Cross-sectional Discs Research Articles

Transformação genética em espécies florestais.

A transformação genética, que compreende a introdução de genes exógenos de forma controlada no genoma de uma célula vegetal e posterior regeneração da planta transgênica, tem contribuído com os programas de melhoramento genético de plantas pela obtenção de genótipos com novas características de interesse. O melhoramento de espécies florestais é limitado por características intrínsecas a tais espécies, como a altura dos indivíduos e o ciclo longo de vida. A transformação genética constitui, portanto, uma alternativa para a obtenção de espécies florestais com características desejáveis em um menor espaço de tempo. Plantas transgênicas com resistência a determinadas pragas, com melhor qualidade de madeira, maior produção de biomassa, tolerância a herbicidas, entre outras características de interesse, já foram obtidas para diferentes espécies florestais de importância econômica como álamo, eucalipto e pinheiros em geral. Este trabalho mostra a importância da transformação genética, associada a outras técnicas biotecnológicas no melhoramento de espécies florestais, as técnicas de transformação mais utilizadas e as características que já foram introduzidas nessas espécies pela transformação.

Tilt of Spruce Trees near Ice Wedges, Mackenzie Delta, Northwest Territories, Canada

Ice wedges are common in the Mackenzie Delta, although troughs may be filled by sediments and obscured by growth of vegetation. At four sites in eastern Mackenzie Delta, over 85% of the trees within 1 m of ice-wedge troughs leaned towards these troughs. The mean angle of lean was 12° from the vertical, with some trees leaning by more than 25°. The angle of tree tilt varied inversely with distance from the ice-wedge trough and most of the trees over 1 m from an adjacent trough leaned away from the ice-wedge. Trees near the troughs are susceptible to toppling because their root systems trail away from the troughs. Reaction-wood rings in cross-sectional disks from trees leaning towards troughs indicated that progressive tilting has been sustained for decades to centuries. Long-term rates of tree tilting are estimated to be between 0.1 and 0.4° a−1. Progressive, unidirectional tilting may eventually destroy the spruce trees. In Mackenzie Delta, where forest fire is infrequent, earth movements associated with ice-wedge polygons may be one mechanism driving forest change in old-growth stands.

Relationship of root rot to black spruce windfall and mortality following strip clear-cutting

Root and butt rots are often implicated as causal factors influencing windfall and mortality of residual trees following partial cutting. Measurements of decay at stump level (i.e., the upward extension of root rot) were made on cross-sectional discs taken from windfallen and standing dead 100- to 130-year-old black spruce (Picea mariana (Mill.) BSP) near Nipigon in northwestern Ontario. Subsequently, causal fungi were identified using laboratory culturing procedures. The incidence and amount of decay in windfallen trees within leave strips following alternate strip clear-cutting was higher than the general stand levels but lower than that found in windfallen trees in uncut forest. The incidence and amount of decay was also higher in windfallen trees near the centres of the leave strips than in those near the edges and corners of these strips. These results indicate a strong association between root rot and windfall and suggest that for comparable windfirmness, trees near the edges of residual stands must have less decay than those in more sheltered locations. Decay levels tended to be lower on poorly drained sites than on well-drained sites. In uncut forest, and especially in the leave strips, more trees were uprooted than died standing or suffered stem breakage. The incidence and amount of decay tended to be lower in uprooted trees than in standing dead trees or those with stem breakage, although in uncut forest virtually all windfallen or standing dead trees had some degree of stump-level decay. Of the 21 wood-rotting Basidiomycetes isolated from windfallen and standing dead trees, Inonotus tomentosus (Fr.:Fr.) Teng was the most frequent, followed in order by Armillaria ostoyae (Romagn.) Herink, Coniophora puteana (Schum.:Fr.) Karst., and Scytinostroma galactinum (Fr.) Donk. The incidence of I. tomentosus, C. puteana, Xeromphalina campanella (Batsch.:Fr.) Kuhner & Maire, and Serpula himantioides (Fr.:Fr.) Karst., but not Armillaria ostoyae, Scytinostroma galactinum, and Sistotrema brinkmanii (Bres.) Erik., was greater in windfallen and standing dead trees from the leave strips than in the general stand populations. In the leave strips, I. tomentosus, Amylostereum chailletii (Pers.:Fr.) Boid., and Trichaptum abietinum (Dickson:Fr.) Ryv. tended to greater relative abundance in standing dead trees, while the relative abundance of C. puteana and Serpula himantioides was greater in trees with stem breakage. Armillaria ostoyae and Scytinostroma galactinum were as abundant in uprooted trees as in standing dead trees or those with stem breakage. Ascocoryne sarcoides (Jacq.:Fr.) G. & W., a staining fungus that may protect against decay fungi, was frequently isolated in this study.

