Berichte

Ohne Zusammenfassung     

A family of segmented polynomial functions for modelling the border effect on the diameter growth of Ayous (Triplochiton scleroxylon K. Schum)

This paper introduces a family of four segmented (or grafted) polynomial functions for modelling the decrease in the diameter of Ayous (Triplochiton scleroxylon K. Schum) with distance from the border of the plantation. The functions, each comprising two segments of second degree or less, were fitted to data collected in the Cameroon rain forest. A comparative assessment of the fit was carried out using criteria such as mean deviation, root mean squared deviation, and fit index.

The border effect extended to 10 m inside the plantation where a 50% decrease in diameter occurred. Beyond that distance, the diameter appeared to be stable except for random variation. The estimated functions performed equally well as they all provided a good fit to the data, with a small bias. Most importantly, they proved to be flexible and thus adaptable to a wide variety of situations.

Recommendations are made concerning setting up a guard area and ways of improving the silviculture of Ayous. Also, the possibilities for an agrisilvipastoral system are explored.     

Where's the beef?: Incorporating cattle into sustainable agroforestry systems in the Amazon Basin

Low external input agroforestry systems hold great promise as alternative, sustainable production systems for small-to-medium farmers in the Amazon Basin. The design of such systems is considered essential to stabilize agricultural production and avoid the cycle of continuing destruction of primary forest [Anderson A (1990) In: Anderson A (ed) Alternatives to Deforestation: Steps toward Sustainable Use of the Amazon Rain Forest pp 3–23. Columbia University Press, New York]. In order to be successful, these systems must be compatible with local ecological conditions and adoptable by farmers. Currently, many small-to-medium producers in the Amazon Basin use a slash and burn agricultural strategy that combines annual cropping with cattle grazing in mixed farming systems. While cattle play an important role in household economic survival, grazing-induced land degradation threatens the long-term viability of these farms [Loker W (1993) Human Organization 52(1)14–24]. This paper presents a model of a low external input agroforestry system that incorporates farmer preferences and practices but uses well-adapted grass-legume pastures, rotational grazing and the management of natural forest regeneration to enhance productivity in an ecologically sound manner. This system provides farmers with the benefits of both annual crops and cattle raising, avoids the land degradation that characterizes current practices and effectively incorporates trees into the production system.     

Lignin-carbohydrate bonds in a residual soda spruce pulp lignin

Summary The behaviour of lignin-polysaccharide complex of spruce wood in soda pulping was studied by the characterization of lignin-saccharide fractions isolated from a series of soda pulps. The dioxane pulp lignins contain 8–14% of carbohydrates in which glucose was the predominant component. Its content increased with increasing degree of delignification indicating the formation of secondary lignin-carbohydrate linkage. Both glycosidic and ether type of bond between residual lignin and cellulose in pulp was proved by methylation analysis of the pulp dioxane lignin.The work was supported by the Slovak Academy of Sciences grant number 2/999389/92.     

Kinetics and mechanism of acetic acid pulping of detannined Pinus pinaster bark

Summary The observed kinetics of Pinus pinaster bark with acetic acid after alkali treatment, with or without intervening acid prehydrolysis, are satisfactorily explained by a model involving both solubilization and condensation reactions.This study was subsidised by the Xunta de Galicia. J. González is grateful to DGICYT for a research grant     

Modified algorithm to determine localized modulus of elasticity of lumber

Summary A procedure has been developed to determine the cut-off frequency in an algorithm to evaluate the localized modulus of elasticity (MOE) in lumber. MOE profiles have been artificially generated to serve as input for evaluation of the procedure. A noise component has also been added to the input record to test the robustness and accuracy of the procedure. Good agreement between program predictions and the known localized MOE values has been obtained. The efficiency of the procedure has also been tested using MOE profiles collected from experiments. The program performed efficiently and program predictions seemed reasonable.     

Vascular tissue anatomy of Norway spruce needles and twigs in relation to magnesium deficiency

Vascular tissues of needles and twigs of Norway spruce with low foliar magnesium concentrations were examined by light microscopy. Observations were made on samples from (1) apparently healthy trees, (2) trees exhibiting progressive symptoms of decline, including the yellowing and fall of needles and the death of twigs and branches in the subapical canopy, and (3) trees recovering from symptoms of decline after fertilization with magnesium sulfate. Abnormalities in cambium and phloem anatomy, which were apparent in 2-year-old needles of declining trees, were seen only in needles at least 4 years old in healthy trees, suggesting that needles of declining trees are susceptible to precocious aging. Abnormalities in xylem anatomy were observed in needles 3 years or more in age in declining trees, but were never seen in needles of healthy trees. Over time, anatomical abnormalities in declining trees were seen in progressively younger twigs, which may explain the acropetal development of decline symptoms. After fertilization with magnesium sulfate, normal phloem and xylem were observed in the newly formed tissues.     

Changes in photosynthesis and water status of developing leaves of Brachystegia spiciformis Benth

Changes in net carbon assimilation and water status were studied during leaf development in the deciduous, tropical species Brachystegia spiciformis Benth. In this upland savanna African tree, bud-burst and leaf development occur approximately two months before the rainy season. The newly formed leaves synthesize anthocyanin until the fully expanded leaves of the whole canopy are red. This foliage is referred to as "spring flush" foliage. Subsequently, the anthocyanins are metabolized and the pre-rain leaves become green. Carbon dioxide assimilation exhibited a bimodal diurnal pattern and was similar for pre-rain green leaves and fully expanded flushing leaves, although pre-rain green leaves showed a net uptake of carbon throughout the daylight period, whereas flushing leaves exhibited only brief periods of net photosynthesis in the morning and early afternoon. Measurements of leaf water potential and relative water content showed a diurnal pattern with considerable variation throughout the day. Leaf water potential and relative water content values decreased soon after sunrise reaching a minimum at a time corresponding to the afternoon peak in CO(2) assimilation. Stomatal conductance was closely related to transpiration rate in both flushing and pre-rain green leaves, although flushing leaves had lower stomatal conductances than pre-rain green leaves. Pre-rain green leaves exhibited a compensation irradiance of approximately 180 micro mol m(-2) s(-1), whereas flushing leaves had positive net photosynthesis only at PPFDs greater than 300 micro mol m(-2) s(-1). Rate of photosynthesis (expressed per leaf area or chlorophyll unit) increased as anthocyanin concentration decreased, although the photosynthetic rate continued to increase long after the leaf anthocyanins had been degraded to low, visually undetectable amounts. Post-rain green leaves had chlorophyll concentrations, transpiration rates and stomatal conductances similar to those of pre-rain green leaves; however, photosynthetic rates in post-rain leaves were more than three times higher. Thus, during the early stages of the spring flush, carbon asimilation rates of the flushing leaves were inversely related to leaf anthocyanin concentrations. In pre-rain green leaves, photosynthesis was limited by other non-stomatal factors.     

A review of measurement options for multipurpose trees

There is an urgent need to standardize the methods used to assess the growth of multipurpose trees. Most of the standard methods so far described have been developed specifically for use in multilocational trial networks. This paper was prepared for the F/FRED/ICRAF Workshop on MPTS Assessment Methods, held in Thailand in May 1991 to develop internationally-recognised standards for assessment methodology. It critically reviews the methods prescribed by different networks for height and diameter measurement, and for biomass estimation, giving researchers a range of methodological options to consider and re-emphasizing the need, all too often neglected, to define assessment methods clearly and unambiguously.