Bois et forêts des tropiques

Abstracts & articles: n░ 330
(4th quarter 2016)


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(In French, English and Spanish)

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Issue 330


 

SEASONAL VARIATIONS IN DIAMETER GROWTH AND LEAF AND REPRODUCTIVE PHENOLOGY IN THREE CENTRAL AFRICAN COMMERCIAL TIMBER SPECIES

F. FÚtÚkÚ, A. Fayolle, K. Dainou, N. Bourland, A. DiÚ, P. Lejeune, J.-L. Doucet, H. Beeckman

The intra-annual rhythms of diameter growth is known for only a very few tropical African timber species. For this study, we used several methods in combination ľ sequential cambium marking, anatomical analysis and growth ring measurements ľ to determine the periodicity and variations of diameter growth in three Central African tree species producing very high quality timber: Baillonella toxisperma (Moabi), Entandrophragma cylindricum (Sapelli) and Erythrophleum suaveolens (Tali). We also sought to identify interactions between climate and foliar and reproductive phenology. All three species have anatomically distinct annual growth rings that form as the season advances, reaching their maximum rate of growth during the short rainy season (March to May). The seasonal variations in growth rates proved to be significant in Moabi and Sapelli and not significant in Tali. The climate parameters with a determining role in these variations were temperature and hours of sunshine. The dendrochronological analysis opened up interesting prospects for the long-term acquisition of the growth data needed to define parameters for the management of natural stands of these species.

Keywords: Baillonella toxisperma, Entandrophragma cylindricum, Erythrophleum suaveolens, growth, cambium activity, phenology, seasonal growth ring development, semi-deciduous forest, Central Africa.


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ASSESSMENT OF COLOUR VARIATIONS IN PISTACIA ATLANTICA DESF. WOOD FROM NORTHERN ALGERIA

M. Boudouaya, H. Benhassaini, F. Z. Bendimered-Mouri, F. Mothe, M. Fournier

Among the characteristic properties of timber from natural tree stands, particularly those in arid and semi-arid zones, variations in colour are decisive in the uses made of the wood as a high added- value visible material, in joinery and cabinet-making for example. This study was conducted to help promote the aesthetic value of a woody species which is common in Algeria but under-researched, the Mt. Atlas mastic tree, Pistacia atlantica Desf. Variations in wood colour were assessed from samples cut from the sapwood and heartwood of mastic trees from two different bioclimatic regions in north-western Algeria. The colour assessments were made at the Forest and Timber Resources Laboratory (LERFoB) in Nancy, France, using a spectrophotometer with measurement and display software. The results indicate variations between the two regions in the colour of Mt. Atlas mastic tree wood (for the three chromatic components L*, a* and b*) and among the different trees (component L*). The colorimetric components of the lighter-coloured sapwood, especially brightness (L*) and the red-green component (a*), are very different to those of the heartwood. From this we infer that environmental factors have an influence on the colorimetric characteristics of the wood in this species, as well as the intrinsic individual characteristics of each tree. Finally, brightness (L*) and the red-green (a*) and blue-yellow (b*) components vary between the different types of mastic tree wood.

Keywords: Pistacia atlantica Desf., transition zone, CIELab, colour space, heartwood, sapwood, north-western Algeria.


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ASSESSMENT OF TEAK PRODUCTION CHARACTERISTICS USING 1 M SPACING IN A PLANTATION IN NICARAGUA

P. Haninec, P. Maděra, M. Smola, H. Habrová, M. Šenfeldr, L. Úradníček, M. Rajnoch, J. Pavliš, J. Cafourek, K. Novosadová, R. Šmudla

This investigation was carried out in a forestry plantation in Central America, near the city of Diriamba in Nicaragua, where 48.9 ha of a 76.5 ha afforested area has been repeatedly planted with teak since 2006 (2006: 7.90 ha; 2007: 13.63 ha; 2008: 11.93 ha; 2009: 12.87 ha; 2010: 21.70 ha). This plantation is unusual because of the unique 1x1 m spacing of the teak trees and the limiting ecological factors of this arid tropical zone. The aim of the 1x1m spacing was to promote the growth of tall teak stems, inhibit branching to prevent the formation of a wide crown and begin production from the first thinning with teak poles, which are suitable for some types of construction. In 2011, experimental plots were established and the growth parameters (height and circumference) of teaks in the plantation were measured. Additional data were recorded, such as mortality, or twisted and snapped trees. A field methodology was designed and the growth results recorded were formatted into tables and charts. Based on the measurements made in the experimental plots marked out in the plantation, a statistical assessment of the growth parameters was conducted. Teak seedlings planted in the same years were compared according to provenance in terms of height, circumference, yields and mortality. Altogether, 10,955 trees in 143 experimental plots were measured. The stands were 1 to 5 years of age, the total calculated growing stock was 1,287.89 m3, the mean wood mass per hectare was 17.89 m3, with a mean stand height of 3.03 m and mean DBH of 2.74 cm. Snapped trees amounted to 5.64%, twisted trees to 5.66% and mean mortality was 21.48%.

Keywords: Tectona, teak, plantation, Nicaragua.


