Dendrochronological Potential and Impact of Climate Factors on Radial Growth of Two Species in the Sahelian Zone: <i>Boscia senegalensis</i>(Pers.) Lam. ex Poir and <i>Sclerocarya birrea</i>(A. Rich) Hoscht (Ferlo Nord/Senegal)

The objective of this study is to analyze the dendrochronological potential of two Sahelian species (B. senegalensis and S. birrea) and to evaluate the relationships between their growth rings and the climate. The study was conducted in 2016 in the Ferlo area of Senegal. The biological material consists of wood slices, taken from the trunks of these adult woody species at 0.30 m and 1.30 m from the ground after they have been felled. The technique used to examine the slices consists in identifying their rings, establishing their structures, inter-dating them and studying the relationship between the identified rings and climatic factors. The results showed that the species had thin, clear, highly visible and sharp rings. The limit of growth is marked by a line of parenchyma. Intradatation series carried out on the chronologies made it possible to estimate the ages of the individuals, which vary from 10 to 38 years for B. senegalensis and from 29 to 50 years for S. birrea. Their average growth rates are estimated at 0.906 mm/year and 0.89 mm/year respectively. The chronological sequences are 29 years (1987-2016) for B. senegalensis and 38 years (1964-2012) for S. birrea. The results revealed that there is no significant correlation between the growth chronologies of B. senegalensis and the climatic regressors (temperature and precipitation). In contrast, the ring-climate relationship shows that in S. birrea winter precipitation positively influences ring growth while temperature has no effect on ring growth in this species. This study provides a better understanding of the response of forest ecosystems to possible climate change, particularly in the current context of sustainable forest management.

Agro-Morphological Characterization of Cassava (Manihot esculenta Crantz) Cultivars from Chad

Cassava is a considerable source of food and income for the rural community of the south of Chad. Despite the importance of the diversity of cultivars in situ, their morphological traits and agronomic performance are under investigated. The aim of this study is to characterize and analyze the variability structure of the cassava’s germplasm. Fifty nine cultivars collected from five main cassava growing regions, were evaluated by forty five agro-morphological descriptors in a Fisher design replicated three times. Data were collected at three, six, nine and twelve months after planting. High phenotypic variability was shown within the collection for the color of apical leaf, vein leaf, petiole, roots and pulp. The same case was observed for the root peduncle, the shape of the central leaflet and the root, the cortex root thickness and the texture of root epidermis. Significant to highly significant differences were observed for all the quantitative traits. High variability were shown for the size of the leaf lobe, petiole length, plant height, root number and length, harvest index, above-ground biomass and fresh root weight. Positive correlations were found between the leaflet and leaf lobe number. Fresh root weight was also positively correlated to the root number, length and diameter. Principal component analysis (PCA) on quantitative variable revealed four groups with two of them containing performant cultivars: Group II with small root, high potential yield but less leaflet and leaf lobe and group III characterized by some cultivars with high productivity, more leaflet and leaf lobe, more and bigger roots. At regional level, significant differences were shown within cultivars which were discriminated in relation to their origin region by the number of the leaf lobes. The better cultivars and the interesting traits could be used to improve cassava production in Chad.

人类活动与生态水文因素对塞内加尔北部费罗临时池塘周边的草本植物区系物种多样性的影响

在萨赫勒,临时池塘在保护物种多样性方面起着重要作用。本研究考察了塞内加尔北部费罗地区的两个放牧池塘以及一个未放牧池塘,探讨了人类活动与生态水文因素对池塘周边植物多样性的影响。每个池塘建立两条植物生态样带,确定并记录每条样带上平均植被单元情况(包括植被覆盖度、土壤暴露度、土壤质地、土壤湿度和酸碱度、平均高度以及坡度等)。研究结果表明,3个池塘周边共有草本植物22科41属55种。放牧池塘周边多为禾本科植物,尤其是画眉草属(Eragrostis tremula)与肠须草属(Enteropogon prieurii)植物,未放牧池塘周边则主要为其他科类植物,如牛膝属(Achyranthes sp.)、鸭跖草属(Commelina forsskaolii)、黄麻属(Corchorus sp.)植物等。Wendu Marodi池塘(未放牧池塘)的香农物种多样性指数(H′)为4.9,略高于Belel Lougal池塘和Belel Sow池塘(放牧池塘),这两个池塘的香农物种多样性指数分别为4.8和4.5。3个池塘的种类平均性指数相对都较高,分别为0.85、0.83和0.78。根据生态因子可分出4个物种群:蒺藜(Tribulus terrestris)种群,集中在限牧区与过度放牧区;平枝马唐(Digitaria horizontalis)种群与孟仁草(Chloris barbata)种群,见于过度带;以及土牛膝(Achyranthes aspera)种群,生长在人类活动较少且草本植物丰富的湿地。本研究强调了维持未放牧池塘或半保护池塘与放牧池塘景观镶嵌结构的重要性,以保护塞内加尔中心与萨赫勒地区草本植物的多样性。