M. Avana - Academia.edu (original) (raw)

Papers by M. Avana

Over the centuries, paper has been made from a wide variety of materials. Today fiber comes mainl... more Over the centuries, paper has been made from a wide variety of materials. Today fiber comes mainly from two sources: wood and recycled paper products. Gnidia glauca bark was used in neighbouring Oku for local paper production. The properties of wood and bark of Gnidia glauca have been less explored in the literature. Therefore, in this study, the anatomical properties were investigated to evaluate the potential utilization of this species especially in pulp and paper production. Sections (transversal, tangential and radial) with a thickness of about 15-30µm were obtained from eight samples and contain phloem, cambial zone and secondary xylem. The sections were stained with 0.1% safranin O. to determine the fiber length and vessel element, we used maceration. Densities of vessels, cambial zone thickness, fiber wall thickness, fiber length were measured in brightfield microscopy images using AnalySIS Pro 3.2 software. The results show that our species contain short wood fiber (1.32 mm in average) while the fiber bark are longer. Gnidia wood fibers are the longest among Ailanthus altissima trunk fiber, wheat straw, canola stalks, cotton stalks and Aspen. Fiber diameter of bark is about twice of those of common papermaking and lumen width is the smallest. Cell wall thickness of Gnidia glauca fiber bark is thicker than those of Gnidia wood and non-wood fibers; consequently, the Runkel ratio is highest (7.35). The flexibility coefficient of Gnidia glauca xylem fibers is 54.51, so it is included in the elastic fibers group while phloem fibers is 12.15 and it is included in the highly rigid fiber. The results of anatomical study of Gnidia glauca show that its xylem fiber dimensions are in the normal range for hardwood and are suitable for paper manufacturing.

1. Objectif general Evaluer le niveau de vulnerabilite aux changements climatiques des population... more 1. Objectif general Evaluer le niveau de vulnerabilite aux changements climatiques des populations Baka et Bantou de la Boumba et Ngoko. 2. Objectifs specifiques (OS) OS1 : Evaluer les perceptions aux changements climatiques des populations Baka et Bantou de la Boumba et Ngoko. OS2 : Evaluer le niveau d’exposition et de sensibilite des Bantou et des Baka dans la Boumba et Ngoko. OS3 : Evaluer la capacite d’adaptation aux changements climatiques de chacun de ces groupes ethniques. 3. Hypothese Les populations Baka et Bantou de la Boumba et Ngoko sont differemment vulnerables aux changements climatiques. 4. Methodologie - Site d’etude L’etude s’est deroulee dans 7 villages du canton Bidjouki situe le long de l’axe Yokadouma-Mboy II a Yokadouma, chef-lieu du departement de la Boumba et Ngoko, Region de l’Est Cameroun. -Methode de collecte des donnees La methodologie utilisee est celle adaptee a partir de l’indice CCVI (Climate Change Vulnerability Index) en ce qui concerne l’expositio...

Trees are a traditional component of urban spaces where they provide ecosystem services critical ... more Trees are a traditional component of urban spaces where they provide ecosystem services critical to urban wellbeing. In the Tropics, urban trees’ seed origins have rarely been characterized. Yet, understanding the social dynamics linked to tree planting is critical given their influence on the distribution of associated genetic diversity. This study examines elements of these dynamics (seed exchange networks) in an emblematic indigenous fruit tree species from Central Africa, the African plum tree (Dacryodes edulis, Burseraceae), within the urban context of Yaoundé. We further evaluate the consequences of these social dynamics on the distribution of the genetic diversity of the species in the city. Urban trees were planted predominantly using seeds sourced from outside the city, resulting in a level of genetic diversity as high in Yaoundé as in a whole region of production of the species. Debating the different drivers that foster the genetic diversity in planted urban trees, the st...

Molecular Biology Reports, 2020

Microsatellites were designed and characterized in the African fruit tree species Dacryodes eduli... more Microsatellites were designed and characterized in the African fruit tree species Dacryodes edulis (Burseraceae). The fruits are commercialized throughout Central Africa and the species is present in forested environments as well as cultivated systems. The high variability of these markers makes them suitable to investigate the structure of genetic diversity in this important food tree species from Central Africa. From a genomic library obtained by next-generation sequencing, 21 new polymorphic microsatellite loci were developed. Tested on 95 individuals from four populations coming from three countries of the Congo Basin, the microsatellites displayed two to 20 alleles (mean 7.5; expected heterozygosity 0.003 to 0.937, mean 0.666). The transferability of microsatellites was effective for four other Dacryodes species (D. buettneri, D. igaganga, D. osika, D. pubescens). This set of newly developed microsatellite markers will be useful for assessing the genetic diversity and differentiation as well as gene flow patterns of D. edulis in tropical forests from Central Africa.