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EFFECTS OF NANO-SILANE ON THE PHYSICAL AND MECHANICAL PROPERTIES OF ORIENTED STRAND LUMBER (OSL)

H. R. Taghiyari, Sadegh Maleki, Vahid Hassani

The effects of resin content and nano-silane (NS) compounds on oriented strand lumber (OSL), an important engineered wood product, were studied here. OSL panels were produced using two different urea-formaldehyde (UF) resin contents of 8% and 10%, based on the dry weight of the wood strips; two NS contents were applied based on the UF resin content. Our results show that treatments with the two different resin contents produce very similar values for modulus of rupture (MOR), modulus of elasticity (MOE), impact bending (IB), and tensile strength (TS). This revealed that the high compactness of strips in the OSL matrix was the predominant factor determining the overall mechanical properties of the composite panels. The interaction between NS and UF-resin significantly reduced these properties with most treatments at 10% NS, while 20% NS was enough to contribute actively to the process of binding the strips together and compensated for part of the loss. Cluster analysis indicated that the mechanical properties were generally dependent on the compactness of the composite matrix rather than on the resin content. Based on these findings, the study concluded that NS is not to be recommended to the industry because of its negative effects on most physical and mechanical properties in OSL panels.

Keywords: nano-materials, oriented strand lumber (OSL), particleboard, silane compounds, wood-composite, zycosil , Iran.


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EFFECTS OF ECTOMYCORRHIZAL INOCULATION ON GROWTH AND NUTRITION OF ATLAS CEDAR NURSERY SEEDLINGS IN ALGERIA

H. Gaba-Chahboub, M. S. Lamhamedi, O. Abrous-Belbachir

Mycorrhizal inoculation of Atlas cedar seedlings in tree nurseries is one of the recommended technics for improving the survival and growth of trees in reforestation sites. However, most trials have not succeeded in obtaining high rates of mycorrhization in seedlings inoculated with spores. The aim of this study was to determine the influence of sporal inoculum from three species of ectomycorrhizal fungi, Cortinarius cedretorum, Amanita vaginata and Inocybe geophylla, on the growth and mineral nutrition of Cedrus atlantica seedlings. The carpophores, seeds and organic forest soils used to produce the seedlings were taken from beneath a pure stand of Atlas cedar. The sporal inoculum was made up of crushed and sieved carpophores. The different growth parameters were assessed after 12 months of culturing: seedling height, length of the main root, number of fine roots, mycorrhization rate, total biomass, number of mycorrhized root tips and concentrations of mineral elements in the leaves. Mycorrhization rates for the three fungi species assessed ranged from 55% to 65%, which is exceptionally high for Atlas cedars inoculated with spores. The results show that inoculation with these three ectomycorrhizal fungi significantly increases leaf concentrations of phosphorus and nitrogen. Total biomass of the Atlas cedar seedlings was significantly higher with these three inocula than in the control seedlings.

Keywords: Cedrus atlantica, sporal inoculum, mycorrhization, growth, mineral nutrition, Algeria.


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USING DRONE TECHNOLOGY TO MAP VILLAGE LANDS IN PROTECTED AREAS OF THE DEMOCRATIC REPUBLIC OF CONGO

J. Semeki Ngabinzeke, J. Linchant, S. Quevauvillers, J.-M. Kahindo Muhongya, P. Lejeune, C. Vermeulen

Protected areas of the Democratic Republic of Congo (DRC) are under threat from various human pressures that need to be monitored accurately and on a regular basis. A small Falcon drone mounted with a Sony NEX-7 camera was used for mapping missions to track the dynamics of village lands in the Mondo Missa Game Reserve, which lies along the eastern border of Garamba National Park in north- eastern DRC. The mapping missions collected a total of 3,143 photos taken in April and July 2015, covering an area of 114 ha with a ground resolution of 8 cm/ pixel. The images were then ortho-rectified, and the resulting ortho-images segmented. The segments were then classified manually by photo-interpretation. Significant changes had occurred between the two periods: 6.5 ha of natural forest and savannah had been lost (declining from 86.6 to 80.1 ha), fallow areas had increased from 16.9 to 8.2 ha and cleared land from 4.1 to 10.0 ha. The variations in seasonal crop areas ranged from 3.2 to 11.8 ha. The average size of cultivated plots was 0.2 ha (s = 0.14 ha, n=50). Finally, the area covered by isolated trees had increased very slightly (from 1.3 to 1.9 ha) while the area occupied by human settlements remained constant (1.7 ha). These results show that the expansion of itinerant slash-and-burn cultivation results in the conversion of natural habitats and modifies plant communities. Unmanned aerial systems can thus help to produce accurate maps and undertake rapid monitoring of small-scale land use changes in protected areas in tropical forests and savannah. They offer an efficient solution for assessments of deforestation and degradation in areas used by local communities. Such assessments are an issue of considerable importance in the REDD+ process, which is aiming to quantify these changes accurately.

Keywords: village lands, land use, itinerant slash-and-burn cultivation, detection of changes, habitat conversion, fragmentation, drone, protected areas, Democratic Republic of Congo.


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