INFLUENCE OF ECOLOGICAL GROUP COMPOSITION, PLANTATION SPACING AND ARRANGEMENT IN THE RESTORATION OF RIPARIAN FOREST ON RESERVOIR SHORES

Este trabalho teve como objetivo avaliar o efeito do espaçamento, arranjo e composição de grupos ecológicos das mudas plantadas no processo de restauração de margem de reservatório artificial no sudeste do Brasil. As avaliações foram realizadas 12 anos após a implantação do experimento em que cinco modelos de plantios mistos foram testados. Primeiramente, fez-se uma avalição geral do povoamento por meio de levantamentos do estrato arbóreo, regenerante, banco de sementes e de análise química e textural do solo. Em seguida, lançou-se mão dos indicadores de recuperação de sobrevivência das árvores plantadas, área basal e densidade da comunidade arbórea, acúmulo de serapilheira sobre o solo e índice de fechamento do dossel para comparar os modelos e checar a influência dos fatores experimentais nestes parâmetros. Como resultado da análise geral, obteve-se que o povoamento encontra-se em situação de baixa diversidade, com regeneração deficiente e banco de sementes dominado majoritariamente por uma espécie arbórea exótica utilizada no plantio e espécies herbáceas invasoras, o que pode comprometer a automanutenção do povoamento no futuro. O fator que mais influenciou os modelos foi a composição de grupos ecológicos com os melhores resultados apresentados pelos modelos em que se usaram ambos os grupos das pioneiras e não pioneiras. Provavelmente, o arranjo e o espaçamento de plantio não tiveram muita influência devido à mortalidade das mudas e à regeneração natural que se desenvolveu até esta idade. Assim, recomenda-se que na implantação de povoamentos para reconstituição de matas ciliares não sejam utilizadas apenas espécies pioneiras e sugere-se que a proporção de 50% de espécies pioneiras e 50% de não pioneiras, com o maior número possível de espécies, seja utilizada em áreas com deficiência da regeneração natural

The Effects of Initial Spacing and Rectangularity on the Early Growth of Hybrid Poplar

Hybrid poplar (Populus trichocarpa Torr. and Gray × Populus deltoides Marsh.) plantations, at two locations in southern British Columbia, were examined 9 years after planting, to determine the effects of plantation spacing on individual-tree and per-hectare growth and development. At both locations, spacing had a direct, significant effect on virtually all of the individual-tree characteristics examined. For a given amount of growing space per tree, rectangularity (within-row/between-row spacing ratios) had no significant effect on individual-tree diameter, height, or total bole volume. Virtually all of the per-hectare characteristics examined were not significantly affected by spacing at either location.

Nitrogen isotope fractionation in the fodder tree tagasaste (Chamaecytisus proliferus) and assessment of N2 fixation inputs in deep sandy soils of Western Australia

Nitrogen (N) isotope fractionation and symbiotic N fixation were investigated in the shrub legume tagasaste, growing in the glasshouse and field. In a pot study of effectively nodulated plants supplied with 0, 1, 5 and 10 mM nitrate [stable isotope 15N (δ15N) of 3.45‰], the δ15N of dry matter N of fully symbiotic cultures indicated a greater isotope fractionation during distribution of N between nodules, stems, leaves and roots than for N2 fixation itself, with whole-plant δ15N being near zero (–0.46 to 0.42‰). Regardless of whether plants were field-grown, pot-cultured, fixing N2 or utilising mineral N, woody stems were depleted in 15N relative to all other plant parts. The similar orders of ranking of δ15N for plant components of the nitrate-treated and fully symbiotic plants, and a general increase in δ15N as plants were exposed to increasing concentrations of nitrate, indicated that N isotope fractionation can be accounted for, and thus not undermine 15N natural abundance as means of measuring N2 fixation inputs in tagasaste trees. In pot culture the percentage of plant N derived from the atmosphere (%Ndfa) by symbiotic N2 fixation fell from 85 to 37% when the nitrate supply was increased from 1 to 10 mM, with evidence of nitrate N being preferentially allocated to roots. δ15N natural abundance assessments of N2 fixation of 4-year-old trees of field-grown tagasaste in alley (550 trees ha-1) or plantation (2330 trees ha-1) spacing were undertaken at a study site at Moora, Western Australia, over a 2-year period of shoot regrowth (coppicing). Cumulative N yields and %Ndfa were similar for trees of alley and plantation spacing, with much less coppice N accumulation in the first compared to the second year after cutting. Scaling values from a tree to plot area basis, and using a mean %Ndfa value of 83% for all trees at the site, inputs of fixed N into current biomass plus fallen litter over the 2 years of coppicing were calculated to be 83 kg N ha-1 year-1 for the alley and 390 kg N ha-1 year-1 for the plantation spacing. Although the plantation tagasaste fixed 587 kg N ha-1 in the second year, close to the maximum value reported in the literature for any N2-fixing system, this should not be seen as typical where the trees are used for animal production, since grazing and cutting management will substantially reduce productivity and N2 fixation input.

Impact of Feller Bunchers and Plantation Spacing on Thinning

There are articulated rubber-tired machines which can selectively thin plantations effectively, if the plantations are established with wide rows with little deviation. The best time to thin to ensure good treatment is planting time. Considering effects of planting on later intermediate thinning treatments provides a greater selection of prescriptions when thinning is undertaken. Machines for selective thinning can best be improved by increasing their maximum angles of left and right articulation. If these angles could be safely increased on existing machines, significantly more marked trees could be removed by articulated feller bunchers in almost all spacings.