Economic Botany, 2019

Highly valued for its edible fruits, the safou tree, Dacryodes edulis, is a major component of fa... more Highly valued for its edible fruits, the safou tree, Dacryodes edulis, is a major component of farming systems in Central Africa. In Cameroon, the species has drawn much attention since the 1990s because of its market potential. Among other fruit tree species, safou trees are integrated within cocoa-coffee agroforests as a means of diversification. In Western Cameroon, farmers' strategies for safou production and commercialization are influenced by a gradient of the species' market integration. Based on semi-structured interviews with farmers and inventories of trees on their farms, this ethnoecological study addresses the relationship between the market integration of production areas, farmers' agricultural practices, and the distribution of local varieties. Interviews revealed that farmers in high-cultivation areas use more diversified planting techniques, but select and use similar planting material. At the local scale, we found a wide range of varieties, defined according to a combination of selected fruit traits. Varieties appearing at multiple sites were also the ones with the most desirable sets of characteristics. The agricultural strategies depicted help us to understand the specificities of the ongoing market integration of indigenous species in the tropics. Le safoutier, Dacryodes edulis, est l'un des arbres fruitiers les plus présents dans les systèmes de culture d'Afrique Centrale, et suscite un intérêt commercial fort depuis une vingtaine d'années au Cameroun. Au côté d'autres espèces fruitières, des safoutiers sont intégrés dans les agroforêts à caféiers ou cacaoyers comme éléments de diversification. Dans la région Ouest du Cameroun, les stratégies des cultivateurs pour la production et la commercialisation des safous sont influencées par leur intégration au marché. A partir d'entretiens avec des cultivateurs et d'inventaires dans leurs champs, la relation entre le degré d'intégration de la culture dans le marché local, les 1

Phytotaxa, 2016

As a preliminary step to the taxonomic revision of the genus Cyrtorchis , a synoptic revision of ... more As a preliminary step to the taxonomic revision of the genus Cyrtorchis , a synoptic revision of the species occurring in Central Africa was undertaken. Based on a detailed examination of 1,039 herbarium specimens, including nomenclatural types, we have recognized 14 species in Central Africa (one of which is divided into two subspecies), including one new species that the study brought to light, described here as Cyrtorchis submontana . The new species closely resembles C. guillaumetii and C. brownii in general aspect, but differs from them in having thinner, small elliptic leaves and shorter, fewer-flowered, more lax inflorescences with shorter bracts. The species is restricted to submontane vegetation of Central Africa and is assessed as Endangered following the IUCN Red List Categories and Criteria. Cyrtorchis latibracteata and C. subcylindrifolia are lectotypified, and the latter is placed as a synonym under C. henriquesiana . Many new records are reported, and for each taxon the distribution, habitat and ecology are given. An identification key for the Central African taxa is also provided.

Agroforestry Systems - AGROFOREST SYST, 2002

Forests, Trees and Livelihoods, 2004

The vegetative propagation of leafy stem cuttings of high-value tropical trees using non-mist pro... more The vegetative propagation of leafy stem cuttings of high-value tropical trees using non-mist propagators is an important part of the World Agroforestry Centre&amp;amp;amp;#39;s tree domestication programme. As the programme develops in the region, the need to scale-up the technology is becoming urgent. A vegetative propagation technology that is robust, adaptable and attractive to small-scale rural farmers without the need for

Forests, Trees and Livelihoods, 2002

Air layering (or marcotting) of ‘safou’ (Dacryodes edulis) is most successful with large diameter... more Air layering (or marcotting) of ‘safou’ (Dacryodes edulis) is most successful with large diameter, horizontal branches with thick bark. However, rooting remains slow and severance is only possible five months after setting the marcots. Application of growth regulators helps to accelerate rooting and reduces the severance period from five to three months. The best results were obtained with IBA. The