Provenance and site variation of wood density in Eucalyptus globulus Labill. at harvest age and its relation to a non-destructive early assessment

The wood density of Eucalyptus globulus is, next to growth, the most important selection parameter in breeding programs for pulping. It was measured as basic density in 9-year-old trees from 37 provenances grown in three sites, on cross-sectional discs taken at b.h. The wood density was highly significantly influenced by provenance but not by site. The across site range of variation of wood density in the different provenances was between 492 and 600 kg/m3. The provenances of subspecies maidenii had a significantly higher density in relation to those from spp. globulus and bicostata (584 kg/m3 vs. 533 and 543 kg/m3). No correlation between growth and density was found. Compared to an earlier assessment of density using cores at 7 years of age, the values at 9 years were significantly higher. The overall ranking of provenances by wood density showed a reasonable coincidence between the non-destructive 7-year assessment and the 9-year measurement, thereby allowing an early assessment of density in breeding programs.

Correlation of bone mineral density and femoral neck hardness in bovine and human samples.

Bone mineral density (BMD) is a predictor of fracture risk. The purpose of this study was to determine whether a correlation exists between femoral neck BMD and an indicator of mechanical bone strength in human and bovine samples. Human proximal femurs were obtained from seven men and two women undergoing total hip arthroplasty (THA), mean age 60.3 years. Preoperative BMD measurements of the femoral neck were obtained (Lunar DPX). A 3 cm2 area of interest on each excised femoral neck corresponding to the preoperative BMD measurement site was carefully marked and BMD was remeasured postoperatively. Ten excised bovine femoral necks were also measured for BMD. A bicortical core, each cortex 2.8 cm2 in area, containing the center of the area of interest was removed from the human and bovine femoral necks, cut into multiple 7-mm thick, multiple cross-sectional discs, and measured for hardness by indent depth (Rockwell International Hardness Tester, Wilson Mechanical Instruments, New York, NY). In vivo human femoral neck BMD measurements correlated with in vitro BMD measurements (r = 0.99). BMD measurements of human femoral necks were significantly lower than BMD measurements of bovine femoral necks (P < 0.05). Inverse relationships were found between in vivo and in vitro human BMD measurements and indent depth (r = -0.58 and -0.59, respectively). Bovine BMD measurements and indent depth were also inversely related (r = -0.64).(ABSTRACT TRUNCATED AT 250 WORDS)

Centroid of wood density, bole eccentricity, and tree-ring width in relation to vector winds in wave forests

Circular statistics are used to analyse directional data inherent in X-ray densitometric data that pertain to cross-sectional discs sampled from balsam fir wave forest trees at Spirity Cove, Newfoundland. The analysis concentrates on directionality of centroids of mean wood density, bole eccentricity, and tree-ring width in eight directions from the pith. The results show that the centroid of mean wood density, bole cross sections, and mean tree-ring width are significantly directional and correspond closely with the mean vector wind direction.

Testing a Photographic Method for Measuring Stem Cross-Sections

Abstract Digitized measurements from four photographic procedures using standard 3½ x 5 in. prints were evaluated for measurement of annual radial increments on cross-sectional discs from felled trees. All four procedures worked well for fast-growing trees. Growth increments for slow-growing trees were estimated relatively poorly, but varied over different photographic methods. For the slow-growing trees, 5 x 7 in. enlargements of black and white photographs of unplaned discs provided measurements that were not significantly different from hand-measured radial increments. For. Sci. 33(3):784-789.

Shock reflection transition in three-dimensional steady flow about interfering bodies

A numerical study of the three-dimensional flowfield produced by the interaction of an axisymmetric shock and a planar wall is presented. These types of flowfields are encountered when a store is in close proximity to an aircraft. The flow is assumed inviscid and everywhere supersonic. This work is based upon the numerical solution of Euler's equations with all shock waves fit as discontinuiti es. The axisymmetric shock reflects from the plate first in a regular fashion, but, ultimately, this reflection becomes a Mach reflection. The transition from regular to Mach reflection and the subsequent development of a cross-sectional Mach disk is computed explicitly and studied in detail. The computational procedure is outlined and numerical results are compared with experimental data.

THE SUPPRESSION OF GROWTH RINGS IN JACK PINE IN RELATION TO DEFOLIATION BY THE SWAINE JACK-PINE SAWFLY

An investigation of the radial growth of jack pine (Pinus banksiana Lamb.) defoliated by the Swaine jack-pine sawfly (Neodiprion swainei Midd.) disclosed that growth rings were discontinuous and missing in cross-sectional disks from severely damaged trees. In young and open-grown trees with dead tops, the incidence of such deficiencies in radial growth was especially high in disks from upper regions of the stems, in the vicinity of the dead tops; radial growth was suspended for 1 year and subsequently resumed in disks from the lower regions of some stems. Cambial inactivity was more generalized in trees from an old and dense stand and it was detected in disks representing major portions of some of the stems sampled; the death of some trees followed 2 to 6 years of cambial inactivity in disks cut at various heights along their entire stems. Growth deficiencies in the young stand were clearly effects of severe sawfly defoliation. Data from the old, dense stand indicated that sawfly defoliation had perhaps merely hastened the gradual deterioration of the stand in which intertree competition was intense.