Bois et forêts des tropiques

Abstracts & articles: n° 329
(3rd quarter 2016)


All abstracts
(In French, English and Spanish)

New issue

Issue 329


 

RADIAL GROWTH AND SENSITIVITY TO CLIMATE OF THE MOUNT ATLAS MASTIC TREE, PISTACIA ATLANTICA DESF., IN ALGERIA

N. Ifticene-Habani, M. Messaoudene

Few studies have been made of the Mount Atlas mastic tree, Pistacia atlantica Desf., despite its importance as part of Algeria’s steppe and desert ecosystems (Ahaggar: central Sahara). The species is of particular ecological and biogeographical interest as its association with other characteristic species of arid and semi-arid Saharan habitats point to a high degree of resistance to global changes, especially climate change. The question addressed here is to understand how this tree species is responding to climate change along an aridity gradient. A dendro-ecological study was undertaken to identify the climatic factors governing radial growth in the species. Using this approach makes it possible to identify the relationships, at different scales in space and time, between climate variability and the variability of radial growth in the Mount Atlas mastic tree. The tree’s response to extreme climatic events was investigated through analyses of characteristic years. Four populations in two different regions were analysed: the high steppes around Djelfa and the pre-Saharan region around Béchar. The analysis showed that characteristic years are highly dependent on both average annual precipitation and average annual temperature. Years with high growth are the wetter years, while years with low growth are the drier years. The response of the Mount Atlas mastic tree to wide climate variability is reflected in high values for the average sensitivity coefficient. Response function analysis shows the importance of precipitation in the radial growth of the species, and the lesser importance of temperature under conditions that vary with the biotope.

Keywords: Pistacia atlantica, arid climate, radial growth, dendro-ecology, Mount Atlas mastic tree, Saharan climate.


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EFFECTS OF STATION-SPECIFIC FACTORS ON RADIAL GROWTH AND RESPONSES TO CLIMATE IN ALEPPO PINES IN ALGERIA’S OUARSENIS RANGE

M. Sarmoum, F. Guibal, F. Abdoun

The relationships between climate and radial growth from 1967 to 2010 in nine Aleppo pine stands in the Ouarsenis range (north-western Algeria) were studied according to station-specific factors (substrate, altitude, exposure and age of the trees) using dendro-chronological methods, with an analysis of interannual variations in the thickness of growth rings. A retrospective analysis of radial growth showed high interannual variability in growth ring thickness within the same stand. The statistical parameters calculated showed highly variable radial growth between the different stands, which was related to station-specific factors and to tree age. Average growth ring thickness and persistence declined with the age of the trees. Average sensitivity to climate tended to be greater in trees growing on sandstone or schist substrates than on limestone. Our analysis of the relationships between climate and growth rings shows that the Aleppo pine is responsive to precipitation before or during the formation of growth rings. Higher temperatures, especially when they reach their maximum, have a negative effect on radial growth. The relationships between Aleppo pines and climatic conditions are modulated by station-specific factors, especially the substrate. The most responsive stands tend to be growing on a sandstone substrate. These results provide a useful description to help understand the ecological flexibility of the Aleppo pine and how it responds to climate change, with a view to proposing better ways of protecting pine forests that have been under threat for several decades.

Keywords: Pinus halepensis, station-specific factors, radial growth, relationships between growth rings and climate, drought, Ouarsenis.


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SOCIOCULTURAL AND ENVIRONMENTAL BENEFITS FROM FAMILY ORCHARDS IN THE CENTRAL HIGHLANDS OF MEXICO

J. C. García Flores, J. G. Gutiérrez Cedillo, M. Á. Balderas Plata, M. R. Araújo Santana

The aim of this study was to analyze perceptions of agroecosystems in terms of their sociocultural and environmental benefits among owners of family orchards in the State of Mexico’s ecological transition zone. A 3-stage methodology was used: 1) geographic characterization of localities and agroecosystems; 2) analysis of social benefits from orchards; 3) analysis of the potential of family orchards and problems encountered. The investigation was conducted in twelve localities belonging to three municipalities in the State of Mexico, using semi-structured interviews complemented by direct observations in the field. Family orchards provide multiple social, environmental, ecological and cultural benefits: they contribute to the wellbeing of families as a rich source of edibles, condiments and ceremonial plants for home consumption, sale or barter. These orchards are also used for small-scale animal breeding as well as for fuelwood, building materials, fencing materials and ornaments. Family orchards should therefore be considered as important agroecosystems, in the knowledge that they function through complex relationships between all their components. The sociocultural and environmental benefits provided by these productive multifunctional agroecosystems could make important contributions to social cohesion and food security strategies for rural families, while also helping to preserve the region’s natural resources.

Keywords: family orchards, sociocultural benefits, rural families, environmental benefits, agroecosystems, Mexico.


