Bois et forêts des tropiques

Abstracts & articles: n° 328
(2nd quarter 2016)


All abstracts
(In French, English and Spanish)

New issue

Issue 328


 

DESTRUCTION OF FOREST AREAS AS A RESULT OF LOGGING AND HARVESTING IN AFRICAN OR AMERICAN DENSE TROPICAL RAINFORESTS

J. Estève

Articles in the media that point to logging as the main driver of tropical forest loss have become commonplace. However, this is a misconception that can be attributed to inadequate knowledge of actual forest conditions on the one hand, and to the conflation of logging and agricultural clearance on the other hand. This article, written by a practitioner with a thorough knowledge of the tropical forest context, sets out to assess the impacts of logging on dense tropical rainforests in Africa and South America. In the interests of accuracy, the article distinguishes between the different phases of a logging operation: establishment of the base camp, building of logging roads to ship out the timber and actual felling. Different scenarios are described according to the richness of forest environments, where harvested volumes vary from 3 to 15 m3/ha. These estimations confirm that the destruction of forest cover is so low that, except in radical situations, logging is not a threat to the sustainability of tropical forests. Opening up road networks and logging roads affects 4.5% to 5.5% of forest cover. Clear-felled areas never exceed 4% of the forest cover and the figure drops to less than 2% in highly or moderately species-rich forests. Logging is therefore directly responsible for only 5.5% to 8.5% of forest destruction. Although the figure can rise to 12% to 16% in rich forest environments, it does not take into account the natural dynamics of biomass reconstitution between logging sequences. In Southeast Asia where logging is more intensive due to very high commercial potential, forest cover reconstitutes within 20 years. While the economic value of dense tropical rainforests declines with logging, their ecological and biological value remains virtually intact.

Keywords: forest degradation, deforestation, logging road, logging site, forest planning, logging, Africa, South America.


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LOGGING ROADS IN TROPICAL FORESTS: SYNTHESIS OF LITERATURE WRITTEN IN FRENCH AND ENGLISH HIGHLIGHTS ENVIRONMENTAL IMPACT REDUCTION THROUGH IMPROVED ENGINEERING

F. Kleinschroth, S. Gourlet-Fleury, V. Gond, P. Sist, J. R. Healey

Logging roads are considered to be a major cause of forest degradation because of their direct and indirect impacts on ecosystem functioning and biodiversity. Given the prevalence of logging in tropical forests around the world, effective road management is of crucial importance to reduce both logging- related environmental impacts and the costs of logging operations. Through a review of the literature, our study analysed how logging roads have been addressed in scientific articles to date. We compared studies published over the past 65 years in the Bois et Forêts des Tropiques journal (BFT), mostly written in French, with a range of more recent articles from the Scopus and Web of Knowledge databases. Half of the articles in BFT were published before 1972, while the more generalist databases show a steady increase in publications on the subject since then, up to the current peak number. From the entire body of literature, we selected 126 articles dealing with impacts and management of logging roads in tropical forests around the world for critical appraisal. The BFT articles were characterized by a strong focus on practical issues in forest road engineering, while the focus of many publications written in English was on the identification of road impacts on forest ecosystems. Road-related environmental impacts stem from the loss of forest cover during construction, the increase in edge effects, soil erosion and interference with wildlife, as well as from the resulting easier access to the forest for hunting and agricultural colonization. Based on this review, we present a list of recommended measures to reduce these impacts. We conclude that, despite the continuing attention given to the subject of logging roads, little is known about how they evolve in the forest landscape over the long term.

Keywords: sustainable forest management, low-impact logging, road ecology, selective logging, forest degradation, biodiversity conservation, soils.


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THE SHORT AND FORGOTTEN HISTORY OF RUBBER IN MADAGASCAR: THE FIRST CONTROVERSY BETWEEN BIODIVERSITY CONSERVATION AND NATURAL RESOURCE EXPLOITATION

P. Danthu, H. Razakamanarivo, B. Deville-Danthu, L. Razafy Fara, Y. Le Roux, E. Penot

From 1891 to 1914, Madagascar was producing forest rubber for export to Europe. Although Madagascar’s contribution to the world rubber market was very modest, this episode had major consequences for the island’s ecology. Many endemic species were exploited, with a view to maximising short-term productivity with no consideration for sustainability. This was one of the first cases of biological resource exploitation in Madagascar for industrial purposes, and was one of the factors that triggered awareness of the value of Madagascar’s biodiversity and the threats to which it might be exposed because of badly managed human activities. Highly repressive legislation was introduced and imposed on the local populations, who were considered mostly to blame for these threats. However, naturalists considered these policies to be ineffective and responded in deliberately alarmist terms designed to provoke a reaction from allegedly over-lenient policy- makers. Their position was caught on the wrong foot in 1942-45, when the war effort revitalised Malagasy rubber production. Nevertheless, the episode was one of the factors behind the creation, in 1927, of a network of protected areas managed by naturalists, making Madagascar a conservation pioneer in Africa. Meanwhile, efforts were made to promote the domestication and/or introduction of high-potential rubber species. With the emergence of Asian rubber production, however, all attempts at rubber cultivation in Madagascar were abandoned, thus sparing Madagascar’s forests from further destruction. This episode shows how Malagasy rubber species survived not thanks to naturalist discourse, the creation of protected areas or the enforcement of repressive legislation, but because an unprofitable sector was abandoned for reasons of economic realism.