Biodiversity, 2006

Forest loss and fragmentation over the past decades in the West and central Africa region is havi... more Forest loss and fragmentation over the past decades in the West and central Africa region is having a direct effect on the habitats of valuable plants, driving species isolation, reductions in species populations and in some cases, increasing extinction rates of potentially useful plants. Furthermore, some tropical rainforest plants exhibit hampered seed germination or seedling establishment through hampered natural regeneration in disturbed ecosystems. Nevertheless, these forests in West and central Africa remain important sites, habitats and sources of potentially useful plant diversity. Many tropical tree species and their products have been documented regarding the roles they play as food, medicine and other services they provide to local peoples. The exploitation, use and commercialisation of these tree products constitute an important activity to people living around forests and beyond within the region. For some of these species, existing markets have expanded within and outside their wide ecological range. As well, great potential exists for further development at the industrial level.Since 1998, the World Agroforestry Centre, Africa Humid Tropics, in partnership with several local and regional stakeholders in West and central Africa, have been implementing a Tree Domestication Programme aimed at diversifying smallholder livelihood options through the selection, multiplication, integration, management and marketing of indigenous trees/plants and their products, ensuring that they provide both livelihood and environmental services. As tree domestication itself depends on existing plant diversity, biodiversity at genetic, species and ecosystem levels have been important considerations in cultivar selection, farming systems diversification and contributing towards ecosystems resilience, respectively.This tree domestication programme is being implemented in Cameroon, Nigeria, Gabon, Equatorial Guinea and more recently in the Democratic Republic of Congo. The programme started with the prioritisation of a range of indigenous fruit and medicinal tree species at local community levels. Emphasis then moved to capacity-building: training, followup and information dissemination focussing on a range of low-tech and adaptable propagation, marketing, selection, cultivation and management techniques for local level stakeholders, and training, backstopping and dissemination, for a range of regional government and non-governmental partners, in order to enhance ownership and adoption of the process. The programme has contributed to the building of both natural assets of resource-poor farmers to increase their access to a diverse range of agroforestry trees and products, and human assets for perpetuating the knowledge and experience in the region. As well, mechanisms have been developed for increasing and diversifying household revenue through better marketing of indigenous agroforestry tree products, protecting biodiversity on-farm and recognizing the value in maintaining both intra and inter-specific diversity on farms. The programme has also developed multispecies, on-farm needs-based live gene banks as well as classical ones of regionally important high-value indigenous tree species in both Cameroon and Nigeria.As the programme develops in the region, increasing emphasis is being placed on building strategic partnerships in order to achieve greater and more far-reaching impact by increasing the potential contribution that diverse agroforestry trees make to household revenue, and environmental management at farm and landscape scales.

The region of West and Central Africa is endowed with high-value fruit trees and medicinal plants... more The region of West and Central Africa is endowed with high-value fruit trees and medicinal plants, which are currently traded locally as well as on regional and international markets. Unfortunately, they are all exploited from the wild and there has been little or no focussed effort to domesticate and cultivate them. Prunus africana is one of these important medicinal plant under domestication. A series of nursery experiments were conducted to assess the effects of rooting medium (sawdust, sand and a 50:50 mixture of sand and sawdust), auxin concentration (0, 50, 100, 150, and 200 µg IBA), and leaf area (0, 5, 10, 20, and 25 cm 2 ) on rooting success of juvenile cuttings of P. africana. The percentage of cuttings rooted was significantly greater (P < 0.05) in sawdust (80%), than in sand alone (72%) or in mixture with sawdust (71%). Leaf area also significantly affected the percentage of rooting. Leafless cuttings did not root and were all dead by week 6, but in leafy cuttings rooting ability increased proportionally with leaf area up to 20 cm 2 (79%). Larger leaf cuttings (25 cm 2 ) rooted at the same level as those of 20 cm 2 . The cuttings with the largest leaves also had the greatest mean number of roots per cutting (14 roots cutting -1 ), while those with the smallest (5 cm 2 ) leaf area produced the fewest roots (5 roots cutting -1 ). The application of auxin (IBA) promoted rooting (P < 0.05) up to an optimum application of 100-200 µg IBA per cutting, but 300 µg was supraoptimal. It can be concluded that P. africana is amenable to vegetative propagation.

Molecular Biology Reports, 2020

Economic Botany, 2019

Phytotaxa, 2016

Agroforestry Systems - AGROFOREST SYST, 2002

Forests, Trees and Livelihoods, 2004

Forests, Trees and Livelihoods, 2002

Biodiversity, 2006