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SURVIVAL OF SWIETENIA MACROPHYLLA SEEDS SOWN IN SLASH-AND-BURN FIELDS IN QUINTANA ROO, MEXICO

P. Negreros-Castillo, I. Martínez-Salazar, K. F. Kellner, C. W. Mize, R. K. Swihart, M. A. Navarro-Martínez

In tropical America, regeneration of bigleaf mahogany, Swietenia macrophylla King, the most important commercial tree species, is problematic because of its fruiting and dispersal characteristics, very low tolerance of shade and response to logging. In Quintana Roo, Mexico, abandoned slash-and-burn cropfields are excellent candidates for seedling establishment, but an efficient way to establish mahogany seedlings has not been identified. This study assessed the probability of predation on directly sown mahogany seeds, examining the effects of three treatments (four types of seed protection, two sowing methods, two times of day for sowing). The mean percentage of seeds either partially consumed or removed during a 12-hour period varied from 1.1 to 7.7% among the four seed protection treatments and did not differ between the two sowing methods. Precipitation had an important positive effect on survival, and minimum daily temperature had a marginal negative effect on survival. The Julian calendar date had a positive effect on seed survival. Seed predation did not differ among the seed protection treatments that allowed access only to rodents, only to insects, and to both types of seed predators, and predation was greater with these three treatments than with the no-access treatment. Seed predation was not influenced by the time of day of sowing. Direct sowing offers a good option for regenerating mahogany, especially if the mahogany seeds are soaked for at least 2 weeks before sowing to reduce predation risks and increase prospects for seed survival and seedling establishment.

Keywords: Swietenia macrophylla, mahogany, regeneration, silviculture, tropical forest, seed predation, Mexico.


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ECOLOGICAL DIVERSITY AND CONSERVATION OF WILD EDIBLE FRUIT TREE SPECIES IN THE LAMA FOREST RESERVE IN BENIN

S. Agbahoungba, A. E. Assogbadjo, F. J. Chadare, R. Idohou, V. K. Salako, E. E. Agoyi, R. L. Gièlè Kakaï

Understanding interactions between forests and neighbouring human communities is crucial to participative management of forest resources. This study aimed to determine the ecological diversity of wild edible fruit tree (WEFT) species in the Lama Forest Reserve, a protected area in southern Benin, and strategies for their conservation. An inventory of WEFT species was carried out in 53 systematically delimited plots in typical dense forest, degraded dense forest and young and old fallows in the Lama Forest Reserve. An ethnobotanical survey was conducted with 136 respondents and the WEFT species habitats were identified by applying a Simple Correspondence Analysis to the density data. A list of priority species was generated using the Compound Ranking System method. The results revealed ten WEFT species, including Dialium guineense, Diospyros mespiliformis, Drypetes floribunda, Mimusops andogensis and Pterocarpus santalinoides in typical dense forest; Pancovia bijuga, Psidium guajava and Lecaniodiscus cupanioides in degraded dense forest; and Ficus capensis and Spondias mombin in fallows. Unlike the other species, the average density of D. guineense, D. mespiliformis, D. floribunda, L. cupanioides and M. andongensis varied significantly (P < 0.01) from one vegetation type to another. The WEFT species recorded were mainly used for food and medicinal purposes. Top priority species for conservation were P. guajava, S. mombin, F. capensis, P. santalinoides and P. bijuga. More protection efforts should target the degraded dense forest and fallow areas to ensure the conservation of these species. Further, priority WEFT species need to be included in plantation programmes to reduce pressure from riparian populations.

Keywords: conservation, Lama forest reserve, diversity, wild edible fruit tree.


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TIMBER EXPORTS FROM CAMEROON TO CHAD: COMMERCIALLY SUCCESSFUL, LEGALLY QUESTIONABLE

G. Lescuyer, M. Tal

The scale and the means allotted to imports of sawn wood into Chad from Cameroon are little documented. Two surveys were carried out to produce an up-to-date diagnosis of the trade: sawn wood flows were monitored at N’Djamena and Moundou from July to December 2015, and interviews were conducted with 16 people to characterise the import and customs clearance processes in use for timber from Cameroon. According to our survey results, 79,000 m3. of timber entered Chad from Cameroon during the monitoring period, so that the annual total probably amounts to about 210,000 m3. This is more than double the figure estimated in 2009. Virtually all of the timber imported into Chad is “white wood” produced by small-scale logging. Only 25% of this volume is cleared through Chad’s customs. Official import procedures are time-consuming and costly in Chad. Those involved have therefore set up a “fast-track” customs clearance process for timber, characterised by bribery and under-reporting of the volumes imported. As result, Chad is losing some 3 billion F CFA in tax revenues, but the practice is highly lucrative for customs officers, freight forwarders, traders and final users of the sawn wood. Various measures can be considered to change these informal practices. On the demand side, in Chad, legalising the trade could be facilitated by combining a change in the tax status of timber products with ad hoc penalties, at a minimum, for some of those in breach of the law and the introduction of premiums for proper law enforcement by tax inspectors. On the supply side, in Cameroon, the priority issue is more effective regulation of logging and timber trade practices in community forests.

Keywords: saw-wood, customs, intra-African trade, corruption, community forest, Congo basin.


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