Keywords: environmental history, natural resource exploitation, non-timber forest products, natural rubber, naturalist discourse, war effort, Madagascar.


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CHARCOAL AS THE MAIN SOURCE OF FUEL FOR CITY DWELLERS: A SERIOUS PROBLEM FOR THE CONSERVATION OF BURUNDI’S FOREST COVER

F. Bangirinama, B. Nzitwanayo, P. Hakizimana

The issue of domestic energy remains a major concern worldwide and particularly in developing countries, where the majority of the population still uses firewood, charcoal and agricultural residues as fuel for cooking. In Burundi, where wood is the main source of domestic energy and accounts for 96.6% of total energy use, 77% of all charcoal supplies are used by city dwellers. The results of a survey conducted along major roads show that the urban populations of Bujumbura and Gitega consume a total of 70,100 tonnes of charcoal (56,548 and 13,552 tonnes respectively). Annual charcoal consumption by the country’s entire urban population was estimated in our study at 104 718 tonnes. Charcoal consumption in Gitega and Bujumbura alone destroys 3,505-4,673 ha of forest cover per year, with the figure for Burundi’s total urban population reaching 5,236 to 6,980 ha. At this rate, Burundi’s entire forest cover, currently estimated at 171,625 ha, will disappear in about 25 to 33 years. For the system to be sustainable, new techniques and practices must be adopted, such as planting trees along roads, assisted natural regeneration, research on the most suitable and productive species or varieties, increased use of renewable energy, waste-to-energy techniques and energy efficiency improvements (e.g. improved stoves).

Keywords: domestic energy, charcoal, deforestation, urbanisation, sustainability, Burundi.


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SELECTION OF PLUS TREES FOR GENETICALLY IMPROVED TEAK VARIETIES PRODUCED IN BENIN AND TOGO

A. D. Kokutse, A. D. Akpenè, O. Monteuuis, A. Akossou, P. Langbour, D. Guibal, M. F. Tomazello, E. Gbadoe, G. Chaix, K. Kokou

The aim of this study is to select “Plus Trees” based on dendrometric characteristics and wood properties in teak plantations in Benin and Togo. For this purpose, growth performance was assessed in 569 trees in 5 forests in Togo and 90 trees in 3 forests in Benin, based on diameter at breast height, total height and bole height measurements. Wood properties – density, percentage of heartwood and colour – were also measured for the final selection of Plus trees. Heartwood natural durability, fibre saturation point, modulus of elasticity and shrinkage were assessed against previous near infrared spectroscopy models. The results showed that in Togo, inter-tree variability in the forests was relatively high for Annual Height (0.81 ± 0.27 m) and Annual Circumference Increments (2.95 ± 1.02 cm) and for bole heights (10.64 ± 3.51m). In Benin, while the dendrometric performance of the trees did not vary significantly between the forests, the coefficient of variation values were higher (40%) for bole heights (10.99 ± 3.80 m) in Koto forest. The final multi-criteria selection including wood properties showed that the Avetonou and Tchorogo tree populations in Togo make up a homogenous group with the highest values for wood density and heartwood percentage. The trees in Haho-Baloe and Eto forests had lower natural durability and modulus of elasticity, a lower percentage of heartwood and lower wood density. In Benin, the Agrimey forest trees had a higher wood density but the 3 forests were similar in terms of fibre saturation point, natural durability and shrinkage. Based on the variability of dendrometric performance and wood quality of the candidate trees, we were able to select 33 Plus trees.

Keywords: Teak populations, Plus Tree, selection, growth performance, wood properties, Benin, Togo.


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EFFECTIVENESS OF PROTECTED AREAS FOR THE CONSERVATION OF FAVOURABLE AND PRIORITY HABITATS FOR VALUABLE TREE SPECIES IN BENIN

S. G. C. Adjahossou, G. N. Gouwakinnou, D. T. Houehanou, A. I. Sode, A. S. Yaoitcha, M. R. B. Houinato, B. Sinsin

The aim of this study was to assess the effectiveness of protected areas in Benin for the conservation of favourable and priority habitats for the following tree species of socio-economic importance: Afzelia africana, Anogeissus leiocarpa, Burkea africana, Daniellia oliveri, Detarium microcarpum, Prosopis africana and Khaya senegalensis. We combined maximum entropy (Maxent) techniques with GIS to predict potentially favourable areas for cultivating and conserving these species. Zonation software was used to model priority habitats. Data points where the species were present were collected and linked to bioclimatic variables derived from monthly temperature and rainfall figures from the Africlim database and to edaphic (soil) variables. In term of environmental determinism, the most favourable areas were predicted by bioclimatic variables such as mean diurnal temperature range (Bio2), mean annual rainfall (Bio12), potential evapotranspiration (PET) and a biophysical ground variable. The most favourable protected areas for the seven tree species extended northwards from the Ketou listed forest (7°43’N) in the Guinean zone, from the Agoua listed forest (8°30’N) in the Sudano- Guinean zone and from the Pendjari National Park area (10°35’N) in the Sudanian zone. Gap analysis of habitat conservation showed that the protected area network was effective in the Sudanian zone (9°75’-12°27’N), minimally effective in the Guinean zone (6°50’- 7°40’N) and not effective at all in the Sudano-Guinean zone.

Keywords: favourable habitats, environmental determinism, protected areas, priority habitats, Benin.


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