recent work of Becker and Mugele, who reached a similar conclusion by analyzing the dynamics of squeeze-out fronts in OMCTS [T. Becker and F. Mugele, Phys. Rev. Lett. {\bf 91} 166104(2003)]. Furthermore, we show that the confinement rate controls the nature of the thinning transitions: layer-by-layer expulsion of molecules in metastable, slowly confined films proceeds by a nucleation/growth mechanism, whereas deeply and rapidly quenched films are unstable and undergo thinning transitions akin to spinodal decomposition

New modeling of the Vostok ice flow line and implication for the glaciological chronology of the Vostok ice core

International audienceWe have used new spaceborne (elevation) and airborne (ice thickness) data to constrain a 2D1/2 model of snow accumulation and ice flow along the Ridge B‐Vostok station ice flow line (East Antarctica). We show that new evaluations of the ice flow line geometry (from the surface elevation), ice thickness (from low‐frequency radar data), and basal melting and sliding change significantly the chronology of the Vostok ice core. This new Vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the Dome Fuji glaciological timescale. At the same time, the new model shows significantly older ages than the previous GT4 timescale for the last glacial part, being thus in better agreement with the GRIP and GISP2 chronologies

An allometry-based approach for understanding forest structure, predicting tree-size distribution and assessing the degree of disturbance

Tree-size distribution is one of the most investigated subjects in plant population biology. The forestry literature reports that tree-size distribution trajectories vary across different stands and/or species, while the metabolic scaling theory suggests that the tree number scales universally as -2 power of diameter. Here, we propose a simple functional scaling model in which these two opposing results are reconciled. Basic principles related to crown shape, energy optimization and the finite size scaling approach were used to define a set of relationships based on a single parameter, which allows us to predict the slope of the tree-size distributions in a steady state condition. We tested the model predictions on four temperate mountain forests. Plots (4 ha each, fully mapped) were selected with different degrees of human disturbance (semi-natural stands vs. formerly managed). Results showed that the size distribution range successfully fitted by the model is related to the degree of forest disturbance: in semi-natural forests the range is wide, while in formerly managed forests, the agreement with the model is confined to a very restricted range. We argue that simple allometric relationships, at individual level, shape the structure of the whole forest community.Comment: 22 pages, 4 figure

Dislocation loops in overheated free-standing smectic films

Static and dynamic phenomena in overheated free-standing smectic-A films are studied using a generalization of de Gennes' theory for a confined presmectic liquid. A static application is to determine the profile of the film meniscus and the meniscus contact angle, the results being compared with those of a recent study employing de Gennes' original theory. The dynamical generalization of the theory is based on on a time-dependent Ginzburg-Landau approach. This is used to compare two modes for layer-thinning transitions in overheated films, namely "uniform thinning" vs. nucleation of dislocation loops. Properties such as the line tension and velocity of a moving dislocation line are evaluated self-consistently by the theory.Comment: 16 pages, 8 figure